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| 1 | +use crate::ffi::OsString; |
| 2 | +use crate::io; |
| 3 | +use crate::os::unix::ffi::OsStringExt; |
| 4 | +use crate::sys::pal::os::errno; |
| 5 | + |
| 6 | +pub fn hostname() -> io::Result<OsString> { |
| 7 | + // Query the system for the maximum host name length. |
| 8 | + let host_name_max = match unsafe { libc::sysconf(libc::_SC_HOST_NAME_MAX) } { |
| 9 | + // If this fails (possibly because there is no maximum length), then |
| 10 | + // assume a maximum length of _POSIX_HOST_NAME_MAX (255). |
| 11 | + -1 => 255, |
| 12 | + max => max as usize, |
| 13 | + }; |
| 14 | + |
| 15 | + // Reserve space for the nul terminator too. |
| 16 | + let mut buf = Vec::<u8>::try_with_capacity(host_name_max + 1)?; |
| 17 | + loop { |
| 18 | + // SAFETY: `buf.capacity()` bytes of `buf` are writable. |
| 19 | + let r = unsafe { libc::gethostname(buf.as_mut_ptr().cast(), buf.capacity()) }; |
| 20 | + match (r != 0).then(errno) { |
| 21 | + None => { |
| 22 | + // Unfortunately, the UNIX specification says that the name will |
| 23 | + // be truncated if it does not fit in the buffer, without returning |
| 24 | + // an error. As additionally, the truncated name may still be null- |
| 25 | + // terminated, there is no reliable way to detect truncation. |
| 26 | + // Fortunately, most platforms ignore what the specification says |
| 27 | + // and return an error (mostly ENAMETOOLONG). Should that not be |
| 28 | + // the case, the following detects truncation if the null-terminator |
| 29 | + // was omitted. Note that this check does not impact performance at |
| 30 | + // all as we need to find the length of the string anyways. |
| 31 | + // |
| 32 | + // Use `strnlen` as it does not place an initialization requirement |
| 33 | + // on the bytes after the nul terminator. |
| 34 | + // |
| 35 | + // SAFETY: `buf.capacity()` bytes of `buf` are accessible, and are |
| 36 | + // initialized up to and including a possible nul terminator. |
| 37 | + let len = unsafe { libc::strnlen(buf.as_ptr().cast(), buf.capacity()) }; |
| 38 | + if len < buf.capacity() { |
| 39 | + // If the string is nul-terminated, we assume that is has not |
| 40 | + // been truncated, as the capacity *should be* enough to hold |
| 41 | + // `HOST_NAME_MAX` bytes. |
| 42 | + // SAFETY: `len + 1` bytes have been initialized (we exclude |
| 43 | + // the nul terminator from the string). |
| 44 | + unsafe { buf.set_len(len) }; |
| 45 | + return Ok(OsString::from_vec(buf)); |
| 46 | + } |
| 47 | + } |
| 48 | + // As `buf.capacity()` is always less than or equal to `isize::MAX` |
| 49 | + // (Rust allocations cannot exceed that limit), the only way `EINVAL` |
| 50 | + // can be returned is if the system uses `EINVAL` to report that the |
| 51 | + // name does not fit in the provided buffer. In that case (or in the |
| 52 | + // case of `ENAMETOOLONG`), resize the buffer and try again. |
| 53 | + Some(libc::EINVAL | libc::ENAMETOOLONG) => {} |
| 54 | + // Other error codes (e.g. EPERM) have nothing to do with the buffer |
| 55 | + // size and should be returned to the user. |
| 56 | + Some(err) => return Err(io::Error::from_raw_os_error(err)), |
| 57 | + } |
| 58 | + |
| 59 | + // Resize the buffer (according to `Vec`'s resizing rules) and try again. |
| 60 | + buf.try_reserve(buf.capacity() + 1)?; |
| 61 | + } |
| 62 | +} |
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