Implement read_exact for the Read trait

[cesarb]

This implements the proposed "read_exact" RFC (rust-lang/rfcs#980).

Tracking issue: #27585

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @huonw (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[sfackler]

Might want to say "unspecified" instead of "undefined" here to avoid conflating with undefined behavior.

[alexcrichton]

Looking good to me, thanks @cesarb! Just one minor nit and I think this is good to go

[huonw]

r? @alexcrichton

[alexcrichton]

Oh oops, sorry for the delay @cesarb! Feel free to ping a PR whenever it's updated as unfortunately github doesn't send out notifications for force-pushes or new commits.

As one final thing, could you squash these commits together? Thanks!

[cesarb]

As one final thing, could you squash these commits together?

Done. Do you need me to also rebase this on top of a more recent master?

Feel free to ping a PR whenever it's updated as unfortunately github doesn't send out notifications for force-pushes or new commits.

Sorry, I hadn't noticed that. I'll make sure to write a dummy comment whenever I update a pull request from now on.

[sfackler]

@bors r=alexcrichton

[bors]

📌 Commit ff81920 has been approved by alexcrichton

[bors]

⌛ Testing commit ff81920 with merge 20ffe32...

[bors]

💔 Test failed - auto-mac-64-nopt-t

[sfackler]

Looks like UnexpectedEOF and read_exact need an associated issue:

../src/libstd/io/error.rs:160:5: 160:18 error: non-deprecated unstable items need to point to an issue with `issue = "NNN"`
../src/libstd/io/error.rs:160 UnexpectedEOF,
^~~~~~~~~~~~~
../src/libstd/io/mod.rs:596:5: 611:6 error: non-deprecated unstable items need to point to an issue with `issue = "NNN"`
../src/libstd/io/mod.rs:596 fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
../src/libstd/io/mod.rs:597 while !buf.is_empty() {
../src/libstd/io/mod.rs:598 match self.read(buf) {
../src/libstd/io/mod.rs:599 Ok(0) => break,
../src/libstd/io/mod.rs:600 Ok(n) => { let tmp = buf; buf = &mut tmp[n..]; }
../src/libstd/io/mod.rs:601 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
...
error: aborting due to 2 previous errors

[cesarb]

There seems to be a catch-22 here:

• This can only be merged if an issue number is added to the unstable declaration;
• It doesn't make sense to create a stabilization issue for a feature which hasn't even been merged yet.

What should be done to break this deadlock?

[alexcrichton]

Ah feel free to use the RFC tracking issue, #27585, for the issue number

[cesarb]

I made a commit adding the issue number to the unstable declarations, and it seems to have been accepted by travis-ci.

[alexcrichton]

@bors: r+ 73e7a72

[bors]

⌛ Testing commit 73e7a72 with merge 29da43e...

[bors]

💔 Test failed - auto-linux-64-nopt-t

[sfackler]

@bors retry

[bors]

⌛ Testing commit 73e7a72 with merge abe5dd0...

[bors]

💔 Test failed - auto-linux-64-nopt-t

[sfackler]

@bors retry

[bors]

⌛ Testing commit 73e7a72 with merge 4bb9023...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt