1 // Copyright 2009 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
7 // Simple byte buffer for marshaling data.
15 // smallBufferSize is an initial allocation minimal capacity.
16 const smallBufferSize
= 64
18 // A Buffer is a variable-sized buffer of bytes with Read and Write methods.
19 // The zero value for Buffer is an empty buffer ready to use.
21 buf
[]byte // contents are the bytes buf[off : len(buf)]
22 off
int // read at &buf[off], write at &buf[len(buf)]
23 lastRead readOp
// last read operation, so that Unread* can work correctly.
26 // The readOp constants describe the last action performed on
27 // the buffer, so that UnreadRune and UnreadByte can check for
28 // invalid usage. opReadRuneX constants are chosen such that
29 // converted to int they correspond to the rune size that was read.
32 // Don't use iota for these, as the values need to correspond with the
33 // names and comments, which is easier to see when being explicit.
35 opRead readOp
= -1 // Any other read operation.
36 opInvalid readOp
= 0 // Non-read operation.
37 opReadRune1 readOp
= 1 // Read rune of size 1.
38 opReadRune2 readOp
= 2 // Read rune of size 2.
39 opReadRune3 readOp
= 3 // Read rune of size 3.
40 opReadRune4 readOp
= 4 // Read rune of size 4.
43 // ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer.
44 var ErrTooLarge
= errors
.New("bytes.Buffer: too large")
45 var errNegativeRead
= errors
.New("bytes.Buffer: reader returned negative count from Read")
47 const maxInt
= int(^uint(0) >> 1)
49 // Bytes returns a slice of length b.Len() holding the unread portion of the buffer.
50 // The slice is valid for use only until the next buffer modification (that is,
51 // only until the next call to a method like Read, Write, Reset, or Truncate).
52 // The slice aliases the buffer content at least until the next buffer modification,
53 // so immediate changes to the slice will affect the result of future reads.
54 func (b
*Buffer
) Bytes() []byte { return b
.buf
[b
.off
:] }
56 // String returns the contents of the unread portion of the buffer
57 // as a string. If the Buffer is a nil pointer, it returns "<nil>".
59 // To build strings more efficiently, see the strings.Builder type.
60 func (b
*Buffer
) String() string {
62 // Special case, useful in debugging.
65 return string(b
.buf
[b
.off
:])
68 // empty reports whether the unread portion of the buffer is empty.
69 func (b
*Buffer
) empty() bool { return len(b
.buf
) <= b
.off
}
71 // Len returns the number of bytes of the unread portion of the buffer;
72 // b.Len() == len(b.Bytes()).
73 func (b
*Buffer
) Len() int { return len(b
.buf
) - b
.off
}
75 // Cap returns the capacity of the buffer's underlying byte slice, that is, the
76 // total space allocated for the buffer's data.
77 func (b
*Buffer
) Cap() int { return cap(b
.buf
) }
79 // Truncate discards all but the first n unread bytes from the buffer
80 // but continues to use the same allocated storage.
81 // It panics if n is negative or greater than the length of the buffer.
82 func (b
*Buffer
) Truncate(n
int) {
87 b
.lastRead
= opInvalid
88 if n
< 0 || n
> b
.Len() {
89 panic("bytes.Buffer: truncation out of range")
91 b
.buf
= b
.buf
[:b
.off
+n
]
94 // Reset resets the buffer to be empty,
95 // but it retains the underlying storage for use by future writes.
96 // Reset is the same as Truncate(0).
97 func (b
*Buffer
) Reset() {
100 b
.lastRead
= opInvalid
103 // tryGrowByReslice is a inlineable version of grow for the fast-case where the
104 // internal buffer only needs to be resliced.
105 // It returns the index where bytes should be written and whether it succeeded.
106 func (b
*Buffer
) tryGrowByReslice(n
int) (int, bool) {
107 if l
:= len(b
.buf
); n
<= cap(b
.buf
)-l
{
114 // grow grows the buffer to guarantee space for n more bytes.
115 // It returns the index where bytes should be written.
116 // If the buffer can't grow it will panic with ErrTooLarge.
117 func (b
*Buffer
) grow(n
int) int {
119 // If buffer is empty, reset to recover space.
120 if m
== 0 && b
.off
!= 0 {
123 // Try to grow by means of a reslice.
124 if i
, ok
:= b
.tryGrowByReslice(n
); ok
{
127 if b
.buf
== nil && n
<= smallBufferSize
{
128 b
.buf
= make([]byte, n
, smallBufferSize
)
133 // We can slide things down instead of allocating a new
134 // slice. We only need m+n <= c to slide, but
135 // we instead let capacity get twice as large so we
136 // don't spend all our time copying.
137 copy(b
.buf
, b
.buf
[b
.off
:])
138 } else if c
> maxInt
-c
-n
{
141 // Not enough space anywhere, we need to allocate.
142 buf
:= makeSlice(2*c
+ n
)
143 copy(buf
, b
.buf
[b
.off
:])
146 // Restore b.off and len(b.buf).
152 // Grow grows the buffer's capacity, if necessary, to guarantee space for
153 // another n bytes. After Grow(n), at least n bytes can be written to the
154 // buffer without another allocation.
155 // If n is negative, Grow will panic.
156 // If the buffer can't grow it will panic with ErrTooLarge.
157 func (b
*Buffer
) Grow(n
int) {
159 panic("bytes.Buffer.Grow: negative count")
165 // Write appends the contents of p to the buffer, growing the buffer as
166 // needed. The return value n is the length of p; err is always nil. If the
167 // buffer becomes too large, Write will panic with ErrTooLarge.
168 func (b
*Buffer
) Write(p
[]byte) (n
int, err error
) {
169 b
.lastRead
= opInvalid
170 m
, ok
:= b
.tryGrowByReslice(len(p
))
174 return copy(b
.buf
[m
:], p
), nil
177 // WriteString appends the contents of s to the buffer, growing the buffer as
178 // needed. The return value n is the length of s; err is always nil. If the
179 // buffer becomes too large, WriteString will panic with ErrTooLarge.
180 func (b
*Buffer
) WriteString(s
string) (n
int, err error
) {
181 b
.lastRead
= opInvalid
182 m
, ok
:= b
.tryGrowByReslice(len(s
))
186 return copy(b
.buf
[m
:], s
), nil
189 // MinRead is the minimum slice size passed to a Read call by
190 // Buffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond
191 // what is required to hold the contents of r, ReadFrom will not grow the
192 // underlying buffer.
195 // ReadFrom reads data from r until EOF and appends it to the buffer, growing
196 // the buffer as needed. The return value n is the number of bytes read. Any
197 // error except io.EOF encountered during the read is also returned. If the
198 // buffer becomes too large, ReadFrom will panic with ErrTooLarge.
199 func (b
*Buffer
) ReadFrom(r io
.Reader
) (n
int64, err error
) {
200 b
.lastRead
= opInvalid
204 m
, e
:= r
.Read(b
.buf
[i
:cap(b
.buf
)])
206 panic(errNegativeRead
)
212 return n
, nil // e is EOF, so return nil explicitly
220 // makeSlice allocates a slice of size n. If the allocation fails, it panics
222 func makeSlice(n
int) []byte {
223 // If the make fails, give a known error.
225 if recover() != nil {
229 return make([]byte, n
)
232 // WriteTo writes data to w until the buffer is drained or an error occurs.
233 // The return value n is the number of bytes written; it always fits into an
234 // int, but it is int64 to match the io.WriterTo interface. Any error
235 // encountered during the write is also returned.
236 func (b
*Buffer
) WriteTo(w io
.Writer
) (n
int64, err error
) {
237 b
.lastRead
= opInvalid
238 if nBytes
:= b
.Len(); nBytes
> 0 {
239 m
, e
:= w
.Write(b
.buf
[b
.off
:])
241 panic("bytes.Buffer.WriteTo: invalid Write count")
248 // all bytes should have been written, by definition of
249 // Write method in io.Writer
251 return n
, io
.ErrShortWrite
254 // Buffer is now empty; reset.
259 // WriteByte appends the byte c to the buffer, growing the buffer as needed.
260 // The returned error is always nil, but is included to match bufio.Writer's
261 // WriteByte. If the buffer becomes too large, WriteByte will panic with
263 func (b
*Buffer
) WriteByte(c
byte) error
{
264 b
.lastRead
= opInvalid
265 m
, ok
:= b
.tryGrowByReslice(1)
273 // WriteRune appends the UTF-8 encoding of Unicode code point r to the
274 // buffer, returning its length and an error, which is always nil but is
275 // included to match bufio.Writer's WriteRune. The buffer is grown as needed;
276 // if it becomes too large, WriteRune will panic with ErrTooLarge.
277 func (b
*Buffer
) WriteRune(r rune
) (n
int, err error
) {
278 // Compare as uint32 to correctly handle negative runes.
279 if uint32(r
) < utf8
.RuneSelf
{
283 b
.lastRead
= opInvalid
284 m
, ok
:= b
.tryGrowByReslice(utf8
.UTFMax
)
286 m
= b
.grow(utf8
.UTFMax
)
288 n
= utf8
.EncodeRune(b
.buf
[m
:m
+utf8
.UTFMax
], r
)
293 // Read reads the next len(p) bytes from the buffer or until the buffer
294 // is drained. The return value n is the number of bytes read. If the
295 // buffer has no data to return, err is io.EOF (unless len(p) is zero);
296 // otherwise it is nil.
297 func (b
*Buffer
) Read(p
[]byte) (n
int, err error
) {
298 b
.lastRead
= opInvalid
300 // Buffer is empty, reset to recover space.
307 n
= copy(p
, b
.buf
[b
.off
:])
315 // Next returns a slice containing the next n bytes from the buffer,
316 // advancing the buffer as if the bytes had been returned by Read.
317 // If there are fewer than n bytes in the buffer, Next returns the entire buffer.
318 // The slice is only valid until the next call to a read or write method.
319 func (b
*Buffer
) Next(n
int) []byte {
320 b
.lastRead
= opInvalid
325 data
:= b
.buf
[b
.off
: b
.off
+n
]
333 // ReadByte reads and returns the next byte from the buffer.
334 // If no byte is available, it returns error io.EOF.
335 func (b
*Buffer
) ReadByte() (byte, error
) {
337 // Buffer is empty, reset to recover space.
347 // ReadRune reads and returns the next UTF-8-encoded
348 // Unicode code point from the buffer.
349 // If no bytes are available, the error returned is io.EOF.
350 // If the bytes are an erroneous UTF-8 encoding, it
351 // consumes one byte and returns U+FFFD, 1.
352 func (b
*Buffer
) ReadRune() (r rune
, size
int, err error
) {
354 // Buffer is empty, reset to recover space.
359 if c
< utf8
.RuneSelf
{
361 b
.lastRead
= opReadRune1
362 return rune(c
), 1, nil
364 r
, n
:= utf8
.DecodeRune(b
.buf
[b
.off
:])
366 b
.lastRead
= readOp(n
)
370 // UnreadRune unreads the last rune returned by ReadRune.
371 // If the most recent read or write operation on the buffer was
372 // not a successful ReadRune, UnreadRune returns an error. (In this regard
373 // it is stricter than UnreadByte, which will unread the last byte
374 // from any read operation.)
375 func (b
*Buffer
) UnreadRune() error
{
376 if b
.lastRead
<= opInvalid
{
377 return errors
.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune")
379 if b
.off
>= int(b
.lastRead
) {
380 b
.off
-= int(b
.lastRead
)
382 b
.lastRead
= opInvalid
386 var errUnreadByte
= errors
.New("bytes.Buffer: UnreadByte: previous operation was not a successful read")
388 // UnreadByte unreads the last byte returned by the most recent successful
389 // read operation that read at least one byte. If a write has happened since
390 // the last read, if the last read returned an error, or if the read read zero
391 // bytes, UnreadByte returns an error.
392 func (b
*Buffer
) UnreadByte() error
{
393 if b
.lastRead
== opInvalid
{
396 b
.lastRead
= opInvalid
403 // ReadBytes reads until the first occurrence of delim in the input,
404 // returning a slice containing the data up to and including the delimiter.
405 // If ReadBytes encounters an error before finding a delimiter,
406 // it returns the data read before the error and the error itself (often io.EOF).
407 // ReadBytes returns err != nil if and only if the returned data does not end in
409 func (b
*Buffer
) ReadBytes(delim
byte) (line
[]byte, err error
) {
410 slice
, err
:= b
.readSlice(delim
)
411 // return a copy of slice. The buffer's backing array may
412 // be overwritten by later calls.
413 line
= append(line
, slice
...)
417 // readSlice is like ReadBytes but returns a reference to internal buffer data.
418 func (b
*Buffer
) readSlice(delim
byte) (line
[]byte, err error
) {
419 i
:= IndexByte(b
.buf
[b
.off
:], delim
)
425 line
= b
.buf
[b
.off
:end
]
431 // ReadString reads until the first occurrence of delim in the input,
432 // returning a string containing the data up to and including the delimiter.
433 // If ReadString encounters an error before finding a delimiter,
434 // it returns the data read before the error and the error itself (often io.EOF).
435 // ReadString returns err != nil if and only if the returned data does not end
437 func (b
*Buffer
) ReadString(delim
byte) (line
string, err error
) {
438 slice
, err
:= b
.readSlice(delim
)
439 return string(slice
), err
442 // NewBuffer creates and initializes a new Buffer using buf as its
443 // initial contents. The new Buffer takes ownership of buf, and the
444 // caller should not use buf after this call. NewBuffer is intended to
445 // prepare a Buffer to read existing data. It can also be used to set
446 // the initial size of the internal buffer for writing. To do that,
447 // buf should have the desired capacity but a length of zero.
449 // In most cases, new(Buffer) (or just declaring a Buffer variable) is
450 // sufficient to initialize a Buffer.
451 func NewBuffer(buf
[]byte) *Buffer
{ return &Buffer
{buf
: buf
} }
453 // NewBufferString creates and initializes a new Buffer using string s as its
454 // initial contents. It is intended to prepare a buffer to read an existing
457 // In most cases, new(Buffer) (or just declaring a Buffer variable) is
458 // sufficient to initialize a Buffer.
459 func NewBufferString(s
string) *Buffer
{
460 return &Buffer
{buf
: []byte(s
)}