1 files changed, 98 insertions, 0 deletions
diff --git a/third_party/rust/fuchsia-zircon/src/fifo.rs b/third_party/rust/fuchsia-zircon/src/fifo.rs
new file mode 100644
index 0000000000..20af6f5236
--- /dev/null
+++ b/third_party/rust/fuchsia-zircon/src/fifo.rs
@@ -0,0 +1,98 @@
+// Copyright 2017 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+//! Type-safe bindings for Zircon fifo objects.
+
+use {AsHandleRef, HandleBased, Handle, HandleRef, Status};
+use {sys, ok};
+
+/// An object representing a Zircon fifo.
+///
+/// As essentially a subtype of `Handle`, it can be freely interconverted.
+#[derive(Debug, Eq, PartialEq)]
+pub struct Fifo(Handle);
+impl_handle_based!(Fifo);
+
+impl Fifo {
+    /// Create a pair of fifos and return their endpoints. Writing to one endpoint enqueues an
+    /// element into the fifo from which the opposing endpoint reads. Wraps the
+    /// [zx_fifo_create](https://fuchsia.googlesource.com/zircon/+/master/docs/syscalls/fifo_create.md)
+    /// syscall.
+    pub fn create(elem_count: u32, elem_size: u32)
+        -> Result<(Fifo, Fifo), Status>
+    {
+        let mut out0 = 0;
+        let mut out1 = 0;
+        let options = 0;
+        let status = unsafe {
+            sys::zx_fifo_create(elem_count, elem_size, options, &mut out0, &mut out1)
+        };
+        ok(status)?;
+        unsafe { Ok((
+            Self::from(Handle::from_raw(out0)),
+            Self::from(Handle::from_raw(out1))
+        ))}
+    }
+
+    /// Attempts to write some number of elements into the fifo. The number of bytes written will be
+    /// rounded down to a multiple of the fifo's element size.
+    /// Return value (on success) is number of elements actually written.
+    ///
+    /// Wraps
+    /// [zx_fifo_write](https://fuchsia.googlesource.com/zircon/+/master/docs/syscalls/fifo_write.md).
+    pub fn write(&self, bytes: &[u8]) -> Result<u32, Status> {
+        let mut num_entries_written = 0;
+        let status = unsafe {
+            sys::zx_fifo_write(self.raw_handle(), bytes.as_ptr(), bytes.len(),
+                &mut num_entries_written)
+        };
+        ok(status).map(|()| num_entries_written)
+    }
+
+    /// Attempts to read some number of elements out of the fifo. The number of bytes read will
+    /// always be a multiple of the fifo's element size.
+    /// Return value (on success) is number of elements actually read.
+    ///
+    /// Wraps
+    /// [zx_fifo_read](https://fuchsia.googlesource.com/zircon/+/master/docs/syscalls/fifo_read.md).
+    pub fn read(&self, bytes: &mut [u8]) -> Result<u32, Status> {
+        let mut num_entries_read = 0;
+        let status = unsafe {
+            sys::zx_fifo_read(self.raw_handle(), bytes.as_mut_ptr(), bytes.len(),
+                &mut num_entries_read)
+        };
+        ok(status).map(|()| num_entries_read)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn fifo_basic() {
+        let (fifo1, fifo2) = Fifo::create(4, 2).unwrap();
+
+        // Trying to write less than one element should fail.
+        assert_eq!(fifo1.write(b""), Err(Status::OUT_OF_RANGE));
+        assert_eq!(fifo1.write(b"h"), Err(Status::OUT_OF_RANGE));
+
+        // Should write one element "he" and ignore the last half-element as it rounds down.
+        assert_eq!(fifo1.write(b"hex").unwrap(), 1);
+
+        // Should write three elements "ll" "o " "wo" and drop the rest as it is full.
+        assert_eq!(fifo1.write(b"llo worlds").unwrap(), 3);
+
+        // Now that the fifo is full any further attempts to write should fail.
+        assert_eq!(fifo1.write(b"blah blah"), Err(Status::SHOULD_WAIT));
+
+        // Read all 4 entries from the other end.
+        let mut read_vec = vec![0; 8];
+        assert_eq!(fifo2.read(&mut read_vec).unwrap(), 4);
+        assert_eq!(read_vec, b"hello wo");
+
+        // Reading again should fail as the fifo is empty.
+        assert_eq!(fifo2.read(&mut read_vec), Err(Status::SHOULD_WAIT));
+    }
+}