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. 4 5package bytes 6 7// Simple byte buffer for marshaling data. 8 9import ( 10 "errors" 11 "io" 12 "unicode/utf8" 13) 14 15// smallBufferSize is an initial allocation minimal capacity. 16const smallBufferSize = 64 17 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. 20type Buffer struct { 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. 24 25 // FIXME: it would be advisable to align Buffer to cachelines to avoid false 26 // sharing. 27} 28 29// The readOp constants describe the last action performed on 30// the buffer, so that UnreadRune and UnreadByte can check for 31// invalid usage. opReadRuneX constants are chosen such that 32// converted to int they correspond to the rune size that was read. 33type readOp int8 34 35// Don't use iota for these, as the values need to correspond with the 36// names and comments, which is easier to see when being explicit. 37const ( 38 opRead readOp = -1 // Any other read operation. 39 opInvalid readOp = 0 // Non-read operation. 40 opReadRune1 readOp = 1 // Read rune of size 1. 41 opReadRune2 readOp = 2 // Read rune of size 2. 42 opReadRune3 readOp = 3 // Read rune of size 3. 43 opReadRune4 readOp = 4 // Read rune of size 4. 44) 45 46// ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer. 47var ErrTooLarge = errors.New("bytes.Buffer: too large") 48var errNegativeRead = errors.New("bytes.Buffer: reader returned negative count from Read") 49 50const maxInt = int(^uint(0) >> 1) 51 52// Bytes returns a slice of length b.Len() holding the unread portion of the buffer. 53// The slice is valid for use only until the next buffer modification (that is, 54// only until the next call to a method like Read, Write, Reset, or Truncate). 55// The slice aliases the buffer content at least until the next buffer modification, 56// so immediate changes to the slice will affect the result of future reads. 57func (b *Buffer) Bytes() []byte { return b.buf[b.off:] } 58 59// String returns the contents of the unread portion of the buffer 60// as a string. If the Buffer is a nil pointer, it returns "<nil>". 61// 62// To build strings more efficiently, see the strings.Builder type. 63func (b *Buffer) String() string { 64 if b == nil { 65 // Special case, useful in debugging. 66 return "<nil>" 67 } 68 return string(b.buf[b.off:]) 69} 70 71// empty reports whether the unread portion of the buffer is empty. 72func (b *Buffer) empty() bool { return len(b.buf) <= b.off } 73 74// Len returns the number of bytes of the unread portion of the buffer; 75// b.Len() == len(b.Bytes()). 76func (b *Buffer) Len() int { return len(b.buf) - b.off } 77 78// Cap returns the capacity of the buffer's underlying byte slice, that is, the 79// total space allocated for the buffer's data. 80func (b *Buffer) Cap() int { return cap(b.buf) } 81 82// Truncate discards all but the first n unread bytes from the buffer 83// but continues to use the same allocated storage. 84// It panics if n is negative or greater than the length of the buffer. 85func (b *Buffer) Truncate(n int) { 86 if n == 0 { 87 b.Reset() 88 return 89 } 90 b.lastRead = opInvalid 91 if n < 0 || n > b.Len() { 92 panic("bytes.Buffer: truncation out of range") 93 } 94 b.buf = b.buf[:b.off+n] 95} 96 97// Reset resets the buffer to be empty, 98// but it retains the underlying storage for use by future writes. 99// Reset is the same as Truncate(0). 100func (b *Buffer) Reset() { 101 b.buf = b.buf[:0] 102 b.off = 0 103 b.lastRead = opInvalid 104} 105 106// tryGrowByReslice is a inlineable version of grow for the fast-case where the 107// internal buffer only needs to be resliced. 108// It returns the index where bytes should be written and whether it succeeded. 109func (b *Buffer) tryGrowByReslice(n int) (int, bool) { 110 if l := len(b.buf); n <= cap(b.buf)-l { 111 b.buf = b.buf[:l+n] 112 return l, true 113 } 114 return 0, false 115} 116 117// grow grows the buffer to guarantee space for n more bytes. 118// It returns the index where bytes should be written. 119// If the buffer can't grow it will panic with ErrTooLarge. 120func (b *Buffer) grow(n int) int { 121 m := b.Len() 122 // If buffer is empty, reset to recover space. 123 if m == 0 && b.off != 0 { 124 b.Reset() 125 } 126 // Try to grow by means of a reslice. 127 if i, ok := b.tryGrowByReslice(n); ok { 128 return i 129 } 130 if b.buf == nil && n <= smallBufferSize { 131 b.buf = make([]byte, n, smallBufferSize) 132 return 0 133 } 134 c := cap(b.buf) 135 if n <= c/2-m { 136 // We can slide things down instead of allocating a new 137 // slice. We only need m+n <= c to slide, but 138 // we instead let capacity get twice as large so we 139 // don't spend all our time copying. 140 copy(b.buf, b.buf[b.off:]) 141 } else if c > maxInt-c-n { 142 panic(ErrTooLarge) 143 } else { 144 // Not enough space anywhere, we need to allocate. 145 buf := makeSlice(2*c + n) 146 copy(buf, b.buf[b.off:]) 147 b.buf = buf 148 } 149 // Restore b.off and len(b.buf). 150 b.off = 0 151 b.buf = b.buf[:m+n] 152 return m 153} 154 155// Grow grows the buffer's capacity, if necessary, to guarantee space for 156// another n bytes. After Grow(n), at least n bytes can be written to the 157// buffer without another allocation. 158// If n is negative, Grow will panic. 159// If the buffer can't grow it will panic with ErrTooLarge. 160func (b *Buffer) Grow(n int) { 161 if n < 0 { 162 panic("bytes.Buffer.Grow: negative count") 163 } 164 m := b.grow(n) 165 b.buf = b.buf[:m] 166} 167 168// Write appends the contents of p to the buffer, growing the buffer as 169// needed. The return value n is the length of p; err is always nil. If the 170// buffer becomes too large, Write will panic with ErrTooLarge. 171func (b *Buffer) Write(p []byte) (n int, err error) { 172 b.lastRead = opInvalid 173 m, ok := b.tryGrowByReslice(len(p)) 174 if !ok { 175 m = b.grow(len(p)) 176 } 177 return copy(b.buf[m:], p), nil 178} 179 180// WriteString appends the contents of s to the buffer, growing the buffer as 181// needed. The return value n is the length of s; err is always nil. If the 182// buffer becomes too large, WriteString will panic with ErrTooLarge. 183func (b *Buffer) WriteString(s string) (n int, err error) { 184 b.lastRead = opInvalid 185 m, ok := b.tryGrowByReslice(len(s)) 186 if !ok { 187 m = b.grow(len(s)) 188 } 189 return copy(b.buf[m:], s), nil 190} 191 192// MinRead is the minimum slice size passed to a Read call by 193// Buffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond 194// what is required to hold the contents of r, ReadFrom will not grow the 195// underlying buffer. 196const MinRead = 512 197 198// ReadFrom reads data from r until EOF and appends it to the buffer, growing 199// the buffer as needed. The return value n is the number of bytes read. Any 200// error except io.EOF encountered during the read is also returned. If the 201// buffer becomes too large, ReadFrom will panic with ErrTooLarge. 202func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) { 203 b.lastRead = opInvalid 204 for { 205 i := b.grow(MinRead) 206 b.buf = b.buf[:i] 207 m, e := r.Read(b.buf[i:cap(b.buf)]) 208 if m < 0 { 209 panic(errNegativeRead) 210 } 211 212 b.buf = b.buf[:i+m] 213 n += int64(m) 214 if e == io.EOF { 215 return n, nil // e is EOF, so return nil explicitly 216 } 217 if e != nil { 218 return n, e 219 } 220 } 221} 222 223// makeSlice allocates a slice of size n. If the allocation fails, it panics 224// with ErrTooLarge. 225func makeSlice(n int) []byte { 226 // If the make fails, give a known error. 227 defer func() { 228 if recover() != nil { 229 panic(ErrTooLarge) 230 } 231 }() 232 return make([]byte, n) 233} 234 235// WriteTo writes data to w until the buffer is drained or an error occurs. 236// The return value n is the number of bytes written; it always fits into an 237// int, but it is int64 to match the io.WriterTo interface. Any error 238// encountered during the write is also returned. 239func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) { 240 b.lastRead = opInvalid 241 if nBytes := b.Len(); nBytes > 0 { 242 m, e := w.Write(b.buf[b.off:]) 243 if m > nBytes { 244 panic("bytes.Buffer.WriteTo: invalid Write count") 245 } 246 b.off += m 247 n = int64(m) 248 if e != nil { 249 return n, e 250 } 251 // all bytes should have been written, by definition of 252 // Write method in io.Writer 253 if m != nBytes { 254 return n, io.ErrShortWrite 255 } 256 } 257 // Buffer is now empty; reset. 258 b.Reset() 259 return n, nil 260} 261 262// WriteByte appends the byte c to the buffer, growing the buffer as needed. 263// The returned error is always nil, but is included to match bufio.Writer's 264// WriteByte. If the buffer becomes too large, WriteByte will panic with 265// ErrTooLarge. 266func (b *Buffer) WriteByte(c byte) error { 267 b.lastRead = opInvalid 268 m, ok := b.tryGrowByReslice(1) 269 if !ok { 270 m = b.grow(1) 271 } 272 b.buf[m] = c 273 return nil 274} 275 276// WriteRune appends the UTF-8 encoding of Unicode code point r to the 277// buffer, returning its length and an error, which is always nil but is 278// included to match bufio.Writer's WriteRune. The buffer is grown as needed; 279// if it becomes too large, WriteRune will panic with ErrTooLarge. 280func (b *Buffer) WriteRune(r rune) (n int, err error) { 281 if r < utf8.RuneSelf { 282 b.WriteByte(byte(r)) 283 return 1, nil 284 } 285 b.lastRead = opInvalid 286 m, ok := b.tryGrowByReslice(utf8.UTFMax) 287 if !ok { 288 m = b.grow(utf8.UTFMax) 289 } 290 n = utf8.EncodeRune(b.buf[m:m+utf8.UTFMax], r) 291 b.buf = b.buf[:m+n] 292 return n, nil 293} 294 295// Read reads the next len(p) bytes from the buffer or until the buffer 296// is drained. The return value n is the number of bytes read. If the 297// buffer has no data to return, err is io.EOF (unless len(p) is zero); 298// otherwise it is nil. 299func (b *Buffer) Read(p []byte) (n int, err error) { 300 b.lastRead = opInvalid 301 if b.empty() { 302 // Buffer is empty, reset to recover space. 303 b.Reset() 304 if len(p) == 0 { 305 return 0, nil 306 } 307 return 0, io.EOF 308 } 309 n = copy(p, b.buf[b.off:]) 310 b.off += n 311 if n > 0 { 312 b.lastRead = opRead 313 } 314 return n, nil 315} 316 317// Next returns a slice containing the next n bytes from the buffer, 318// advancing the buffer as if the bytes had been returned by Read. 319// If there are fewer than n bytes in the buffer, Next returns the entire buffer. 320// The slice is only valid until the next call to a read or write method. 321func (b *Buffer) Next(n int) []byte { 322 b.lastRead = opInvalid 323 m := b.Len() 324 if n > m { 325 n = m 326 } 327 data := b.buf[b.off : b.off+n] 328 b.off += n 329 if n > 0 { 330 b.lastRead = opRead 331 } 332 return data 333} 334 335// ReadByte reads and returns the next byte from the buffer. 336// If no byte is available, it returns error io.EOF. 337func (b *Buffer) ReadByte() (byte, error) { 338 if b.empty() { 339 // Buffer is empty, reset to recover space. 340 b.Reset() 341 return 0, io.EOF 342 } 343 c := b.buf[b.off] 344 b.off++ 345 b.lastRead = opRead 346 return c, nil 347} 348 349// ReadRune reads and returns the next UTF-8-encoded 350// Unicode code point from the buffer. 351// If no bytes are available, the error returned is io.EOF. 352// If the bytes are an erroneous UTF-8 encoding, it 353// consumes one byte and returns U+FFFD, 1. 354func (b *Buffer) ReadRune() (r rune, size int, err error) { 355 if b.empty() { 356 // Buffer is empty, reset to recover space. 357 b.Reset() 358 return 0, 0, io.EOF 359 } 360 c := b.buf[b.off] 361 if c < utf8.RuneSelf { 362 b.off++ 363 b.lastRead = opReadRune1 364 return rune(c), 1, nil 365 } 366 r, n := utf8.DecodeRune(b.buf[b.off:]) 367 b.off += n 368 b.lastRead = readOp(n) 369 return r, n, nil 370} 371 372// UnreadRune unreads the last rune returned by ReadRune. 373// If the most recent read or write operation on the buffer was 374// not a successful ReadRune, UnreadRune returns an error. (In this regard 375// it is stricter than UnreadByte, which will unread the last byte 376// from any read operation.) 377func (b *Buffer) UnreadRune() error { 378 if b.lastRead <= opInvalid { 379 return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune") 380 } 381 if b.off >= int(b.lastRead) { 382 b.off -= int(b.lastRead) 383 } 384 b.lastRead = opInvalid 385 return nil 386} 387 388// 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. 392func (b *Buffer) UnreadByte() error { 393 if b.lastRead == opInvalid { 394 return errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read") 395 } 396 b.lastRead = opInvalid 397 if b.off > 0 { 398 b.off-- 399 } 400 return nil 401} 402 403// 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 408// delim. 409func (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...) 414 return line, err 415} 416 417// readSlice is like ReadBytes but returns a reference to internal buffer data. 418func (b *Buffer) readSlice(delim byte) (line []byte, err error) { 419 i := IndexByte(b.buf[b.off:], delim) 420 end := b.off + i + 1 421 if i < 0 { 422 end = len(b.buf) 423 err = io.EOF 424 } 425 line = b.buf[b.off:end] 426 b.off = end 427 b.lastRead = opRead 428 return line, err 429} 430 431// 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 436// in delim. 437func (b *Buffer) ReadString(delim byte) (line string, err error) { 438 slice, err := b.readSlice(delim) 439 return string(slice), err 440} 441 442// 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. 448// 449// In most cases, new(Buffer) (or just declaring a Buffer variable) is 450// sufficient to initialize a Buffer. 451func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} } 452 453// 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 455// string. 456// 457// In most cases, new(Buffer) (or just declaring a Buffer variable) is 458// sufficient to initialize a Buffer. 459func NewBufferString(s string) *Buffer { 460 return &Buffer{buf: []byte(s)} 461} 462