From 6ea8222913de9f628edac825c1f3d599762aa96f Mon Sep 17 00:00:00 2001
From: Steven Allen <steven@stebalien.com>
Date: Mon, 7 Mar 2016 16:35:37 -0500
Subject: [PATCH 1/2] Never return an error after a partial write

If LineWriter fails to flush, return the number of bytes written instead
of an error.

Fixes #32085
---
 src/libstd/io/buffered.rs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/libstd/io/buffered.rs b/src/libstd/io/buffered.rs
index ccebf3682c217..bc26b63c153c8 100644
--- a/src/libstd/io/buffered.rs
+++ b/src/libstd/io/buffered.rs
@@ -762,8 +762,10 @@ impl<W: Write> Write for LineWriter<W> {
         match memchr::memrchr(b'\n', buf) {
             Some(i) => {
                 let n = try!(self.inner.write(&buf[..i + 1]));
-                if n != i + 1 { return Ok(n) }
-                try!(self.inner.flush());
+                if n != i + 1 || self.inner.flush().is_err() {
+                    // Do not return errors on partial writes.
+                    return Ok(n);
+                }
                 self.inner.write(&buf[i + 1..]).map(|i| n + i)
             }
             None => self.inner.write(buf),

From c516335815c0bda958d81ca5f964473c212e5a4d Mon Sep 17 00:00:00 2001
From: Steven Allen <steven@stebalien.com>
Date: Mon, 7 Mar 2016 18:00:22 -0500
Subject: [PATCH 2/2] Add test case for #32085

---
 src/libstd/io/buffered.rs | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/src/libstd/io/buffered.rs b/src/libstd/io/buffered.rs
index bc26b63c153c8..08877fe9744c9 100644
--- a/src/libstd/io/buffered.rs
+++ b/src/libstd/io/buffered.rs
@@ -984,6 +984,34 @@ mod tests {
         assert_eq!(v, []);
     }
 
+    #[test]
+    fn test_line_buffer_fail_flush() {
+        // Issue #32085
+        struct FailFlushWriter<'a>(&'a mut Vec<u8>);
+
+        impl<'a> Write for FailFlushWriter<'a> {
+            fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+                self.0.extend_from_slice(buf);
+                Ok(buf.len())
+            }
+            fn flush(&mut self) -> io::Result<()> {
+                Err(io::Error::new(io::ErrorKind::Other, "flush failed"))
+            }
+        }
+
+        let mut buf = Vec::new();
+        {
+            let mut writer = LineWriter::new(FailFlushWriter(&mut buf));
+            let to_write = b"abc\ndef";
+            if let Ok(written) = writer.write(to_write) {
+                assert!(written < to_write.len(), "didn't flush on new line");
+                // PASS
+                return;
+            }
+        }
+        assert!(buf.is_empty(), "write returned an error but wrote data");
+    }
+
     #[test]
     fn test_line_buffer() {
         let mut writer = LineWriter::new(Vec::new());