oracular (3) curl_ws_meta.3.gz

NAME

       curl_ws_meta - meta data WebSocket information

SYNOPSIS

       #include <curl/curl.h>

       const 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 curl_ws_frame

       struct curl_ws_frame {
         int age;
         int flags;
         curl_off_t offset;
         curl_off_t bytesleft;
       };

       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
              does 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 is 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.

PROTOCOLS

       This functionality affects ws only

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;
         const struct curl_ws_frame *m = curl_ws_meta(c->easy);

         printf("flags: %x\n", m->flags);
       }

       int main(void)
       {
         CURL *curl = curl_easy_init();
         if(curl) {
           struct customdata custom;
           custom.easy = curl;
           custom.ptr = NULL;
           curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writecb);
           curl_easy_setopt(curl, CURLOPT_WRITEDATA, &custom);

           curl_easy_perform(curl);

         }
       }

AVAILABILITY

       Added in curl 7.86.0

RETURN VALUE

       This function returns a pointer to a curl_ws_frame struct with read-only 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_getinfo(3), curl_easy_setopt(3), curl_ws_recv(3), curl_ws_send(3), libcurl-ws(3)