DragonFly On-Line Manual Pages

curl_ws_meta(3)                     libcurl                    curl_ws_meta(3)

NAME
       curl_ws_meta - meta data WebSocket information

SYNOPSIS
       #include <curl/easy.h>

       struct curl_ws_frame {
         int age;              /* zero */
         int flags;            /* See the CURLWS_* defines */
         curl_off_t offset;    /* the offset of this data into the frame */
         curl_off_t bytesleft; /* number of pending bytes left of the payload */
       };

       struct curl_ws_frame *curl_ws_meta(CURL *curl);

DESCRIPTION
       This function call is EXPERIMENTAL.

       When the write callback (CURLOPT_WRITEFUNCTION(3)) is invoked on
       received WebSocket traffic, curl_ws_meta(3) can be called from within
       the callback to provide additional information about the current frame.

       This function only works from within the callback, and only when
       receiving WebSocket data.

       This function requires an easy handle as input argument for libcurl to
       know what transfer the question is about, but as there is no such
       pointer provided to the callback by libcurl itself, applications that
       want to use curl_ws_meta(3) need to pass it on to the callback on its
       own.

struct fields
       age    This field specify the age of this struct. It is always zero for
              now.

       flags  This is a bitmask with individual bits set that describes the
              WebSocket data. See the list below.

       offset When this frame is a continuation of fragment data already
              delivered, this is the offset into the final fragment where this
              piece belongs.

       bytesleft
              If this is not a complete fragment, the bytesleft field informs
              about how many additional bytes are expected to arrive before
              this fragment is complete.

FLAGS
       CURLWS_TEXT
              The buffer contains text data. Note that this makes a difference
              to WebSocket but libcurl itself will not make any verification
              of the content or precautions that you actually receive valid
              UTF-8 content.

       CURLWS_BINARY
              This is binary data.

       CURLWS_CONT
              This is not the final fragment of the message, it implies that
              there will be another fragment coming as part of the same
              message.

       CURLWS_CLOSE
              This transfer is now closed.

       CURLWS_PING
              This as an incoming ping message, that expects a pong response.

EXAMPLE

       /* we pass a pointer to this struct to the callback */
       struct customdata {
         CURL *easy;
         void *ptr;
       };

       static size_t writecb(unsigned char *buffer,
                             size_t size, size_t nitems, void *p)
       {
         struct customdata *c = (struct customdata *)p;
         struct curl_ws_frame *m = curl_ws_meta(c->easy);

         /* m->flags tells us about the traffic */
       }

       {
         struct customdata custom;
         custom.easy = easy;
         custom.ptr = NULL;
         curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writecb);
         curl_easy_setopt(curl, CURLOPT_WRITEDATA, &custom);
       }

AVAILABILITY
       Added in 7.86.0.

RETURN VALUE
       This function returns a pointer to a curl_ws_frame struct with
       information that is valid for this specific callback invocation. If it
       cannot return this information, or if the function is called in the
       wrong context, it returns NULL.

SEE ALSO
       curl_easy_setopt(3),  curl_easy_getinfo(3),  curl_ws_send(3),
       curl_ws_recv(3),

libcurl 8.1.2                   April 26, 2023                 curl_ws_meta(3)