mirror of https://github.com/curl/curl.git synced 2025-01-06 13:44:52 +08:00

Daniel Stenberg eefcc1bda4

docs: introduce "curldown" for libcurl man page format

curldown is this new file format for libcurl man pages. It is markdown
inspired with differences:

- Each file has a set of leading headers with meta-data
- Supports a small subset of markdown
- Uses .md file extensions for editors/IDE/GitHub to treat them nicely
- Generates man pages very similar to the previous ones
- Generates man pages that still convert nicely to HTML on the website
- Detects and highlights mentions of curl symbols automatically (when
  their man page section is specified)

tools:

- cd2nroff: converts from curldown to nroff man page
- nroff2cd: convert an (old) nroff man page to curldown
- cdall: convert many nroff pages to curldown versions
- cd2cd: verifies and updates a curldown to latest curldown

This setup generates .3 versions of all the curldown versions at build time.

CI:

Since the documentation is now technically markdown in the eyes of many
things, the CI runs many more tests and checks on this documentation,
including proselint, link checkers and tests that make sure we capitalize the
first letter after a period...

Closes #12730

2024-01-23 00:29:02 +01:00

2.8 KiB

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SPDX-License-Identifier

Title

Section

Source

See-also

curl

CURLOPT_SEEKFUNCTION

libcurl

CURLOPT_DEBUGFUNCTION (3)

CURLOPT_IOCTLFUNCTION (3)

CURLOPT_SEEKDATA (3)

CURLOPT_STDERR (3)

NAME

CURLOPT_SEEKFUNCTION - user callback for seeking in input stream

SYNOPSIS

#include <curl/curl.h>

/* These are the return codes for the seek callbacks */
#define CURL_SEEKFUNC_OK       0
#define CURL_SEEKFUNC_FAIL     1 /* fail the entire transfer */
#define CURL_SEEKFUNC_CANTSEEK 2 /* tell libcurl seeking cannot be done, so
                                    libcurl might try other means instead */

int seek_callback(void *clientp, curl_off_t offset, int origin);

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SEEKFUNCTION, seek_callback);

DESCRIPTION

Pass a pointer to your callback function, which should match the prototype shown above.

This function gets called by libcurl to seek to a certain position in the input stream and can be used to fast forward a file in a resumed upload (instead of reading all uploaded bytes with the normal read function/callback). It is also called to rewind a stream when data has already been sent to the server and needs to be sent again. This may happen when doing an HTTP PUT or POST with a multi-pass authentication method, or when an existing HTTP connection is reused too late and the server closes the connection. The function shall work like fseek(3) or lseek(3) and it gets SEEK_SET, SEEK_CUR or SEEK_END as argument for origin, although libcurl currently only passes SEEK_SET.

clientp is the pointer you set with CURLOPT_SEEKDATA(3).

The callback function must return CURL_SEEKFUNC_OK on success, CURL_SEEKFUNC_FAIL to cause the upload operation to fail or CURL_SEEKFUNC_CANTSEEK to indicate that while the seek failed, libcurl is free to work around the problem if possible. The latter can sometimes be done by instead reading from the input or similar.

If you forward the input arguments directly to fseek(3) or lseek(3), note that the data type for offset is not the same as defined for curl_off_t on many systems!

DEFAULT

By default, this is NULL and unused.

PROTOCOLS

HTTP, FTP, SFTP

EXAMPLE

#include <unistd.h> /* for lseek */

struct data {
  int our_fd;
};
static int seek_cb(void *clientp, curl_off_t offset, int origin)
{
  struct data *d = (struct data *)clientp;
  lseek(d->our_fd, offset, origin);
  return CURL_SEEKFUNC_OK;
}

int main(void)
{
  struct data seek_data;
  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_SEEKFUNCTION, seek_cb);
    curl_easy_setopt(curl, CURLOPT_SEEKDATA, &seek_data);
  }
}

AVAILABILITY

Added in 7.18.0

RETURN VALUE

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

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