Move memchr behind an optional feature

.github/workflows/ci.yml

@@ -42,7 +42,7 @@ jobs:
         uses: taiki-e/install-action@cargo-hack
       - run: cargo build --all --all-features --all-targets
       - run: cargo hack build --feature-powerset --no-dev-deps
-      - run: cargo hack build --feature-powerset --no-dev-deps --target thumbv7m-none-eabi --skip std,default
+      - run: cargo hack build --feature-powerset --no-dev-deps --target thumbv7m-none-eabi --skip std,default,memchr
       - run: cargo test
       - run: cargo test --no-default-features
       - run: cargo test --no-default-features --features alloc

Cargo.toml

@@ -21,7 +21,7 @@ exclude = ["/.*"]
 
 [features]
 default = ["race", "std"]
-std = ["alloc", "fastrand/std", "futures-io", "parking", "memchr"]
+std = ["alloc", "fastrand/std", "futures-io", "parking"]
 alloc = []
 race = ["fastrand"]
 

src/io.rs

@@ -1811,7 +1811,7 @@ fn read_until_internal<R: AsyncBufReadExt + ?Sized>(
         let (done, used) = {
             let available = ready!(reader.as_mut().poll_fill_buf(cx))?;
 
-            if let Some(i) = memchr::memchr(byte, available) {
+            if let Some(i) = memchr(byte, available) {
                 buf.extend_from_slice(&available[..=i]);
                 (true, i + 1)
             } else {
@@ -3091,3 +3091,12 @@ impl<T: AsyncWrite + Unpin> AsyncWrite for WriteHalf<T> {
         Pin::new(&mut *inner).poll_close(cx)
     }
 }
+
+#[cfg(feature = "memchr")]
+use memchr::memchr;
+
+/// Unoptimized memchr fallback.
+#[cfg(not(feature = "memchr"))]
+fn memchr(needle: u8, haystack: &[u8]) -> Option<usize> {
+    haystack.iter().position(|&b| b == needle)
+}