diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs index 475a1d9fd99..a8d6645794a 100644 --- a/library/std/src/lib.rs +++ b/library/std/src/lib.rs @@ -294,6 +294,8 @@ #![feature(std_internals)] #![feature(str_internals)] #![feature(strict_provenance)] +#![feature(maybe_uninit_uninit_array)] +#![feature(const_maybe_uninit_uninit_array)] // // Library features (alloc): #![feature(alloc_layout_extra)] diff --git a/library/std/src/net/ip.rs b/library/std/src/net/ip.rs index 41ca9ba8425..189754a161e 100644 --- a/library/std/src/net/ip.rs +++ b/library/std/src/net/ip.rs @@ -3,12 +3,14 @@ mod tests; use crate::cmp::Ordering; -use crate::fmt::{self, Write as FmtWrite}; -use crate::io::Write as IoWrite; +use crate::fmt::{self, Write}; use crate::mem::transmute; use crate::sys::net::netc as c; use crate::sys_common::{FromInner, IntoInner}; +mod display_buffer; +use display_buffer::IpDisplayBuffer; + /// An IP address, either IPv4 or IPv6. /// /// This enum can contain either an [`Ipv4Addr`] or an [`Ipv6Addr`], see their @@ -991,21 +993,19 @@ impl From for IpAddr { impl fmt::Display for Ipv4Addr { fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { let octets = self.octets(); - // Fast Path: if there's no alignment stuff, write directly to the buffer + + // If there are no alignment requirements, write the IP address directly to `f`. + // Otherwise, write it to a local buffer and then use `f.pad`. if fmt.precision().is_none() && fmt.width().is_none() { write!(fmt, "{}.{}.{}.{}", octets[0], octets[1], octets[2], octets[3]) } else { - const IPV4_BUF_LEN: usize = 15; // Long enough for the longest possible IPv4 address - let mut buf = [0u8; IPV4_BUF_LEN]; - let mut buf_slice = &mut buf[..]; + const LONGEST_IPV4_ADDR: &str = "255.255.255.255"; - // Note: The call to write should never fail, hence the unwrap - write!(buf_slice, "{}.{}.{}.{}", octets[0], octets[1], octets[2], octets[3]).unwrap(); - let len = IPV4_BUF_LEN - buf_slice.len(); + let mut buf = IpDisplayBuffer::<{ LONGEST_IPV4_ADDR.len() }>::new(); + // Buffer is long enough for the longest possible IPv4 address, so this should never fail. + write!(buf, "{}.{}.{}.{}", octets[0], octets[1], octets[2], octets[3]).unwrap(); - // This unsafe is OK because we know what is being written to the buffer - let buf = unsafe { crate::str::from_utf8_unchecked(&buf[..len]) }; - fmt.pad(buf) + fmt.pad(buf.as_str()) } } } @@ -1708,8 +1708,8 @@ impl Ipv6Addr { #[stable(feature = "rust1", since = "1.0.0")] impl fmt::Display for Ipv6Addr { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - // If there are no alignment requirements, write out the IP address to - // f. Otherwise, write it to a local buffer, then use f.pad. + // If there are no alignment requirements, write the IP address directly to `f`. + // Otherwise, write it to a local buffer and then use `f.pad`. if f.precision().is_none() && f.width().is_none() { let segments = self.segments(); @@ -1780,22 +1780,13 @@ impl fmt::Display for Ipv6Addr { } } } else { - // Slow path: write the address to a local buffer, then use f.pad. - // Defined recursively by using the fast path to write to the - // buffer. + const LONGEST_IPV6_ADDR: &str = "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff"; - // This is the largest possible size of an IPv6 address - const IPV6_BUF_LEN: usize = (4 * 8) + 7; - let mut buf = [0u8; IPV6_BUF_LEN]; - let mut buf_slice = &mut buf[..]; + let mut buf = IpDisplayBuffer::<{ LONGEST_IPV6_ADDR.len() }>::new(); + // Buffer is long enough for the longest possible IPv6 address, so this should never fail. + write!(buf, "{}", self).unwrap(); - // Note: This call to write should never fail, so unwrap is okay. - write!(buf_slice, "{}", self).unwrap(); - let len = IPV6_BUF_LEN - buf_slice.len(); - - // This is safe because we know exactly what can be in this buffer - let buf = unsafe { crate::str::from_utf8_unchecked(&buf[..len]) }; - f.pad(buf) + f.pad(buf.as_str()) } } } diff --git a/library/std/src/net/ip/display_buffer.rs b/library/std/src/net/ip/display_buffer.rs new file mode 100644 index 00000000000..bd852d5da8e --- /dev/null +++ b/library/std/src/net/ip/display_buffer.rs @@ -0,0 +1,40 @@ +use crate::fmt; +use crate::mem::MaybeUninit; +use crate::str; + +/// Used for slow path in `Display` implementations when alignment is required. +pub struct IpDisplayBuffer { + buf: [MaybeUninit; SIZE], + len: usize, +} + +impl IpDisplayBuffer { + #[inline] + pub const fn new() -> Self { + Self { buf: MaybeUninit::uninit_array(), len: 0 } + } + + #[inline] + pub fn as_str(&self) -> &str { + // SAFETY: `buf` is only written to by the `fmt::Write::write_str` implementation + // which writes a valid UTF-8 string to `buf` and correctly sets `len`. + unsafe { + let s = MaybeUninit::slice_assume_init_ref(&self.buf[..self.len]); + str::from_utf8_unchecked(s) + } + } +} + +impl fmt::Write for IpDisplayBuffer { + fn write_str(&mut self, s: &str) -> fmt::Result { + let bytes = s.as_bytes(); + + if let Some(buf) = self.buf.get_mut(self.len..(self.len + bytes.len())) { + MaybeUninit::write_slice(buf, bytes); + self.len += bytes.len(); + Ok(()) + } else { + Err(fmt::Error) + } + } +}