std: net: Add function to return the system hostname #135141

orowith2os · 2025-01-06T00:10:05Z

Resolves rust-lang/libs-team#330
Tracking issue: #135142

Now you can retrieve the system hostname, without relying on anything other than std!

This is my first pull request to the Rust standard library (or anything inside rust-lang/rust, period, quite possible rust-lang itself), so there are bound to be issues. I'll try my best to resolve them.

rustbot · 2025-01-06T00:10:13Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @joboet (or someone else) some time within the next two weeks.

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library/std/src/net/hostname.rs

library/std/src/net/mod.rs

orowith2os · 2025-01-06T01:03:33Z

forgive all the updates, I was having troubles updating my branch properly. Figured it out.

orowith2os · 2025-01-16T19:52:49Z

@rustbot ready

orowith2os · 2025-01-16T19:58:35Z

Sorry for that last push - I updated the doc comment on gethostname to specify when it should be able to error out, so it's not just a black box.

joboet · 2025-01-17T13:40:15Z

Right, that covers most platforms. Some targets are still missing, though (to find these I basically went through the directories in sys/pal and looked for platforms with a net module):

wasm32-wasip1 and wasm32-wasip2 (tier 2)
x86_64-fortanix-unknown-sgx (tier 2)
aarch64-kmc-solid_asp3 (tier 3)
riscv32imac-unknown-xous-elf (tier 3)
x86_64-unknown-hermit (tier 3)

joshtriplett · 2025-01-17T14:29:04Z

DNS names can only be ASCII, but hostnames are not just DNS names. I've seen hostnames for phones and computers that have Unicode characters in them, and I would be unsurprised to discover hostnames that use local character sets.

That said, if we define this to be a form of hostname that works as a valid DNS component, then 👍 for making it String.

orowith2os · 2025-01-17T15:07:22Z

@joboet would it be fine to mark them as TODO in the tracking issue?

joboet · 2025-01-17T15:20:16Z

@joboet would it be fine to mark them as TODO in the tracking issue?

For the tier 3 targets, yeah that's fine. The tier 2 targets are built in the merge CI, so they'll need to compile (stubbing the function out is fine).

joboet · 2025-01-21T12:44:01Z

DNS names can only be ASCII, but hostnames are not just DNS names. I've seen hostnames for phones and computers that have Unicode characters in them, and I would be unsurprised to discover hostnames that use local character sets.

That said, if we define this to be a form of hostname that works as a valid DNS component, then 👍 for making it String.

T-libs-api, what do you think? I think this should be clarified before merging, since OsString is not the correct output type on Windows – gethostname can return any bytes, whereas OsString must be correct WTF-8, so it either can't represent all possible outputs or can hold too many outputs, depending on whether you consider non-ASCII hostnames to be invalid.

@rustbot label +I-libs-api-nominated

Amanieu · 2025-01-21T16:42:46Z

We discussed this in the libs-api meeting: on Windows this should call GetHostByNameW to get a UTF-16 string, which can then be converted to an OsString.

orowith2os · 2025-01-21T17:01:44Z

Then I'll keep it as OsString, but I won't implement the Windows bits. I'll leave that to someone willing to pick it up.

joboet · 2025-01-24T15:13:47Z

@orowith2os I've opened orowith2os#1 on your fork and implemented the Windows bit there.

…code resilient against bad platform behaviour

joboet · 2025-01-24T15:20:51Z

I shouldn't review my own code, so
r? @ChrisDenton (you probably know best about the Windows stuff)

ChrisDenton

The code looks fine. Note though that Windows 7 doesn't have GetHostNameW so it'd need. a fallback, However, it's also tier 3 so can be left to a follow up by the target maintainer.

ChrisDenton · 2025-01-24T21:40:51Z

library/std/src/sys/pal/windows/net.rs

+    // always enough.
+    let mut buffer = [0; 256];
+    // SAFETY: these parameters specify a valid, writable region of memory.
+    let ret = unsafe { c::GetHostNameW(buffer.as_mut_ptr(), buffer.len() as i32) };


I guess my one nitpick is that maybe the max buffer len could be a constant instead of using as i32, which is often a code smell but in this case it's narrowly scoped enough that I don't feel strongly about it.

valaphee · 2025-01-27T08:03:51Z

Didn't know that there is a dedicated GetHostName function in WSA, would have expected GetComputerNameExW. Implemented since Windows 2000, and doesn't require WS2 init.

As per rust-lang#117276, this PR moves `sys_common::net` and the `sys::pal::net` into the newly created `sys::net` module. In order to support rust-lang#135141, I've moved all the current network code into a separate `connection` module, future functions like `hostname` can live in separate modules. I'll probably do a follow-up PR and clean up some of the actual code, this is mostly just a reorganization.

rustbot assigned joboet Jan 6, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jan 6, 2025