eefcc1bda4
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
120 lines
3.7 KiB
Markdown
120 lines
3.7 KiB
Markdown
---
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c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
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SPDX-License-Identifier: curl
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Title: curl_multi_fdset
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Section: 3
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Source: libcurl
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See-also:
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- curl_multi_cleanup (3)
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- curl_multi_init (3)
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- curl_multi_perform (3)
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- curl_multi_timeout (3)
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- curl_multi_wait (3)
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- select (2)
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---
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# NAME
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curl_multi_fdset - extracts file descriptor information from a multi handle
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# SYNOPSIS
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~~~c
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#include <curl/curl.h>
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CURLMcode curl_multi_fdset(CURLM *multi_handle,
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fd_set *read_fd_set,
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fd_set *write_fd_set,
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fd_set *exc_fd_set,
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int *max_fd);
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~~~
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# DESCRIPTION
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This function extracts file descriptor information from a given multi_handle.
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libcurl returns its *fd_set* sets. The application can use these to
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select() on, but be sure to *FD_ZERO* them before calling this function as
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curl_multi_fdset(3) only adds its own descriptors, it does not zero or
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otherwise remove any others. The curl_multi_perform(3) function should
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be called as soon as one of them is ready to be read from or written to.
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The *read_fd_set* argument should point to an object of type **fd_set**
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that on returns specifies the file descriptors to be checked for being ready
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to read.
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The *write_fd_set* argument should point to an object of type **fd_set**
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that on return specifies the file descriptors to be checked for being ready to
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write.
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The *exc_fd_set* argument should point to an object of type **fd_set**
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that on return specifies the file descriptors to be checked for error
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conditions.
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If no file descriptors are set by libcurl, *max_fd* contain -1 when this
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function returns. Otherwise it contains the highest descriptor number libcurl
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set. When libcurl returns -1 in *max_fd*, it is because libcurl currently
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does something that is not possible for your application to monitor with a
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socket and unfortunately you can then not know exactly when the current action
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is completed using select(). You then need to wait a while before you proceed
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and call curl_multi_perform(3) anyway. How long to wait? Unless
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curl_multi_timeout(3) gives you a lower number, we suggest 100
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milliseconds or so, but you may want to test it out in your own particular
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conditions to find a suitable value.
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When doing select(), you should use curl_multi_timeout(3) to figure out
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how long to wait for action. Call curl_multi_perform(3) even if no
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activity has been seen on the **fd_sets** after the timeout expires as
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otherwise internal retries and timeouts may not work as you would think and
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want.
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If one of the sockets used by libcurl happens to be larger than what can be
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set in an **fd_set**, which on POSIX systems means that the file descriptor
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is larger than **FD_SETSIZE**, then libcurl tries to not set it. Setting a
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too large file descriptor in an **fd_set** implies an out of bounds write
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which can cause crashes, or worse. The effect of NOT storing it might possibly
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save you from the crash, but makes your program NOT wait for sockets it should
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wait for...
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# EXAMPLE
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~~~c
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int main(void)
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{
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fd_set fdread;
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fd_set fdwrite;
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fd_set fdexcep;
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int maxfd;
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int rc;
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CURLMcode mc;
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struct timeval timeout = {1, 0};
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CURLM *multi = curl_multi_init();
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do {
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/* call curl_multi_perform() */
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/* get file descriptors from the transfers */
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mc = curl_multi_fdset(multi, &fdread, &fdwrite, &fdexcep, &maxfd);
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if(mc != CURLM_OK) {
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fprintf(stderr, "curl_multi_fdset() failed, code %d.\n", mc);
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break;
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}
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/* wait for activity on one of the sockets */
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rc = select(maxfd + 1, &fdread, &fdwrite, &fdexcep, &timeout);
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} while(!mc);
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}
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~~~
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# AVAILABILITY
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Added in 7.9.6
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# RETURN VALUE
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**CURLMcode** type, general libcurl multi interface error code. See
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libcurl-errors(3)
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