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Comment by hedora

2 days ago

People don't RTFM, either on HN or when implementing "standards compliant" stuff like MUSL.

No error handling scheme can fix that problem. For instance, if a Rust API says I should return a Result<String, ENOSYS>, I can always write code like `if(ENOSYS) { return Ok("*") } instead of returning Err(ENOSYS).

Then my code would be compatible with MUSL.

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hedora

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zbentley  2 days ago

Sure, but if you didn't do that, and returned the tagged union (in Rust or whatever language), your users would necessarily be forced to handle it in order to process the result.

The only reason this library did the insane thing of returning "*" is because it was extremely easy to cause crashes or false-positives (NULL == NULL) by returning NULL+errno. The reason that was easy is because C lacks a means of making error handling mandatory (exceptions, tuple returns, tagged unions, whatever).

If you return a tagged union, users might mis-handle it, it's true (https://blog.cloudflare.com/18-november-2025-outage/). But they have to handle it, which is a requirement that C APIs are incapable of providing.

  • hedora  2 days ago

    You have to handle NULL in C, or your program crashes (though I suppose a misguided optimization of strcmp could do "a == b || really_strcmp(a, b)", which gets us back to your bug).

    Also, in things like rust you can just do result.unwrap() if you want. In general, language constructs don't really save you from bad programmers.

    • jstanley  1 day ago

      > You have to handle NULL in C, or your program crashes

      But it crashes at runtime, so such a bug can exist for years with nobody noticing.

      The existence of such bugs is what motivated the musl developers to return "*" instead of NULL.

    • zbentley  2 days ago

      > a misguided optimization of strcmp could do "a == b || really_strcmp(a, b)",

      In practice, that's less of a risk than:

          char* x = function_that_might_return_null_and_error();
    dangerous_function();
    if (x == NULL) {...}

      Or code for which pointer identity is relevant (e.g. accessing slices/subparts of a data structure):

          char* x = returns_null_or_a_slice_pointer(data_structure);
    char* y = other_function_that_returns_null_or_a_slice_pointer(data_structure);
    if (x == y) { puts("you're fucked now!"); }

      And for sure there are much better ways to write both kinds of code! But people routinely do not do that.

      2 replies →

dns_snek  2 days ago

> I can always write code like `if(ENOSYS) { return Ok("*") } instead of returning Err(ENOSYS)

You can do that but it's going to feel bad to write that and it's going to stand out like a sore thumb to anyone who reads it. But "errno" is just ambient state that's completely invisible unless you happen to have the manpage fresh in your memory.

  • hedora  2 days ago

    They had to write

       if(ENOSYS) {
     return "*";
   }

    after seeing that other implementations use different sentries like "*0" and that the spec says they MUST return NULL. That must have felt bad too.