experimental (unsafe) SSL support using polarssl/mbedtls. also cmake cleanup.

This commit is contained in:
fgenesis 2015-04-24 00:47:22 +02:00
parent f71e1cc396
commit 587deb0e0e
5 changed files with 453 additions and 93 deletions

View file

@ -2,29 +2,24 @@ cmake_minimum_required(VERSION 2.6)
project(minihttp)
if(MSVC)
if(NOT CMAKE_C_STANDARD_LIBRARIES MATCHES ".*lws2_32.lib.*")
set(CMAKE_C_STANDARD_LIBRARIES "${CMAKE_C_STANDARD_LIBRARIES} ws2_32.lib" CACHE STRING "Default C libs" FORCE)
endif()
if(NOT CMAKE_CXX_STANDARD_LIBRARIES MATCHES ".*lws2_32.lib.*")
set(CMAKE_CXX_STANDARD_LIBRARIES "${CMAKE_CXX_STANDARD_LIBRARIES} ws2_32.lib" CACHE STRING "Default C++ libs" FORCE)
endif()
else()
option(MINIHTTP_USE_POLARSSL FALSE)
set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/cmake/")
set(EXTRA_LIBS "")
if(WIN32)
if(NOT CMAKE_C_STANDARD_LIBRARIES MATCHES ".*-lws2_32.*")
set(CMAKE_C_STANDARD_LIBRARIES "${CMAKE_C_STANDARD_LIBRARIES} -lws2_32" CACHE STRING "Default C libs" FORCE)
endif()
if(NOT CMAKE_CXX_STANDARD_LIBRARIES MATCHES ".*-lws2_32.*")
set(CMAKE_CXX_STANDARD_LIBRARIES "${CMAKE_CXX_STANDARD_LIBRARIES} -lws2_32" CACHE STRING "Default C++ libs" FORCE)
endif()
set(EXTRA_LIBS ${EXTRA_LIBS} ws2_32)
endif()
# non-msvc needs build type - if no build type was provided, set a default one
if(NOT CMAKE_BUILD_TYPE)
set(CMAKE_BUILD_TYPE Release CACHE STRING "Choose the type of build (Debug, Release, RelWithDebInfo, MinSizeRel)" FORCE)
if(MINIHTTP_USE_POLARSSL)
add_definitions(-DMINIHTTP_USE_POLARSSL)
find_package(polarssl)
include_directories(${POLARSSL_INCLUDE_DIRS})
set(EXTRA_LIBS ${EXTRA_LIBS} ${POLARSSL_LIBRARIES})
endif()
endif()
add_executable(htt minihttp.cpp minihttp.h main.cpp)
target_link_libraries(htt ${EXTRA_LIBS})

28
cmake/Findpolarssl.cmake Normal file
View file

@ -0,0 +1,28 @@
#find_package(PkgConfig)
#pkg_check_modules(PC_polarssl QUIET polarssl)
#set(POLARSSL_DEFINITIONS ${PC_polarssl_CFLAGS_OTHER})
find_path(POLARSSL_INCLUDE_DIR ssl_ciphersuites.h ssl.h ssl_ciphersuites.h
HINTS $ENV{POLARSSL_DIR} $ENV{MBEDTLS_DIR}
PATH_SUFFIXES include/polarssl include
PATHS ~/Library/Frameworks /Library/Frameworks /usr/local /usr /sw /opt/local /opt/csw /opt
)
find_library(POLARSSL_LIBRARY
NAMES polarssl mbedtls
HINTS $ENV{POLARSSL_DIR} $ENV{MBEDTLS_DIR}
PATH_SUFFIXES lib64 lib
PATHS ~/Library/Frameworks /Library/Frameworks /usr/local /usr /sw /opt/local /opt/csw /opt
)
include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(polarssl DEFAULT_MSG POLARSSL_LIBRARY POLARSSL_INCLUDE_DIR)
if(POLARSSL_FOUND)
set(POLARSSL_INCLUDE_DIRS "${POLARSSL_INCLUDE_DIR}" CACHE STRING "" FORCE)
set(POLARSSL_LIBRARIES "${POLARSSL_LIBRARY}" CACHE STRING "" FORCE)
endif(POLARSSL_FOUND)
mark_as_advanced(POLARSSL_INCLUDE_DIR POLARSSL_INCLUDE_DIRS)
mark_as_advanced(POLARSSL_LIBRARY POLARSSL_LIBRARIES)

View file

@ -22,6 +22,8 @@ protected:
virtual void _OnOpen()
{
puts("_OnOpen()");
minihttp::SSLResult sr = verifySSL();
printf("SSL status flags (0 is good): 0x%x\n", sr);
minihttp::HttpSocket::_OnOpen();
}
@ -30,7 +32,7 @@ protected:
printf("_OnRequestDone(): %s\n", GetCurrentRequest().resource.c_str());
}
virtual void _OnRecv(char *buf, unsigned int size)
virtual void _OnRecv(void *buf, unsigned int size)
{
if(!size)
return;
@ -48,9 +50,10 @@ int main(int argc, char *argv[])
ht->SetKeepAlive(3);
ht->SetBufsizeIn(64 * 1024);
ht->Download("http://www.ietf.org/rfc/rfc2616.txt");
ht->Download("http://example.com"); // Queue another one
//ht->Download("http://www.ietf.org/rfc/rfc2616.txt");
//ht->Download("http://example.com"); // Queue another one
//ht->Download("https://example.com"); // SSL connection
ht->Download("raw.githubusercontent.com/fgenesis/minihttp/master/minihttp.h"); // transparent HTTP -> HTTPS redirection
minihttp::SocketSet ss;

View file

@ -39,6 +39,14 @@
#include <cctype>
#include <cerrno>
#include <algorithm>
#include <assert.h>
#ifdef MINIHTTP_USE_POLARSSL
# include "polarssl/net.h"
# include "polarssl/ssl.h"
# include "polarssl/entropy.h"
# include "polarssl/ctr_drbg.h"
#endif
#include "minihttp.h"
@ -58,6 +66,71 @@
namespace minihttp {
#ifdef MINIHTTP_USE_POLARSSL
// ------------------------ SSL STUFF -------------------------
bool HasSSL() { return true; }
struct SSLCtx
{
SSLCtx() : _inited(0)
{
entropy_init(&entropy);
x509_crt_init(&cacert);
memset(&ssl, 0, sizeof(ssl_context));
}
~SSLCtx()
{
entropy_free(&entropy);
x509_crt_free(&cacert);
ssl_free(&ssl);
if(_inited & 1)
ctr_drbg_free(&ctr_drbg);
if(_inited & 2)
ssl_free(&ssl);
}
bool init()
{
const char *pers = "minihttp";
const size_t perslen = strlen(pers);
int err = ctr_drbg_init(&ctr_drbg, entropy_func, &entropy, (unsigned char *)pers, perslen);
if(err)
{
traceprint("SSLCtx::init(): ctr_drbg_init() returned %d\n", err);
return false;
}
_inited |= 1;
err = ssl_init(&ssl);
if(err)
{
traceprint("SSLCtx::init(): ssl_init() returned %d\n", err);
return false;
}
_inited |= 2;
return true;
}
void reset()
{
ssl_session_reset(&ssl);
}
entropy_context entropy;
ctr_drbg_context ctr_drbg;
ssl_context ssl;
x509_crt cacert;
private:
unsigned _inited;
};
// ------------------------------------------------------------
#else// MINIHTTP_USE_POLARSSL
bool HasSSL() { return false; }
#endif
#define DEFAULT_BUFSIZE 4096
inline int _GetError()
@ -71,14 +144,19 @@ inline int _GetError()
inline std::string _GetErrorStr(int e)
{
std::string ret;
#ifdef _WIN32
LPTSTR s;
::FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM, NULL, e, 0, (LPTSTR)&s, 0, NULL);
std::string ret = s;
if(s)
ret = s;
::LocalFree(s);
return ret;
#else
const char *s = strerror(e);
if(s)
ret = s;
#endif
return strerror(e);
return ret;
}
bool InitNetwork()
@ -133,18 +211,27 @@ static bool _Resolve(const char *host, unsigned int port, struct sockaddr_in *ad
// FIXME: this does currently not handle links like:
// http://example.com/index.html#pos
bool SplitURI(const std::string& uri, std::string& host, std::string& file, int& port)
bool SplitURI(const std::string& uri, std::string& host, std::string& file, int& port, bool& useSSL)
{
const char *p = uri.c_str();
const char *sl = strstr(p, "//");
unsigned int offs = 0;
bool ssl = false;
if(sl)
{
if(strncmp(p, "http://", 7) == 0)
offs = 7;
if(strncmp(p, "http://", offs))
else if(strncmp(p, "https://", 8) == 0)
{
ssl = true;
offs = 8;
}
else
return false;
p = sl + 2;
}
sl = strchr(p, '/');
if(!sl)
{
@ -164,6 +251,7 @@ bool SplitURI(const std::string& uri, std::string& host, std::string& file, int&
port = atoi(host.c_str() + colon);
host.erase(port);
}
useSSL = ssl;
return true;
}
@ -172,7 +260,12 @@ static bool _SetNonBlocking(SOCKET s, bool nonblock)
{
if(!SOCKETVALID(s))
return false;
#ifdef _WIN32
#ifdef MINIHTTP_USE_POLARSSL
if(nonblock)
return net_set_nonblock(s) == 0;
else
return net_set_block(s) == 0;
#elif defined(_WIN32)
ULONG tmp = !!nonblock;
if(::ioctlsocket(s, FIONBIO, &tmp) == SOCKET_ERROR)
return false;
@ -188,7 +281,7 @@ static bool _SetNonBlocking(SOCKET s, bool nonblock)
TcpSocket::TcpSocket()
: _s(INVALID_SOCKET), _inbuf(NULL), _inbufSize(0), _recvSize(0),
_readptr(NULL), _lastport(0)
_readptr(NULL), _lastport(0), _sslctx(NULL)
{
}
@ -197,6 +290,9 @@ TcpSocket::~TcpSocket()
close();
if(_inbuf)
free(_inbuf);
#ifdef MINIHTTP_USE_POLARSSL
shutdownSSL();
#endif
}
bool TcpSocket::isOpen(void)
@ -211,11 +307,18 @@ void TcpSocket::close(void)
_OnCloseInternal();
#ifdef MINIHTTP_USE_POLARSSL
if(_sslctx)
((SSLCtx*)_sslctx)->reset();
net_close(_s);
#else
# ifdef _WIN32
::closesocket((SOCKET)_s);
# else
::close(_s);
# endif
#endif
_s = INVALID_SOCKET;
}
@ -241,33 +344,18 @@ void TcpSocket::SetBufsizeIn(unsigned int s)
_readptr = _writeptr = _inbuf;
}
bool TcpSocket::open(const char *host /* = NULL */, unsigned int port /* = 0 */)
static bool _openSocket(SOCKET *ps, const char *host, unsigned port)
{
if(isOpen())
#ifdef MINIHTTP_USE_POLARSSL
int s;
int err = net_connect(&s, host, port);
if(err)
{
if( (host && host != _host) || (port && port != _lastport) )
close();
// ... and continue connecting to new host/port
else
return true; // still connected, to same host and port.
}
sockaddr_in addr;
if(host)
_host = host;
else
host = _host.c_str();
if(port)
_lastport = port;
else
{
port = _lastport;
if(!port)
traceprint("open_ssl: net_connect(%s, %u) returned %d\n", host, port, err);
return false;
}
#else
sockaddr_in addr;
if(!_Resolve(host, port, &addr))
{
traceprint("RESOLV ERROR: %s\n", _GetErrorStr(_GetError()).c_str());
@ -287,22 +375,222 @@ bool TcpSocket::open(const char *host /* = NULL */, unsigned int port /* = 0 */)
traceprint("CONNECT ERROR: %s\n", _GetErrorStr(_GetError()).c_str());
return false;
}
#endif
_SetNonBlocking(s, _nonblocking); // restore setting if it was set in invalid state. static call because _s is intentionally still invalid here.
_s = s; // set the socket handle when we are really sure we are connected, and things are set up
*ps = s;
return true;
}
#ifdef MINIHTTP_USE_POLARSSL
void traceprint_ssl(void *ctx, int level, const char *str )
{
(void)ctx;
printf("ssl: [%d] %s\n", level, str);
}
static bool _openSSL(void *ps, SSLCtx *ctx)
{
ssl_set_endpoint(&ctx->ssl, SSL_IS_CLIENT);
ssl_set_authmode(&ctx->ssl, SSL_VERIFY_OPTIONAL);
ssl_set_ca_chain(&ctx->ssl, &ctx->cacert, NULL, NULL);
/* SSLv3 is deprecated, set minimum to TLS 1.0 */
ssl_set_min_version(&ctx->ssl, SSL_MAJOR_VERSION_3, SSL_MINOR_VERSION_1);
/* RC4 is deprecated, disable it */
ssl_set_arc4_support(&ctx->ssl, SSL_ARC4_DISABLED );
ssl_set_rng(&ctx->ssl, ctr_drbg_random, &ctx->ctr_drbg);
ssl_set_dbg(&ctx->ssl, traceprint_ssl, NULL);
//ssl_set_ciphersuites( &ctx->ssl, ssl_default_ciphersuites); // FIXME
ssl_set_bio(&ctx->ssl, net_recv, ps, net_send, ps);
int err;
while( (err = ssl_handshake(&ctx->ssl)) )
{
if(err != POLARSSL_ERR_NET_WANT_READ && err != POLARSSL_ERR_NET_WANT_WRITE)
{
traceprint("open_ssl: ssl_handshake returned -0x%x\n\n", -err);
return false;
}
}
return true;
}
#endif
bool TcpSocket::open(const char *host /* = NULL */, unsigned int port /* = 0 */)
{
if(isOpen())
{
if( (host && host != _host) || (port && port != _lastport) )
close();
// ... and continue connecting to new host/port
else
return true; // still connected, to same host and port.
}
if(host)
_host = host;
else
host = _host.c_str();
if(port)
_lastport = port;
else
{
port = _lastport;
if(!port)
return false;
}
assert(!SOCKETVALID(_s));
{
SOCKET s;
if(!_openSocket(&s, host, port))
return false;
_s = s;
}
_SetNonBlocking(_s, _nonblocking); // restore setting if it was set in invalid state. static call because _s is intentionally still invalid here.
#ifdef MINIHTTP_USE_POLARSSL
if(_sslctx)
if(!_openSSL(&_s, (SSLCtx*)_sslctx))
{
close();
return false;
}
#endif
_OnOpen();
return true;
}
bool TcpSocket::SendBytes(const char *str, unsigned int len)
#ifdef MINIHTTP_USE_POLARSSL
void TcpSocket::shutdownSSL()
{
delete ((SSLCtx*)_sslctx);
_sslctx = NULL;
}
bool TcpSocket::initSSL(const char *certs)
{
SSLCtx *ctx = (SSLCtx*)_sslctx;
if(ctx)
ctx->reset();
else
{
ctx = new SSLCtx();
_sslctx = ctx;
if(!ctx->init())
{
shutdownSSL();
return false;
}
}
if(certs)
{
int err = x509_crt_parse(&ctx->cacert, (const unsigned char*)certs, strlen(certs));
if(err)
{
shutdownSSL();
traceprint("x509_crt_parse() returned %d\n", err);
return false;
}
}
return true;
}
SSLResult TcpSocket::verifySSL()
{
if(!_sslctx)
return SSLR_NO_SSL;
SSLCtx *ctx = (SSLCtx*)_sslctx;
unsigned r = SSLR_OK;
int res = ssl_get_verify_result(&ctx->ssl);
if(res)
{
if(res & BADCERT_EXPIRED)
r |= SSLR_CERT_EXPIRED;
if(res & BADCERT_REVOKED)
r |= SSLR_CERT_REVOKED;
if(res & BADCERT_CN_MISMATCH)
r |= SSLR_CERT_CN_MISMATCH;
if(res & BADCERT_NOT_TRUSTED)
r |= SSLR_CERT_NOT_TRUSTED;
if(res & BADCERT_MISSING)
r |= SSLR_CERT_MISSING;
if(res & BADCERT_SKIP_VERIFY)
r |= SSLR_CERT_SKIP_VERIFY;
if(res & BADCERT_FUTURE)
r |= SSLR_CERT_FUTURE;
// More than just this?
if(res != BADCERT_SKIP_VERIFY)
r |= SSLR_FAIL;
}
return (SSLResult)r;
}
#else // MINIHTTP_USE_POLARSSL
void TcpSocket::shutdownSSL() {}
bool TcpSocket::initSSL(const char *certs) { return false; }
SSLResult TcpSocket::verifySSL() { return SSLR_NO_SSL; }
#endif
bool TcpSocket::SendBytes(const void *str, unsigned int len)
{
if(!SOCKETVALID(_s))
return false;
//traceprint("SEND: '%s'\n", str);
return ::send(_s, str, len, 0) >= 0;
// TODO: check _GetError()
unsigned written = 0;
while(true) // FIXME: buffer bytes to an internal queue instead?
{
int ret = _writeBytes((const unsigned char*)str + written, len - written);
if(ret >= 0)
{
assert((unsigned)ret <= len);
written += (unsigned)ret;
if(written >= len)
break;
}
else
{
#ifdef MINIHTTP_USE_POLARSSL
if(ret == POLARSSL_ERR_NET_WANT_WRITE) // FIXME: wait? queue? try later?
continue;
#endif
traceprint("SendBytes: error %d\n", ret);
return false;
}
}
assert(written == len);
return true;
}
int TcpSocket::_writeBytes(const unsigned char *buf, size_t len)
{
#ifdef MINIHTTP_USE_POLARSSL
if(_sslctx)
return ssl_write(&((SSLCtx*)_sslctx)->ssl, buf, len);
else
return net_send(&_s, buf, len);
#else
return ::send(_s, buf, len, 0);
#endif
}
void TcpSocket::_ShiftBuffer(void)
@ -319,6 +607,18 @@ void TcpSocket::_OnData()
_OnRecv(_readptr, _recvSize);
}
int TcpSocket::_readBytes(unsigned char *buf, size_t maxlen)
{
#ifdef MINIHTTP_USE_POLARSSL
if(_sslctx)
return ssl_read(&((SSLCtx*)_sslctx)->ssl, buf, maxlen);
else
return net_recv(&_s, buf, maxlen);
#else
return recv(_s, buf, maxlen, 0); // last char is used as string terminator
#endif
}
bool TcpSocket::update(void)
{
if(!_OnUpdate())
@ -330,8 +630,7 @@ bool TcpSocket::update(void)
if(!_inbuf)
SetBufsizeIn(DEFAULT_BUFSIZE);
int bytes = recv(_s, _writeptr, _writeSize, 0); // last char is used as string terminator
int bytes = _readBytes((unsigned char*)_writeptr, _writeSize);
if(bytes > 0) // we received something
{
_inbuf[bytes] = 0;
@ -342,36 +641,38 @@ bool TcpSocket::update(void)
_readptr = _writeptr = _inbuf;
_OnData();
return true;
}
else if(bytes == 0) // remote has closed the connection
{
_recvSize = 0;
close();
return true;
}
else // whoops, error?
{
int e = _GetError();
switch(e)
{
case EWOULDBLOCK:
#if defined(EAGAIN) && (EWOULDBLOCK != EAGAIN)
case EAGAIN: // linux man pages say this can also happen instead of EWOULDBLOCK
#endif
return false;
default:
traceprint("SOCKET UPDATE ERROR: (%d): %s\n", e, _GetErrorStr(e).c_str());
case ECONNRESET:
case ENOTCONN:
case ETIMEDOUT:
#ifdef _WIN32
case WSAECONNABORTED:
case WSAESHUTDOWN:
#endif
#ifdef MINIHTTP_USE_POLARSSL
case 0: // no error from the network API, but notification that the SSL connection was terminated
#endif
close();
break;
case EWOULDBLOCK:
#if defined(EAGAIN) && (EWOULDBLOCK != EAGAIN)
case EAGAIN: // linux man pages say this can also happen instead of EWOULDBLOCK
#endif
return false;
}
traceprint("SOCKET UPDATE ERROR: (%d): %s\n", e, _GetErrorStr(e).c_str());
}
return true;
}
@ -429,9 +730,9 @@ bool HttpSocket::Download(const std::string& url, void *user /* = NULL */)
{
Request req;
req.user = user;
SplitURI(url, req.host, req.resource, req.port);
SplitURI(url, req.host, req.resource, req.port, req.useSSL);
if(req.port < 0)
req.port = 80;
req.port = req.useSSL ? 443 : 80;
return SendGet(req, false);
}
@ -512,6 +813,11 @@ bool HttpSocket::_OpenRequest(const Request& req)
traceprint("HttpSocket::_OpenRequest(): _inProgress == true, should not be called.");
return false;
}
if(req.useSSL && !hasSSL())
{
traceprint("HttpSocket::_OpenRequest(): Is an SSL connection, but SSL was not inited, doing that now\n");
initSSL(NULL); // FIXME: supply cert list?
}
if(!open(req.host.c_str(), req.port))
return false;
_inProgress = true;
@ -769,7 +1075,7 @@ void HttpSocket::_OnClose()
_FinishRequest();
}
void HttpSocket::_OnRecvInternal(char *buf, unsigned int size)
void HttpSocket::_OnRecvInternal(void *buf, unsigned int size)
{
if(_status == 200 || _alwaysHandle)
_OnRecv(buf, size);

View file

@ -22,9 +22,25 @@ namespace minihttp
bool InitNetwork();
void StopNetwork();
bool HasSSL();
bool SplitURI(const std::string& uri, std::string& host, std::string& file, int& port);
enum SSLResult
{
SSLR_OK = 0x0,
SSLR_NO_SSL = 0x1,
SSLR_FAIL = 0x2,
SSLR_CERT_EXPIRED = 0x4,
SSLR_CERT_REVOKED = 0x8,
SSLR_CERT_CN_MISMATCH = 0x10,
SSLR_CERT_NOT_TRUSTED = 0x20,
SSLR_CERT_MISSING = 0x40,
SSLR_CERT_SKIP_VERIFY = 0x80,
SSLR_CERT_FUTURE = 0x100,
_SSLR_FORCE32BIT = 0x7fffffff
};
class TcpSocket
{
@ -44,13 +60,19 @@ public:
bool SetNonBlocking(bool nonblock);
unsigned int GetBufSize() { return _inbufSize; }
const char *GetHost(void) { return _host.c_str(); }
bool SendBytes(const char *str, unsigned int len);
bool SendBytes(const void *buf, unsigned int len);
// SSL related
bool initSSL(const char *certs);
bool hasSSL() const { return !!_sslctx; }
void shutdownSSL();
SSLResult verifySSL();
protected:
virtual void _OnCloseInternal();
virtual void _OnData(); // data received callback. Internal, should only be overloaded to call _OnRecv()
virtual void _OnRecv(char *buf, unsigned int size) = 0;
virtual void _OnRecv(void *buf, unsigned int size) = 0;
virtual void _OnClose() {}; // close callback
virtual void _OnOpen() {} // called when opened
virtual bool _OnUpdate() { return true; } // called before reading from the socket
@ -72,6 +94,11 @@ protected:
intptr_t _s; // socket handle. really an int, but to be sure its 64 bit compatible as it seems required on windows, we use this.
std::string _host;
private:
int _writeBytes(const unsigned char *buf, size_t len);
int _readBytes(unsigned char *buf, size_t maxlen);
void *_sslctx;
};
} // end namespace minihttp
@ -97,13 +124,14 @@ struct Request
{
Request() : port(80), user(NULL) {}
Request(const std::string& h, const std::string& res, int p = 80, void *u = NULL)
: host(h), resource(res), port(80), user(u) {}
: host(h), resource(res), port(80), user(u), useSSL(false) {}
std::string host;
std::string header; // set by socket
std::string resource;
int port;
void *user;
bool useSSL;
};
class HttpSocket : public TcpSocket
@ -145,7 +173,7 @@ protected:
virtual void _OnCloseInternal();
virtual void _OnClose();
virtual void _OnData(); // data received callback. Internal, should only be overloaded to call _OnRecv()
virtual void _OnRecv(char *buf, unsigned int size) = 0;
virtual void _OnRecv(void *buf, unsigned int size) = 0;
virtual void _OnOpen(); // called when opene
virtual bool _OnUpdate(); // called before reading from the socket
@ -160,7 +188,7 @@ protected:
void _ParseHeaderFields(const char *s, size_t size);
bool _HandleStatus(); // Returns whether the processed request was successful, or not
void _FinishRequest();
void _OnRecvInternal(char *buf, unsigned int size);
void _OnRecvInternal(void *buf, unsigned int size);
std::string _user_agent;
std::string _accept_encoding; // Default empty.