fmem's Introduction

fmem

Forked from Snaipe, since he hasn't reviewed pull request in the last 6 years.

A cross-platform library for opening memory-backed libc streams.

This library was written for Criterion to implement stringification functions for user-defined types.

Rationale

C doesn't define any way to open "virtual" streams that write to memory rather than a real file. A lot of libc implementations roll their own nonstandard mechanisms to achieve this, namely open_memstream, or fmemopen. Other implementations provide more generic functions to call users functions for various operations on the file, like funopen or fopencookie. Finally, some implementations support none of these nonstandard functions.

fmem tries in sequence the following implementations:

open_memstream.
fopencookie, with growing dynamic buffer.
funopen, with growing dynamic buffer.
WinAPI temporary memory-backed file.

When no other mean is available, fmem falls back to tmpfile().

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fmem's Issues

Add tests to all implementations

Currently implementations only 2 implementations are tested, one for every OS, we should be more thorough

Add MSVC to github actions

I'll accept pull requests that can add MSVC runner with github actions, I don't know how to do it. So feel free to try.

Potential memory leak if using fmem-tmpfile.c

I can see a potential memory leak, when using fmem_mem with tmpfile. I assume that

What happens is when

void* ptr = nullptr;
fmem_mem(&fmInstance, &ptr, &size_val);

free(ptr); // required for tmpfile, but causes error for winapi-tmpfile

I can see two solutions to this:

In fmem-tmpfile.c, I don't see cv.impl->buf being assigned at all. If we assign cv.impl->buf to the newly malloc-ed memory, the destructor function can take care of this allocation
Provide an explicit USING_TMPFILE macro or some way to detect if we are using tmpfile or not. This way, we can manually free the memory conditionally when using tmpfile.

Additionally, I also see another segfault point - in line 46, free(cv.impl->buf); is called without prior checking if buf is NULL or not. This can cause segmentation fault

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