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// 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 "".

func (b *Buffer) String() string {

        if b == nil {

                // Special case, useful in debugging.

                return ""

        }

        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 {

                        // 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

}

// Write appends the contents of p to the buffer.  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.  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.

// 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) {

                m, e := w.Write(b.buf[b.off:])

                b.off += m

                n = int64(m)

                if e != nil {

                        return n, e

                }

                // otherwise all bytes were written, by definition of

                // Write method in io.Writer

        }

        // Buffer is now empty; reset.

        b.Truncate(0)

        return

}

// WriteByte appends the byte c to the buffer.

// 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.

// If the buffer 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) {

        i := IndexByte(b.buf[b.off:], delim)

        size := i + 1

        if i < 0 {

                size = len(b.buf) - b.off

                err = io.EOF

        }

        line = make([]byte, size)

        copy(line, b.buf[b.off:])

        b.off += size

        return

}

// 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) {

        bytes, err := b.ReadBytes(delim)

        return string(bytes), 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)}

}