explain_listen(3)

💖 explain_listen 💖 — the explain_listen(3) page, bestie edition

okay so you're in the Library Functions Manual and the star of the show is explain_listen(3). grab a boba, we're decoding socket errors together 🧋✨

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🌸 NAME 🌸

explain_listen — explain listen(2) errors

like, the error whisperer for listen(2). it tells you why it flopped. no cap 💅

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🎀 SYNOPSIS 🎀

#include <libexplain/listen.h>
const char *explain_listen(int fildes, int backlog);
const char *explain_errno_listen(int errnum, int fildes, int backlog);
void explain_message_listen(char *message, int message_size, int fildes,
int backlog);
void explain_message_errno_listen(char *message, int message_size, int
errnum, int fildes, int backlog);

four functions, all here to hold your hand when listen(2) is being dramatic 🫶

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🦋 DESCRIPTION 🦋

these functions hand you explanations for errors that come back from the listen(2) system call. they are literally the friend who explains what the text really meant.

✨ explain_listen ✨

const char *explain_listen(int fildes, int backlog);

so explain_listen gets you an explanation of an error returned by the listen(2) system call. the least the message will contain is the value of strerror(errno), but usually it does much better and tells you the underlying cause in more detail. it ate, fr fr.

the errno global variable is what's used to grab the error value that gets decoded. she reads your mind (well, your errno).

this function is meant to be used in a fashion similar to the following example:

if (listen(fildes, backlog) < 0)
{
    fprintf(stderr, "%s\n", explain_listen(fildes, backlog));
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_listen_or_die(3) function. iconic, honestly.

• fildes — the original fildes, exactly as passed to the listen(2) system call. like, verbatim, don't get creative.
• backlog — the original backlog, exactly as passed to the listen(2) system call. same energy.

Returns:

the message explaining the error. this message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. it will be overwritten by the next call to any libexplain function which shares this buffer, including other threads. so don't get attached 😭

Note: this function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library. bestie, protect your buffers.

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🌈 explain_errno_listen 🌈

const char *explain_errno_listen(int errnum, int fildes, int backlog);

explain_errno_listen gets you an explanation of an error returned by the listen(2) system call. the least the message will contain is the value of strerror(errnum), but usually it will do much better and indicate the underlying cause in more detail. periodt.

this function is meant to be used in a fashion similar to the following example:

if (listen(fildes, backlog) < 0)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_listen(err, fildes, backlog));
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_listen_or_die(3) function. 🫶

• errnum — the error value to be decoded, usually obtained from the errno global variable just before this function is called. this is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno. yes, they're messy like that 💀
• fildes — the original fildes, exactly as passed to the listen(2) system call.
• backlog — the original backlog, exactly as passed to the listen(2) system call.

Returns:

the message explaining the error. this message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. this will be overwritten by the next call to any libexplain function which shares this buffer, including other threads. tragic but true 🙈

Note: this function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

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💜 explain_message_listen 💜

void explain_message_listen(char *message, int message_size, int fildes,
int backlog);

explain_message_listen may be used to obtain an explanation of an error returned by the listen(2) system call. the least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail. she's thorough 💅

the errno global variable will be used to obtain the error value to be decoded.

this function is intended to be used in a fashion similar to the following example:

if (listen(fildes, backlog) < 0)
{
    char message[3000];
    explain_message_listen(message, sizeof(message), fildes, backlog);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_listen_or_die(3) function. ✨

• message — the location in which to store the returned message. if a suitable message return buffer is supplied, this function is thread safe. self-care 💖
• message_size — the size in bytes of the location in which to store the returned message.
• fildes — the original fildes, exactly as passed to the listen(2) system call.
• backlog — the original backlog, exactly as passed to the listen(2) system call.

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🍓 explain_message_errno_listen 🍓

void explain_message_errno_listen(char *message, int message_size, int
errnum, int fildes, int backlog);

explain_message_errno_listen may be used to obtain an explanation of an error returned by the listen(2) system call. the least the message will contain is the value of strerror(errnum), but usually it will do much better, and indicate the underlying cause in more detail. lowkey the most useful one, ngl.

this function is intended to be used in a fashion similar to the following example:

if (listen(fildes, backlog) < 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_listen(message, sizeof(message), err,
        fildes, backlog);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_listen_or_die(3) function. 🌟

• message — the location in which to store the returned message. if a suitable message return buffer is supplied, this function is thread safe. queen behavior 👑
• message_size — the size in bytes of the location in which to store the returned message.
• errnum — the error value to be decoded, usually obtained from the errno global variable just before this function is called. this is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno. they really do be like that 😭
• fildes — the original fildes, exactly as passed to the listen(2) system call.
• backlog — the original backlog, exactly as passed to the listen(2) system call.

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👀 SEE ALSO 👀

• listen(2) — listen for connections on a socket
• explain_listen_or_die(3) — listen for connections on a socket and report errors

go read those too, iykyk 🧚

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💀 COPYRIGHT 💀

libexplain version 1.4 Copyright (C) 2008 Peter Miller

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and that's the whole page, bestie 🎀 go forth and listen(2) responsibly. this was explain_listen(3) from libexplain version 1.4, copyright 2008 Peter Miller — mwah, thanks Peter 💋✨🌈