1 files changed, 412 insertions, 0 deletions
diff --git a/src/bytes/buffer.go b/src/bytes/buffer.go
new file mode 100644
index 000000000..46ca1d5ad
--- /dev/null
+++ b/src/bytes/buffer.go
@@ -0,0 +1,412 @@
+// 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 bytes
+
+// Simple byte buffer for marshaling data.
+
+import (
+	"errors"
+	"io"
+	"unicode/utf8"
+)
+
+// A Buffer is a variable-sized buffer of bytes with Read and Write methods.
+// The zero value for Buffer is an empty buffer ready to use.
+type Buffer struct {
+	buf       []byte            // contents are the bytes buf[off : len(buf)]
+	off       int               // read at &buf[off], write at &buf[len(buf)]
+	runeBytes [utf8.UTFMax]byte // avoid allocation of slice on each WriteByte or Rune
+	bootstrap [64]byte          // memory to hold first slice; helps small buffers (Printf) avoid allocation.
+	lastRead  readOp            // last read operation, so that Unread* can work correctly.
+}
+
+// The readOp constants describe the last action performed on
+// the buffer, so that UnreadRune and UnreadByte can
+// check for invalid usage.
+type readOp int
+
+const (
+	opInvalid  readOp = iota // Non-read operation.
+	opReadRune               // Read rune.
+	opRead                   // Any other read operation.
+)
+
+// ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer.
+var ErrTooLarge = errors.New("bytes.Buffer: too large")
+
+// Bytes returns a slice of the contents of the unread portion of the buffer;
+// len(b.Bytes()) == b.Len().  If the caller changes the contents of the
+// returned slice, the contents of the buffer will change provided there
+// are no intervening method calls on the Buffer.
+func (b *Buffer) Bytes() []byte { return b.buf[b.off:] }
+
+// String returns the contents of the unread portion of the buffer
+// as a string.  If the Buffer is a nil pointer, it returns "<nil>".
+func (b *Buffer) String() string {
+	if b == nil {
+		// Special case, useful in debugging.
+		return "<nil>"
+	}
+	return string(b.buf[b.off:])
+}
+
+// Len returns the number of bytes of the unread portion of the buffer;
+// b.Len() == len(b.Bytes()).
+func (b *Buffer) Len() int { return len(b.buf) - b.off }
+
+// Truncate discards all but the first n unread bytes from the buffer.
+// It panics if n is negative or greater than the length of the buffer.
+func (b *Buffer) Truncate(n int) {
+	b.lastRead = opInvalid
+	switch {
+	case n < 0 || n > b.Len():
+		panic("bytes.Buffer: truncation out of range")
+	case n == 0:
+		// Reuse buffer space.
+		b.off = 0
+	}
+	b.buf = b.buf[0 : b.off+n]
+}
+
+// Reset resets the buffer so it has no content.
+// b.Reset() is the same as b.Truncate(0).
+func (b *Buffer) Reset() { b.Truncate(0) }
+
+// grow grows the buffer to guarantee space for n more bytes.
+// It returns the index where bytes should be written.
+// If the buffer can't grow it will panic with ErrTooLarge.
+func (b *Buffer) grow(n int) int {
+	m := b.Len()
+	// If buffer is empty, reset to recover space.
+	if m == 0 && b.off != 0 {
+		b.Truncate(0)
+	}
+	if len(b.buf)+n > cap(b.buf) {
+		var buf []byte
+		if b.buf == nil && n <= len(b.bootstrap) {
+			buf = b.bootstrap[0:]
+		} else if m+n <= cap(b.buf)/2 {
+			// We can slide things down instead of allocating a new
+			// slice. We only need m+n <= cap(b.buf) to slide, but
+			// we instead let capacity get twice as large so we
+			// don't spend all our time copying.
+			copy(b.buf[:], b.buf[b.off:])
+			buf = b.buf[:m]
+		} else {
+			// not enough space anywhere
+			buf = makeSlice(2*cap(b.buf) + n)
+			copy(buf, b.buf[b.off:])
+		}
+		b.buf = buf
+		b.off = 0
+	}
+	b.buf = b.buf[0 : b.off+m+n]
+	return b.off + m
+}
+
+// Grow grows the buffer's capacity, if necessary, to guarantee space for
+// another n bytes. After Grow(n), at least n bytes can be written to the
+// buffer without another allocation.
+// If n is negative, Grow will panic.
+// If the buffer can't grow it will panic with ErrTooLarge.
+func (b *Buffer) Grow(n int) {
+	if n < 0 {
+		panic("bytes.Buffer.Grow: negative count")
+	}
+	m := b.grow(n)
+	b.buf = b.buf[0:m]
+}
+
+// Write appends the contents of p to the buffer, growing the buffer as
+// needed. The return value n is the length of p; err is always nil. If the
+// buffer becomes too large, Write will panic with ErrTooLarge.
+func (b *Buffer) Write(p []byte) (n int, err error) {
+	b.lastRead = opInvalid
+	m := b.grow(len(p))
+	return copy(b.buf[m:], p), nil
+}
+
+// WriteString appends the contents of s to the buffer, growing the buffer as
+// needed. The return value n is the length of s; err is always nil. If the
+// buffer becomes too large, WriteString will panic with ErrTooLarge.
+func (b *Buffer) WriteString(s string) (n int, err error) {
+	b.lastRead = opInvalid
+	m := b.grow(len(s))
+	return copy(b.buf[m:], s), nil
+}
+
+// MinRead is the minimum slice size passed to a Read call by
+// Buffer.ReadFrom.  As long as the Buffer has at least MinRead bytes beyond
+// what is required to hold the contents of r, ReadFrom will not grow the
+// underlying buffer.
+const MinRead = 512
+
+// ReadFrom reads data from r until EOF and appends it to the buffer, growing
+// the buffer as needed. The return value n is the number of bytes read. Any
+// error except io.EOF encountered during the read is also returned. If the
+// buffer becomes too large, ReadFrom will panic with ErrTooLarge.
+func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {
+	b.lastRead = opInvalid
+	// If buffer is empty, reset to recover space.
+	if b.off >= len(b.buf) {
+		b.Truncate(0)
+	}
+	for {
+		if free := cap(b.buf) - len(b.buf); free < MinRead {
+			// not enough space at end
+			newBuf := b.buf
+			if b.off+free < MinRead {
+				// not enough space using beginning of buffer;
+				// double buffer capacity
+				newBuf = makeSlice(2*cap(b.buf) + MinRead)
+			}
+			copy(newBuf, b.buf[b.off:])
+			b.buf = newBuf[:len(b.buf)-b.off]
+			b.off = 0
+		}
+		m, e := r.Read(b.buf[len(b.buf):cap(b.buf)])
+		b.buf = b.buf[0 : len(b.buf)+m]
+		n += int64(m)
+		if e == io.EOF {
+			break
+		}
+		if e != nil {
+			return n, e
+		}
+	}
+	return n, nil // err is EOF, so return nil explicitly
+}
+
+// makeSlice allocates a slice of size n. If the allocation fails, it panics
+// with ErrTooLarge.
+func makeSlice(n int) []byte {
+	// If the make fails, give a known error.
+	defer func() {
+		if recover() != nil {
+			panic(ErrTooLarge)
+		}
+	}()
+	return make([]byte, n)
+}
+
+// WriteTo writes data to w until the buffer is drained or an error occurs.
+// The return value n is the number of bytes written; it always fits into an
+// int, but it is int64 to match the io.WriterTo interface. Any error
+// encountered during the write is also returned.
+func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) {
+	b.lastRead = opInvalid
+	if b.off < len(b.buf) {
+		nBytes := b.Len()
+		m, e := w.Write(b.buf[b.off:])
+		if m > nBytes {
+			panic("bytes.Buffer.WriteTo: invalid Write count")
+		}
+		b.off += m
+		n = int64(m)
+		if e != nil {
+			return n, e
+		}
+		// all bytes should have been written, by definition of
+		// Write method in io.Writer
+		if m != nBytes {
+			return n, io.ErrShortWrite
+		}
+	}
+	// Buffer is now empty; reset.
+	b.Truncate(0)
+	return
+}
+
+// WriteByte appends the byte c to the buffer, growing the buffer as needed.
+// The returned error is always nil, but is included to match bufio.Writer's
+// WriteByte. If the buffer becomes too large, WriteByte will panic with
+// ErrTooLarge.
+func (b *Buffer) WriteByte(c byte) error {
+	b.lastRead = opInvalid
+	m := b.grow(1)
+	b.buf[m] = c
+	return nil
+}
+
+// WriteRune appends the UTF-8 encoding of Unicode code point r to the
+// buffer, returning its length and an error, which is always nil but is
+// included to match bufio.Writer's WriteRune. The buffer is grown as needed;
+// if it becomes too large, WriteRune will panic with ErrTooLarge.
+func (b *Buffer) WriteRune(r rune) (n int, err error) {
+	if r < utf8.RuneSelf {
+		b.WriteByte(byte(r))
+		return 1, nil
+	}
+	n = utf8.EncodeRune(b.runeBytes[0:], r)
+	b.Write(b.runeBytes[0:n])
+	return n, nil
+}
+
+// Read reads the next len(p) bytes from the buffer or until the buffer
+// is drained.  The return value n is the number of bytes read.  If the
+// buffer has no data to return, err is io.EOF (unless len(p) is zero);
+// otherwise it is nil.
+func (b *Buffer) Read(p []byte) (n int, err error) {
+	b.lastRead = opInvalid
+	if b.off >= len(b.buf) {
+		// Buffer is empty, reset to recover space.
+		b.Truncate(0)
+		if len(p) == 0 {
+			return
+		}
+		return 0, io.EOF
+	}
+	n = copy(p, b.buf[b.off:])
+	b.off += n
+	if n > 0 {
+		b.lastRead = opRead
+	}
+	return
+}
+
+// Next returns a slice containing the next n bytes from the buffer,
+// advancing the buffer as if the bytes had been returned by Read.
+// If there are fewer than n bytes in the buffer, Next returns the entire buffer.
+// The slice is only valid until the next call to a read or write method.
+func (b *Buffer) Next(n int) []byte {
+	b.lastRead = opInvalid
+	m := b.Len()
+	if n > m {
+		n = m
+	}
+	data := b.buf[b.off : b.off+n]
+	b.off += n
+	if n > 0 {
+		b.lastRead = opRead
+	}
+	return data
+}
+
+// ReadByte reads and returns the next byte from the buffer.
+// If no byte is available, it returns error io.EOF.
+func (b *Buffer) ReadByte() (c byte, err error) {
+	b.lastRead = opInvalid
+	if b.off >= len(b.buf) {
+		// Buffer is empty, reset to recover space.
+		b.Truncate(0)
+		return 0, io.EOF
+	}
+	c = b.buf[b.off]
+	b.off++
+	b.lastRead = opRead
+	return c, nil
+}
+
+// ReadRune reads and returns the next UTF-8-encoded
+// Unicode code point from the buffer.
+// If no bytes are available, the error returned is io.EOF.
+// If the bytes are an erroneous UTF-8 encoding, it
+// consumes one byte and returns U+FFFD, 1.
+func (b *Buffer) ReadRune() (r rune, size int, err error) {
+	b.lastRead = opInvalid
+	if b.off >= len(b.buf) {
+		// Buffer is empty, reset to recover space.
+		b.Truncate(0)
+		return 0, 0, io.EOF
+	}
+	b.lastRead = opReadRune
+	c := b.buf[b.off]
+	if c < utf8.RuneSelf {
+		b.off++
+		return rune(c), 1, nil
+	}
+	r, n := utf8.DecodeRune(b.buf[b.off:])
+	b.off += n
+	return r, n, nil
+}
+
+// UnreadRune unreads the last rune returned by ReadRune.
+// If the most recent read or write operation on the buffer was
+// not a ReadRune, UnreadRune returns an error.  (In this regard
+// it is stricter than UnreadByte, which will unread the last byte
+// from any read operation.)
+func (b *Buffer) UnreadRune() error {
+	if b.lastRead != opReadRune {
+		return errors.New("bytes.Buffer: UnreadRune: previous operation was not ReadRune")
+	}
+	b.lastRead = opInvalid
+	if b.off > 0 {
+		_, n := utf8.DecodeLastRune(b.buf[0:b.off])
+		b.off -= n
+	}
+	return nil
+}
+
+// UnreadByte unreads the last byte returned by the most recent
+// read operation.  If write has happened since the last read, UnreadByte
+// returns an error.
+func (b *Buffer) UnreadByte() error {
+	if b.lastRead != opReadRune && b.lastRead != opRead {
+		return errors.New("bytes.Buffer: UnreadByte: previous operation was not a read")
+	}
+	b.lastRead = opInvalid
+	if b.off > 0 {
+		b.off--
+	}
+	return nil
+}
+
+// ReadBytes reads until the first occurrence of delim in the input,
+// returning a slice containing the data up to and including the delimiter.
+// If ReadBytes encounters an error before finding a delimiter,
+// it returns the data read before the error and the error itself (often io.EOF).
+// ReadBytes returns err != nil if and only if the returned data does not end in
+// delim.
+func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) {
+	slice, err := b.readSlice(delim)
+	// return a copy of slice. The buffer's backing array may
+	// be overwritten by later calls.
+	line = append(line, slice...)
+	return
+}
+
+// readSlice is like ReadBytes but returns a reference to internal buffer data.
+func (b *Buffer) readSlice(delim byte) (line []byte, err error) {
+	i := IndexByte(b.buf[b.off:], delim)
+	end := b.off + i + 1
+	if i < 0 {
+		end = len(b.buf)
+		err = io.EOF
+	}
+	line = b.buf[b.off:end]
+	b.off = end
+	b.lastRead = opRead
+	return line, err
+}
+
+// ReadString reads until the first occurrence of delim in the input,
+// returning a string containing the data up to and including the delimiter.
+// If ReadString encounters an error before finding a delimiter,
+// it returns the data read before the error and the error itself (often io.EOF).
+// ReadString returns err != nil if and only if the returned data does not end
+// in delim.
+func (b *Buffer) ReadString(delim byte) (line string, err error) {
+	slice, err := b.readSlice(delim)
+	return string(slice), err
+}
+
+// NewBuffer creates and initializes a new Buffer using buf as its initial
+// contents.  It is intended to prepare a Buffer to read existing data.  It
+// can also be used to size the internal buffer for writing. To do that,
+// buf should have the desired capacity but a length of zero.
+//
+// In most cases, new(Buffer) (or just declaring a Buffer variable) is
+// sufficient to initialize a Buffer.
+func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} }
+
+// NewBufferString creates and initializes a new Buffer using string s as its
+// initial contents. It is intended to prepare a buffer to read an existing
+// string.
+//
+// In most cases, new(Buffer) (or just declaring a Buffer variable) is
+// sufficient to initialize a Buffer.
+func NewBufferString(s string) *Buffer {
+	return &Buffer{buf: []byte(s)}
+}