Merge branch 'b11.16' into 'master'11.16

add upstream 11.16

See merge request opensource-tracking/FreeFileSync!40

4 files changed, 436 insertions, 380 deletions

diff --git a/libcurl/curl_wrap.cpp b/libcurl/curl_wrap.cpp
new file mode 100644
index 00000000..88bde50e
--- /dev/null
+++ b/libcurl/curl_wrap.cpp
@@ -0,0 +1,398 @@
+// *****************************************************************************
+// * This file is part of the FreeFileSync project. It is distributed under    *
+// * GNU General Public License: https://www.gnu.org/licenses/gpl-3.0          *
+// * Copyright (C) Zenju (zenju AT freefilesync DOT org) - All Rights Reserved *
+// *****************************************************************************
+
+#include "curl_wrap.h"
+#include <zen/sys_info.h>
+#include <zen/http.h>
+#include <zen/open_ssl.h>
+#include <zen/thread.h>
+    #include <fcntl.h>
+
+using namespace zen;
+
+
+namespace
+{
+int curlInitLevel = 0; //support interleaving initialization calls!
+//zero-initialized POD => not subject to static initialization order fiasco
+}
+
+void zen::libcurlInit()
+{
+    assert(runningOnMainThread()); //all OpenSSL/libssh2/libcurl require init on main thread!
+    assert(curlInitLevel >= 0);
+    if (++curlInitLevel != 1) //non-atomic => require call from main thread
+        return;
+
+
+    openSslInit();
+
+    [[maybe_unused]] const CURLcode rc2 = ::curl_global_init(CURL_GLOBAL_NOTHING /*CURL_GLOBAL_DEFAULT = CURL_GLOBAL_SSL|CURL_GLOBAL_WIN32*/);
+    assert(rc2 == CURLE_OK);
+}
+
+
+void zen::libcurlTearDown()
+{
+    assert(runningOnMainThread()); //+ avoid race condition on "curlInitLevel"
+    assert(curlInitLevel >= 1);
+    if (--curlInitLevel != 0)
+        return;
+
+    ::curl_global_cleanup();
+    openSslTearDown();
+}
+
+
+HttpSession::HttpSession(const Zstring& server, bool useTls, const Zstring& caCertFilePath, std::chrono::seconds timeOut) : //throw SysError
+    serverPrefix_((useTls ? "https://" : "http://") + utfTo<std::string>(server)),
+    caCertFilePath_(utfTo<std::string>(caCertFilePath)),
+    timeOutSec_(timeOut) {}
+
+
+HttpSession::~HttpSession()
+{
+    if (easyHandle_)
+        ::curl_easy_cleanup(easyHandle_);
+}
+
+
+HttpSession::Result HttpSession::perform(const std::string& serverRelPath,
+                                         const std::vector<std::string>& extraHeaders, const std::vector<CurlOption>& extraOptions,
+                                         const std::function<void  (std::span<const char> buf)>& writeResponse /*throw X*/, //
+                                         const std::function<size_t(std::span<      char> buf)>& readRequest   /*throw X*/, //optional
+                                         const std::function<void  (const std::string_view& header)>& receiveHeader /*throw X*/) //throw SysError, X
+{
+    if (!easyHandle_)
+    {
+        easyHandle_ = ::curl_easy_init();
+        if (!easyHandle_)
+            throw SysError(formatSystemError("curl_easy_init", formatCurlStatusCode(CURLE_OUT_OF_MEMORY), L""));
+    }
+    else
+        ::curl_easy_reset(easyHandle_);
+
+
+    std::vector<CurlOption> options;
+
+    char curlErrorBuf[CURL_ERROR_SIZE] = {};
+    options.emplace_back(CURLOPT_ERRORBUFFER, curlErrorBuf);
+
+    options.emplace_back(CURLOPT_USERAGENT, "FreeFileSync"); //default value; may be overwritten by caller
+
+    //lifetime: keep alive until after curl_easy_setopt() below
+    const std::string curlPath = serverPrefix_ + serverRelPath;
+    options.emplace_back(CURLOPT_URL, curlPath.c_str());
+
+    options.emplace_back(CURLOPT_ACCEPT_ENCODING, ""); //libcurl: generate Accept-Encoding header containing all built-in supported encodings
+    //=> usually generates "Accept-Encoding: deflate, gzip" - note: "gzip" used by Google Drive
+
+    options.emplace_back(CURLOPT_NOSIGNAL, 1); //thread-safety: https://curl.haxx.se/libcurl/c/threadsafe.html
+
+    options.emplace_back(CURLOPT_CONNECTTIMEOUT, timeOutSec_.count());
+
+    //CURLOPT_TIMEOUT: "Since this puts a hard limit for how long time a request is allowed to take, it has limited use in dynamic use cases with varying transfer times."
+    options.emplace_back(CURLOPT_LOW_SPEED_TIME, timeOutSec_.count());
+    options.emplace_back(CURLOPT_LOW_SPEED_LIMIT, 1); //[bytes], can't use "0" which means "inactive", so use some low number
+
+
+    std::exception_ptr userCallbackException;
+
+    //libcurl does *not* set FD_CLOEXEC for us! https://github.com/curl/curl/issues/2252
+    auto onSocketCreate = [&](curl_socket_t curlfd, curlsocktype purpose)
+    {
+        assert(::fcntl(curlfd, F_GETFD) == 0);
+        if (::fcntl(curlfd, F_SETFD, FD_CLOEXEC) == -1) //=> RACE-condition if other thread calls fork/execv before this thread sets FD_CLOEXEC!
+        {
+            userCallbackException = std::make_exception_ptr(SysError(formatSystemError("fcntl(FD_CLOEXEC)", errno)));
+            return CURL_SOCKOPT_ERROR;
+        }
+        return CURL_SOCKOPT_OK;
+    };
+
+    using SocketCbType = decltype(onSocketCreate);
+    using SocketCbWrapperType =            int (*)(SocketCbType* clientp, curl_socket_t curlfd, curlsocktype purpose); //needed for cdecl function pointer cast
+    SocketCbWrapperType onSocketCreateWrapper = [](SocketCbType* clientp, curl_socket_t curlfd, curlsocktype purpose)
+    {
+        return (*clientp)(curlfd, purpose); //free this poor little C-API from its shackles and redirect to a proper lambda
+    };
+
+    options.emplace_back(CURLOPT_SOCKOPTFUNCTION, onSocketCreateWrapper);
+    options.emplace_back(CURLOPT_SOCKOPTDATA, &onSocketCreate);
+
+    //libcurl forwards this char-string to OpenSSL as is, which - thank god - accepts UTF8
+    if (caCertFilePath_.empty())
+    {
+        options.emplace_back(CURLOPT_CAINFO, 0); //see remarks in ftp.cpp
+        options.emplace_back(CURLOPT_SSL_VERIFYPEER, 0);
+        options.emplace_back(CURLOPT_SSL_VERIFYHOST, 0);
+    }
+    else
+        options.emplace_back(CURLOPT_CAINFO, caCertFilePath_.c_str()); //hopefully latest version from https://curl.haxx.se/docs/caextract.html
+    //CURLOPT_SSL_VERIFYPEER => already active by default
+    //CURLOPT_SSL_VERIFYHOST =>
+
+    //---------------------------------------------------
+    auto onHeaderReceived = [&](const void* buffer, size_t len)
+    {
+        try
+        {
+            receiveHeader({static_cast<const char*>(buffer), len}); //throw X
+            return len;
+        }
+        catch (...)
+        {
+            userCallbackException = std::current_exception();
+            return len + 1; //signal error condition => CURLE_WRITE_ERROR
+        }
+    };
+    using HeaderCbType = decltype(onHeaderReceived);
+    using HeaderCbWrapperType =           size_t (*)(const void* buffer, size_t size, size_t nitems, HeaderCbType* callbackData); //needed for cdecl function pointer cast
+    HeaderCbWrapperType onHeaderReceivedWrapper = [](const void* buffer, size_t size, size_t nitems, HeaderCbType* callbackData)
+    {
+        return (*callbackData)(buffer, size * nitems); //free this poor little C-API from its shackles and redirect to a proper lambda
+    };
+    //---------------------------------------------------
+    auto onBytesReceived = [&](const void* buffer, size_t len)
+    {
+        try
+        {
+            writeResponse({static_cast<const char*>(buffer), len}); //throw X
+            return len;
+        }
+        catch (...)
+        {
+            userCallbackException = std::current_exception();
+            return len + 1; //signal error condition => CURLE_WRITE_ERROR
+        }
+    };
+    using ReadCbType = decltype(onBytesReceived);
+    using ReadCbWrapperType =          size_t (*)(const void* buffer, size_t size, size_t nitems, ReadCbType* callbackData); //needed for cdecl function pointer cast
+    ReadCbWrapperType onBytesReceivedWrapper = [](const void* buffer, size_t size, size_t nitems, ReadCbType* callbackData)
+    {
+        return (*callbackData)(buffer, size * nitems); //free this poor little C-API from its shackles and redirect to a proper lambda
+    };
+    //---------------------------------------------------
+    auto getBytesToSend = [&](void* buffer, size_t len) -> size_t
+    {
+        try
+        {
+            //libcurl calls back until 0 bytes are returned (Posix read() semantics), or,
+            //if CURLOPT_INFILESIZE_LARGE was set, after exactly this amount of bytes
+            const size_t bytesRead = readRequest({static_cast<char*>(buffer), len});//throw X; return "bytesToRead" bytes unless end of stream!
+            return bytesRead;
+        }
+        catch (...)
+        {
+            userCallbackException = std::current_exception();
+            return CURL_READFUNC_ABORT; //signal error condition => CURLE_ABORTED_BY_CALLBACK
+        }
+    };
+    using WriteCbType = decltype(getBytesToSend);
+    using WriteCbWrapperType =         size_t (*)(void* buffer, size_t size, size_t nitems, WriteCbType* callbackData);
+    WriteCbWrapperType getBytesToSendWrapper = [](void* buffer, size_t size, size_t nitems, WriteCbType* callbackData)
+    {
+        return (*callbackData)(buffer, size * nitems); //free this poor little C-API from its shackles and redirect to a proper lambda
+    };
+    //---------------------------------------------------
+    if (receiveHeader)
+    {
+        options.emplace_back(CURLOPT_HEADERDATA, &onHeaderReceived);
+        options.emplace_back(CURLOPT_HEADERFUNCTION, onHeaderReceivedWrapper);
+    }
+    if (writeResponse)
+    {
+        options.emplace_back(CURLOPT_WRITEDATA, &onBytesReceived);
+        options.emplace_back(CURLOPT_WRITEFUNCTION, onBytesReceivedWrapper);
+    }
+    if (readRequest)
+    {
+        if (std::all_of(extraOptions.begin(), extraOptions.end(), [](const CurlOption& o) { return o.option != CURLOPT_POST; }))
+        /**/options.emplace_back(CURLOPT_UPLOAD, 1); //issues HTTP PUT
+        options.emplace_back(CURLOPT_READDATA, &getBytesToSend);
+        options.emplace_back(CURLOPT_READFUNCTION, getBytesToSendWrapper);
+    }
+
+    if (std::any_of(extraOptions.begin(), extraOptions.end(), [](const CurlOption& o) { return o.option == CURLOPT_WRITEFUNCTION || o.option == CURLOPT_READFUNCTION; }))
+    /**/ throw std::logic_error("Contract violation! " + std::string(__FILE__) + ':' + numberTo<std::string>(__LINE__)); //Option already used here!
+
+    if (readRequest && std::any_of(extraOptions.begin(), extraOptions.end(), [](const CurlOption& o) { return o.option == CURLOPT_POSTFIELDS; }))
+    /**/ throw std::logic_error("Contract violation! " + std::string(__FILE__) + ':' + numberTo<std::string>(__LINE__)); //Contradicting options: CURLOPT_READFUNCTION, CURLOPT_POSTFIELDS
+
+    //---------------------------------------------------
+    curl_slist* headers = nullptr; //"libcurl will not copy the entire list so you must keep it!"
+    ZEN_ON_SCOPE_EXIT(::curl_slist_free_all(headers));
+
+    for (const std::string& headerLine : extraHeaders)
+        headers = ::curl_slist_append(headers, headerLine.c_str());
+
+    //WTF!!! 1-sec delay when server doesn't support "Expect: 100-continue"!! https://stackoverflow.com/questions/49670008/how-to-disable-expect-100-continue-in-libcurl
+    headers = ::curl_slist_append(headers, "Expect:"); //guess, what: www.googleapis.com doesn't support it! e.g. gdriveUploadFile()
+
+    if (headers)
+        options.emplace_back(CURLOPT_HTTPHEADER, headers);
+    //---------------------------------------------------
+
+    append(options, extraOptions);
+
+    applyCurlOptions(easyHandle_, options); //throw SysError
+
+    //=======================================================================================================
+    const CURLcode rcPerf = ::curl_easy_perform(easyHandle_);
+    //WTF: curl_easy_perform() considers FTP response codes 4XX, 5XX as failure, but for HTTP response codes 4XX are considered success!! CONSISTENCY, people!!!
+    //=> at least libcurl is aware: CURLOPT_FAILONERROR: "request failure on HTTP response >= 400"; default: "0, do not fail on error"
+    //https://curl.haxx.se/docs/faq.html#curl_doesn_t_return_error_for_HT
+    //=> Curiously Google also screws up in their REST API design and returns HTTP 4XX status for domain-level errors!
+    //=> let caller handle HTTP status to work around this mess!
+
+    if (userCallbackException)
+        std::rethrow_exception(userCallbackException); //throw X
+    //=======================================================================================================
+
+    long httpStatus = 0; //optional
+    /*const CURLcode rc = */ ::curl_easy_getinfo(easyHandle_, CURLINFO_RESPONSE_CODE, &httpStatus);
+
+    if (rcPerf != CURLE_OK)
+    {
+        std::wstring errorMsg = trimCpy(utfTo<std::wstring>(curlErrorBuf)); //optional
+
+        if (httpStatus != 0) //optional
+            errorMsg += (errorMsg.empty() ? L"" : L"\n") + formatHttpError(httpStatus);
+#if 0
+        //utfTo<std::wstring>(::curl_easy_strerror(ec)) is uninteresting
+        //use CURLINFO_OS_ERRNO ?? https://curl.haxx.se/libcurl/c/CURLINFO_OS_ERRNO.html
+        long nativeErrorCode = 0;
+        if (::curl_easy_getinfo(easyHandle, CURLINFO_OS_ERRNO, &nativeErrorCode) == CURLE_OK)
+            if (nativeErrorCode != 0)
+                errorMsg += (errorMsg.empty() ? L"" : L"\n") + std::wstring(L"Native error code: ") + numberTo<std::wstring>(nativeErrorCode);
+#endif
+        throw SysError(formatSystemError("curl_easy_perform", formatCurlStatusCode(rcPerf), errorMsg));
+    }
+
+    lastSuccessfulUseTime_ = std::chrono::steady_clock::now();
+    return {static_cast<int>(httpStatus) /*, contentType ? contentType : ""*/};
+}
+
+
+std::wstring zen::formatCurlStatusCode(CURLcode sc)
+{
+    switch (sc)
+    {
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OK);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_UNSUPPORTED_PROTOCOL);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FAILED_INIT);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_URL_MALFORMAT);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_NOT_BUILT_IN);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_COULDNT_RESOLVE_PROXY);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_COULDNT_RESOLVE_HOST);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_COULDNT_CONNECT);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_WEIRD_SERVER_REPLY);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_REMOTE_ACCESS_DENIED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_ACCEPT_FAILED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_WEIRD_PASS_REPLY);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_ACCEPT_TIMEOUT);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_WEIRD_PASV_REPLY);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_WEIRD_227_FORMAT);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_CANT_GET_HOST);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_HTTP2);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_COULDNT_SET_TYPE);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_PARTIAL_FILE);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_COULDNT_RETR_FILE);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE20);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_QUOTE_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_HTTP_RETURNED_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_WRITE_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE24);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_UPLOAD_FAILED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_READ_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OUT_OF_MEMORY);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OPERATION_TIMEDOUT);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE29);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_PORT_FAILED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_COULDNT_USE_REST);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE32);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_RANGE_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_HTTP_POST_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_CONNECT_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_BAD_DOWNLOAD_RESUME);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FILE_COULDNT_READ_FILE);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_LDAP_CANNOT_BIND);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_LDAP_SEARCH_FAILED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE40);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FUNCTION_NOT_FOUND);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_ABORTED_BY_CALLBACK);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_BAD_FUNCTION_ARGUMENT);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE44);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_INTERFACE_FAILED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE46);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TOO_MANY_REDIRECTS);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_UNKNOWN_OPTION);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SETOPT_OPTION_SYNTAX);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE50);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE51);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_GOT_NOTHING);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_ENGINE_NOTFOUND);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_ENGINE_SETFAILED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SEND_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_RECV_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE57);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_CERTPROBLEM);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_CIPHER);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_PEER_FAILED_VERIFICATION);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_BAD_CONTENT_ENCODING);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_LDAP_INVALID_URL);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FILESIZE_EXCEEDED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_USE_SSL_FAILED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SEND_FAIL_REWIND);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_ENGINE_INITFAILED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_LOGIN_DENIED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TFTP_NOTFOUND);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TFTP_PERM);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_REMOTE_DISK_FULL);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TFTP_ILLEGAL);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TFTP_UNKNOWNID);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_REMOTE_FILE_EXISTS);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TFTP_NOSUCHUSER);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_CONV_FAILED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_CONV_REQD);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_CACERT_BADFILE);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_REMOTE_FILE_NOT_FOUND);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSH);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_SHUTDOWN_FAILED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_AGAIN);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_CRL_BADFILE);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_ISSUER_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_PRET_FAILED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_RTSP_CSEQ_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_RTSP_SESSION_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_BAD_FILE_LIST);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_CHUNK_FAILED);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_NO_CONNECTION_AVAILABLE);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_PINNEDPUBKEYNOTMATCH);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_INVALIDCERTSTATUS);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_HTTP2_STREAM);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_RECURSIVE_API_CALL);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_AUTH_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_HTTP3);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_QUIC_CONNECT_ERROR);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_PROXY);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_CLIENTCERT);
+            ZEN_CHECK_CASE_FOR_CONSTANT(CURL_LAST);
+    }
+    static_assert(CURL_LAST == CURLE_SSL_CLIENTCERT + 1);
+
+    return replaceCpy<std::wstring>(L"Curl status %x", L"%x", numberTo<std::wstring>(static_cast<int>(sc)));
+}
+
+
+void zen::applyCurlOptions(CURL* easyHandle, const std::vector<CurlOption>& options) //throw SysError
+{
+    for (const CurlOption& opt : options)
+        if (const CURLcode rc = ::curl_easy_setopt(easyHandle, opt.option, opt.value);
+            rc != CURLE_OK)
+            throw SysError(formatSystemError("curl_easy_setopt(" + numberTo<std::string>(static_cast<int>(opt.option)) + ")",
+                                             formatCurlStatusCode(rc), utfTo<std::wstring>(::curl_easy_strerror(rc))));
+}
diff --git a/libcurl/curl_wrap.h b/libcurl/curl_wrap.h
index 810d735f..ba9fbc13 100644
--- a/libcurl/curl_wrap.h
+++ b/libcurl/curl_wrap.h
@@ -7,9 +7,11 @@
 #ifndef CURL_WRAP_H_2879058325032785032789645
 #define CURL_WRAP_H_2879058325032785032789645
 
-#include <zen/scope_guard.h>
+#include <chrono>
+#include <span>
+#include <functional>
 #include <zen/sys_error.h>
-
+#include <zen/zstring.h>
 
 
 //-------------------------------------------------
@@ -22,6 +24,10 @@
 
 namespace zen
 {
+void libcurlInit();
+void libcurlTearDown();
+
+
 struct CurlOption
 {
     template <class T>
@@ -34,128 +40,40 @@ struct CurlOption
     uint64_t value = 0;
 };
 
-namespace
-{
-std::wstring formatCurlStatusCode(CURLcode sc)
+
+class HttpSession
 {
-    switch (sc)
+public:
+    HttpSession(const Zstring& server, bool useTls, const Zstring& caCertFilePath /*optional*/, std::chrono::seconds timeOut); //throw SysError
+    ~HttpSession();
+
+    struct Result
     {
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OK);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_UNSUPPORTED_PROTOCOL);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FAILED_INIT);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_URL_MALFORMAT);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_NOT_BUILT_IN);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_COULDNT_RESOLVE_PROXY);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_COULDNT_RESOLVE_HOST);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_COULDNT_CONNECT);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_WEIRD_SERVER_REPLY);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_REMOTE_ACCESS_DENIED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_ACCEPT_FAILED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_WEIRD_PASS_REPLY);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_ACCEPT_TIMEOUT);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_WEIRD_PASV_REPLY);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_WEIRD_227_FORMAT);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_CANT_GET_HOST);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_HTTP2);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_COULDNT_SET_TYPE);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_PARTIAL_FILE);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_COULDNT_RETR_FILE);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE20);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_QUOTE_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_HTTP_RETURNED_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_WRITE_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE24);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_UPLOAD_FAILED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_READ_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OUT_OF_MEMORY);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OPERATION_TIMEDOUT);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE29);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_PORT_FAILED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_COULDNT_USE_REST);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE32);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_RANGE_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_HTTP_POST_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_CONNECT_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_BAD_DOWNLOAD_RESUME);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FILE_COULDNT_READ_FILE);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_LDAP_CANNOT_BIND);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_LDAP_SEARCH_FAILED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE40);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FUNCTION_NOT_FOUND);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_ABORTED_BY_CALLBACK);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_BAD_FUNCTION_ARGUMENT);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE44);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_INTERFACE_FAILED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE46);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TOO_MANY_REDIRECTS);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_UNKNOWN_OPTION);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SETOPT_OPTION_SYNTAX);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE50);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE51);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_GOT_NOTHING);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_ENGINE_NOTFOUND);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_ENGINE_SETFAILED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SEND_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_RECV_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_OBSOLETE57);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_CERTPROBLEM);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_CIPHER);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_PEER_FAILED_VERIFICATION);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_BAD_CONTENT_ENCODING);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_LDAP_INVALID_URL);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FILESIZE_EXCEEDED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_USE_SSL_FAILED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SEND_FAIL_REWIND);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_ENGINE_INITFAILED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_LOGIN_DENIED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TFTP_NOTFOUND);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TFTP_PERM);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_REMOTE_DISK_FULL);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TFTP_ILLEGAL);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TFTP_UNKNOWNID);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_REMOTE_FILE_EXISTS);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_TFTP_NOSUCHUSER);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_CONV_FAILED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_CONV_REQD);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_CACERT_BADFILE);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_REMOTE_FILE_NOT_FOUND);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSH);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_SHUTDOWN_FAILED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_AGAIN);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_CRL_BADFILE);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_ISSUER_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_PRET_FAILED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_RTSP_CSEQ_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_RTSP_SESSION_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_FTP_BAD_FILE_LIST);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_CHUNK_FAILED);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_NO_CONNECTION_AVAILABLE);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_PINNEDPUBKEYNOTMATCH);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_INVALIDCERTSTATUS);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_HTTP2_STREAM);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_RECURSIVE_API_CALL);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_AUTH_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_HTTP3);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_QUIC_CONNECT_ERROR);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_PROXY);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURLE_SSL_CLIENTCERT);
-            ZEN_CHECK_CASE_FOR_CONSTANT(CURL_LAST);
-    }
-    static_assert(CURL_LAST == CURLE_SSL_CLIENTCERT + 1);
-
-    return replaceCpy<std::wstring>(L"Curl status %x", L"%x", numberTo<std::wstring>(static_cast<int>(sc)));
-}
+        int statusCode = 0;
+        //std::string contentType;
+    };
+    Result perform(const std::string& serverRelPath,
+                   const std::vector<std::string>& extraHeaders, const std::vector<CurlOption>& extraOptions,
+                   const std::function<void  (std::span<const char> buf)>& writeResponse /*throw X*/,  //
+                   const std::function<size_t(std::span<      char> buf)>& readRequest   /*throw X*/,  //optional
+                   const std::function<void  (const std::string_view& header)>& receiveHeader /*throw X*/); //throw SysError, X
 
+    std::chrono::steady_clock::time_point getLastUseTime() const { return lastSuccessfulUseTime_; }
 
-void applyCurlOptions(CURL* easyHandle, const std::vector<CurlOption>& options) //throw SysError
-{
-    for (const CurlOption& opt : options)
-        if (const CURLcode rc = ::curl_easy_setopt(easyHandle, opt.option, opt.value);
-            rc != CURLE_OK)
-            throw SysError(formatSystemError("curl_easy_setopt(" + numberTo<std::string>(static_cast<int>(opt.option)) + ")",
-                                             formatCurlStatusCode(rc), utfTo<std::wstring>(::curl_easy_strerror(rc))));
-}
-}
+private:
+    HttpSession           (const HttpSession&) = delete;
+    HttpSession& operator=(const HttpSession&) = delete;
+
+    const std::string serverPrefix_;
+    const std::string caCertFilePath_; //optional
+    const std::chrono::seconds timeOutSec_;
+    CURL* easyHandle_ = nullptr;
+    std::chrono::steady_clock::time_point lastSuccessfulUseTime_ = std::chrono::steady_clock::now();
+};
+
+
+std::wstring formatCurlStatusCode(CURLcode sc);
+void applyCurlOptions(CURL* easyHandle, const std::vector<CurlOption>& options); //throw SysError
 }
 
 #else
diff --git a/libcurl/rest.cpp b/libcurl/rest.cpp
deleted file mode 100644
index e80a4961..00000000
--- a/libcurl/rest.cpp
+++ /dev/null
@@ -1,208 +0,0 @@
-// *****************************************************************************
-// * This file is part of the FreeFileSync project. It is distributed under    *
-// * GNU General Public License: https://www.gnu.org/licenses/gpl-3.0          *
-// * Copyright (C) Zenju (zenju AT freefilesync DOT org) - All Rights Reserved *
-// *****************************************************************************
-
-#include "rest.h"
-#include <zen/sys_info.h>
-#include <zen/http.h>
-    #include <fcntl.h>
-
-using namespace zen;
-
-
-HttpSession::HttpSession(const Zstring& server, const Zstring& caCertFilePath, std::chrono::seconds timeOut) : //throw SysError
-    server_(utfTo<std::string>(server)),
-    caCertFilePath_(utfTo<std::string>(caCertFilePath)),
-    timeOutSec_(timeOut) {}
-
-
-HttpSession::~HttpSession()
-{
-    if (easyHandle_)
-        ::curl_easy_cleanup(easyHandle_);
-}
-
-
-HttpSession::Result HttpSession::perform(const std::string& serverRelPath,
-                                         const std::vector<std::string>& extraHeaders, const std::vector<CurlOption>& extraOptions, //throw SysError
-                                         const std::function<void  (const void* buffer, size_t bytesToWrite)>& writeResponse /*throw X*/, //optional
-                                         const std::function<size_t(      void* buffer, size_t bytesToRead )>& readRequest   /*throw X*/) //
-{
-    if (!easyHandle_)
-    {
-        easyHandle_ = ::curl_easy_init();
-        if (!easyHandle_)
-            throw SysError(formatSystemError("curl_easy_init", formatCurlStatusCode(CURLE_OUT_OF_MEMORY), L""));
-    }
-    else
-        ::curl_easy_reset(easyHandle_);
-
-
-    std::vector<CurlOption> options;
-
-    char curlErrorBuf[CURL_ERROR_SIZE] = {};
-    options.emplace_back(CURLOPT_ERRORBUFFER, curlErrorBuf);
-
-    options.emplace_back(CURLOPT_USERAGENT, "FreeFileSync"); //default value; may be overwritten by caller
-
-    //lifetime: keep alive until after curl_easy_setopt() below
-    std::string curlPath = "https://" + server_ + serverRelPath;
-    options.emplace_back(CURLOPT_URL, curlPath.c_str());
-
-    options.emplace_back(CURLOPT_ACCEPT_ENCODING, "gzip"); //won't hurt + used by Google Drive
-
-    options.emplace_back(CURLOPT_NOSIGNAL, 1L); //thread-safety: https://curl.haxx.se/libcurl/c/threadsafe.html
-
-    options.emplace_back(CURLOPT_CONNECTTIMEOUT, timeOutSec_.count());
-
-    //CURLOPT_TIMEOUT: "Since this puts a hard limit for how long time a request is allowed to take, it has limited use in dynamic use cases with varying transfer times."
-    options.emplace_back(CURLOPT_LOW_SPEED_TIME, timeOutSec_.count());
-    options.emplace_back(CURLOPT_LOW_SPEED_LIMIT, 1L); //[bytes], can't use "0" which means "inactive", so use some low number
-
-
-    std::exception_ptr userCallbackException;
-
-    //libcurl does *not* set FD_CLOEXEC for us! https://github.com/curl/curl/issues/2252
-    auto onSocketCreate = [&](curl_socket_t curlfd, curlsocktype purpose)
-    {
-        assert(::fcntl(curlfd, F_GETFD) == 0);
-        if (::fcntl(curlfd, F_SETFD, FD_CLOEXEC) == -1) //=> RACE-condition if other thread calls fork/execv before this thread sets FD_CLOEXEC!
-        {
-            userCallbackException = std::make_exception_ptr(SysError(formatSystemError("fcntl(FD_CLOEXEC)", errno)));
-            return CURL_SOCKOPT_ERROR;
-        }
-        return CURL_SOCKOPT_OK;
-    };
-
-    using SocketCbType = decltype(onSocketCreate);
-    using SocketCbWrapperType =            int (*)(SocketCbType* clientp, curl_socket_t curlfd, curlsocktype purpose); //needed for cdecl function pointer cast
-    SocketCbWrapperType onSocketCreateWrapper = [](SocketCbType* clientp, curl_socket_t curlfd, curlsocktype purpose)
-    {
-        return (*clientp)(curlfd, purpose); //free this poor little C-API from its shackles and redirect to a proper lambda
-    };
-
-    options.emplace_back(CURLOPT_SOCKOPTFUNCTION, onSocketCreateWrapper);
-    options.emplace_back(CURLOPT_SOCKOPTDATA, &onSocketCreate);
-
-    //libcurl forwards this char-string to OpenSSL as is, which - thank god - accepts UTF8
-    options.emplace_back(CURLOPT_CAINFO, caCertFilePath_.c_str()); //hopefully latest version from https://curl.haxx.se/docs/caextract.html
-    //CURLOPT_SSL_VERIFYPEER => already active by default
-    //CURLOPT_SSL_VERIFYHOST =>
-
-    //---------------------------------------------------
-    auto onBytesReceived = [&](const void* buffer, size_t len)
-    {
-        try
-        {
-            writeResponse(buffer, len); //throw X
-            return len;
-        }
-        catch (...)
-        {
-            userCallbackException = std::current_exception();
-            return len + 1; //signal error condition => CURLE_WRITE_ERROR
-        }
-    };
-    using ReadCbType = decltype(onBytesReceived);
-    using ReadCbWrapperType =          size_t (*)(const void* buffer, size_t size, size_t nitems, ReadCbType* callbackData); //needed for cdecl function pointer cast
-    ReadCbWrapperType onBytesReceivedWrapper = [](const void* buffer, size_t size, size_t nitems, ReadCbType* callbackData)
-    {
-        return (*callbackData)(buffer, size * nitems); //free this poor little C-API from its shackles and redirect to a proper lambda
-    };
-    //---------------------------------------------------
-    auto getBytesToSend = [&](void* buffer, size_t len) -> size_t
-    {
-        try
-        {
-            //libcurl calls back until 0 bytes are returned (Posix read() semantics), or,
-            //if CURLOPT_INFILESIZE_LARGE was set, after exactly this amount of bytes
-            const size_t bytesRead = readRequest(buffer, len);//throw X; return "bytesToRead" bytes unless end of stream!
-            return bytesRead;
-        }
-        catch (...)
-        {
-            userCallbackException = std::current_exception();
-            return CURL_READFUNC_ABORT; //signal error condition => CURLE_ABORTED_BY_CALLBACK
-        }
-    };
-    using WriteCbType = decltype(getBytesToSend);
-    using WriteCbWrapperType =         size_t (*)(void* buffer, size_t size, size_t nitems, WriteCbType* callbackData);
-    WriteCbWrapperType getBytesToSendWrapper = [](void* buffer, size_t size, size_t nitems, WriteCbType* callbackData)
-    {
-        return (*callbackData)(buffer, size * nitems); //free this poor little C-API from its shackles and redirect to a proper lambda
-    };
-    //---------------------------------------------------
-    if (writeResponse)
-    {
-        options.emplace_back(CURLOPT_WRITEDATA, &onBytesReceived);
-        options.emplace_back(CURLOPT_WRITEFUNCTION, onBytesReceivedWrapper);
-    }
-    if (readRequest)
-    {
-        if (std::all_of(extraOptions.begin(), extraOptions.end(), [](const CurlOption& o) { return o.option != CURLOPT_POST; }))
-        /**/options.emplace_back(CURLOPT_UPLOAD, 1L); //issues HTTP PUT
-        options.emplace_back(CURLOPT_READDATA, &getBytesToSend);
-        options.emplace_back(CURLOPT_READFUNCTION, getBytesToSendWrapper);
-    }
-
-    if (std::any_of(extraOptions.begin(), extraOptions.end(), [](const CurlOption& o) { return o.option == CURLOPT_WRITEFUNCTION || o.option == CURLOPT_READFUNCTION; }))
-    throw std::logic_error("Contract violation! " + std::string(__FILE__) + ':' + numberTo<std::string>(__LINE__)); //Option already used here!
-
-    if (readRequest && std::any_of(extraOptions.begin(), extraOptions.end(), [](const CurlOption& o) { return o.option == CURLOPT_POSTFIELDS; }))
-    throw std::logic_error("Contract violation! " + std::string(__FILE__) + ':' + numberTo<std::string>(__LINE__)); //Contradicting options: CURLOPT_READFUNCTION, CURLOPT_POSTFIELDS
-
-    //---------------------------------------------------
-    curl_slist* headers = nullptr; //"libcurl will not copy the entire list so you must keep it!"
-    ZEN_ON_SCOPE_EXIT(::curl_slist_free_all(headers));
-
-    for (const std::string& headerLine : extraHeaders)
-        headers = ::curl_slist_append(headers, headerLine.c_str());
-
-    //WTF!!! 1-sec delay when server doesn't support "Expect: 100-continue"!! https://stackoverflow.com/questions/49670008/how-to-disable-expect-100-continue-in-libcurl
-    headers = ::curl_slist_append(headers, "Expect:"); //guess, what: www.googleapis.com doesn't support it! e.g. gdriveUploadFile()
-
-    if (headers)
-        options.emplace_back(CURLOPT_HTTPHEADER, headers);
-    //---------------------------------------------------
-
-    append(options, extraOptions);
-
-    applyCurlOptions(easyHandle_, options); //throw SysError
-
-    //=======================================================================================================
-    const CURLcode rcPerf = ::curl_easy_perform(easyHandle_);
-    //WTF: curl_easy_perform() considers FTP response codes 4XX, 5XX as failure, but for HTTP response codes 4XX are considered success!! CONSISTENCY, people!!!
-    //=> at least libcurl is aware: CURLOPT_FAILONERROR: "request failure on HTTP response >= 400"; default: "0, do not fail on error"
-    //https://curl.haxx.se/docs/faq.html#curl_doesn_t_return_error_for_HT
-    //=> Curiously Google also screws up in their REST API design and returns HTTP 4XX status for domain-level errors!
-    //=> let caller handle HTTP status to work around this mess!
-
-    if (userCallbackException)
-        std::rethrow_exception(userCallbackException); //throw X
-    //=======================================================================================================
-
-    long httpStatus = 0; //optional
-    /*const CURLcode rc = */ ::curl_easy_getinfo(easyHandle_, CURLINFO_RESPONSE_CODE, &httpStatus);
-
-    if (rcPerf != CURLE_OK)
-    {
-        std::wstring errorMsg = trimCpy(utfTo<std::wstring>(curlErrorBuf)); //optional
-
-        if (httpStatus != 0) //optional
-            errorMsg += (errorMsg.empty() ? L"" : L"\n") + formatHttpError(httpStatus);
-#if 0
-        //utfTo<std::wstring>(::curl_easy_strerror(ec)) is uninteresting
-        //use CURLINFO_OS_ERRNO ?? https://curl.haxx.se/libcurl/c/CURLINFO_OS_ERRNO.html
-        long nativeErrorCode = 0;
-        if (::curl_easy_getinfo(easyHandle, CURLINFO_OS_ERRNO, &nativeErrorCode) == CURLE_OK)
-            if (nativeErrorCode != 0)
-                errorMsg += (errorMsg.empty() ? L"" : L"\n") + std::wstring(L"Native error code: ") + numberTo<std::wstring>(nativeErrorCode);
-#endif
-        throw SysError(formatSystemError("curl_easy_perform", formatCurlStatusCode(rcPerf), errorMsg));
-    }
-
-    lastSuccessfulUseTime_ = std::chrono::steady_clock::now();
-    return {static_cast<int>(httpStatus) /*, contentType ? contentType : ""*/};
-}
diff --git a/libcurl/rest.h b/libcurl/rest.h
deleted file mode 100644
index df41a3cc..00000000
--- a/libcurl/rest.h
+++ /dev/null
@@ -1,52 +0,0 @@
-// *****************************************************************************
-// * This file is part of the FreeFileSync project. It is distributed under    *
-// * GNU General Public License: https://www.gnu.org/licenses/gpl-3.0          *
-// * Copyright (C) Zenju (zenju AT freefilesync DOT org) - All Rights Reserved *
-// *****************************************************************************
-
-#ifndef REST_H_07018456781346523454
-#define REST_H_07018456781346523454
-
-#include <chrono>
-#include <functional>
-#include <zen/sys_error.h>
-#include <zen/zstring.h>
-#include "curl_wrap.h" //DON'T include <curl/curl.h> directly!
-
-
-namespace zen
-{
-//Initialization requirement: 1. WSAStartup 2. OpenSSL 3. curl_global_init()
-// => use UniCounterCookie!
-
-class HttpSession
-{
-public:
-    HttpSession(const Zstring& server, const Zstring& caCertFilePath, std::chrono::seconds timeOut); //throw SysError
-    ~HttpSession();
-
-    struct Result
-    {
-        int statusCode = 0;
-        //std::string contentType;
-    };
-    Result perform(const std::string& serverRelPath,
-                   const std::vector<std::string>& extraHeaders, const std::vector<CurlOption>& extraOptions, //throw SysError
-                   const std::function<void  (const void* buffer, size_t bytesToWrite)>& writeResponse /*throw X*/, //optional
-                   const std::function<size_t(      void* buffer, size_t bytesToRead )>& readRequest   /*throw X*/); //
-
-    std::chrono::steady_clock::time_point getLastUseTime() const { return lastSuccessfulUseTime_; }
-
-private:
-    HttpSession           (const HttpSession&) = delete;
-    HttpSession& operator=(const HttpSession&) = delete;
-
-    const std::string server_;
-    const std::string caCertFilePath_;
-    const std::chrono::seconds timeOutSec_;
-    CURL* easyHandle_ = nullptr;
-    std::chrono::steady_clock::time_point lastSuccessfulUseTime_ = std::chrono::steady_clock::now();
-};
-}
-
-#endif //REST_H_07018456781346523454