auto merge of #11376 : alexcrichton/rust/remove-eof, r=pcwalton

This is something I have been meaning to do for awhile, but upon inspection of the `eof` method on all of the `Reader` impls you may find some interesting surprises. The method returns a good answer for almost all wrapped I/O objects (buffered readers, mem readers, util readers, etc), but the actual return value on all I/O objects themselves is almost always useless.

Almost no I/O object other than a file actually knows when it's hit EOF or not. I think that pretending that all objects know when they've hit the end when almost none do is probably a bad idea. I can't really come up with a good answer to "is this file descriptor at eof" or "is this tcp stream at eof" much less "is this udp socket at eof". Due to being unable to answer these questions for *all* readers, I believe that it shouldn't be a part of the core `Reader` trait.

14 files changed, 18 insertions, 142 deletions

diff --git a/src/libstd/io/buffered.rs b/src/libstd/io/buffered.rs
index 96cb59ce778..d0894bef413 100644
--- a/src/libstd/io/buffered.rs
+++ b/src/libstd/io/buffered.rs
@@ -66,7 +66,8 @@ pub struct BufferedReader<R> {
     priv inner: R,
     priv buf: ~[u8],
     priv pos: uint,
-    priv cap: uint
+    priv cap: uint,
+    priv eof: bool,
 }
 
 impl<R: Reader> BufferedReader<R> {
@@ -84,7 +85,8 @@ impl<R: Reader> BufferedReader<R> {
             inner: inner,
             buf: buf,
             pos: 0,
-            cap: 0
+            cap: 0,
+            eof: false,
         }
     }
 
@@ -113,7 +115,7 @@ impl<R: Reader> Buffer for BufferedReader<R> {
                     self.pos = 0;
                     self.cap = cap;
                 }
-                None => {}
+                None => { self.eof = true; }
             }
         }
         return self.buf.slice(self.pos, self.cap);
@@ -134,15 +136,11 @@ impl<R: Reader> Reader for BufferedReader<R> {
             nread
         };
         self.pos += nread;
-        if nread == 0 && self.inner.eof() && buf.len() != 0 {
-                return None;
+        if nread == 0 && buf.len() != 0 && self.eof {
+            return None;
         }
         Some(nread)
     }
-
-    fn eof(&mut self) -> bool {
-        self.pos == self.cap && self.inner.eof()
-    }
 }
 
 /// Wraps a Writer and buffers output to it
@@ -270,7 +268,6 @@ impl<W> InternalBufferedWriter<W> {
 
 impl<W: Reader> Reader for InternalBufferedWriter<W> {
     fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.get_mut_ref().inner.read(buf) }
-    fn eof(&mut self) -> bool { self.get_mut_ref().inner.eof() }
 }
 
 /// Wraps a Stream and buffers input and output to and from it
@@ -325,7 +322,6 @@ impl<S: Stream> Buffer for BufferedStream<S> {
 
 impl<S: Stream> Reader for BufferedStream<S> {
     fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.inner.read(buf) }
-    fn eof(&mut self) -> bool { self.inner.eof() }
 }
 
 impl<S: Stream> Writer for BufferedStream<S> {
@@ -351,10 +347,6 @@ mod test {
         fn read(&mut self, _: &mut [u8]) -> Option<uint> {
             None
         }
-
-        fn eof(&mut self) -> bool {
-            true
-        }
     }
 
     impl Writer for NullStream {
@@ -370,10 +362,6 @@ mod test {
         fn read(&mut self, _: &mut [u8]) -> Option<uint> {
             self.lengths.shift_opt()
         }
-
-        fn eof(&mut self) -> bool {
-            self.lengths.len() == 0
-        }
     }
 
     #[test]
@@ -385,24 +373,20 @@ mod test {
         let nread = reader.read(buf);
         assert_eq!(Some(2), nread);
         assert_eq!([0, 1, 0], buf);
-        assert!(!reader.eof());
 
         let mut buf = [0];
         let nread = reader.read(buf);
         assert_eq!(Some(1), nread);
         assert_eq!([2], buf);
-        assert!(!reader.eof());
 
         let mut buf = [0, 0, 0];
         let nread = reader.read(buf);
         assert_eq!(Some(1), nread);
         assert_eq!([3, 0, 0], buf);
-        assert!(!reader.eof());
 
         let nread = reader.read(buf);
         assert_eq!(Some(1), nread);
         assert_eq!([4, 0, 0], buf);
-        assert!(reader.eof());
 
         assert_eq!(None, reader.read(buf));
     }
@@ -466,13 +450,11 @@ mod test {
 
         impl io::Reader for S {
             fn read(&mut self, _: &mut [u8]) -> Option<uint> { None }
-            fn eof(&mut self) -> bool { true }
         }
 
         let mut stream = BufferedStream::new(S);
         let mut buf = [];
         stream.read(buf);
-        stream.eof();
         stream.write(buf);
         stream.flush();
     }
@@ -539,6 +521,7 @@ mod test {
         assert_eq!(reader.read(buf), Some(2));
         assert_eq!(reader.read(buf), Some(0));
         assert_eq!(reader.read(buf), Some(1));
+        assert_eq!(reader.read(buf), Some(0));
         assert_eq!(reader.read(buf), None);
     }
 
diff --git a/src/libstd/io/comm_adapters.rs b/src/libstd/io/comm_adapters.rs
index 7a79857e754..e15b9a861ca 100644
--- a/src/libstd/io/comm_adapters.rs
+++ b/src/libstd/io/comm_adapters.rs
@@ -77,8 +77,6 @@ impl Reader for PortReader {
             Some(num_read)
         }
     }
-
-    fn eof(&mut self) -> bool { self.closed }
 }
 
 /// Allows writing to a chan.
@@ -133,22 +131,17 @@ mod test {
         let mut reader = PortReader::new(port);
         let mut buf = ~[0u8, ..3];
 
-        assert_eq!(false, reader.eof());
 
         assert_eq!(Some(0), reader.read([]));
-        assert_eq!(false, reader.eof());
 
         assert_eq!(Some(3), reader.read(buf));
-        assert_eq!(false, reader.eof());
         assert_eq!(~[1,2,3], buf);
 
         assert_eq!(Some(3), reader.read(buf));
-        assert_eq!(false, reader.eof());
         assert_eq!(~[4,5,6], buf);
 
         assert_eq!(Some(2), reader.read(buf));
         assert_eq!(~[7,8,6], buf);
-        assert_eq!(true, reader.eof());
 
         let mut err = None;
         let result = io::io_error::cond.trap(|io::standard_error(k, _, _)| {
@@ -158,7 +151,6 @@ mod test {
         });
         assert_eq!(Some(io::EndOfFile), err);
         assert_eq!(None, result);
-        assert_eq!(true, reader.eof());
         assert_eq!(~[7,8,6], buf);
 
         // Ensure it continues to fail in the same way.
@@ -170,7 +162,6 @@ mod test {
         });
         assert_eq!(Some(io::EndOfFile), err);
         assert_eq!(None, result);
-        assert_eq!(true, reader.eof());
         assert_eq!(~[7,8,6], buf);
     }
 
diff --git a/src/libstd/io/extensions.rs b/src/libstd/io/extensions.rs
index 3ad05348960..09876f15a8b 100644
--- a/src/libstd/io/extensions.rs
+++ b/src/libstd/io/extensions.rs
@@ -150,9 +150,6 @@ mod test {
                 Some(1)
             }
         }
-        fn eof(&mut self) -> bool {
-            false
-        }
     }
 
     struct EofReader;
@@ -161,9 +158,6 @@ mod test {
         fn read(&mut self, _: &mut [u8]) -> Option<uint> {
             None
         }
-        fn eof(&mut self) -> bool {
-            false
-        }
     }
 
     struct ErroringReader;
@@ -173,9 +167,6 @@ mod test {
             io_error::cond.raise(placeholder_error());
             None
         }
-        fn eof(&mut self) -> bool {
-            false
-        }
     }
 
     struct PartialReader {
@@ -195,9 +186,6 @@ mod test {
                 Some(2)
             }
         }
-        fn eof(&mut self) -> bool {
-            false
-        }
     }
 
     struct ErroringLaterReader {
@@ -215,9 +203,6 @@ mod test {
                 None
             }
         }
-        fn eof(&mut self) -> bool {
-            false
-        }
     }
 
     struct ThreeChunkReader {
@@ -240,9 +225,6 @@ mod test {
                 None
             }
         }
-        fn eof(&mut self) -> bool {
-            false
-        }
     }
 
     #[test]
diff --git a/src/libstd/io/flate.rs b/src/libstd/io/flate.rs
index c56bdf5bec8..0cf00b2c1a9 100644
--- a/src/libstd/io/flate.rs
+++ b/src/libstd/io/flate.rs
@@ -49,6 +49,4 @@ impl<R: Reader> InflateReader<R> {
 
 impl<R: Reader> Reader for InflateReader<R> {
     fn read(&mut self, _buf: &mut [u8]) -> Option<uint> { fail!() }
-
-    fn eof(&mut self) -> bool { fail!() }
 }
diff --git a/src/libstd/io/fs.rs b/src/libstd/io/fs.rs
index cf203f2782c..a3f84fe2afa 100644
--- a/src/libstd/io/fs.rs
+++ b/src/libstd/io/fs.rs
@@ -205,6 +205,14 @@ impl File {
     pub fn truncate(&mut self, size: i64) {
         self.fd.truncate(size).map_err(|e| io_error::cond.raise(e));
     }
+
+    /// Tests whether this stream has reached EOF.
+    ///
+    /// If true, then this file will no longer continue to return data via
+    /// `read`.
+    pub fn eof(&self) -> bool {
+        self.last_nread == 0
+    }
 }
 
 /// Unlink a file from the underlying filesystem.
@@ -597,8 +605,6 @@ impl Reader for File {
             }
         }
     }
-
-    fn eof(&mut self) -> bool { self.last_nread == 0 }
 }
 
 impl Writer for File {
diff --git a/src/libstd/io/mem.rs b/src/libstd/io/mem.rs
index 95cf7ab4078..53aa176134d 100644
--- a/src/libstd/io/mem.rs
+++ b/src/libstd/io/mem.rs
@@ -124,7 +124,7 @@ impl MemReader {
 
 impl Reader for MemReader {
     fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        { if self.eof() { return None; } }
+        if self.pos == self.buf.len() { return None }
 
         let write_len = min(buf.len(), self.buf.len() - self.pos);
         {
@@ -138,8 +138,6 @@ impl Reader for MemReader {
 
         return Some(write_len);
     }
-
-    fn eof(&mut self) -> bool { self.pos == self.buf.len() }
 }
 
 impl Seek for MemReader {
@@ -222,7 +220,7 @@ impl<'a> BufReader<'a> {
 
 impl<'a> Reader for BufReader<'a> {
     fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        { if self.eof() { return None; } }
+        if self.pos == self.buf.len() { return None }
 
         let write_len = min(buf.len(), self.buf.len() - self.pos);
         {
@@ -236,8 +234,6 @@ impl<'a> Reader for BufReader<'a> {
 
         return Some(write_len);
      }
-
-    fn eof(&mut self) -> bool { self.pos == self.buf.len() }
 }
 
 impl<'a> Seek for BufReader<'a> {
@@ -369,9 +365,7 @@ mod test {
         assert_eq!(buf, [1, 2, 3, 4]);
         assert_eq!(reader.read(buf), Some(3));
         assert_eq!(buf.slice(0, 3), [5, 6, 7]);
-        assert!(reader.eof());
         assert_eq!(reader.read(buf), None);
-        assert!(reader.eof());
     }
 
     #[test]
@@ -391,9 +385,7 @@ mod test {
         assert_eq!(buf, [1, 2, 3, 4]);
         assert_eq!(reader.read(buf), Some(3));
         assert_eq!(buf.slice(0, 3), [5, 6, 7]);
-        assert!(reader.eof());
         assert_eq!(reader.read(buf), None);
-        assert!(reader.eof());
     }
 
     #[test]
diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index a40999a8042..3ab710e9356 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -502,26 +502,6 @@ pub trait Reader {
     /// Is it actually possible for 0 bytes to be read successfully?
     fn read(&mut self, buf: &mut [u8]) -> Option<uint>;
 
-    /// Return whether the Reader has reached the end of the stream.
-    ///
-    /// # Example
-    ///
-    /// ```rust
-    /// use std::io;
-    /// # let _g = ::std::io::ignore_io_error();
-    /// let mut reader = io::stdin();
-    ///
-    /// let mut bytes = [0, .. 10];
-    /// reader.read(bytes);
-    ///
-    /// if reader.eof() { println("stdin() had at most 10 bytes of data."); }
-    /// ```
-    ///
-    /// # Failure
-    ///
-    /// Returns `true` on failure.
-    fn eof(&mut self) -> bool;
-
     // Convenient helper methods based on the above methods
 
     /// Reads a single byte. Returns `None` on EOF.
@@ -864,12 +844,10 @@ pub trait Reader {
 
 impl Reader for ~Reader {
     fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.read(buf) }
-    fn eof(&mut self) -> bool { self.eof() }
 }
 
 impl<'a> Reader for &'a mut Reader {
     fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.read(buf) }
-    fn eof(&mut self) -> bool { self.eof() }
 }
 
 fn extend_sign(val: u64, nbytes: uint) -> i64 {
diff --git a/src/libstd/io/net/tcp.rs b/src/libstd/io/net/tcp.rs
index c2a70e0120d..023a9bddca9 100644
--- a/src/libstd/io/net/tcp.rs
+++ b/src/libstd/io/net/tcp.rs
@@ -67,8 +67,6 @@ impl Reader for TcpStream {
             }
         }
     }
-
-    fn eof(&mut self) -> bool { fail!() }
 }
 
 impl Writer for TcpStream {
diff --git a/src/libstd/io/net/udp.rs b/src/libstd/io/net/udp.rs
index eaee48dc6e0..8a866c2a357 100644
--- a/src/libstd/io/net/udp.rs
+++ b/src/libstd/io/net/udp.rs
@@ -86,8 +86,6 @@ impl Reader for UdpStream {
             }
         })
     }
-
-    fn eof(&mut self) -> bool { fail!() }
 }
 
 impl Writer for UdpStream {
diff --git a/src/libstd/io/net/unix.rs b/src/libstd/io/net/unix.rs
index 01b409d4316..232ca670597 100644
--- a/src/libstd/io/net/unix.rs
+++ b/src/libstd/io/net/unix.rs
@@ -67,7 +67,6 @@ impl UnixStream {
 
 impl Reader for UnixStream {
     fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.obj.read(buf) }
-    fn eof(&mut self) -> bool { self.obj.eof() }
 }
 
 impl Writer for UnixStream {
diff --git a/src/libstd/io/option.rs b/src/libstd/io/option.rs
index 65fa71dd415..e2eec652d9d 100644
--- a/src/libstd/io/option.rs
+++ b/src/libstd/io/option.rs
@@ -48,16 +48,6 @@ impl<R: Reader> Reader for Option<R> {
             }
         }
     }
-
-    fn eof(&mut self) -> bool {
-        match *self {
-            Some(ref mut reader) => reader.eof(),
-            None => {
-                io_error::cond.raise(prev_io_error());
-                true
-            }
-        }
-    }
 }
 
 impl<S: Seek> Seek for Option<S> {
@@ -145,7 +135,6 @@ mod test {
         let mut buf = [0, 0];
         reader.read(buf);
         assert_eq!(buf, [0, 1]);
-        assert!(!reader.eof());
     }
 
     #[test]
@@ -161,14 +150,5 @@ mod test {
             reader.read(buf);
         });
         assert!(called);
-
-        let mut called = false;
-        io_error::cond.trap(|err| {
-            assert_eq!(err.kind, PreviousIoError);
-            called = true;
-        }).inside(|| {
-            assert!(reader.eof());
-        });
-        assert!(called);
     }
 }
diff --git a/src/libstd/io/pipe.rs b/src/libstd/io/pipe.rs
index e3f2cc2384c..799adff37e3 100644
--- a/src/libstd/io/pipe.rs
+++ b/src/libstd/io/pipe.rs
@@ -66,8 +66,6 @@ impl Reader for PipeStream {
             }
         }
     }
-
-    fn eof(&mut self) -> bool { false }
 }
 
 impl Writer for PipeStream {
diff --git a/src/libstd/io/stdio.rs b/src/libstd/io/stdio.rs
index 6e6cdfb25de..f3177276bc2 100644
--- a/src/libstd/io/stdio.rs
+++ b/src/libstd/io/stdio.rs
@@ -272,8 +272,6 @@ impl Reader for StdReader {
             }
         }
     }
-
-    fn eof(&mut self) -> bool { false }
 }
 
 /// Representation of a writer to a standard output stream
diff --git a/src/libstd/io/util.rs b/src/libstd/io/util.rs
index 0f64e9f874b..612c757ad4c 100644
--- a/src/libstd/io/util.rs
+++ b/src/libstd/io/util.rs
@@ -36,10 +36,6 @@ impl<'a, R: Reader> Reader for LimitReader<'a, R> {
             len
         })
     }
-
-    fn eof(&mut self) -> bool {
-        self.limit == 0 || self.inner.eof()
-    }
 }
 
 /// A `Writer` which ignores bytes written to it, like /dev/null.
@@ -59,11 +55,6 @@ impl Reader for ZeroReader {
         buf.set_memory(0);
         Some(buf.len())
     }
-
-    #[inline]
-    fn eof(&mut self) -> bool {
-        false
-    }
 }
 
 /// A `Reader` which is always at EOF, like /dev/null.
@@ -74,11 +65,6 @@ impl Reader for NullReader {
     fn read(&mut self, _buf: &mut [u8]) -> Option<uint> {
         None
     }
-
-    #[inline]
-    fn eof(&mut self) -> bool {
-        true
-    }
 }
 
 /// A `Writer` which multiplexes writes to a set of `Writers`.
@@ -140,10 +126,6 @@ impl<R: Reader, I: Iterator<R>> Reader for ChainedReader<I, R> {
         }
         None
     }
-
-    fn eof(&mut self) -> bool {
-        self.cur_reader.is_none()
-    }
 }
 
 /// A `Reader` which forwards input from another `Reader`, passing it along to
@@ -174,10 +156,6 @@ impl<R: Reader, W: Writer> Reader for TeeReader<R, W> {
             len
         })
     }
-
-    fn eof(&mut self) -> bool {
-        self.reader.eof()
-    }
 }
 
 /// Copies all data from a `Reader` to a `Writer`.
@@ -204,7 +182,6 @@ mod test {
             let mut r = LimitReader::new(&mut r, 4);
             assert_eq!(~[0, 1, 2], r.read_to_end());
         }
-        assert!(r.eof());
     }
 
     #[test]
@@ -238,7 +215,6 @@ mod test {
         let mut r = NullReader;
         let mut buf = ~[0];
         assert_eq!(r.read(buf), None);
-        assert!(r.eof());
     }
 
     #[test]
@@ -289,7 +265,6 @@ mod test {
         let mut r = MemReader::new(~[0, 1, 2, 3, 4]);
         let mut w = MemWriter::new();
         copy(&mut r, &mut w);
-        assert!(r.eof());
         assert_eq!(~[0, 1, 2, 3, 4], w.unwrap());
     }
 }