explain_getsockopt(3)

💖 explain_getsockopt(3) — Library Functions Manual 💖

okay bestie, so this is the explain_getsockopt(3) page, it lives in the Library Functions Manual, and it's genuinely one of those glow-up pages where the vibe is "your socket just told you no and we're gonna find out why." no cap. let's go 🦋

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✨ NAME ✨

explain_getsockopt — bestie, it explains getsockopt(2) errors. that's it. that's the job. 💅

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🌸 SYNOPSIS 🌸

#include <libexplain/getsockopt.h>
const char *explain_getsockopt(int fildes, int level, int name, void
*data, socklen_t *data_size);
const char *explain_errno_getsockopt(int errnum, int fildes, int level,
int name, void *data, socklen_t *data_size);
void explain_message_getsockopt(char *message, int message_size, int
fildes, int level, int name, void *data, socklen_t *data_size);
void explain_message_errno_getsockopt(char *message, int message_size,
int errnum, int fildes, int level, int name, void *data, socklen_t
*data_size);

like. four little functions. four little besties. each one is a slightly different flavor of "please tell me what went wrong" 🫶

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🌈 DESCRIPTION 🌈

okay so the whole point of these functions: you can use them to obtain explanations for errors returned by the getsockopt(2) system call. that's the mission statement. that's the whole personality. 💖

🎀 explain_getsockopt 🎀

const char *explain_getsockopt(int fildes, int level, int name, void
*data, socklen_t *data_size);

the explain_getsockopt function is your girl for obtaining an explanation of an error returned by the getsockopt(2) system call. the least the message will contain is the value of strerror(errno), but usually it does much better than that and indicates the underlying cause in way more detail. lowkey overachiever energy. ✨

the errno global variable will be used to obtain the error value to be decoded. (yes, that errno. the global one. she's the main character here.)

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

if (getsockopt(fildes, level, name, data, data_size) < 0)
{
    fprintf(stderr, "%s\n", explain_getsockopt(fildes,
        level, name, data, data_size));
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_getsockopt_or_die(3) function. (convenience!! we love her!!)

• fildes — the original fildes, exactly as passed to the getsockopt(2) system call.
• level — the original level, exactly as passed to the getsockopt(2) system call.
• name — the original name, exactly as passed to the getsockopt(2) system call.
• data — the original data, exactly as passed to the getsockopt(2) system call.
• data_size — the original data_size, exactly as passed to the getsockopt(2) system call.

Returns:

the message explaining the error. 💀 and here's the tea: 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 like... screenshot it or copy it, bestie, because it will not survive the next call. 😭

Note: this function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library. it's giving "one communal water bottle at the function." 🥤

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💜 explain_errno_getsockopt 💜

const char *explain_errno_getsockopt(int errnum, int fildes, int level,
int name, void *data, socklen_t *data_size);

the explain_errno_getsockopt function is used to obtain an explanation of an error returned by the getsockopt(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. iconic behavior honestly. 👑

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

if (getsockopt(fildes, level, name, data, data_size) < 0)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_getsockopt(err,
        fildes, level, name, data, data_size));
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_getsockopt_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. so yeah — grab that errno immediately, no detours, she does not wait for you. 🏃‍♀️
• fildes — the original fildes, exactly as passed to the getsockopt(2) system call.
• level — the original level, exactly as passed to the getsockopt(2) system call.
• name — the original name, exactly as passed to the getsockopt(2) system call.
• data — the original data, exactly as passed to the getsockopt(2) system call.
• data_size — the original data_size, exactly as passed to the getsockopt(2) system call.

Returns:

the message explaining the error. same situation as before: 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. fr fr, it's temporary. 💔

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_getsockopt 🦋

void explain_message_getsockopt(char *message, int message_size, int
fildes, int level, int name, void *data, socklen_t *data_size);

the explain_message_getsockopt function may be used to obtain an explanation of an error returned by the getsockopt(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. she's thoughtful. she brought a buffer. 💅

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 (getsockopt(fildes, level, name, data, data_size) < 0)
{
    char message[3000];
    explain_message_getsockopt(message, sizeof(message),
        fildes, level, name, data, data_size);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_getsockopt_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. 🎉 (you brought your own cup, so no sharing germs!!)
• 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 getsockopt(2) system call.
• level — the original level, exactly as passed to the getsockopt(2) system call.
• name — the original name, exactly as passed to the getsockopt(2) system call.
• data — the original data, exactly as passed to the getsockopt(2) system call.
• data_size — the original data_size, exactly as passed to the getsockopt(2) system call.

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🧚 explain_message_errno_getsockopt 🧚

void explain_message_errno_getsockopt(char *message, int message_size,
int errnum, int fildes, int level, int name, void *data, socklen_t
*data_size);

the explain_message_errno_getsockopt function may be used to obtain an explanation of an error returned by the getsockopt(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. this one is the full combo meal: your own buffer and your own errnum. ate. 🍓

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

if (getsockopt(fildes, level, name, data, data_size) < 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_getsockopt(message, sizeof(message),
        err, fildes, level, name, data, data_size);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_getsockopt_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. ✨
• 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. (say it with me: save errno FIRST.) 🙈
• fildes — the original fildes, exactly as passed to the getsockopt(2) system call.
• level — the original level, exactly as passed to the getsockopt(2) system call.
• name — the original name, exactly as passed to the getsockopt(2) system call.
• data — the original data, exactly as passed to the getsockopt(2) system call.
• data_size — the original data_size, exactly as passed to the getsockopt(2) system call.

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👀 SEE ALSO 👀

• getsockopt(2) — get and set options on sockets
• explain_getsockopt_or_die(3) — get and set options on sockets and report errors

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💌 COPYRIGHT 💌

and that's the page, bestie!! 🫶

this was libexplain version 1.4, and it's Copyright (C) 2009 Peter Miller. thank you Peter, you absolute legend, for writing the error messages so the rest of us don't have to guess. 👑💖

stay hydrated, save your errno, and don't share your return buffer. periodt. ✨🎀🦋