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133 lines
5.2 KiB
Groff
133 lines
5.2 KiB
Groff
.\" generated by cd2nroff 0.1 from curl_easy_header.md
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.TH curl_easy_header 3 "2024-06-01" libcurl
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.SH NAME
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curl_easy_header \- get an HTTP header
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.SH SYNOPSIS
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.nf
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#include <curl/curl.h>
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CURLHcode curl_easy_header(CURL *easy,
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const char *name,
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size_t index,
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unsigned int origin,
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int request,
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struct curl_header **hout);
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.fi
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.SH DESCRIPTION
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\fIcurl_easy_header(3)\fP returns a pointer to a "curl_header" struct in \fBhout\fP
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with data for the HTTP response header \fIname\fP. The case insensitive
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null\-terminated header name should be specified without colon.
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\fIindex\fP 0 means asking for the first instance of the header. If the returned
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header struct has \fBamount\fP set larger than 1, it means there are more
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instances of the same header name available to get. Asking for a too big index
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makes \fBCURLHE_BADINDEX\fP get returned.
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The \fIorigin\fP argument is for specifying which headers to receive, as a single
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HTTP transfer might provide headers from several different places and they may
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then have different importance to the user and headers using the same name
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might be used. The \fIorigin\fP is a bitmask for what header sources you want. See
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the descriptions below.
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The \fIrequest\fP argument tells libcurl from which request you want headers
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from. A single transfer might consist of a series of HTTP requests and this
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argument lets you specify which particular individual request you want the
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headers from. 0 being the first request and then the number increases for
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further redirects or when multi\-state authentication is used. Passing in \-1 is
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a shortcut to "the last" request in the series, independently of the actual
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amount of requests used.
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libcurl stores and provides the actually used "correct" headers. If for
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example two headers with the same name arrive and the latter overrides the
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former, then only the latter is provided. If the first header survives the
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second, then only the first one is provided. An application using this API
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does not have to bother about multiple headers used wrongly.
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The memory for the returned struct is associated with the easy handle and
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subsequent calls to \fIcurl_easy_header(3)\fP clobber the struct used in the
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previous calls for the same easy handle. Applications need to copy the data if
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it wants to keep it around. The memory used for the struct gets freed with
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calling \fIcurl_easy_cleanup(3)\fP of the easy handle.
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The first line in an HTTP response is called the status line. It is not
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considered a header by this function. Headers are the "name: value" lines
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following the status.
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This function can be used before (all) headers have been received and is fine
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to call from within libcurl callbacks. It returns the state of the headers at
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the time it is called.
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.SH The header struct
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.nf
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struct curl_header {
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char *name;
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char *value;
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size_t amount;
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size_t index;
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unsigned int origin;
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void *anchor;
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};
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.fi
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The data \fBname\fP field points to, is the same as the requested name, but
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might have a different case.
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The data \fBvalue\fP field points to, comes exactly as delivered over the
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network but with leading and trailing whitespace and newlines stripped
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off. The \fIvalue\fP data is null\-terminated. For legacy HTTP/1 "folded headers",
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this API provides the full single value in an unfolded manner with a single
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whitespace between the lines.
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\fBamount\fP is how many headers using this name that exist, within the origin
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and request scope asked for.
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\fBindex\fP is the zero based entry number of this particular header, which in
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case this header was used more than once in the requested scope can be larger
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than 0 but is always less than \fBamount\fP.
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The \fBorigin\fP field in the "curl_header" struct has one of the origin bits
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set, indicating where from the header originates. At the time of this writing,
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there are 5 bits with defined use. The undocumented 27 remaining bits are
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reserved for future use and must not be assumed to have any particular value.
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\fBanchor\fP is a private handle used by libcurl internals. Do not modify.
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.SH ORIGINS
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.IP CURLH_HEADER
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The header arrived as a header from the server.
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.IP CURLH_TRAILER
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The header arrived as a trailer. A header that arrives after the body.
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.IP CURLH_CONNECT
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The header arrived in a CONNECT response. A CONNECT request is being done to
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setup a transfer "through" an HTTP(S) proxy.
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.IP CURLH_1XX
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The header arrived in an HTTP 1xx response. A 1xx response is an "intermediate"
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response that might happen before the "real" response.
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.IP CURLH_PSEUDO
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The header is an HTTP/2 or HTTP/3 pseudo header
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.SH PROTOCOLS
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HTTP
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.SH EXAMPLE
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.nf
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int main(void)
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{
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struct curl_header *type;
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CURL *curl = curl_easy_init();
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if(curl) {
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CURLHcode h;
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curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
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curl_easy_perform(curl);
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h = curl_easy_header(curl, "Content-Type", 0, CURLH_HEADER, -1, &type);
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curl_easy_cleanup(curl);
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}
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}
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.fi
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.SH AVAILABILITY
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Added in 7.83.0. Officially supported since 7.84.0.
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.SH RETURN VALUE
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This function returns a CURLHcode indicating success or error.
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.SH SEE ALSO
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.BR CURLINFO_CONTENT_TYPE (3),
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.BR CURLOPT_HEADERFUNCTION (3),
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.BR curl_easy_nextheader (3),
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.BR curl_easy_perform (3),
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.BR libcurl-errors (3)
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