io: use memchr from libc (#5960)

tokio/Cargo.toml

@@ -42,7 +42,7 @@ full = [
 ]
 
 fs = []
-io-util = ["memchr", "bytes"]
+io-util = ["bytes"]
 # stdin, stdout, stderr
 io-std = []
 macros = ["tokio-macros"]
@@ -108,7 +108,6 @@ pin-project-lite = "0.2.0"
 
 # Everything else is optional...
 bytes = { version = "1.0.0", optional = true }
-memchr = { version = "2.2", optional = true }
 mio = { version = "0.8.1", optional = true, default-features = false }
 socket2 = { version = "0.4.4", optional = true, features = [ "all" ] }
 num_cpus = { version = "1.8.0", optional = true }

tokio/src/io/util/read_until.rs

@@ -1,4 +1,5 @@
 use crate::io::AsyncBufRead;
+use crate::util::memchr;
 
 use pin_project_lite::pin_project;
 use std::future::Future;

tokio/src/util/memchr.rs

@@ -0,0 +1,74 @@
+//! Search for a byte in a byte array using libc.
+//!
+//! When nothing pulls in libc, then just use a trivial implementation. Note
+//! that we only depend on libc on unix.
+
+#[cfg(not(all(unix, feature = "libc")))]
+pub(crate) fn memchr(needle: u8, haystack: &[u8]) -> Option<usize> {
+    haystack.iter().position(|val| needle == *val)
+}
+
+#[cfg(all(unix, feature = "libc"))]
+pub(crate) fn memchr(needle: u8, haystack: &[u8]) -> Option<usize> {
+    let start = haystack.as_ptr();
+
+    // SAFETY: `start` is valid for `haystack.len()` bytes.
+    let ptr = unsafe { libc::memchr(start.cast(), needle as _, haystack.len()) };
+
+    if ptr.is_null() {
+        None
+    } else {
+        Some(ptr as usize - start as usize)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::memchr;
+
+    #[test]
+    fn memchr_test() {
+        let haystack = b"123abc456\0\xffabc\n";
+
+        assert_eq!(memchr(b'1', haystack), Some(0));
+        assert_eq!(memchr(b'2', haystack), Some(1));
+        assert_eq!(memchr(b'3', haystack), Some(2));
+        assert_eq!(memchr(b'4', haystack), Some(6));
+        assert_eq!(memchr(b'5', haystack), Some(7));
+        assert_eq!(memchr(b'6', haystack), Some(8));
+        assert_eq!(memchr(b'7', haystack), None);
+        assert_eq!(memchr(b'a', haystack), Some(3));
+        assert_eq!(memchr(b'b', haystack), Some(4));
+        assert_eq!(memchr(b'c', haystack), Some(5));
+        assert_eq!(memchr(b'd', haystack), None);
+        assert_eq!(memchr(b'A', haystack), None);
+        assert_eq!(memchr(0, haystack), Some(9));
+        assert_eq!(memchr(0xff, haystack), Some(10));
+        assert_eq!(memchr(0xfe, haystack), None);
+        assert_eq!(memchr(1, haystack), None);
+        assert_eq!(memchr(b'\n', haystack), Some(14));
+        assert_eq!(memchr(b'\r', haystack), None);
+    }
+
+    #[test]
+    fn memchr_all() {
+        let mut arr = Vec::new();
+        for b in 0..=255 {
+            arr.push(b);
+        }
+        for b in 0..=255 {
+            assert_eq!(memchr(b, &arr), Some(b as usize));
+        }
+        arr.reverse();
+        for b in 0..=255 {
+            assert_eq!(memchr(b, &arr), Some(255 - b as usize));
+        }
+    }
+
+    #[test]
+    fn memchr_empty() {
+        for b in 0..=255 {
+            assert_eq!(memchr(b, b""), None);
+        }
+    }
+}

tokio/src/util/mod.rs

@@ -90,3 +90,6 @@ pub use self::rand::thread_rng_n;
     all(unix, feature = "signal")
 ))]
 pub(crate) mod error;
+
+#[cfg(feature = "io-util")]
+pub(crate) mod memchr;