[jjav]

> the real solution is obvious

If it were obvious it would have been done already. Witness the many variants that try to make it better but don't.

> using proper string buffer types with length and capacity

Which you then can't pass to any other library. String management is very easy to solve within the boundaries of your own code. But you'll need to interact with existing code as well.

[sirwhinesalot]

> If it were obvious it would have been done already. Witness the many variants that try to make it better but don't.

Every other language with mutable strings, including C++, does it like that. It is obvious. The reason it is not done in C is not ignorance, it is laziness.

> Which you then can't pass to any other library. String management is very easy to solve within the boundaries of your own code. But you'll need to interact with existing code as well.

Ignoring the also obvious solution of just keeping a null terminator around (see: C++ std::string), you should only worry about it at the boundary with the other library.

Same as converting from utf-8 to utf-16 to talk to the Windows API for example.

[jjav]

> The reason it is not done in C is not ignorance, it is laziness.

Of course not. C has been around since the dawn of UNIX and the majority of important libraries at the OS level are written in it.

Compatibility with such a vast amount of code is a lot more important than anything else.

If it were so easy why do you think nobody has done it?

> Ignoring the also obvious solution of just keeping a null terminator around

That's not very useful for the general case. If your code relies on the extra metadata (length, size) being correct and you're passing that null-terminated buffer around to libraries outside your code, it won't be correct since nothing else is aware of it.

[sirwhinesalot]

> If it were so easy why do you think nobody has done it?

People have done it, there are plenty strbuf implementations to go around. Even the kernel has seq_buf. How you handle string manipulation internally in your codebase does not matter for compatibility with existing libraries.

> That's not very useful for the general case. If your code relies on the extra metadata (length, size) being correct and you're passing that null-terminated buffer around to libraries outside your code, it won't be correct since nothing else is aware of it.

You can safely pass the char* buffer inside a std::string to any C library with no conversion. You're making up issues in your head. Don't excuse incompetence.

[jjav]

> People have done it, there are plenty strbuf implementations to go around.

Precisely!

Why plenty and why is none of them the standard in C?

[sirwhinesalot]

The TL;DR on that is basically "lazy, security unconscious assholes keep shutting it down".

Dennies Ritchie strongly suggested C should add fat pointers all the way back in 1990. Other people have pointed out the issues with zero terminated strings and arrays decaying into pointers (and the ways to deal with them even with backwards compatibility constraints) for years.

One of the most prominent was Walter Bright's article on "C's Biggest Mistake" back in 2009 and he was a C/C++ commercial compiler developer.

There is no excuse.

[jjav]

It is easy to document mistakes in hindsight, since hindsight is 20/20.

It is very easy to write your own one-off secure string handling library. This is a common assignment in intro to C programming classes.

So why isn't it standard in C already?

You offer a theory that there is a gang of "security unconscious assholes [who] keep shutting it down". This gang is so well organized that they have managed to block an easy improvement for many many decades for unknown reasons. That's a pretty wild theory.

Or Occam's razor suggests a different answer: It's actually difficult.

No, not the writing code part, that's easy. It's the seamlessly integrating with ~60 years of mission critical codebases part that's hard.

[lelanthran]

> you should only worry about it at the boundary with the other library.

If this was a mitigation, it would solve all problems with nul-terminated strings i.e. do strict and error-checked conversions to nul-terminated strings at all boundaries to the program, and then nul-terminated strings and len-specified strings are equivalently dangerous (or safe, depending on your perspective).

The problem is precisely that unsanitised input makes its way into the application, bypassing any checks.

[sirwhinesalot]

It's impossible to avoid "sanitizing" input if you have a conversion step from a library provided char* to a strbuf type. Any use of the strbuf API is guaranteed to be correct.

That's very different from needing to be on your toes with every usage of the strxcpy family.

[lelanthran]

> It's impossible to avoid "sanitizing" input if you have a conversion step from a library provided char* to a strbuf type. Any use of the strbuf API is guaranteed to be correct.

I agree: having a datatype beats sanitising input (I think there's a popular essay somewhere about parsing input vs sanitising input which makes pretty much the same point as you do), but it's still only partially correct.

To get to fully correct you don't need a new string type, you need developers to recognise that the fields "Full Name" and "Email address" and "Phone number", while all being stored as strings, are actually different types and to handle them as such by making those types incompatible so that a `string_copy` function must produce a compilation failure when the destination is "EmailAddressType" and the source is "FullNameType".

Developers in C can, right now, do that with only a few minutes of extra typing effort. Adding a "proper" string type is still going to result in someone, somewhere, parsing a uint8_t from a string into a uint64_t, and then (after some computation) reversing that (now overflowing) uint64_t back into a uint8_t.

If you're doing the right thing and creating types because "Parse, Don't Validate", a better string type doesn't bring any benefits. If you're doing the wrong thing and validating inputs, then you're going to miss one anyway, no matter the underlying string type.

[sirwhinesalot]

Sure but now we're talking about a universal problem across languages, rather than a C-specific problem.

[lelanthran]

> Sure but now we're talking about a universal problem across languages, rather than a C-specific problem.

Of course, but that's my point - C already gives you the ability to fix the incorrect typing problem, using the existing foundational `str*` functions.

A team who is not using the compiler's ability to warn when mixing types are still going to mix types when there is a safe strbuf_t type.

The problem with the `str*` functions can be fixed today without modifying the language or it's stdlib.

Most C programmers don't do it (myself included). I think that, in one sense, you are correct in that removing the existing string representation (and functions for them) and replacing them with len+data representation for strings will fix some problems.

Trouble is, a lot of useful tokenising/parsing/etc string problems are not possible in a len+data representation (each strtok() type function, for example, needs to make a copy of what it returns) so programmers are just going to do their best to bypass them.

Having programmers trained to create new string types using existing C is just easier, because then you solve the whole 'mixing types' problem even when looking at replacements for things like `strtok`.

Or ... maybe I'm completely off-base and the reason that programmers don't create different types for string-stored data is because it is too much work in current C-as-we-know-it.

[jandrese]

For me the "real" solution looks something like this:

    ssize_t strxcpy(char* restrict dst, const char* restrict src, ssize_t len)

Strxcpy copies the string from src to dst. The len parameter is the number of bytes available in the dst buffer. The dst buffer is always terminated with a null byte, so the maximum length of string that can be copied into it is len - 1. strxcpy returns the number of characters copied on success, but can return the following negative values:

    E_INVALID_PARAMETER: Ether dst or src are NULL or len < 1, no data was copied
    W_TRUNCATED: len - 1 bytes were copied but more characters were available in src.

strxcat would work similarly. I have not decided if the return value should include the terminating null or not.

[jjav]

How is this useful though? I mean yes, it is useful in avoiding the buffer overruns. But that's not the only consideration, you also want code that handles data correctly. This just truncates at buffer size so data is lost.

So, if you want the code to work correctly, you need to either check the return code and reallocate dst and call the copy again. But if you're going to do that might as well check src len and allocate dst correctly before calling it so it never fails. But if you're already doing that, you can call strcpy just fine and never have a problem.

[jandrese]

Sometimes truncation is fine or at least can be managed. Yes, strdup() is a better choice in a lot of situations, but depending on how your data is structured it may not be the correct option. I would say my version is useful in any situation where you were previously using strncpy/cat or strlcpy/cat.