io: panic when in-memory pipe is created with zero capacity (#8397)

tokio/src/io/util/mem.rs

@@ -100,6 +100,11 @@ pub struct SimplexStream {
 ///
 /// The `max_buf_size` argument is the maximum amount of bytes that can be
 /// written to a side before the write returns `Poll::Pending`.
+///
+/// # Panics
+///
+/// This function panics if `max_buf_size` is 0.
+#[track_caller]
 #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
 pub fn duplex(max_buf_size: usize) -> (DuplexStream, DuplexStream) {
     let one = Arc::new(Mutex::new(SimplexStream::new_unsplit(max_buf_size)));
@@ -207,6 +212,11 @@ impl Drop for DuplexStream {
 /// # Ok(())
 /// # }
 /// ```
+///
+/// # Panics
+///
+/// This function panics if `max_buf_size` is 0.
+#[track_caller]
 #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
 pub fn simplex(max_buf_size: usize) -> (ReadHalf<SimplexStream>, WriteHalf<SimplexStream>) {
     split(SimplexStream::new_unsplit(max_buf_size))
@@ -218,8 +228,14 @@ impl SimplexStream {
     ///
     /// The `max_buf_size` argument is the maximum amount of bytes that can be
     /// written to a buffer before it returns `Poll::Pending`.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if `max_buf_size` is 0.
+    #[track_caller]
     #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
     pub fn new_unsplit(max_buf_size: usize) -> SimplexStream {
+        assert!(max_buf_size > 0, "`max_buf_size` must be greater than 0");
         SimplexStream {
             buffer: BytesMut::new(),
             is_closed: false,

tokio/tests/io_panic.rs

@@ -4,7 +4,7 @@
 
 use std::task::{Context, Poll};
 use std::{error::Error, pin::Pin};
-use tokio::io::{self, split, AsyncRead, AsyncWrite, ReadBuf};
+use tokio::io::{self, duplex, simplex, split, AsyncRead, AsyncWrite, ReadBuf, SimplexStream};
 
 mod support {
     pub mod panic;
@@ -131,6 +131,42 @@ fn unsplit_panic_caller() -> Result<(), Box<dyn Error>> {
     Ok(())
 }
 
+#[test]
+fn duplex_zero_capacity_panic_caller() -> Result<(), Box<dyn Error>> {
+    let panic_location_file = test_panic(|| {
+        let _ = duplex(0);
+    });
+
+    // The panic location should be in this file
+    assert_eq!(&panic_location_file.unwrap(), file!());
+
+    Ok(())
+}
+
+#[test]
+fn simplex_zero_capacity_panic_caller() -> Result<(), Box<dyn Error>> {
+    let panic_location_file = test_panic(|| {
+        let _ = simplex(0);
+    });
+
+    // The panic location should be in this file
+    assert_eq!(&panic_location_file.unwrap(), file!());
+
+    Ok(())
+}
+
+#[test]
+fn new_unsplit_zero_capacity_panic_caller() -> Result<(), Box<dyn Error>> {
+    let panic_location_file = test_panic(|| {
+        let _ = SimplexStream::new_unsplit(0);
+    });
+
+    // The panic location should be in this file
+    assert_eq!(&panic_location_file.unwrap(), file!());
+
+    Ok(())
+}
+
 #[test]
 #[cfg(unix)]
 fn async_fd_new_panic_caller() -> Result<(), Box<dyn Error>> {