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.

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[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