curl/docs/libcurl/curl_easy_nextheader.md

c	SPDX-License-Identifier	Title	Section	Source	See-also	Protocol	Added-in
Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.	curl	curl_easy_nextheader	3	libcurl	curl_easy_header (3) curl_easy_perform (3)	HTTP	7.83.0

NAME

curl_easy_nextheader - get the next HTTP header

SYNOPSIS

#include <curl/curl.h>

struct curl_header *curl_easy_nextheader(CURL *easy,
                                         unsigned int origin,
                                         int request,
                                         struct curl_header *prev);

DESCRIPTION

This function lets an application iterate over all previously received HTTP headers.

The origin argument is for specifying which headers to receive, as a single HTTP transfer might provide headers from several different places and they may then have different importance to the user and headers using the same name might be used. The origin is a bitmask for what header sources you want. See the curl_easy_header(3) man page for the origin descriptions.

The request argument tells libcurl from which request you want headers from. A single transfer might consist of a series of HTTP requests and this argument lets you specify which particular individual request you want the headers from. 0 being the first request and then the number increases for further redirects or when multi-state authentication is used. Passing in -1 is a shortcut to "the last" request in the series, independently of the actual amount of requests used.

It is suggested that you pass in the same origin and request when iterating over a range of headers as changing the value mid-loop might give you unexpected results.

If prev is NULL, this function returns a pointer to the first header stored within the given scope (origin + request).

If prev is a pointer to a previously returned header struct, curl_easy_nextheader(3) returns a pointer the next header stored within the given scope. This way, an application can iterate over all available headers.

The memory for the struct this points to, is owned and managed by libcurl and is associated with the easy handle. Applications must copy the data if they want it to survive subsequent API calls or the life-time of the easy handle.

EXAMPLE

int main(void)
{
  struct curl_header *prev = NULL;
  struct curl_header *h;

  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
    curl_easy_perform(curl);

    /* extract the normal headers from the first request */
    while((h = curl_easy_nextheader(curl, CURLH_HEADER, 0, prev))) {
      printf("%s: %s\n", h->name, h->value);
      prev = h;
    }

    /* extract the normal headers + 1xx + trailers from the last request */
    unsigned int origin = CURLH_HEADER| CURLH_1XX | CURLH_TRAILER;
    while((h = curl_easy_nextheader(curl, origin, -1, prev))) {
      printf("%s: %s\n", h->name, h->value);
      prev = h;
    }
  }
}

RETURN VALUE

This function returns the next header, or NULL when there are no more (matching) headers or an error occurred.

If this function returns NULL when prev was set to NULL, then there are no headers available within the scope to return.