Provide optional Read/Write method for stdio

[thaliaarchi]

The raw types for standard I/O across platforms vary by which of the optional io::Read and io::Write methods they provide and most just use the defaults. Only Unix implements read_buf, read_vectored, and write_vectored for its stdio. Provide these methods for the platforms which support them or when useful. Additionally, provide missing methods for StdinRaw, StdoutLock, and StderrLock, which the other similar types provide.

I have checked the code against a target per platform modified, with wasm32-unknown-unknown for unsupported stdio, as well as Linux, macOS, and Windows.

x check library/std --target=x86_64-unknown-hermit
x check library/std --target=aarch64-unknown-linux-gnu
x check library/std --target=aarch64-apple-darwin
x check library/std --target=x86_64-fortanix-unknown-sgx
x check library/std --target=aarch64-kmc-solid_asp3
x check library/std --target=aarch64-unknown-teeos
x check library/std --target=x86_64-unknown-uefi
x check library/std --target=wasm32-unknown-unknown
x check library/std --target=wasm32-wasip1
x check library/std --target=x86_64-pc-windows-gnu
x check library/std --target=riscv32imac-unknown-xous-elf
x check library/std --target=riscv32im-risc0-zkvm-elf

Open questions

I have been unable to find sufficient documentation or a libc for these platforms. Do they support these features?

• TEEOS: vectored write
• Xous: vectored write
• zkvm: vectored read/write

Would any of the other methods be useful to provide for platform stdio types? Those are: read_buf_exact, read_exact, read_to_end, read_to_string, write_all, write_all_vectored, and write_fmt.

Further work

• Windows and UEFI stdio use UTF-16, so will take more work to flesh out. I plan to refactor the WTF-8 abstraction from OsStr to accommodate this.

Progress on optional Read/Write methods is tracked in #136756.

[rustbot]

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[joboet]

This is incorrect, this should return UnexpectedEof instead (which the default implementation does), as the buffer hasn't been filled.

[thaliaarchi]

Ah, good catch. I missed that ebadf is interpreted differently for reading vs writing. Should be fixed now.

[joboet]

We don't do this because the formatting implementations might try to use Stdout themselves, which would lead to panicking.

[thaliaarchi]

Thanks. I had overlooked that this could call user code, and was only thinking about locking concerns on the stdlib side. I dropped that commit now.