gethostname/
lib.rs

1// Copyright Sebastian Wiesner <sebastian@swsnr.de>
2
3// Licensed under the Apache License, Version 2.0 (the "License"); you may not
4// use this file except in compliance with the License. You may obtain a copy of
5// the License at
6
7// 	http://www.apache.org/licenses/LICENSE-2.0
8
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12// License for the specific language governing permissions and limitations under
13// the License.
14
15//! [gethostname()][ghn] for all platforms.
16//!
17//! ```
18//! use gethostname::gethostname;
19//!
20//! println!("Hostname: {:?}", gethostname());
21//! ```
22//!
23//! [ghn]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/gethostname.html
24
25#![deny(warnings, missing_docs, clippy::all, clippy::pedantic)]
26// On the Windows target our doc links don't necessarily work.
27#![cfg_attr(windows, allow(rustdoc::broken_intra_doc_links))]
28
29use std::ffi::OsString;
30
31/// Get the standard host name for the current machine.
32///
33/// On Unix call [`rustix::system::uname`] to obtain the node name, see
34/// [`rustix::system::Uname::nodename`].
35///
36/// On Windows return the DNS host name of the local computer, as returned by
37/// [GetComputerNameExW] with `ComputerNamePhysicalDnsHostname` as `NameType`.
38/// We call this function twice to obtain the appropriate buffer size; there is
39/// a race condition window between these two calls where a change to the node
40/// name would result in a wrong buffer size which could cause this function to
41/// panic.
42///
43/// Note that this host name does not have a well-defined meaning in terms of
44/// network name resolution.  Specifically, it's not guaranteed that the
45/// returned name can be resolved in any particular way, e.g. DNS.
46///
47/// [GetComputerNameExW]: https://docs.microsoft.com/en-us/windows/desktop/api/sysinfoapi/nf-sysinfoapi-getcomputernameexw
48#[must_use]
49pub fn gethostname() -> OsString {
50    #[cfg(unix)]
51    {
52        use std::os::unix::ffi::OsStringExt;
53        OsString::from_vec(rustix::system::uname().nodename().to_bytes().to_vec())
54    }
55    #[cfg(windows)]
56    {
57        get_computer_physical_dns_hostname()
58    }
59}
60
61#[cfg(windows)]
62fn get_computer_physical_dns_hostname() -> OsString {
63    use std::os::windows::ffi::OsStringExt;
64
65    // The DNS host name of the local computer. If the local computer is a node
66    // in a cluster, lpBuffer receives the DNS host name of the local computer,
67    // not the name of the cluster virtual server.
68    pub const COMPUTER_NAME_PHYSICAL_DNS_HOSTNAME: i32 = 5;
69
70    // https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getcomputernameexw
71    ::windows_targets::link!("kernel32.dll" "system" fn GetComputerNameExW(nametype: i32, lpbuffer: *mut u16, nsize: *mut u32) -> i32);
72
73    let mut buffer_size: u32 = 0;
74
75    unsafe {
76        // This call always fails with ERROR_MORE_DATA, because we pass NULL to
77        // get the required buffer size.  GetComputerNameExW then fills buffer_size with the size
78        // of the host name string plus a trailing zero byte.
79        GetComputerNameExW(
80            COMPUTER_NAME_PHYSICAL_DNS_HOSTNAME,
81            std::ptr::null_mut(),
82            &mut buffer_size,
83        )
84    };
85    assert!(
86        0 < buffer_size,
87        "GetComputerNameExW did not provide buffer size"
88    );
89
90    let mut buffer = vec![0_u16; buffer_size as usize];
91    unsafe {
92        if GetComputerNameExW(
93            COMPUTER_NAME_PHYSICAL_DNS_HOSTNAME,
94            buffer.as_mut_ptr(),
95            &mut buffer_size,
96        ) == 0
97        {
98            panic!(
99                "GetComputerNameExW failed to read hostname.
100        Please report this issue to <https://codeberg.org/swsnr/gethostname.rs/issues>!"
101            );
102        }
103    }
104    assert!(
105        // GetComputerNameExW returns the size _without_ the trailing zero byte on the second call
106        buffer_size as usize == buffer.len() - 1,
107        "GetComputerNameExW changed the buffer size unexpectedly"
108    );
109
110    let end = buffer.iter().position(|&b| b == 0).unwrap_or(buffer.len());
111    OsString::from_wide(&buffer[0..end])
112}
113
114#[cfg(test)]
115mod tests {
116    use std::process::Command;
117
118    #[test]
119    fn gethostname_matches_system_hostname() {
120        let mut command = if cfg!(windows) {
121            Command::new("hostname")
122        } else {
123            let mut uname = Command::new("uname");
124            uname.arg("-n");
125            uname
126        };
127        let output = command.output().expect("failed to get hostname");
128        if output.status.success() {
129            let hostname = String::from_utf8_lossy(&output.stdout);
130            assert!(
131                !hostname.is_empty(),
132                "Failed to get hostname: hostname empty?"
133            );
134            // Convert both sides to lowercase; hostnames are case-insensitive
135            // anyway.
136            assert_eq!(
137                super::gethostname().into_string().unwrap().to_lowercase(),
138                hostname.trim_end().to_lowercase()
139            );
140        } else {
141            panic!(
142                "Failed to get hostname! {}",
143                String::from_utf8_lossy(&output.stderr)
144            );
145        }
146    }
147
148    #[test]
149    #[ignore]
150    fn gethostname_matches_fixed_hostname() {
151        assert_eq!(
152            super::gethostname().into_string().unwrap().to_lowercase(),
153            "hostname-for-testing"
154        );
155    }
156}
gethostname/lib.rs

gethostname/
lib.rs
