diff --git a/src/lib/io/bytebuffer.go b/src/lib/io/bytebuffer.go
index 9c78e8566f4..011166e9c0f 100644
--- a/src/lib/io/bytebuffer.go
+++ b/src/lib/io/bytebuffer.go
@@ -11,11 +11,8 @@ import (
 	"os";
 )
 
-
-// TODO(r): Do better memory management.
-
 func bytecopy(dst []byte, doff int, src []byte, soff int, count int) {
-	for i := 0; i < count; i++ {
+	for ; count > 0; count-- {
 		dst[doff] = src[soff];
 		doff++;
 		soff++;
@@ -26,79 +23,68 @@ func bytecopy(dst []byte, doff int, src []byte, soff int, count int) {
 // connected to a buffer of bytes.
 // The zero value for ByteBuffer is an empty buffer ready to use.
 type ByteBuffer struct {
-	buf	[]byte;
-	off	int;	// Read from here
-	len	int;	// Write to here
-	cap	int;
+	buf	[]byte;	// contents are the bytes buf[off : len(buf)]
+	off	int;	// read at &buf[off], write at &buf[len(buf)]
+}
+
+// Data returns the contents of the unread portion of the buffer;
+// len(b.Data()) == b.Len().
+func (b *ByteBuffer) Data() []byte {
+	return b.buf[b.off : len(b.buf)]
+}
+
+// Len returns the number of bytes of the unread portion of the buffer;
+// b.Len() == len(b.Data()).
+func (b *ByteBuffer) Len() int {
+	return len(b.buf) - b.off
 }
 
 // Reset resets the buffer so it has no content.
 func (b *ByteBuffer) Reset() {
-	b.off = 0;
-	b.len = 0;
+	b.off = len(b.buf)
 }
 
 // Write appends the contents of p to the buffer.  The return
-// value is the length of p; err is always nil.
+// value n is the length of p; err is always nil.
 func (b *ByteBuffer) Write(p []byte) (n int, err os.Error) {
-	plen := len(p);
-	if len(b.buf) == 0 {
-		b.cap = plen + 1024;
-		b.buf = make([]byte, b.cap);
-		b.len = 0;
+	m := b.Len();
+	n = len(p);
+
+	if len(b.buf) + n > cap(b.buf) {
+		// not enough space at end
+		buf := b.buf;
+		if m + n > cap(b.buf) {
+			// not enough space anywhere
+			buf = make([]byte, 2*cap(b.buf) + n)
+		}
+		bytecopy(buf, 0, b.buf, b.off, m);
+		b.buf = buf;
+		b.off = 0
 	}
-	if b.len + plen > b.cap {
-		b.cap = 2*(b.cap + plen);
-		nb := make([]byte, b.cap);
-		bytecopy(nb, 0, b.buf, 0, b.len);
-		b.buf = nb;
-	}
-	bytecopy(b.buf, b.len, p, 0, plen);
-	b.len += plen;
-	return plen, nil;
+
+	b.buf = b.buf[0 : b.off + m + n];
+	bytecopy(b.buf, b.off + m, p, 0, n);
+	return n, nil
 }
 
 // Read reads the next len(p) bytes from the buffer or until the buffer
-// is drained.  The return value is the number of bytes read; err is always nil.
+// is drained.  The return value n is the number of bytes read; err is always nil.
 func (b *ByteBuffer) Read(p []byte) (n int, err os.Error) {
-	plen := len(p);
-	if len(b.buf) == 0 {
-		return 0, nil
-	}
-	if b.off == b.len {	// empty buffer
-		b.Reset();
-		return 0, nil
-	}
-	if plen > b.len - b.off {
-		plen = b.len - b.off
-	}
-	bytecopy(p, 0, b.buf, b.off, plen);
-	b.off += plen;
-	return plen, nil;
-}
+	m := b.Len();
+	n = len(p);
 
-// Len returns the length of the underlying buffer.
-func (b *ByteBuffer) Len() int {
-	return b.len
-}
+	if n > m {
+		// more bytes requested than available
+		n = m
+	}
 
-// Off returns the location within the buffer of the next byte to be read.
-func (b *ByteBuffer) Off() int {
-	return b.off
-}
-
-// Data returns the contents of the unread portion of the buffer.
-func (b *ByteBuffer) Data() []byte {
-	return b.buf[b.off:b.len]
+	bytecopy(p, 0, b.buf, b.off, n);
+	b.off += n;
+	return n, nil
 }
 
 // NewByteBufferFromArray creates and initializes a new ByteBuffer
 // with buf as its initial contents.
 func NewByteBufferFromArray(buf []byte) *ByteBuffer {
-	b := new(ByteBuffer);
-	b.buf = buf;
-	b.off = 0;
-	b.len = len(buf);
-	b.cap = len(buf);
-	return b;
+	return &ByteBuffer{buf, 0};
 }
diff --git a/src/lib/io/bytebuffer_test.go b/src/lib/io/bytebuffer_test.go
new file mode 100644
index 00000000000..6a4f3c9b907
--- /dev/null
+++ b/src/lib/io/bytebuffer_test.go
@@ -0,0 +1,146 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package io
+
+import (
+	"io";
+	"rand";
+	"testing";
+)
+
+
+const N = 10000;  // make this bigger for a larger (and slower) test
+var data []byte;  // test data for write tests
+
+
+func init() {
+	data = make([]byte, N);
+	for i := 0; i < len(data); i++ {
+		data[i] = 'a' + byte(i % 26)
+	}
+}
+
+
+// Verify that contents of buf match the string s.
+func check(t *testing.T, testname string, buf *ByteBuffer, s string) {
+	if buf.Len() != len(buf.Data()) {
+		t.Errorf("%s: buf.Len() == %d, len(buf.Data()) == %d\n", testname, buf.Len(), len(buf.Data()))
+	}
+
+	if buf.Len() != len(s) {
+		t.Errorf("%s: buf.Len() == %d, len(s) == %d\n", testname, buf.Len(), len(s))
+	}
+
+	if string(buf.Data()) != s {
+		t.Errorf("%s: string(buf.Data()) == %q, s == %q\n", testname, string(buf.Data()), s)
+	}
+}
+
+
+// Fill buf through n writes of fub.
+// The initial contents of buf corresponds to the string s;
+// the result is the final contents of buf returned as a string.
+func fill(t *testing.T, testname string, buf *ByteBuffer, s string, n int, fub []byte) string {
+	check(t, testname + " (fill 1)", buf, s);
+	for ; n > 0; n-- {
+		m, err := buf.Write(fub);
+		if m != len(fub) {
+			t.Errorf(testname + " (fill 2): m == %d, expected %d\n", m, len(fub));
+		}
+		if err != nil {
+			t.Errorf(testname + " (fill 3): err should always be nil, found err == %s\n", err);
+		}
+		s += string(fub);
+		check(t, testname + " (fill 4)", buf, s);
+	}
+	return s;
+}
+
+
+// Empty buf through repeated reads into fub.
+// The initial contents of buf corresponds to the string s.
+func empty(t *testing.T, testname string, buf *ByteBuffer, s string, fub []byte) {
+	check(t, testname + " (empty 1)", buf, s);
+
+	for {
+		n, err := buf.Read(fub);
+		if n == 0 {
+			break;
+		}
+		if err != nil {
+			t.Errorf(testname + " (empty 2): err should always be nil, found err == %s\n", err);
+		}
+		s = s[n : len(s)];
+		check(t, testname + " (empty 3)", buf, s);
+	}
+
+	check(t, testname + " (empty 4)", buf, "");
+}
+
+
+func TestBasicOperations(t *testing.T) {
+	var buf ByteBuffer;
+
+	for i := 0; i < 5; i++ {
+		check(t, "TestBasicOperations (1)", &buf, "");
+
+		buf.Reset();
+		check(t, "TestBasicOperations (2)", &buf, "");
+
+		n, err := buf.Write(data[0 : 1]);
+		if n != 1 {
+			t.Errorf("wrote 1 byte, but n == %d\n", n);
+		}
+		if err != nil {
+			t.Errorf("err should always be nil, but err == %s\n", err);
+		}
+		check(t, "TestBasicOperations (3)", &buf, "a");
+
+		n, err = buf.Write(data[1 : 26]);
+		if n != 25 {
+			t.Errorf("wrote 25 bytes, but n == %d\n", n);
+		}
+		check(t, "TestBasicOperations (4)", &buf, string(data[0 : 26]));
+
+		empty(t, "TestBasicOperations (5)", &buf, string(data[0 : 26]), make([]byte, 5));
+		empty(t, "TestBasicOperations (6)", &buf, "", make([]byte, 100));
+	}
+}
+
+
+func TestLargeWrites(t *testing.T) {
+	var buf ByteBuffer;
+	for i := 3; i < 30; i += 3 {
+		s := fill(t, "TestLargeWrites (1)", &buf, "", 5, data);
+		empty(t, "TestLargeWrites (2)", &buf, s, make([]byte, len(data)/i));
+	}
+	check(t, "TestLargeWrites (3)", &buf, "");
+}
+
+
+func TestLargeReads(t *testing.T) {
+	var buf ByteBuffer;
+	for i := 3; i < 30; i += 3 {
+		s := fill(t, "TestLargeReads (1)", &buf, "", 5, data[0 : len(data)/i]);
+		empty(t, "TestLargeReads (2)", &buf, s, make([]byte, len(data)));
+	}
+	check(t, "TestLargeReads (3)", &buf, "");
+}
+
+
+func TestMixedReadsAndWrites(t *testing.T) {
+	var buf ByteBuffer;
+	s := "";
+	for i := 0; i < 50; i++ {
+		wlen := rand.Intn(len(data));
+		s = fill(t, "TestMixedReadsAndWrites (1)", &buf, s, 1, data[0 : wlen]);
+
+		rlen := rand.Intn(len(data));
+		fub := make([]byte, rlen);
+		n, err := buf.Read(fub);
+		s = s[n : len(s)];
+	}
+	empty(t, "TestMixedReadsAndWrites (2)", &buf, s, make([]byte, buf.Len()));
+}