curl_easy_setopt: documented CURLSOCKTYPE_ACCEPT for SOCKOPTFUNCTION

312 - custom Content-Length appears in CONNECT, solve it by offering a separate

      option to provide headers for the CONNECT request

314 - CURL_SOCKOPTFUNCTION for accept()ed connection, see Gokhan Sengun's patch

315 - multiple receivers with SMTP and one fails

317 - CURLINFO_SSL_TRUST to return SSL-specific data for a darwinssl build

function(void *clientp, curl_socket_t curlfd, curlsocktype purpose);\fP. This

function gets called by libcurl after the socket() call but before the

connect() call. The callback's \fIpurpose\fP argument identifies the exact

purpose for this particular socket, and currently only one value is supported:

\fICURLSOCKTYPE_IPCXN\fP for the primary connection (meaning the control

connection in the FTP case). Future versions of libcurl may support more

purposes. It passes the newly created socket descriptor so additional

setsockopt() calls can be done at the user's discretion.  Return 0 (zero) from

the callback on success. Return 1 from the callback function to signal an

unrecoverable error to the library and it will close the socket and return

\fICURLE_COULDNT_CONNECT\fP.  (Option added in 7.16.0)

purpose for this particular socket:

\fICURLSOCKTYPE_IPCXN\fP for actively created connections or since 7.28.0

\fICURLSOCKTYPE_ACCEPT\fP for FTP when the connection was setup with PORT/EPSV

(in earlier versions these sockets weren't passed to this callback).

Future versions of libcurl may support more purposes. It passes the newly

created socket descriptor so additional setsockopt() calls can be done at the

user's discretion.  Return 0 (zero) from the callback on success. Return 1

from the callback function to signal an unrecoverable error to the library and

it will close the socket and return \fICURLE_COULDNT_CONNECT\fP.  (Option

added in 7.16.0)

Added in 7.21.5, the callback function may return

\fICURL_SOCKOPT_ALREADY_CONNECTED\fP, which tells libcurl that the socket is

CURLSHOPT_UNLOCKFUNC            7.10.3

CURLSHOPT_UNSHARE               7.10.3

CURLSHOPT_USERDATA              7.10.3

CURLSOCKTYPE_ACCEPT             7.28.0

CURLSOCKTYPE_IPCXN              7.16.0

CURLSSH_AUTH_AGENT              7.28.0

CURLSSH_AUTH_ANY                7.16.1