/******************************************************************************
 *
 * Project:  libcurl based HTTP client
 * Purpose:  libcurl based HTTP client
 * Author:   Frank Warmerdam, warmerdam@pobox.com
 *
 ******************************************************************************
 * Copyright (c) 2006, Frank Warmerdam
 * Copyright (c) 2008-2013, Even Rouault <even dot rouault at mines-paris dot org>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 ****************************************************************************/

#include "cpl_port.h"
#include "cpl_http.h"

#include <cstddef>
#include <cstring>

#include <algorithm>
#include <array>
#include <map>
#include <mutex>
#include <string>
#include <vector>

#include "cpl_http.h"
#include "cpl_error.h"
#include "cpl_multiproc.h"

#ifdef HAVE_CURL
#  include <curl/curl.h>
// CURLINFO_RESPONSE_CODE was known as CURLINFO_HTTP_CODE in libcurl 7.10.7 and
// earlier.
#if LIBCURL_VERSION_NUM < 0x070a07
#define CURLINFO_RESPONSE_CODE CURLINFO_HTTP_CODE
#endif

#ifdef HAVE_OPENSSL_CRYPTO
#include <openssl/err.h>
#include <openssl/ssl.h>
#include <openssl/engine.h>
#include <openssl/x509v3.h>

#if defined(WIN32)
#include <wincrypt.h>
#endif

#endif

#ifdef HAVE_SIGACTION
#include <signal.h>
#endif

#endif // HAVE_CURL

CPL_CVSID("$Id: cpl_http.cpp 78ebfa67fe512cc98e3452fc307a0a17e88d0b68 2019-06-21 00:26:51 +0200 Even Rouault $")

// list of named persistent http sessions

#ifdef HAVE_CURL
static std::map<CPLString, CURL*>* poSessionMap = nullptr;
static std::map<CPLString, CURLM*>* poSessionMultiMap = nullptr;
static CPLMutex *hSessionMapMutex = nullptr;
static bool bHasCheckVersion = false;
static bool bSupportGZip = false;
static bool bSupportHTTP2 = false;
#if defined(WIN32) && defined(HAVE_OPENSSL_CRYPTO)
static std::vector<X509*> *poWindowsCertificateList = nullptr;

#if ( OPENSSL_VERSION_NUMBER < 0x10100000L )
#define EVP_PKEY_get0_RSA(x)            (x->pkey.rsa)
#define EVP_PKEY_get0_DSA(x)            (x->pkey.dsa)
#define X509_get_extension_flags(x)     (x->ex_flags)
#define X509_get_key_usage(x)           (x->ex_kusage)
#define X509_get_extended_key_usage(x)  (x->ex_xkusage)
#endif

#endif // defined(WIN32) && defined(HAVE_OPENSSL_CRYPTO)

#if defined(HAVE_OPENSSL_CRYPTO) && OPENSSL_VERSION_NUMBER < 0x10100000

// Ported from https://curl.haxx.se/libcurl/c/opensslthreadlock.html
static CPLMutex** pahSSLMutex = nullptr;

static void CPLOpenSSLLockingFunction(int mode, int n,
                                 const char * /*file*/, int /*line*/)
{
  if(mode & CRYPTO_LOCK)
  {
      CPLAcquireMutex( pahSSLMutex[n], 3600.0 );
  }
  else
  {
      CPLReleaseMutex( pahSSLMutex[n] );
  }
}

static unsigned long CPLOpenSSLIdCallback(void)
{
  return static_cast<unsigned long>(CPLGetPID());
}

static void CPLOpenSSLInit()
{
    if( strstr(curl_version(), "OpenSSL") &&
        CPLTestBool(CPLGetConfigOption("CPL_OPENSSL_INIT_ENABLED", "YES")) &&
        CRYPTO_get_id_callback() == nullptr )
    {
        pahSSLMutex = static_cast<CPLMutex**>(
                CPLMalloc( CRYPTO_num_locks() * sizeof(CPLMutex*) ) );
        for(int i = 0;  i < CRYPTO_num_locks();  i++)
        {
            pahSSLMutex[i] = CPLCreateMutex();
            CPLReleaseMutex( pahSSLMutex[i] );
        }
        CRYPTO_set_id_callback(CPLOpenSSLIdCallback);
        CRYPTO_set_locking_callback(CPLOpenSSLLockingFunction);
    }
}

static void CPLOpenSSLCleanup()
{
    if( pahSSLMutex )
    {
        for(int i = 0;  i < CRYPTO_num_locks();  i++)
        {
            CPLDestroyMutex(pahSSLMutex[i]);
        }
        CPLFree(pahSSLMutex);
        pahSSLMutex = nullptr;
        CRYPTO_set_id_callback(nullptr);
        CRYPTO_set_locking_callback(nullptr);
    }
}

#endif

#if defined(WIN32) && defined (HAVE_OPENSSL_CRYPTO)

/************************************************************************/
/*                    CPLWindowsCertificateListCleanup()                */
/************************************************************************/

static void CPLWindowsCertificateListCleanup()
{
    if( poWindowsCertificateList )
    {
        for( auto&& pX509: *poWindowsCertificateList )
        {
            X509_free(pX509);
        }
        delete poWindowsCertificateList;
        poWindowsCertificateList = nullptr;
    }
}

/************************************************************************/
/*                       LoadCAPICertificates()                         */
/************************************************************************/

static
CPLErr LoadCAPICertificates(const char *pszName,
                            std::vector<X509*> *poCertificateList)
{
    CPLAssert(pszName);
    CPLAssert(poCertificateList);

    HCERTSTORE pCertStore = CertOpenSystemStore(
        reinterpret_cast<HCRYPTPROV_LEGACY>(nullptr), pszName);
    if( pCertStore == nullptr )
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                 "CPLLoadCAPICertificates(): Unable open system "
                 "certificate store %s.", pszName);
        return CE_Failure;
    }

    PCCERT_CONTEXT pCertificate = CertEnumCertificatesInStore( pCertStore, nullptr );
    while( pCertificate != nullptr )
    {
        X509 *pX509 = d2i_X509( nullptr,
                                const_cast<unsigned char const **>(&pCertificate->pbCertEncoded),
                                pCertificate->cbCertEncoded );
        if( pX509 == nullptr )
        {
            CPLError(CE_Warning, CPLE_AppDefined,
                     "CPLLoadCAPICertificates(): CertEnumCertificatesInStore() "
                     "returned a null certificate, skipping." );
        }
        else
        {
#ifdef DEBUG_VERBOSE
            char szSubject[256] = {0};
            CPLString osSubject;
            X509_NAME *pName = X509_get_subject_name( pX509 );
            if( pName )
            {
                X509_NAME_oneline(pName, szSubject, sizeof(szSubject));
                osSubject = szSubject;
            }
            if( !osSubject.empty() )
                 CPLDebug("HTTP", "SSL Certificate: %s", osSubject.c_str());
#endif
            poCertificateList->push_back(pX509);
        }
        pCertificate = CertEnumCertificatesInStore(pCertStore, pCertificate);
    }
    CertCloseStore(pCertStore, 0);
    return CE_None;
}

/************************************************************************/
/*                       CPL_ssl_ctx_callback()                         */
/************************************************************************/

// Load certificates from Windows Crypto API store.
static
CURLcode CPL_ssl_ctx_callback(CURL *pCurl, void *pSSL, void *)
{
    SSL_CTX *pSSL_CTX = static_cast<SSL_CTX*>(pSSL);
    if( pSSL_CTX == nullptr )
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                  "CPL_ssl_ctx_callback(): OpenSSL context pointer is NULL.");
        return CURLE_ABORTED_BY_CALLBACK;
    }

    static std::mutex goMutex;
    {
        std::lock_guard<std::mutex> oLock(goMutex);
        if( poWindowsCertificateList == nullptr )
        {
            poWindowsCertificateList = new std::vector<X509*>();
            if( !poWindowsCertificateList )
            {
                CPLError(CE_Failure, CPLE_AppDefined,
                         "CPL_ssl_ctx_callback(): Unable to allocate "
                         "structure to hold certificates.");
                return CURLE_FAILED_INIT;
            }

            const std::array<const char*, 3> aszStores
                                            {{"CA", "AuthRoot", "ROOT"}};
            for( auto&& pszStore: aszStores )
            {
                if( LoadCAPICertificates(pszStore, poWindowsCertificateList)
                        == CE_Failure )
                {
                    CPLError(CE_Failure, CPLE_AppDefined,
                             "CPL_ssl_ctx_callback(): Unable to load certificates "
                             "from '%s' store.", pszStore);
                    return CURLE_FAILED_INIT;
                }
            }

            CPLDebug("HTTP",
                     "Loading %d certificates from Windows store.",
                     poWindowsCertificateList->size());
        }
    }

    X509_STORE *pX509Store = SSL_CTX_get_cert_store(pSSL_CTX);
    for( X509 *x509 : *poWindowsCertificateList )
        X509_STORE_add_cert(pX509Store, x509);

    return CURLE_OK;
}

#endif // defined(WIN32) && defined (HAVE_OPENSSL_CRYPTO)

/************************************************************************/
/*                       CheckCurlFeatures()                            */
/************************************************************************/

static void CheckCurlFeatures()
{
    CPLMutexHolder oHolder( &hSessionMapMutex );
    if( !bHasCheckVersion )
    {
        const char* pszVersion = curl_version();
        CPLDebug("HTTP", "%s", pszVersion);
        bSupportGZip = strstr(pszVersion, "zlib/") != nullptr;
        bSupportHTTP2 = strstr(curl_version(), "nghttp2/") != nullptr;
        bHasCheckVersion = true;

        curl_version_info_data* data = curl_version_info(CURLVERSION_NOW);
        if( data->version_num < LIBCURL_VERSION_NUM )
        {
            CPLError(CE_Warning, CPLE_AppDefined,
                     "GDAL was built against curl %d.%d.%d, but is "
                     "running against %s. Runtime failure is likely !",
                     LIBCURL_VERSION_MAJOR,
                     LIBCURL_VERSION_MINOR,
                     LIBCURL_VERSION_PATCH,
                     data->version);
        }
        else if( data->version_num > LIBCURL_VERSION_NUM )
        {
            CPLDebug("HTTP",
                     "GDAL was built against curl %d.%d.%d, but is "
                     "running against %s.",
                     LIBCURL_VERSION_MAJOR,
                     LIBCURL_VERSION_MINOR,
                     LIBCURL_VERSION_PATCH,
                     data->version);
        }

#if defined(HAVE_OPENSSL_CRYPTO) && OPENSSL_VERSION_NUMBER < 0x10100000
        CPLOpenSSLInit();
#endif
    }
}

/************************************************************************/
/*                            CPLWriteFct()                             */
/*                                                                      */
/*      Append incoming text to our collection buffer, reallocating     */
/*      it larger as needed.                                            */
/************************************************************************/


class CPLHTTPResultWithLimit
{
public:
    CPLHTTPResult* psResult = nullptr;
    int            nMaxFileSize = 0;
};

static size_t
CPLWriteFct(void *buffer, size_t size, size_t nmemb, void *reqInfo)

{
    CPLHTTPResultWithLimit *psResultWithLimit =
        static_cast<CPLHTTPResultWithLimit *>(reqInfo);
    CPLHTTPResult* psResult = psResultWithLimit->psResult;

    int nBytesToWrite = static_cast<int>(nmemb)*static_cast<int>(size);
    int nNewSize = psResult->nDataLen + nBytesToWrite + 1;
    if( nNewSize > psResult->nDataAlloc )
    {
        psResult->nDataAlloc = static_cast<int>(nNewSize * 1.25 + 100);
        GByte* pabyNewData = static_cast<GByte *>(
            VSIRealloc(psResult->pabyData, psResult->nDataAlloc));
        if( pabyNewData == nullptr )
        {
            VSIFree(psResult->pabyData);
            psResult->pabyData = nullptr;
            psResult->pszErrBuf = CPLStrdup(CPLString().Printf("Out of memory allocating %d bytes for HTTP data buffer.", psResult->nDataAlloc));
            psResult->nDataAlloc = psResult->nDataLen = 0;

            return 0;
        }
        psResult->pabyData = pabyNewData;
    }

    memcpy( psResult->pabyData + psResult->nDataLen, buffer, nBytesToWrite );

    psResult->nDataLen += nBytesToWrite;
    psResult->pabyData[psResult->nDataLen] = 0;

    if( psResultWithLimit->nMaxFileSize > 0 &&
        psResult->nDataLen > psResultWithLimit->nMaxFileSize )
    {
        CPLError(CE_Failure, CPLE_AppDefined, "Maximum file size reached");
        return 0;
    }

    return nmemb;
}

/************************************************************************/
/*                           CPLHdrWriteFct()                           */
/************************************************************************/
static size_t CPLHdrWriteFct( void *buffer, size_t size, size_t nmemb,
                              void *reqInfo )
{
    CPLHTTPResult *psResult = static_cast<CPLHTTPResult *>(reqInfo);
    // Copy the buffer to a char* and initialize with zeros (zero
    // terminate as well).
    size_t nBytes = size * nmemb;
    char* pszHdr = static_cast<char *>(CPLCalloc(1, nBytes+1));
    memcpy(pszHdr, buffer, nBytes);
    size_t nIdx = nBytes - 1;
    // Remove end of line characters
    while( nIdx > 0 && (pszHdr[nIdx] == '\r' || pszHdr[nIdx] == '\n') )
    {
        pszHdr[nIdx] = 0;
        nIdx --;
    }
    char *pszKey = nullptr;
    const char *pszValue = CPLParseNameValue(pszHdr, &pszKey );
    if( pszKey && pszValue )
    {
        psResult->papszHeaders =
            CSLAddNameValue(psResult->papszHeaders, pszKey, pszValue);
    }
    CPLFree(pszHdr);
    CPLFree(pszKey);
    return nmemb;
}

typedef struct {
    GDALProgressFunc pfnProgress;
    void *pProgressArg;
} CurlProcessData, *CurlProcessDataL;

static int NewProcessFunction(void *p,
                              curl_off_t dltotal, curl_off_t dlnow,
                              curl_off_t ultotal, curl_off_t ulnow)
{
    CurlProcessDataL pData = static_cast<CurlProcessDataL>(p);
    if( nullptr != pData && pData->pfnProgress ) {
        double dfDone = 0.0;
        if( dltotal > 0 )
        {
            dfDone = double(dlnow) / dltotal;
            return pData->pfnProgress(dfDone, "Downloading ...",
                pData->pProgressArg) == TRUE ? 0 : 1;
        }
        else if( ultotal > 0 )
        {
            dfDone = double(ulnow) / ultotal;
            return pData->pfnProgress(dfDone, "Uploading ...",
                pData->pProgressArg) == TRUE ? 0 : 1;
        }
    }
    return 0;
}

static int ProcessFunction(void *p, double dltotal, double dlnow,
                                     double ultotal, double ulnow)
{
    return NewProcessFunction(p, static_cast<curl_off_t>(dltotal),
                              static_cast<curl_off_t>(dlnow),
                              static_cast<curl_off_t>(ultotal),
                              static_cast<curl_off_t>(ulnow));
}

#endif /* def HAVE_CURL */

/************************************************************************/
/*                       CPLHTTPGetOptionsFromEnv()                     */
/************************************************************************/

typedef struct
{
    const char* pszEnvVar;
    const char* pszOptionName;
} TupleEnvVarOptionName;

constexpr TupleEnvVarOptionName asAssocEnvVarOptionName[] =
{
    { "GDAL_HTTP_VERSION", "HTTP_VERSION" },
    { "GDAL_HTTP_CONNECTTIMEOUT", "CONNECTTIMEOUT" },
    { "GDAL_HTTP_TIMEOUT", "TIMEOUT" },
    { "GDAL_HTTP_LOW_SPEED_TIME", "LOW_SPEED_TIME" },
    { "GDAL_HTTP_LOW_SPEED_LIMIT", "LOW_SPEED_LIMIT" },
    { "GDAL_HTTP_USERPWD", "USERPWD" },
    { "GDAL_HTTP_PROXY", "PROXY" },
    { "GDAL_HTTPS_PROXY", "HTTPS_PROXY" },
    { "GDAL_HTTP_PROXYUSERPWD", "PROXYUSERPWD" },
    { "GDAL_PROXY_AUTH", "PROXYAUTH" },
    { "GDAL_HTTP_NETRC", "NETRC" },
    { "GDAL_HTTP_MAX_RETRY", "MAX_RETRY" },
    { "GDAL_HTTP_RETRY_DELAY", "RETRY_DELAY" },
    { "CURL_CA_BUNDLE", "CAINFO" },
    { "SSL_CERT_FILE", "CAINFO" },
    { "GDAL_HTTP_HEADER_FILE", "HEADER_FILE" },
    { "GDAL_HTTP_CAPATH", "CAPATH" },
    { "GDAL_HTTP_SSL_VERIFYSTATUS", "SSL_VERIFYSTATUS" },
    { "GDAL_HTTP_USE_CAPI_STORE", "USE_CAPI_STORE" },
};

char** CPLHTTPGetOptionsFromEnv()
{
    char** papszOptions = nullptr;
    for( size_t i = 0; i < CPL_ARRAYSIZE(asAssocEnvVarOptionName); ++i )
    {
        const char* pszVal = CPLGetConfigOption(
            asAssocEnvVarOptionName[i].pszEnvVar, nullptr);
        if( pszVal != nullptr )
        {
            papszOptions = CSLSetNameValue(papszOptions,
                asAssocEnvVarOptionName[i].pszOptionName, pszVal);
        }
    }
    return papszOptions;
}

/************************************************************************/
/*                      CPLHTTPGetNewRetryDelay()                       */
/************************************************************************/

double CPLHTTPGetNewRetryDelay(int response_code, double dfOldDelay,
                               const char* pszErrBuf,
                               const char* pszCurlError)
{
    if( response_code == 429 || response_code == 500 ||
        (response_code >= 502 && response_code <= 504) ||
        // S3 sends some client timeout errors as 400 Client Error
        (response_code == 400 && pszErrBuf && strstr(pszErrBuf, "RequestTimeout")) ||
        (pszCurlError && strstr(pszCurlError, "Connection timed out")) )
    {
        // Use an exponential backoff factor of 2 plus some random jitter
        // We don't care about cryptographic quality randomness, hence:
        // coverity[dont_call]
        return dfOldDelay * (2 + rand() * 0.5 / RAND_MAX);
    }
    else
    {
        return 0;
    }
}

#ifdef HAVE_CURL

/************************************************************************/
/*                      CPLHTTPEmitFetchDebug()                         */
/************************************************************************/

static void CPLHTTPEmitFetchDebug(const char* pszURL,
                                  const char* pszExtraDebug = "")
{
    const char* pszArobase = strchr(pszURL, '@');
    const char* pszSlash = strchr(pszURL, '/');
    const char* pszColon = (pszSlash) ? strchr(pszSlash, ':') : nullptr;
    if( pszArobase != nullptr && pszColon != nullptr && pszArobase - pszColon > 0 )
    {
        /* http://user:password@www.example.com */
        char* pszSanitizedURL = CPLStrdup(pszURL);
        pszSanitizedURL[pszColon-pszURL] = 0;
        CPLDebug( "HTTP", "Fetch(%s:#password#%s%s)",
                  pszSanitizedURL, pszArobase, pszExtraDebug );
        CPLFree(pszSanitizedURL);
    }
    else
    {
        CPLDebug( "HTTP", "Fetch(%s%s)", pszURL, pszExtraDebug );
    }
}

#endif

/************************************************************************/
/*                           CPLHTTPFetch()                             */
/************************************************************************/

/**
 * \brief Fetch a document from an url and return in a string.
 *
 * @param pszURL valid URL recognized by underlying download library (libcurl)
 * @param papszOptions option list as a NULL-terminated array of strings. May be NULL.
 *                     The following options are handled :
 * <ul>
 * <li>CONNECTTIMEOUT=val, where val is in seconds (possibly with decimals).
 *     This is the maximum delay for the connection to be established before
 *     being aborted (GDAL >= 2.2).</li>
 * <li>TIMEOUT=val, where val is in seconds. This is the maximum delay for the whole
 *     request to complete before being aborted.</li>
 * <li>LOW_SPEED_TIME=val, where val is in seconds. This is the maximum time where the
 *      transfer speed should be below the LOW_SPEED_LIMIT (if not specified 1b/s),
 *      before the transfer to be considered too slow and aborted. (GDAL >= 2.1)</li>
 * <li>LOW_SPEED_LIMIT=val, where val is in bytes/second. See LOW_SPEED_TIME. Has only
 *     effect if LOW_SPEED_TIME is specified too. (GDAL >= 2.1)</li>
 * <li>HEADERS=val, where val is an extra header to use when getting a web page.
 *                  For example "Accept: application/x-ogcwkt"</li>
 * <li>HEADER_FILE=filename: filename of a text file with "key: value" headers.
 *     (GDAL >= 2.2)</li>
 * <li>HTTPAUTH=[BASIC/NTLM/GSSNEGOTIATE/ANY] to specify an authentication scheme to use.</li>
 * <li>USERPWD=userid:password to specify a user and password for authentication</li>
 * <li>POSTFIELDS=val, where val is a nul-terminated string to be passed to the server
 *                     with a POST request.</li>
 * <li>PROXY=val, to make requests go through a proxy server, where val is of the
 *                form proxy.server.com:port_number. This option affects both HTTP and HTTPS
 *                URLs.</li>
 * <li>HTTPS_PROXY=val (GDAL >= 2.4), the same meaning as PROXY, but this option is taken into account only
 *                 for HTTPS URLs.</li>
 * <li>PROXYUSERPWD=val, where val is of the form username:password</li>
 * <li>PROXYAUTH=[BASIC/NTLM/DIGEST/ANY] to specify an proxy authentication scheme to use.</li>
 * <li>NETRC=[YES/NO] to enable or disable use of $HOME/.netrc, default YES.</li>
 * <li>CUSTOMREQUEST=val, where val is GET, PUT, POST, DELETE, etc.. (GDAL >= 1.9.0)</li>
 * <li>FORM_FILE_NAME=val, where val is upload file name. If this option and
 *          FORM_FILE_PATH present, request type will set to POST.</li>
 * <li>FORM_FILE_PATH=val, where val is upload file path.</li>
 * <li>FORM_KEY_0=val...FORM_KEY_N, where val is name of form item.</li>
 * <li>FORM_VALUE_0=val...FORM_VALUE_N, where val is value of the form item.</li>
 * <li>FORM_ITEM_COUNT=val, where val is count of form items.</li>
 * <li>COOKIE=val, where val is formatted as COOKIE1=VALUE1; COOKIE2=VALUE2; ...</li>
 * <li>COOKIEFILE=val, where val is file name to read cookies from (GDAL >= 2.4)</li>
 * <li>COOKIEJAR=val, where val is file name to store cookies to (GDAL >= 2.4)</li>
 * <li>MAX_RETRY=val, where val is the maximum number of retry attempts if a 429, 502, 503 or
 *               504 HTTP error occurs. Default is 0. (GDAL >= 2.0)</li>
 * <li>RETRY_DELAY=val, where val is the number of seconds between retry attempts.
 *                 Default is 30. (GDAL >= 2.0)</li>
 * <li>MAX_FILE_SIZE=val, where val is a number of bytes (GDAL >= 2.2)</li>
 * <li>CAINFO=/path/to/bundle.crt. This is path to Certificate Authority (CA)
 *     bundle file. By default, it will be looked in a system location. If
 *     the CAINFO options is not defined, GDAL will also look if the CURL_CA_BUNDLE
 *     environment variable is defined to use it as the CAINFO value, and as a
 *     fallback to the SSL_CERT_FILE environment variable. (GDAL >= 2.1.3)</li>
 * <li>HTTP_VERSION=1.0/1.1/2/2TLS (GDAL >= 2.3). Specify HTTP version to use.
 *     Will default to 1.1 generally (except on some controlled environments,
 *     like Google Compute Engine VMs, where 2TLS will be the default).
 *     Support for HTTP/2 requires curl 7.33 or later, built against nghttp2.
 *     "2TLS" means that HTTP/2 will be attempted for HTTPS connections only. Whereas
 *     "2" means that HTTP/2 will be attempted for HTTP or HTTPS.</li>
 * <li>SSL_VERIFYSTATUS=YES/NO (GDAL >= 2.3, and curl >= 7.41): determines whether
 *     the status of the server cert using the "Certificate Status Request" TLS
 *     extension (aka. OCSP stapling) should be checked. If this option is enabled
 *     but the server does not support the TLS extension, the verification will fail.
 *     Default to NO.</li>
 * <li>USE_CAPI_STORE=YES/NO (GDAL >= 2.3, Windows only): whether CA certificates from
 *     the Windows certificate store. Defaults to NO.</li>
 * </ul>
 *
 * Alternatively, if not defined in the papszOptions arguments, the
 * CONNECTTIMEOUT, TIMEOUT,
 * LOW_SPEED_TIME, LOW_SPEED_LIMIT, USERPWD, PROXY, HTTPS_PROXY, PROXYUSERPWD, PROXYAUTH, NETRC,
 * MAX_RETRY and RETRY_DELAY, HEADER_FILE, HTTP_VERSION, SSL_VERIFYSTATUS, USE_CAPI_STORE
 * values are searched in the configuration
 * options respectively named GDAL_HTTP_CONNECTTIMEOUT, GDAL_HTTP_TIMEOUT,
 * GDAL_HTTP_LOW_SPEED_TIME, GDAL_HTTP_LOW_SPEED_LIMIT, GDAL_HTTP_USERPWD,
 * GDAL_HTTP_PROXY, GDAL_HTTPS_PROXY, GDAL_HTTP_PROXYUSERPWD, GDAL_PROXY_AUTH,
 * GDAL_HTTP_NETRC, GDAL_HTTP_MAX_RETRY, GDAL_HTTP_RETRY_DELAY,
 * GDAL_HTTP_HEADER_FILE, GDAL_HTTP_VERSION, GDAL_HTTP_SSL_VERIFYSTATUS,
 * GDAL_HTTP_USE_CAPI_STORE
 *
 * @return a CPLHTTPResult* structure that must be freed by
 * CPLHTTPDestroyResult(), or NULL if libcurl support is disabled
 */
CPLHTTPResult *CPLHTTPFetch( const char *pszURL, CSLConstList papszOptions )
{
    return CPLHTTPFetchEx( pszURL, papszOptions, nullptr, nullptr, nullptr, nullptr);
}

/**
 * Fetch a document from an url and return in a string.
 * @param  pszURL       Url to fetch document from web.
 * @param  papszOptions Option list as a NULL-terminated array of strings. Available keys see in CPLHTTPFetch.
 * @param  pfnProgress  Callback for reporting algorithm progress matching the GDALProgressFunc() semantics. May be NULL.
 * @param  pProgressArg Callback argument passed to pfnProgress.
 * @param  pfnWrite     Write function pointer matching the CPLHTTPWriteFunc() semantics. May be NULL.
 * @param  pWriteArg    Argument which will pass to a write function.
 * @return              A CPLHTTPResult* structure that must be freed by
 * CPLHTTPDestroyResult(), or NULL if libcurl support is disabled.
 */
CPLHTTPResult *CPLHTTPFetchEx( const char *pszURL, CSLConstList papszOptions,
                             GDALProgressFunc pfnProgress, void *pProgressArg,
                             CPLHTTPFetchWriteFunc pfnWrite, void *pWriteArg )

{
    if( STARTS_WITH(pszURL, "/vsimem/") &&
        // Disabled by default for potential security issues.
        CPLTestBool(CPLGetConfigOption("CPL_CURL_ENABLE_VSIMEM", "FALSE")) )
    {
        CPLString osURL(pszURL);
        const char* pszCustomRequest =
            CSLFetchNameValue( papszOptions, "CUSTOMREQUEST" );
        if( pszCustomRequest != nullptr )
        {
            osURL += "&CUSTOMREQUEST=";
            osURL += pszCustomRequest;
        }
        const char* pszUserPwd = CSLFetchNameValue( papszOptions, "USERPWD" );
        if( pszUserPwd != nullptr )
        {
            osURL += "&USERPWD=";
            osURL += pszUserPwd;
        }
        const char* pszPost = CSLFetchNameValue( papszOptions, "POSTFIELDS" );
        if( pszPost != nullptr ) // Hack: We append post content to filename.
        {
            osURL += "&POSTFIELDS=";
            osURL += pszPost;
        }
        vsi_l_offset nLength = 0;
        CPLHTTPResult* psResult =
            static_cast<CPLHTTPResult *>(CPLCalloc(1, sizeof(CPLHTTPResult)));
        GByte* pabyData = VSIGetMemFileBuffer( osURL, &nLength, FALSE );
        if( pabyData == nullptr )
        {
            CPLDebug("HTTP", "Cannot find %s", osURL.c_str());
            psResult->nStatus = 1;
            psResult->pszErrBuf =
                CPLStrdup(CPLSPrintf("HTTP error code : %d", 404));
            CPLError( CE_Failure, CPLE_AppDefined, "%s", psResult->pszErrBuf );
        }
        else if( nLength != 0 )
        {
            psResult->nDataLen = static_cast<int>(nLength);
            psResult->pabyData = static_cast<GByte *>(
                CPLMalloc(static_cast<size_t>(nLength) + 1));
            memcpy(psResult->pabyData, pabyData, static_cast<size_t>(nLength));
            psResult->pabyData[static_cast<size_t>(nLength)] = 0;
        }

        if( psResult->pabyData != nullptr &&
            STARTS_WITH(reinterpret_cast<char *>(psResult->pabyData),
                        "Content-Type: ") )
        {
            const char* pszContentType =
                reinterpret_cast<char *>(psResult->pabyData) +
                strlen("Content-type: ");
            const char* pszEOL = strchr(pszContentType, '\r');
            if( pszEOL )
                pszEOL = strchr(pszContentType, '\n');
            if( pszEOL )
            {
                size_t nContentLength = pszEOL - pszContentType;
                psResult->pszContentType =
                    static_cast<char *>(CPLMalloc(nContentLength + 1));
                memcpy(psResult->pszContentType,
                       pszContentType,
                       nContentLength);
                psResult->pszContentType[nContentLength] = 0;
            }
        }

        return psResult;
    }

#ifndef HAVE_CURL
    (void) papszOptions;
    (void) pszURL;
    (void) pfnProgress;
    (void) pProgressArg;
    (void) pfnWrite;
    (void) pWriteArg;

    CPLError( CE_Failure, CPLE_NotSupported,
              "GDAL/OGR not compiled with libcurl support, "
              "remote requests not supported." );
    return nullptr;
#else

/* -------------------------------------------------------------------- */
/*      Are we using a persistent named session?  If so, search for     */
/*      or create it.                                                   */
/*                                                                      */
/*      Currently this code does not attempt to protect against         */
/*      multiple threads asking for the same named session.  If that    */
/*      occurs it will be in use in multiple threads at once, which     */
/*      will lead to potential crashes in libcurl.                      */
/* -------------------------------------------------------------------- */
    CURL *http_handle = nullptr;

    const char *pszPersistent = CSLFetchNameValue( papszOptions, "PERSISTENT" );
    const char *pszClosePersistent =
        CSLFetchNameValue( papszOptions, "CLOSE_PERSISTENT" );
    if( pszPersistent )
    {
        CPLString osSessionName = pszPersistent;
        CPLMutexHolder oHolder( &hSessionMapMutex );

        if( poSessionMap == nullptr )
            poSessionMap = new std::map<CPLString, CURL *>;
        if( poSessionMap->count( osSessionName ) == 0 )
        {
            (*poSessionMap)[osSessionName] = curl_easy_init();
            CPLDebug( "HTTP", "Establish persistent session named '%s'.",
                      osSessionName.c_str() );
        }

        http_handle = (*poSessionMap)[osSessionName];
    }
/* -------------------------------------------------------------------- */
/*      Are we requested to close a persistent named session?           */
/* -------------------------------------------------------------------- */
    else if( pszClosePersistent )
    {
        CPLString osSessionName = pszClosePersistent;
        CPLMutexHolder oHolder( &hSessionMapMutex );

        if( poSessionMap )
        {
            std::map<CPLString, CURL *>::iterator oIter =
                poSessionMap->find( osSessionName );
            if( oIter != poSessionMap->end() )
            {
                curl_easy_cleanup(oIter->second);
                poSessionMap->erase(oIter);
                if( poSessionMap->empty() )
                {
                    delete poSessionMap;
                    poSessionMap = nullptr;
                }
                CPLDebug( "HTTP", "Ended persistent session named '%s'.",
                        osSessionName.c_str() );
            }
            else
            {
                CPLDebug(
                    "HTTP", "Could not find persistent session named '%s'.",
                    osSessionName.c_str() );
            }
        }

        return nullptr;
    }
    else
        http_handle = curl_easy_init();

/* -------------------------------------------------------------------- */
/*      Setup the request.                                              */
/* -------------------------------------------------------------------- */
    char szCurlErrBuf[CURL_ERROR_SIZE+1] = {};

    CPLHTTPEmitFetchDebug(pszURL);

    CPLHTTPResult *psResult =
        static_cast<CPLHTTPResult *>(CPLCalloc(1, sizeof(CPLHTTPResult)));

    struct curl_slist* headers= reinterpret_cast<struct curl_slist*>(
                            CPLHTTPSetOptions(http_handle, pszURL, papszOptions));

    // Set Headers.
    const char *pszHeaders = CSLFetchNameValue( papszOptions, "HEADERS" );
    if( pszHeaders != nullptr ) {
        CPLDebug ("HTTP", "These HTTP headers were set: %s", pszHeaders);
        char** papszTokensHeaders = CSLTokenizeString2(pszHeaders, "\r\n", 0);
        for( int i=0; papszTokensHeaders[i] != nullptr; ++i )
            headers = curl_slist_append(headers, papszTokensHeaders[i]);
        CSLDestroy(papszTokensHeaders);
    }

    if( headers != nullptr )
        curl_easy_setopt(http_handle, CURLOPT_HTTPHEADER, headers);

    // Are we making a head request.
    const char* pszNoBody = nullptr;
    if( (pszNoBody = CSLFetchNameValue( papszOptions, "NO_BODY" )) != nullptr )
    {
        if( CPLTestBool(pszNoBody) )
        {
            CPLDebug ("HTTP", "HEAD Request: %s", pszURL);
            curl_easy_setopt(http_handle, CURLOPT_NOBODY, 1L);
        }
    }

    // Capture response headers.
    curl_easy_setopt(http_handle, CURLOPT_HEADERDATA, psResult);
    curl_easy_setopt(http_handle, CURLOPT_HEADERFUNCTION, CPLHdrWriteFct);

    CPLHTTPResultWithLimit sResultWithLimit;
    if( nullptr == pfnWrite )
    {
        pfnWrite = CPLWriteFct;

        sResultWithLimit.psResult = psResult;
        sResultWithLimit.nMaxFileSize = 0;
        const char* pszMaxFileSize = CSLFetchNameValue(papszOptions,
                                                       "MAX_FILE_SIZE");
        if( pszMaxFileSize != nullptr )
        {
            sResultWithLimit.nMaxFileSize = atoi(pszMaxFileSize);
            // Only useful if size is returned by server before actual download.
            curl_easy_setopt(http_handle, CURLOPT_MAXFILESIZE,
                             sResultWithLimit.nMaxFileSize);
        }
        pWriteArg = &sResultWithLimit;
    }

    curl_easy_setopt(http_handle, CURLOPT_WRITEDATA, pWriteArg );
    curl_easy_setopt(http_handle, CURLOPT_WRITEFUNCTION, pfnWrite );

    CurlProcessData stProcessData = { pfnProgress, pProgressArg };
    if( nullptr != pfnProgress)
    {
        curl_easy_setopt(http_handle, CURLOPT_PROGRESSFUNCTION, ProcessFunction);
        curl_easy_setopt(http_handle, CURLOPT_PROGRESSDATA, &stProcessData);

    #if LIBCURL_VERSION_NUM >= 0x072000
        curl_easy_setopt(http_handle, CURLOPT_XFERINFOFUNCTION, NewProcessFunction);
        curl_easy_setopt(http_handle, CURLOPT_XFERINFODATA, &stProcessData);
    #endif
        curl_easy_setopt(http_handle, CURLOPT_NOPROGRESS, 0L);
    }

    szCurlErrBuf[0] = '\0';

    curl_easy_setopt(http_handle, CURLOPT_ERRORBUFFER, szCurlErrBuf );

    bool bGZipRequested = false;
    if( bSupportGZip &&
        CPLTestBool(CPLGetConfigOption("CPL_CURL_GZIP", "YES")) )
    {
        bGZipRequested = true;
        curl_easy_setopt(http_handle, CURLOPT_ENCODING, "gzip");
    }

    // Fill POST form if present
    const char* pszFormFilePath = CSLFetchNameValue( papszOptions,
        "FORM_FILE_PATH" );
    const char* pszParametersCount = CSLFetchNameValue( papszOptions,
        "FORM_ITEM_COUNT" );
#if LIBCURL_VERSION_NUM >= 0x073800 /* 7.56.0 */
    curl_mime *mime = nullptr;
#else // LIBCURL_VERSION_NUM >= 0x073800
    struct curl_httppost *formpost = nullptr;
#endif // LIBCURL_VERSION_NUM >= 0x073800

    if( pszFormFilePath != nullptr || pszParametersCount != nullptr )
    {
#if LIBCURL_VERSION_NUM >= 0x073800 /* 7.56.0 */
        mime = curl_mime_init(http_handle);
        curl_mimepart *mimepart = curl_mime_addpart(mime);
#else // LIBCURL_VERSION_NUM >= 0x073800
        struct curl_httppost *lastptr = nullptr;
#endif // LIBCURL_VERSION_NUM >= 0x073800
        if( pszFormFilePath != nullptr )
        {
            const char* pszFormFileName = CSLFetchNameValue( papszOptions,
                "FORM_FILE_NAME" );
            if( pszFormFileName == nullptr )
            {
                pszFormFileName = CPLGetFilename( pszFormFilePath );
            }

#if LIBCURL_VERSION_NUM >= 0x073800 /* 7.56.0 */
            curl_mime_name(mimepart, pszFormFileName);
            curl_mime_filedata(mimepart, pszFormFilePath);
#else // LIBCURL_VERSION_NUM >= 0x073800
            curl_formadd(&formpost, &lastptr,
                CURLFORM_COPYNAME, pszFormFileName,
                CURLFORM_FILE, pszFormFilePath,
                CURLFORM_END);
#endif // LIBCURL_VERSION_NUM >= 0x073800

            CPLDebug("HTTP", "Send file: %s, COPYNAME: %s", pszFormFilePath,
                pszFormFileName);
        }

        int nParametersCount = 0;
        if( pszParametersCount != nullptr )
        {
            nParametersCount = atoi( pszParametersCount );
        }

        for(int i = 0; i < nParametersCount; ++i)
        {
            const char *pszKey = CSLFetchNameValue( papszOptions,
                CPLSPrintf("FORM_KEY_%d", i) );
            const char *pszValue = CSLFetchNameValue( papszOptions,
                CPLSPrintf("FORM_VALUE_%d", i) );

#if LIBCURL_VERSION_NUM >= 0x073800 /* 7.56.0 */
            mimepart = curl_mime_addpart(mime);
            curl_mime_name(mimepart, pszKey);
            curl_mime_data(mimepart, pszValue, CURL_ZERO_TERMINATED);
#else // LIBCURL_VERSION_NUM >= 0x073800
            curl_formadd(&formpost, &lastptr,
                CURLFORM_COPYNAME, pszKey,
                CURLFORM_COPYCONTENTS, pszValue,
                CURLFORM_END);
#endif // LIBCURL_VERSION_NUM >= 0x073800

            CPLDebug("HTTP", "COPYNAME: %s, COPYCONTENTS: %s", pszKey, pszValue);
        }

#if LIBCURL_VERSION_NUM >= 0x073800 /* 7.56.0 */
        curl_easy_setopt(http_handle, CURLOPT_MIMEPOST, mime);
#else // LIBCURL_VERSION_NUM >= 0x073800
        curl_easy_setopt(http_handle, CURLOPT_HTTPPOST, formpost);
#endif // LIBCURL_VERSION_NUM >= 0x073800
    }

/* -------------------------------------------------------------------- */
/*      If 429, 502, 503 or 504 status code retry this HTTP call until max   */
/*      retry has been reached                                          */
/* -------------------------------------------------------------------- */
    const char *pszRetryDelay =
        CSLFetchNameValue( papszOptions, "RETRY_DELAY" );
    if( pszRetryDelay == nullptr )
        pszRetryDelay = CPLGetConfigOption( "GDAL_HTTP_RETRY_DELAY",
                                    CPLSPrintf("%f", CPL_HTTP_RETRY_DELAY) );
    const char *pszMaxRetries = CSLFetchNameValue( papszOptions, "MAX_RETRY" );
    if( pszMaxRetries == nullptr )
        pszMaxRetries = CPLGetConfigOption( "GDAL_HTTP_MAX_RETRY",
                                    CPLSPrintf("%d",CPL_HTTP_MAX_RETRY) );
    double dfRetryDelaySecs = CPLAtof(pszRetryDelay);
    int nMaxRetries = atoi(pszMaxRetries);
    int nRetryCount = 0;

    while(true)
    {
/* -------------------------------------------------------------------- */
/*      Execute the request, waiting for results.                       */
/* -------------------------------------------------------------------- */
        void* old_handler = CPLHTTPIgnoreSigPipe();
        psResult->nStatus = static_cast<int>(curl_easy_perform(http_handle));
        CPLHTTPRestoreSigPipeHandler(old_handler);

/* -------------------------------------------------------------------- */
/*      Fetch content-type if possible.                                 */
/* -------------------------------------------------------------------- */
        psResult->pszContentType = nullptr;
        curl_easy_getinfo( http_handle, CURLINFO_CONTENT_TYPE,
                           &(psResult->pszContentType) );
        if( psResult->pszContentType != nullptr )
            psResult->pszContentType = CPLStrdup(psResult->pszContentType);

        long response_code = 0;
        curl_easy_getinfo(http_handle, CURLINFO_RESPONSE_CODE,
                            &response_code);
        if( response_code != 200 )
        {
            const double dfNewRetryDelay = CPLHTTPGetNewRetryDelay(
                    static_cast<int>(response_code),
                    dfRetryDelaySecs,
                    reinterpret_cast<const char*>(psResult->pabyData),
                    szCurlErrBuf);
            if( dfNewRetryDelay > 0 && nRetryCount < nMaxRetries )
            {
                CPLError(CE_Warning, CPLE_AppDefined,
                            "HTTP error code: %d - %s. "
                            "Retrying again in %.1f secs",
                            static_cast<int>(response_code), pszURL,
                            dfRetryDelaySecs);
                CPLSleep(dfRetryDelaySecs);
                dfRetryDelaySecs = dfNewRetryDelay;
                nRetryCount++;

                CPLFree(psResult->pszContentType);
                psResult->pszContentType = nullptr;
                CSLDestroy(psResult->papszHeaders);
                psResult->papszHeaders = nullptr;
                CPLFree(psResult->pabyData);
                psResult->pabyData = nullptr;
                psResult->nDataLen = 0;
                psResult->nDataAlloc = 0;

                continue;
            }
        }

/* -------------------------------------------------------------------- */
/*      Have we encountered some sort of error?                         */
/* -------------------------------------------------------------------- */
        if( strlen(szCurlErrBuf) > 0 )
        {
            bool bSkipError = false;

            // Some servers such as
            // http://115.113.193.14/cgi-bin/world/qgis_mapserv.fcgi?VERSION=1.1.1&SERVICE=WMS&REQUEST=GetCapabilities
            // invalidly return Content-Length as the uncompressed size, with
            // makes curl to wait for more data and time-out finally. If we got
            // the expected data size, then we don't emit an error but turn off
            // GZip requests.
            if( bGZipRequested &&
                strstr(szCurlErrBuf, "transfer closed with") &&
                strstr(szCurlErrBuf, "bytes remaining to read") )
            {
                const char* pszContentLength =
                    CSLFetchNameValue(psResult->papszHeaders, "Content-Length");
                if( pszContentLength && psResult->nDataLen != 0 &&
                    atoi(pszContentLength) == psResult->nDataLen )
                {
                    const char* pszCurlGZIPOption =
                        CPLGetConfigOption("CPL_CURL_GZIP", nullptr);
                    if( pszCurlGZIPOption == nullptr )
                    {
                        CPLSetConfigOption("CPL_CURL_GZIP", "NO");
                        CPLDebug("HTTP",
                                 "Disabling CPL_CURL_GZIP, "
                                 "because %s doesn't support it properly",
                                 pszURL);
                    }
                    psResult->nStatus = 0;
                    bSkipError = true;
                }
            }
            if( !bSkipError )
            {
                psResult->pszErrBuf = CPLStrdup(szCurlErrBuf);
                CPLError( CE_Failure, CPLE_AppDefined,
                        "%s", szCurlErrBuf );
            }
        }
        else
        {
            if( response_code >= 400 && response_code < 600 )
            {
                psResult->pszErrBuf =
                    CPLStrdup(CPLSPrintf("HTTP error code : %d",
                                            static_cast<int>(response_code)));
                CPLError(CE_Failure, CPLE_AppDefined,
                            "%s", psResult->pszErrBuf);
            }
        }
        break;
    }

    if( !pszPersistent )
        curl_easy_cleanup( http_handle );

#if LIBCURL_VERSION_NUM >= 0x073800 /* 7.56.0 */
    if( mime != nullptr )
    {
        curl_mime_free(mime);
    }
#else // LIBCURL_VERSION_NUM >= 0x073800
    if( formpost != nullptr)
    {
        curl_formfree(formpost);
    }
#endif // LIBCURL_VERSION_NUM >= 0x073800

    curl_slist_free_all(headers);

    return psResult;
#endif /* def HAVE_CURL */
}

#ifdef HAVE_CURL
/************************************************************************/
/*                       CPLMultiPerformWait()                          */
/************************************************************************/

bool CPLMultiPerformWait(void* hCurlMultiHandleIn, int& repeats)
{
    CURLM* hCurlMultiHandle = static_cast<CURLM*>(hCurlMultiHandleIn);

    // Wait for events on the sockets
    // Using curl_multi_wait() is preferred to avoid hitting the 1024 file
    // descriptor limit
    // 7.28.0
#if LIBCURL_VERSION_NUM >= 0x071C00
    int numfds = 0;
    if( curl_multi_wait(hCurlMultiHandle, nullptr, 0, 1000, &numfds) != CURLM_OK )
    {
        CPLError(CE_Failure, CPLE_AppDefined, "curl_multi_wait() failed");
        return false;
    }
    /* 'numfds' being zero means either a timeout or no file descriptors to
        wait for. Try timeout on first occurrence, then assume no file
        descriptors and no file descriptors to wait for 100
        milliseconds. */
    if(!numfds)
    {
        repeats++; /* count number of repeated zero numfds */
        if(repeats > 1)
        {
            CPLSleep(0.1); /* sleep 100 milliseconds */
        }
    }
    else
    {
        repeats = 0;
    }
#else
    (void)repeats;

    struct timeval timeout;
    fd_set fdread, fdwrite, fdexcep;
    int maxfd;
    FD_ZERO(&fdread);
    FD_ZERO(&fdwrite);
    FD_ZERO(&fdexcep);
    curl_multi_fdset(hCurlMultiHandle, &fdread, &fdwrite, &fdexcep, &maxfd);
    if( maxfd >= 0 )
    {
        timeout.tv_sec = 0;
        timeout.tv_usec = 100000;
        if( select(maxfd + 1, &fdread, &fdwrite, &fdexcep, &timeout) < 0 )
        {
            CPLError(CE_Failure, CPLE_AppDefined, "select() failed");
            return false;
        }
    }
#endif
    return true;
}

class CPLHTTPErrorBuffer
{
    public:
        char szBuffer[CURL_ERROR_SIZE+1];

        CPLHTTPErrorBuffer() { szBuffer[0] = '\0'; }
};

#endif // HAVE_CURL

/************************************************************************/
/*                           CPLHTTPMultiFetch()                        */
/************************************************************************/

/**
 * \brief Fetch several documents at once
 *
 * @param papszURL array of valid URLs recognized by underlying download library (libcurl)
 * @param nURLCount number of URLs of papszURL
 * @param nMaxSimultaneous maximum number of downloads to issue simultaneously.
 *                         Any negative or zer value means unlimited.
 * @param papszOptions option list as a NULL-terminated array of strings. May be NULL.
 *                     Refer to CPLHTTPFetch() for valid options.
 * @return an array of CPLHTTPResult* structures that must be freed by
 * CPLHTTPDestroyMultiResult() or NULL if libcurl support is disabled
 *
 * @since GDAL 2.3
 */
CPLHTTPResult **CPLHTTPMultiFetch( const char * const * papszURL,
                                   int nURLCount,
                                   int nMaxSimultaneous,
                                   CSLConstList papszOptions)
{
#ifndef HAVE_CURL
    (void) papszURL;
    (void) nURLCount;
    (void) nMaxSimultaneous;
    (void) papszOptions;

    CPLError( CE_Failure, CPLE_NotSupported,
              "GDAL/OGR not compiled with libcurl support, "
              "remote requests not supported." );
    return nullptr;
#else /* def HAVE_CURL */

/* -------------------------------------------------------------------- */
/*      Are we using a persistent named session?  If so, search for     */
/*      or create it.                                                   */
/*                                                                      */
/*      Currently this code does not attempt to protect against         */
/*      multiple threads asking for the same named session.  If that    */
/*      occurs it will be in use in multiple threads at once, which     */
/*      will lead to potential crashes in libcurl.                      */
/* -------------------------------------------------------------------- */
    CURLM *hCurlMultiHandle = nullptr;

    const char *pszPersistent = CSLFetchNameValue( papszOptions, "PERSISTENT" );
    const char *pszClosePersistent =
        CSLFetchNameValue( papszOptions, "CLOSE_PERSISTENT" );
    if( pszPersistent )
    {
        CPLString osSessionName = pszPersistent;
        CPLMutexHolder oHolder( &hSessionMapMutex );

        if( poSessionMultiMap == nullptr )
            poSessionMultiMap = new std::map<CPLString, CURLM *>;
        if( poSessionMultiMap->count( osSessionName ) == 0 )
        {
            (*poSessionMultiMap)[osSessionName] = curl_multi_init();
            CPLDebug( "HTTP", "Establish persistent session named '%s'.",
                      osSessionName.c_str() );
        }

        hCurlMultiHandle = (*poSessionMultiMap)[osSessionName];
    }
/* -------------------------------------------------------------------- */
/*      Are we requested to close a persistent named session?           */
/* -------------------------------------------------------------------- */
    else if( pszClosePersistent )
    {
        CPLString osSessionName = pszClosePersistent;
        CPLMutexHolder oHolder( &hSessionMapMutex );

        if( poSessionMultiMap )
        {
            auto oIter = poSessionMultiMap->find( osSessionName );
            if( oIter != poSessionMultiMap->end() )
            {
                curl_multi_cleanup(oIter->second);
                poSessionMultiMap->erase(oIter);
                if( poSessionMultiMap->empty() )
                {
                    delete poSessionMultiMap;
                    poSessionMultiMap = nullptr;
                }
                CPLDebug( "HTTP", "Ended persistent session named '%s'.",
                        osSessionName.c_str() );
            }
            else
            {
                CPLDebug(
                    "HTTP", "Could not find persistent session named '%s'.",
                    osSessionName.c_str() );
            }
        }

        return nullptr;
    }
    else
    {
        hCurlMultiHandle = curl_multi_init();
    }

    CPLHTTPResult** papsResults = static_cast<CPLHTTPResult**>(
        CPLCalloc(nURLCount, sizeof(CPLHTTPResult*)));
    std::vector<CURL*> asHandles;
    std::vector<CPLHTTPResultWithLimit> asResults;
    asResults.resize(nURLCount);
    std::vector<struct curl_slist*> aHeaders;
    aHeaders.resize(nURLCount);
    std::vector<CPLHTTPErrorBuffer> asErrorBuffers;
    asErrorBuffers.resize(nURLCount);

    for( int i = 0; i < nURLCount; i++ )
    {
        papsResults[i] = static_cast<CPLHTTPResult*>(
                                CPLCalloc(1, sizeof(CPLHTTPResult)));

        const char* pszURL = papszURL[i];
        CURL* http_handle = curl_easy_init();

        aHeaders[i] = reinterpret_cast<struct curl_slist*>(
                            CPLHTTPSetOptions(http_handle, pszURL, papszOptions));

        // Set Headers.
        const char *pszHeaders = CSLFetchNameValue( papszOptions, "HEADERS" );
        if( pszHeaders != nullptr )
        {
            char** papszTokensHeaders = CSLTokenizeString2(pszHeaders, "\r\n", 0);
            for( int j=0; papszTokensHeaders[j] != nullptr; ++j )
                aHeaders[i] = curl_slist_append(aHeaders[i], papszTokensHeaders[j]);
            CSLDestroy(papszTokensHeaders);
        }

        if( aHeaders[i] != nullptr )
            curl_easy_setopt(http_handle, CURLOPT_HTTPHEADER, aHeaders[i]);

        // Capture response headers.
        curl_easy_setopt(http_handle, CURLOPT_HEADERDATA, papsResults[i]);
        curl_easy_setopt(http_handle, CURLOPT_HEADERFUNCTION, CPLHdrWriteFct);

        asResults[i].psResult = papsResults[i];
        const char* pszMaxFileSize = CSLFetchNameValue(papszOptions,
                                                    "MAX_FILE_SIZE");
        if( pszMaxFileSize != nullptr )
        {
            asResults[i].nMaxFileSize = atoi(pszMaxFileSize);
            // Only useful if size is returned by server before actual download.
            curl_easy_setopt(http_handle, CURLOPT_MAXFILESIZE,
                            asResults[i].nMaxFileSize);
        }

        curl_easy_setopt(http_handle, CURLOPT_WRITEDATA, &asResults[i] );
        curl_easy_setopt(http_handle, CURLOPT_WRITEFUNCTION, CPLWriteFct );


        curl_easy_setopt(http_handle, CURLOPT_ERRORBUFFER,
                         asErrorBuffers[i].szBuffer );

        if( bSupportGZip &&
            CPLTestBool(CPLGetConfigOption("CPL_CURL_GZIP", "YES")) )
        {
            curl_easy_setopt(http_handle, CURLOPT_ENCODING, "gzip");
        }

        asHandles.push_back(http_handle);
    }

    int iCurRequest = 0;
    for( ; iCurRequest < std::min(nURLCount,
                    nMaxSimultaneous > 0 ? nMaxSimultaneous : INT_MAX); iCurRequest++ )
    {
        CPLHTTPEmitFetchDebug(papszURL[iCurRequest],
                              CPLSPrintf(" %d/%d",iCurRequest+1, nURLCount));
        curl_multi_add_handle(hCurlMultiHandle, asHandles[iCurRequest]);
    }

    int repeats = 0;
    void* old_handler = CPLHTTPIgnoreSigPipe();
    while( true )
    {
        int still_running = 0;
        while (curl_multi_perform(hCurlMultiHandle, &still_running) ==
                                        CURLM_CALL_MULTI_PERFORM )
        {
            // loop
        }
        if( !still_running && iCurRequest == nURLCount )
        {
            break;
        }

        bool bRequestsAdded = false;
        CURLMsg *msg;
        do
        {
            int msgq = 0;
            msg = curl_multi_info_read(hCurlMultiHandle, &msgq);
            if(msg && (msg->msg == CURLMSG_DONE))
            {
                if( iCurRequest < nURLCount )
                {
                    CPLHTTPEmitFetchDebug(papszURL[iCurRequest],
                              CPLSPrintf(" %d/%d",iCurRequest+1, nURLCount));
                    curl_multi_add_handle(hCurlMultiHandle,
                                          asHandles[iCurRequest]);
                    iCurRequest ++;
                    bRequestsAdded = true;
                }
            }
        }
        while(msg);

        if( !bRequestsAdded )
            CPLMultiPerformWait(hCurlMultiHandle, repeats);
    }
    CPLHTTPRestoreSigPipeHandler(old_handler);

    for( int i = 0; i < nURLCount; i++ )
    {
        if( asErrorBuffers[i].szBuffer[0] != '\0' )
            papsResults[i]->pszErrBuf = CPLStrdup(asErrorBuffers[i].szBuffer);
        else
        {
            long response_code = 0;
            curl_easy_getinfo(asHandles[i], CURLINFO_RESPONSE_CODE,
                              &response_code);

            if( response_code >= 400 && response_code < 600 )
            {
                papsResults[i]->pszErrBuf =
                        CPLStrdup(CPLSPrintf("HTTP error code : %d",
                                             static_cast<int>(response_code)));
            }
        }

        curl_easy_getinfo( asHandles[i], CURLINFO_CONTENT_TYPE,
                           &(papsResults[i]->pszContentType) );
        if( papsResults[i]->pszContentType != nullptr )
            papsResults[i]->pszContentType = CPLStrdup(papsResults[i]->pszContentType);

        curl_multi_remove_handle(hCurlMultiHandle, asHandles[i]);
        curl_easy_cleanup(asHandles[i]);
    }

    if( !pszPersistent )
        curl_multi_cleanup(hCurlMultiHandle);

    for( size_t i = 0; i < aHeaders.size(); i++ )
        curl_slist_free_all(aHeaders[i]);

    return papsResults;
#endif /* def HAVE_CURL */
}

/************************************************************************/
/*                      CPLHTTPDestroyMultiResult()                     */
/************************************************************************/
/**
 * \brief Clean the memory associated with the return value of CPLHTTPMultiFetch()
 *
 * @param papsResults pointer to the return value of CPLHTTPMultiFetch()
 * @param nCount value of the nURLCount parameter passed to CPLHTTPMultiFetch()
 * @since GDAL 2.3
 */
void CPLHTTPDestroyMultiResult( CPLHTTPResult **papsResults, int nCount )
{
    if( papsResults )
    {
        for(int i=0;i<nCount;i++)
        {
            CPLHTTPDestroyResult(papsResults[i]);
        }
        CPLFree(papsResults);
    }
}

#ifdef HAVE_CURL

#ifdef WIN32

#include <windows.h>

/************************************************************************/
/*                     CPLFindWin32CurlCaBundleCrt()                    */
/************************************************************************/

static const char* CPLFindWin32CurlCaBundleCrt()
{
    DWORD nResLen;
    const DWORD nBufSize = MAX_PATH + 1;
    char *pszFilePart = nullptr;

    char *pszPath = static_cast<char*>(CPLCalloc(1, nBufSize));

    nResLen = SearchPathA(nullptr, "curl-ca-bundle.crt", nullptr,
                          nBufSize, pszPath, &pszFilePart);
    if (nResLen > 0)
    {
        const char* pszRet = CPLSPrintf("%s", pszPath);
        CPLFree(pszPath);
        return pszRet;
    }
    CPLFree(pszPath);
    return nullptr;
}

#endif // WIN32

/************************************************************************/
/*                         CPLHTTPSetOptions()                          */
/************************************************************************/

// Note: papszOptions must be kept alive until curl_easy/multi_perform()
// has completed, and we must be careful not to set short lived strings
// with curl_easy_setopt(), as long as we need to support curl < 7.17
// see https://curl.haxx.se/libcurl/c/curl_easy_setopt.html
// caution: if we remove that assumption, we'll needto use CURLOPT_COPYPOSTFIELDS

void *CPLHTTPSetOptions(void *pcurl, const char* pszURL,
                       const char * const* papszOptions)
{
    CheckCurlFeatures();

    CURL *http_handle = reinterpret_cast<CURL *>(pcurl);

    curl_easy_setopt(http_handle, CURLOPT_URL, pszURL);

    if( CPLTestBool(CPLGetConfigOption("CPL_CURL_VERBOSE", "NO")) )
        curl_easy_setopt(http_handle, CURLOPT_VERBOSE, 1);

    const char *pszHttpVersion =
        CSLFetchNameValue( papszOptions, "HTTP_VERSION");
    if( pszHttpVersion == nullptr )
        pszHttpVersion = CPLGetConfigOption( "GDAL_HTTP_VERSION", nullptr );
    if( pszHttpVersion && strcmp(pszHttpVersion, "1.0") == 0 )
        curl_easy_setopt(http_handle, CURLOPT_HTTP_VERSION,
                         CURL_HTTP_VERSION_1_0);
    else if( pszHttpVersion && strcmp(pszHttpVersion, "1.1") == 0 )
        curl_easy_setopt(http_handle, CURLOPT_HTTP_VERSION,
                         CURL_HTTP_VERSION_1_1);
    else if( pszHttpVersion &&
             (strcmp(pszHttpVersion, "2") == 0 ||
              strcmp(pszHttpVersion, "2.0") == 0) )
    {
        // 7.33.0
#if LIBCURL_VERSION_NUM >= 0x72100
        if( bSupportHTTP2 )
        {
            // Try HTTP/2 both for HTTP and HTTPS. With fallback to HTTP/1.1
            curl_easy_setopt(http_handle, CURLOPT_HTTP_VERSION,
                             CURL_HTTP_VERSION_2_0);
        }
        else
#endif
        {
            static bool bHasWarned = false;
            if( !bHasWarned )
            {
#if LIBCURL_VERSION_NUM >= 0x72100
                CPLError(CE_Warning, CPLE_NotSupported,
                        "HTTP/2 not available in this build of Curl. "
                        "It needs to be built against nghttp2");
#else
                CPLError(CE_Warning, CPLE_NotSupported,
                          "HTTP/2 not supported by this version of Curl. "
                          "You need curl 7.33 or later, with nghttp2 support");

#endif
                bHasWarned = true;
            }
        }
    }
    else if( pszHttpVersion == nullptr ||
             strcmp(pszHttpVersion, "2TLS") == 0 )
    {
        // 7.47.0
#if LIBCURL_VERSION_NUM >= 0x72F00
        if( bSupportHTTP2 )
        {
            // Only enable this mode if explicitly required, or if the
            // machine is a GCE instance. On other networks, requesting a
            // file in HTTP/2 is found to be significantly slower than HTTP/1.1
            // for unknown reasons.
            if( pszHttpVersion != nullptr || CPLIsMachineForSureGCEInstance() )
            {
                static bool bDebugEmitted = false;
                if( !bDebugEmitted )
                {
                    CPLDebug("HTTP", "Using HTTP/2 for HTTPS when possible");
                    bDebugEmitted = true;
                }

                // CURL_HTTP_VERSION_2TLS means for HTTPS connection, try to
                // negotiate HTTP/2 with the server (and fallback to HTTP/1.1
                // otherwise), and for HTTP connection do HTTP/1
                curl_easy_setopt(http_handle, CURLOPT_HTTP_VERSION,
                                CURL_HTTP_VERSION_2TLS);
            }
        }
        else
#endif
        if( pszHttpVersion != nullptr )
        {
            static bool bHasWarned = false;
            if( !bHasWarned )
            {
#if LIBCURL_VERSION_NUM >= 0x72F00
                CPLError(CE_Warning, CPLE_NotSupported,
                        "HTTP/2 not available in this build of Curl. "
                        "It needs to be built against nghttp2");
#else
                CPLError(CE_Warning, CPLE_NotSupported,
                         "HTTP_VERSION=2TLS not available in this version "
                         "of Curl. You need curl 7.47 or later");
#endif
                bHasWarned = true;
            }
        }
    }
    else
    {
        CPLError(CE_Warning, CPLE_NotSupported,
                 "HTTP_VERSION=%s not supported", pszHttpVersion);
    }

    // Default value is 1 since curl 7.50.2. But worth applying it on
    // previous versions as well.
    const char* pszTCPNoDelay = CSLFetchNameValueDef( papszOptions,
                                                      "TCP_NODELAY", "1");
    curl_easy_setopt(http_handle, CURLOPT_TCP_NODELAY, atoi(pszTCPNoDelay));

    /* Support control over HTTPAUTH */
    const char *pszHttpAuth = CSLFetchNameValue( papszOptions, "HTTPAUTH" );
    if( pszHttpAuth == nullptr )
        pszHttpAuth = CPLGetConfigOption( "GDAL_HTTP_AUTH", nullptr );
    if( pszHttpAuth == nullptr )
        /* do nothing */;

    /* CURLOPT_HTTPAUTH is defined in curl 7.11.0 or newer */
#if LIBCURL_VERSION_NUM >= 0x70B00
    else if( EQUAL(pszHttpAuth, "BASIC") )
        curl_easy_setopt(http_handle, CURLOPT_HTTPAUTH, CURLAUTH_BASIC );
    else if( EQUAL(pszHttpAuth, "NTLM") )
        curl_easy_setopt(http_handle, CURLOPT_HTTPAUTH, CURLAUTH_NTLM );
    else if( EQUAL(pszHttpAuth, "ANY") )
        curl_easy_setopt(http_handle, CURLOPT_HTTPAUTH, CURLAUTH_ANY );
#ifdef CURLAUTH_GSSNEGOTIATE
    else if( EQUAL(pszHttpAuth, "NEGOTIATE") )
        curl_easy_setopt(http_handle, CURLOPT_HTTPAUTH, CURLAUTH_GSSNEGOTIATE );
#endif
    else
    {
        CPLError( CE_Warning, CPLE_AppDefined,
                  "Unsupported HTTPAUTH value '%s', ignored.",
                  pszHttpAuth );
    }
#else
    else
    {
        CPLError( CE_Warning, CPLE_AppDefined,
                  "HTTPAUTH option needs curl >= 7.11.0" );
    }
#endif

    // Support use of .netrc - default enabled.
    const char *pszHttpNetrc = CSLFetchNameValue( papszOptions, "NETRC" );
    if( pszHttpNetrc == nullptr )
        pszHttpNetrc = CPLGetConfigOption( "GDAL_HTTP_NETRC", "YES" );
    if( pszHttpNetrc == nullptr || CPLTestBool(pszHttpNetrc) )
        curl_easy_setopt(http_handle, CURLOPT_NETRC, 1L);

    // Support setting userid:password.
    const char *pszUserPwd = CSLFetchNameValue( papszOptions, "USERPWD" );
    if( pszUserPwd == nullptr )
        pszUserPwd = CPLGetConfigOption("GDAL_HTTP_USERPWD", nullptr);
    if( pszUserPwd != nullptr )
        curl_easy_setopt(http_handle, CURLOPT_USERPWD, pszUserPwd );

    // Set Proxy parameters.
    const char* pszProxy = CSLFetchNameValue( papszOptions, "PROXY" );
    if( pszProxy == nullptr )
        pszProxy = CPLGetConfigOption("GDAL_HTTP_PROXY", nullptr);
    if( pszProxy )
        curl_easy_setopt(http_handle, CURLOPT_PROXY, pszProxy);

    const char* pszHttpsProxy = CSLFetchNameValue( papszOptions, "HTTPS_PROXY" );
    if ( pszHttpsProxy == nullptr )
        pszHttpsProxy = CPLGetConfigOption("GDAL_HTTPS_PROXY", nullptr);
    if ( pszHttpsProxy && (STARTS_WITH(pszURL, "https")) )
        curl_easy_setopt(http_handle, CURLOPT_PROXY, pszHttpsProxy);

    const char* pszProxyUserPwd =
        CSLFetchNameValue( papszOptions, "PROXYUSERPWD" );
    if( pszProxyUserPwd == nullptr )
        pszProxyUserPwd = CPLGetConfigOption("GDAL_HTTP_PROXYUSERPWD", nullptr);
    if( pszProxyUserPwd )
        curl_easy_setopt(http_handle, CURLOPT_PROXYUSERPWD, pszProxyUserPwd);

    // Support control over PROXYAUTH.
    const char *pszProxyAuth = CSLFetchNameValue( papszOptions, "PROXYAUTH" );
    if( pszProxyAuth == nullptr )
        pszProxyAuth = CPLGetConfigOption( "GDAL_PROXY_AUTH", nullptr );
    if( pszProxyAuth == nullptr )
    {
        // Do nothing.
    }
    // CURLOPT_PROXYAUTH is defined in curl 7.11.0 or newer.
#if LIBCURL_VERSION_NUM >= 0x70B00
    else if( EQUAL(pszProxyAuth, "BASIC") )
        curl_easy_setopt(http_handle, CURLOPT_PROXYAUTH, CURLAUTH_BASIC );
    else if( EQUAL(pszProxyAuth, "NTLM") )
        curl_easy_setopt(http_handle, CURLOPT_PROXYAUTH, CURLAUTH_NTLM );
    else if( EQUAL(pszProxyAuth, "DIGEST") )
        curl_easy_setopt(http_handle, CURLOPT_PROXYAUTH, CURLAUTH_DIGEST );
    else if( EQUAL(pszProxyAuth, "ANY") )
        curl_easy_setopt(http_handle, CURLOPT_PROXYAUTH, CURLAUTH_ANY );
    else
    {
        CPLError( CE_Warning, CPLE_AppDefined,
                  "Unsupported PROXYAUTH value '%s', ignored.",
                  pszProxyAuth );
    }
#else
    else
    {
        CPLError( CE_Warning, CPLE_AppDefined,
                  "PROXYAUTH option needs curl >= 7.11.0" );
    }
#endif

    // CURLOPT_SUPPRESS_CONNECT_HEADERS is defined in curl 7.54.0 or newer.
#if LIBCURL_VERSION_NUM >= 0x073600
    curl_easy_setopt(http_handle, CURLOPT_SUPPRESS_CONNECT_HEADERS, 1L);
#endif

    // Enable following redirections.  Requires libcurl 7.10.1 at least.
    curl_easy_setopt(http_handle, CURLOPT_FOLLOWLOCATION, 1 );
    curl_easy_setopt(http_handle, CURLOPT_MAXREDIRS, 10 );
    curl_easy_setopt(http_handle, CURLOPT_POSTREDIR, CURL_REDIR_POST_ALL );

    // Set connect timeout.
    const char *pszConnectTimeout =
        CSLFetchNameValue( papszOptions, "CONNECTTIMEOUT" );
    if( pszConnectTimeout == nullptr )
        pszConnectTimeout = CPLGetConfigOption("GDAL_HTTP_CONNECTTIMEOUT", nullptr);
    if( pszConnectTimeout != nullptr )
        curl_easy_setopt(http_handle, CURLOPT_CONNECTTIMEOUT_MS,
                         static_cast<int>(1000 * CPLAtof(pszConnectTimeout)) );

    // Set timeout.
    const char *pszTimeout = CSLFetchNameValue( papszOptions, "TIMEOUT" );
    if( pszTimeout == nullptr )
        pszTimeout = CPLGetConfigOption("GDAL_HTTP_TIMEOUT", nullptr);
    if( pszTimeout != nullptr )
        curl_easy_setopt(http_handle, CURLOPT_TIMEOUT_MS,
                         static_cast<int>(1000 * CPLAtof(pszTimeout)) );

    // Set low speed time and limit.
    const char *pszLowSpeedTime =
        CSLFetchNameValue( papszOptions, "LOW_SPEED_TIME" );
    if( pszLowSpeedTime == nullptr )
        pszLowSpeedTime = CPLGetConfigOption("GDAL_HTTP_LOW_SPEED_TIME", nullptr);
    if( pszLowSpeedTime != nullptr )
    {
        curl_easy_setopt(http_handle, CURLOPT_LOW_SPEED_TIME,
                         atoi(pszLowSpeedTime) );

        const char *pszLowSpeedLimit =
            CSLFetchNameValue( papszOptions, "LOW_SPEED_LIMIT" );
        if( pszLowSpeedLimit == nullptr )
            pszLowSpeedLimit =
                CPLGetConfigOption("GDAL_HTTP_LOW_SPEED_LIMIT", "1");
        curl_easy_setopt(http_handle, CURLOPT_LOW_SPEED_LIMIT,
                         atoi(pszLowSpeedLimit) );
    }

    /* Disable some SSL verification */
    const char *pszUnsafeSSL = CSLFetchNameValue( papszOptions, "UNSAFESSL" );
    if( pszUnsafeSSL == nullptr )
        pszUnsafeSSL = CPLGetConfigOption("GDAL_HTTP_UNSAFESSL", nullptr);
    if( pszUnsafeSSL != nullptr && CPLTestBool(pszUnsafeSSL) )
    {
        curl_easy_setopt(http_handle, CURLOPT_SSL_VERIFYPEER, 0L);
        curl_easy_setopt(http_handle, CURLOPT_SSL_VERIFYHOST, 0L);
    }

    const char* pszUseCAPIStore = CSLFetchNameValue( papszOptions, "USE_CAPI_STORE" );
    if( pszUseCAPIStore == nullptr )
         pszUseCAPIStore = CPLGetConfigOption("GDAL_HTTP_USE_CAPI_STORE", "NO");
    if( CPLTestBool( pszUseCAPIStore ) )
    {
#if defined(WIN32) && defined(HAVE_OPENSSL_CRYPTO) && LIBCURL_VERSION_NUM >= 0x70B00
        // Use certificates from Windows certificate store; requires crypt32.lib, OpenSSL crypto and ssl libraries.
        curl_easy_setopt(http_handle, CURLOPT_SSL_CTX_FUNCTION, *CPL_ssl_ctx_callback);
#else
        CPLError(CE_Warning, CPLE_NotSupported,
                 "GDAL_HTTP_USE_CAPI_STORE requested, but libcurl too old, "
                 "non-Windows platform or OpenSSL missing.");
#endif
    }

    // Enable OCSP stapling if requested.
    const char *pszSSLVerifyStatus =
                    CSLFetchNameValue( papszOptions, "SSL_VERIFYSTATUS" );
    if( pszSSLVerifyStatus == nullptr )
        pszSSLVerifyStatus = CPLGetConfigOption("GDAL_HTTP_SSL_VERIFYSTATUS", "NO");
    if( CPLTestBool( pszSSLVerifyStatus) )
    {
    // 7.41.0
#if LIBCURL_VERSION_NUM >= 0x72900
        curl_easy_setopt(http_handle, CURLOPT_SSL_VERIFYSTATUS, 1L);
#else
        CPLError(CE_Warning, CPLE_NotSupported,
                 "GDAL_HTTP_SSL_VERIFYSTATUS requested, but libcurl too old "
                 "to support it.");
#endif
    }

    // Custom path to SSL certificates.
    const char* pszCAInfo = CSLFetchNameValue( papszOptions, "CAINFO" );
    if( pszCAInfo == nullptr )
        // Name of environment variable used by the curl binary
        pszCAInfo = CPLGetConfigOption("CURL_CA_BUNDLE", nullptr);
    if( pszCAInfo == nullptr )
        // Name of environment variable used by the curl binary (tested
        // after CURL_CA_BUNDLE
        pszCAInfo = CPLGetConfigOption("SSL_CERT_FILE", nullptr);
#ifdef WIN32
    if( pszCAInfo == nullptr )
    {
        pszCAInfo = CPLFindWin32CurlCaBundleCrt();
    }
#endif
    if( pszCAInfo != nullptr )
    {
        curl_easy_setopt(http_handle, CURLOPT_CAINFO, pszCAInfo);
    }

    const char* pszCAPath = CSLFetchNameValue( papszOptions, "CAPATH" );
    if( pszCAPath != nullptr )
    {
        curl_easy_setopt(http_handle, CURLOPT_CAPATH, pszCAPath);
    }

    /* Set Referer */
    const char *pszReferer = CSLFetchNameValue(papszOptions, "REFERER");
    if( pszReferer != nullptr )
        curl_easy_setopt(http_handle, CURLOPT_REFERER, pszReferer);

    /* Set User-Agent */
    const char *pszUserAgent = CSLFetchNameValue(papszOptions, "USERAGENT");
    if( pszUserAgent == nullptr )
        pszUserAgent = CPLGetConfigOption("GDAL_HTTP_USERAGENT", nullptr);
    if( pszUserAgent != nullptr )
        curl_easy_setopt(http_handle, CURLOPT_USERAGENT, pszUserAgent);

    /* NOSIGNAL should be set to true for timeout to work in multithread
     * environments on Unix, requires libcurl 7.10 or more recent.
     * (this force avoiding the use of signal handlers)
     */
#if LIBCURL_VERSION_NUM >= 0x070A00
    curl_easy_setopt(http_handle, CURLOPT_NOSIGNAL, 1 );
#endif

    const char* pszFormFilePath = CSLFetchNameValue( papszOptions, "FORM_FILE_PATH" );
    const char* pszParametersCount = CSLFetchNameValue( papszOptions, "FORM_ITEM_COUNT" );
    if( pszFormFilePath == nullptr && pszParametersCount == nullptr )
    {
        /* Set POST mode */
        const char* pszPost = CSLFetchNameValue( papszOptions, "POSTFIELDS" );
        if( pszPost != nullptr )
        {
            CPLDebug("HTTP", "These POSTFIELDS were sent:%.4000s", pszPost);
            curl_easy_setopt(http_handle, CURLOPT_POST, 1 );
            curl_easy_setopt(http_handle, CURLOPT_POSTFIELDS, pszPost );
        }

        const char* pszCustomRequest =
            CSLFetchNameValue( papszOptions, "CUSTOMREQUEST" );
        if( pszCustomRequest != nullptr )
        {
            curl_easy_setopt(http_handle, CURLOPT_CUSTOMREQUEST, pszCustomRequest );
        }
    }

    const char* pszCookie = CSLFetchNameValue(papszOptions, "COOKIE");
    if( pszCookie == nullptr )
        pszCookie = CPLGetConfigOption("GDAL_HTTP_COOKIE", nullptr);
    if( pszCookie != nullptr )
        curl_easy_setopt(http_handle, CURLOPT_COOKIE, pszCookie);

    const char* pszCookieFile = CSLFetchNameValue(papszOptions, "COOKIEFILE");
    if( pszCookieFile == nullptr )
        pszCookieFile = CPLGetConfigOption("GDAL_HTTP_COOKIEFILE", nullptr);
    if( pszCookieFile != nullptr )
        curl_easy_setopt(http_handle, CURLOPT_COOKIEFILE, pszCookieFile);

    const char* pszCookieJar = CSLFetchNameValue(papszOptions, "COOKIEJAR");
    if( pszCookieJar == nullptr )
        pszCookieJar = CPLGetConfigOption("GDAL_HTTP_COOKIEJAR", nullptr);
    if( pszCookieJar != nullptr )
        curl_easy_setopt(http_handle, CURLOPT_COOKIEJAR, pszCookieJar);


    struct curl_slist* headers = nullptr;
    const char *pszHeaderFile = CSLFetchNameValue( papszOptions, "HEADER_FILE" );
    if( pszHeaderFile == nullptr )
        pszHeaderFile = CPLGetConfigOption( "GDAL_HTTP_HEADER_FILE", nullptr );
    if( pszHeaderFile != nullptr )
    {
        VSILFILE *fp = nullptr;
        // Do not allow /vsicurl/ access from /vsicurl because of GetCurlHandleFor()
        // e.g. "/vsicurl/,HEADER_FILE=/vsicurl/,url= " would cause use of
        // memory after free
        if( strstr(pszHeaderFile, "/vsicurl/") == nullptr &&
            strstr(pszHeaderFile, "/vsicurl?") == nullptr &&
            strstr(pszHeaderFile, "/vsis3/") == nullptr &&
            strstr(pszHeaderFile, "/vsigs/") == nullptr &&
            strstr(pszHeaderFile, "/vsiaz/") == nullptr &&
            strstr(pszHeaderFile, "/vsioss/") == nullptr &&
            strstr(pszHeaderFile, "/vsiswift/") == nullptr )
        {
            fp = VSIFOpenL( pszHeaderFile, "rb" );
        }
        if( fp == nullptr )
        {
            CPLError(CE_Failure, CPLE_FileIO,
                     "Cannot read %s", pszHeaderFile);
        }
        else
        {
            const char* pszLine = nullptr;
            while( (pszLine = CPLReadLineL(fp)) != nullptr )
            {
                headers = curl_slist_append(headers, pszLine);
            }
            VSIFCloseL(fp);
        }
    }

    return headers;
}

/************************************************************************/
/*                         CPLHTTPIgnoreSigPipe()                       */
/************************************************************************/

/* If using OpenSSL with Curl, openssl can cause SIGPIPE to be triggered */
/* As we set CURLOPT_NOSIGNAL = 1, we must manually handle this situation */

void* CPLHTTPIgnoreSigPipe()
{
#if defined(SIGPIPE) && defined(HAVE_SIGACTION)
    struct sigaction old_pipe_act;
    struct sigaction action;
    /* Get previous handler */
    memset(&old_pipe_act, 0, sizeof(struct sigaction));
    sigaction(SIGPIPE, nullptr, &old_pipe_act);

    /* Install new handler */
    action = old_pipe_act;
    action.sa_handler = SIG_IGN;
    sigaction(SIGPIPE, &action, nullptr);

    void* ret = CPLMalloc(sizeof(old_pipe_act));
    memcpy(ret, &old_pipe_act, sizeof(old_pipe_act));
    return ret;
#else
    return nullptr;
#endif
}

/************************************************************************/
/*                     CPLHTTPRestoreSigPipeHandler()                   */
/************************************************************************/

void CPLHTTPRestoreSigPipeHandler(void* old_handler)
{
#if defined(SIGPIPE) && defined(HAVE_SIGACTION)
    sigaction(SIGPIPE, static_cast<struct sigaction*>(old_handler), nullptr);
    CPLFree(old_handler);
#else
    (void)old_handler;
#endif
}

#endif  // def HAVE_CURL

/************************************************************************/
/*                           CPLHTTPEnabled()                           */
/************************************************************************/

/**
 * \brief Return if CPLHTTP services can be useful
 *
 * Those services depend on GDAL being build with libcurl support.
 *
 * @return TRUE if libcurl support is enabled
 */
int CPLHTTPEnabled()

{
#ifdef HAVE_CURL
    return TRUE;
#else
    return FALSE;
#endif
}

/************************************************************************/
/*                           CPLHTTPCleanup()                           */
/************************************************************************/

/**
 * \brief Cleanup function to call at application termination
 */
void CPLHTTPCleanup()

{
#ifdef HAVE_CURL
    if( !hSessionMapMutex )
        return;

    {
        CPLMutexHolder oHolder( &hSessionMapMutex );
        if( poSessionMap )
        {
            for( std::map<CPLString, CURL *>::iterator oIt =
                     poSessionMap->begin();
                 oIt != poSessionMap->end();
                 oIt++ )
            {
                curl_easy_cleanup( oIt->second );
            }
            delete poSessionMap;
            poSessionMap = nullptr;
        }
        if( poSessionMultiMap )
        {
            for( std::map<CPLString, CURLM *>::iterator oIt =
                     poSessionMultiMap->begin();
                 oIt != poSessionMultiMap->end();
                 oIt++ )
            {
                curl_multi_cleanup( oIt->second );
            }
            delete poSessionMultiMap;
            poSessionMultiMap = nullptr;
        }
    }

    // Not quite a safe sequence.
    CPLDestroyMutex( hSessionMapMutex );
    hSessionMapMutex = nullptr;

#if defined(WIN32) && defined(HAVE_OPENSSL_CRYPTO)
    // This cleanup must be absolutely done before CPLOpenSSLCleanup()
    // for some unknown reason, but otherwise X509_free() in
    // CPLWindowsCertificateListCleanup() will crash.
    CPLWindowsCertificateListCleanup();
#endif

#if defined(HAVE_OPENSSL_CRYPTO) && OPENSSL_VERSION_NUMBER < 0x10100000
    CPLOpenSSLCleanup();
#endif

#endif
}

/************************************************************************/
/*                        CPLHTTPDestroyResult()                        */
/************************************************************************/

/**
 * \brief Clean the memory associated with the return value of CPLHTTPFetch()
 *
 * @param psResult pointer to the return value of CPLHTTPFetch()
 */
void CPLHTTPDestroyResult( CPLHTTPResult *psResult )

{
    if( psResult )
    {
        CPLFree( psResult->pabyData );
        CPLFree( psResult->pszErrBuf );
        CPLFree( psResult->pszContentType );
        CSLDestroy( psResult->papszHeaders );

        for( int i = 0; i < psResult->nMimePartCount; i++ )
        {
            CSLDestroy( psResult->pasMimePart[i].papszHeaders );
        }
        CPLFree(psResult->pasMimePart);

        CPLFree( psResult );
    }
}

/************************************************************************/
/*                     CPLHTTPParseMultipartMime()                      */
/************************************************************************/

/**
 * \brief Parses a MIME multipart message.
 *
 * This function will iterate over each part and put it in a separate
 * element of the pasMimePart array of the provided psResult structure.
 *
 * @param psResult pointer to the return value of CPLHTTPFetch()
 * @return TRUE if the message contains MIME multipart message.
 */
int CPLHTTPParseMultipartMime( CPLHTTPResult *psResult )

{
/* -------------------------------------------------------------------- */
/*      Is it already done?                                             */
/* -------------------------------------------------------------------- */
    if( psResult->nMimePartCount > 0 )
        return TRUE;

/* -------------------------------------------------------------------- */
/*      Find the boundary setting in the content type.                  */
/* -------------------------------------------------------------------- */
    const char *pszBound = nullptr;

    if( psResult->pszContentType != nullptr )
        pszBound = strstr(psResult->pszContentType, "boundary=");

    if( pszBound == nullptr )
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "Unable to parse multi-part mime, no boundary setting." );
        return FALSE;
    }

    CPLString osBoundary;
    char **papszTokens =
        CSLTokenizeStringComplex( pszBound + 9, "\n ;",
                                  TRUE, FALSE );

    if( CSLCount(papszTokens) == 0 || strlen(papszTokens[0]) == 0 )
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "Unable to parse multi-part mime, boundary not parsable." );
        CSLDestroy( papszTokens );
        return FALSE;
    }

    osBoundary = "--";
    osBoundary += papszTokens[0];
    CSLDestroy( papszTokens );

/* -------------------------------------------------------------------- */
/*      Find the start of the first chunk.                              */
/* -------------------------------------------------------------------- */
    char *pszNext =
        psResult->pabyData ?
            strstr(reinterpret_cast<char *>(psResult->pabyData),
               osBoundary.c_str()) : nullptr;

    if( pszNext == nullptr )
    {
        CPLError( CE_Failure, CPLE_AppDefined, "No parts found." );
        return FALSE;
    }

    pszNext += osBoundary.size();
    while( *pszNext != '\n' && *pszNext != '\r' && *pszNext != '\0' )
        pszNext++;
    if( *pszNext == '\r' )
        pszNext++;
    if( *pszNext == '\n' )
        pszNext++;

/* -------------------------------------------------------------------- */
/*      Loop over parts...                                              */
/* -------------------------------------------------------------------- */
    while( true )
    {
        psResult->nMimePartCount++;
        psResult->pasMimePart = static_cast<CPLMimePart *>(
            CPLRealloc(psResult->pasMimePart,
                       sizeof(CPLMimePart) * psResult->nMimePartCount));

        CPLMimePart *psPart = psResult->pasMimePart+psResult->nMimePartCount-1;

        memset( psPart, 0, sizeof(CPLMimePart) );

/* -------------------------------------------------------------------- */
/*      Collect headers.                                                */
/* -------------------------------------------------------------------- */
        while( *pszNext != '\n' && *pszNext != '\r' && *pszNext != '\0' )
        {
            if( !STARTS_WITH(pszNext, "Content-") ) {
                break;
            }
            char *pszEOL = strstr(pszNext, "\n");

            if( pszEOL == nullptr )
            {
                CPLError(CE_Failure, CPLE_AppDefined,
                         "Error while parsing multipart content (at line %d)",
                         __LINE__);
                return FALSE;
            }

            *pszEOL = '\0';
            bool bRestoreAntislashR = false;
            if( pszEOL - pszNext > 1 && pszEOL[-1] == '\r' )
            {
                bRestoreAntislashR = true;
                pszEOL[-1] = '\0';
            }
            char *pszKey = nullptr;
            const char *pszValue = CPLParseNameValue(pszNext, &pszKey );
            if( pszKey && pszValue )
            {
                psPart->papszHeaders =
                    CSLSetNameValue(psPart->papszHeaders, pszKey, pszValue);
            }
            CPLFree(pszKey);
            if( bRestoreAntislashR )
                pszEOL[-1] = '\r';
            *pszEOL = '\n';

            pszNext = pszEOL + 1;
        }

        if( *pszNext == '\r' )
            pszNext++;
        if( *pszNext == '\n' )
            pszNext++;

/* -------------------------------------------------------------------- */
/*      Work out the data block size.                                   */
/* -------------------------------------------------------------------- */
        psPart->pabyData = reinterpret_cast<GByte *>(pszNext);

        int nBytesAvail =
            psResult->nDataLen -
            static_cast<int>(
                pszNext - reinterpret_cast<char *>(psResult->pabyData));

        while( nBytesAvail > 0
               && (*pszNext != '-'
                   || strncmp(pszNext, osBoundary, osBoundary.size()) != 0) )
        {
            pszNext++;
            nBytesAvail--;
        }

        if( nBytesAvail == 0 )
        {
            CPLError(CE_Failure, CPLE_AppDefined,
                     "Error while parsing multipart content (at line %d)",
                     __LINE__);
            return FALSE;
        }

        psPart->nDataLen =
            static_cast<int>(
                pszNext - reinterpret_cast<char *>(psPart->pabyData));
        // Normally the part should end with "\r\n--boundary_marker"
        if( psPart->nDataLen >= 2 && pszNext[-2] == '\r' &&
            pszNext[-1] == '\n' )
        {
            psPart->nDataLen -= 2;
        }

        pszNext += osBoundary.size();

        if( STARTS_WITH(pszNext, "--") )
        {
            break;
        }

        if( *pszNext == '\r' )
            pszNext++;
        if( *pszNext == '\n' )
            pszNext++;
        else
        {
            CPLError(CE_Failure, CPLE_AppDefined,
                     "Error while parsing multipart content (at line %d)",
                     __LINE__);
            return FALSE;
        }
    }

    return TRUE;
}
