core: Add C++ classes for read-only memory-mapped files and UNIX file descriptors; Remove Zstandard's dependency on Boost.

[LinZhihao-723]

Description

Motivation:

As we plan to publish an npm package for the JavaScript clp-ffi library, we need to remove standard Decompressor's boost dependency to build the necessary components properly. To achieve this milestone, we should replace boost's memory-mapped file with our own implementation. This change is first introduced in PR #387

Implementation

This PR introduces two classes necessary to wrap mmap system call:

• FileDescriptor: This is a wrapper class to a raw file descriptor. With RAII, it is easier to handle failures/exceptions where a raw file descriptor is required. To handle to potential failure in the destructor, we provide a customizable callback if users don't want to swallow the error.
• MemoryMappedFileView: This is a wrapper class to mmap system call. It maintains the mapped memory region using RAII, and provides methods to access an immutable view of the file. The memory region is unmapped in the destructor.

With the above two classes, we can replace boost's mmap support with our implementation in standard Decompressor.

Validation performed

1. Ensure the code can be successfully built for all the relevant build targets.
2. Ensure all existing unit tests are passed. The current streaming compression unit tests will call the above implementation to decompress zstd format files.
3. Add new unit tests to test memory-mapped file functionalities separately. It also tests the special case where the mapped file is empty.

[junhaoliao]

lgtm thanks!

I believe the code changes are sufficient to get rid of the "boost" header dependencies for Emscripten (WASM) compilation for the Zstd decompressor. Looking at cleaning up the CLP repo, can we now also remove references to boost::iostreams in the CMakeList.txt files? (May we need to replace all memeory-mapped file implementations with ours. )

[LinZhihao-723]

lgtm thanks!

I believe the code changes are sufficient to get rid of the "boost" header dependencies for Emscripten (WASM) compilation for the Zstd decompressor. Looking at cleaning up the CLP repo, can we now also remove references to boost::iostreams in the CMakeList.txt files? (May we need to replace all memeory-mapped file implementations with ours. )

I agree that we can do more cleaning. However, this is already a non-trivial PR. I think we should delay the rest of the cleanup to the future PRs. Arguably speaking, this PR should only contain two new classes. We should delay the boost deprecation in zstd decompressor to the next PR. What do u think? @kirkrodrigues

[kirkrodrigues]

A few things to resolve.

[kirkrodrigues]

However, this is already a non-trivial PR. I think we should delay the rest of the cleanup to the future PRs. Arguably speaking, this PR should only contain two new classes. We should delay the boost deprecation in zstd decompressor to the next PR. What do u think? @kirkrodrigues

Leaving further clean-up to another PR sounds good.

[kirkrodrigues]

For the PR title, how about:

core: Add C++ classes for read-only memory-mapped files and UNIX file descriptors; Remove Zstandard's dependency on Boost.

[LinZhihao-723]

For the PR title, how about:

core: Add C++ classes for read-only memory-mapped files and UNIX file descriptors; Remove Zstandard's dependency on Boost.

lgtm