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 5 package bytes 6 7 // Simple byte buffer for marshaling data. 8 9 import ( 10 "errors" 11 "io" 12 "unicode/utf8" 13 ) 14 15 // smallBufferSize is an initial allocation minimal capacity. 16 const 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. 20 type 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 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. 30 type readOp int8 31 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. 34 const ( 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. 41 ) 42 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") 46 47 const maxInt = int(^uint(0) >> 1) 48 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:] } 55 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>". 58 // 59 // To build strings more efficiently, see the strings.Builder type. 60 func (b *Buffer) String() string { 61 if b == nil { 62 // Special case, useful in debugging. 63 return "<nil>" 64 } 65 return string(b.buf[b.off:]) 66 } 67 68 // empty reports whether the unread portion of the buffer is empty. 69 func (b *Buffer) empty() bool { return len(b.buf) <= b.off } 70 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 } 74 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) } 78 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) { 83 if n == 0 { 84 b.Reset() 85 return 86 } 87 b.lastRead = opInvalid 88 if n < 0 || n > b.Len() { 89 panic("bytes.Buffer: truncation out of range") 90 } 91 b.buf = b.buf[:b.off+n] 92 } 93 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() { 98 b.buf = b.buf[:0] 99 b.off = 0 100 b.lastRead = opInvalid 101 } 102 103 // 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 { 108 b.buf = b.buf[:l+n] 109 return l, true 110 } 111 return 0, false 112 } 113 114 // 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 { 118 m := b.Len() 119 // If buffer is empty, reset to recover space. 120 if m == 0 && b.off != 0 { 121 b.Reset() 122 } 123 // Try to grow by means of a reslice. 124 if i, ok := b.tryGrowByReslice(n); ok { 125 return i 126 } 127 if b.buf == nil && n <= smallBufferSize { 128 b.buf = make([]byte, n, smallBufferSize) 129 return 0 130 } 131 c := cap(b.buf) 132 if n <= c/2-m { 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 { 139 panic(ErrTooLarge) 140 } else { 141 // Add b.off to account for b.buf[:b.off] being sliced off the front. 142 b.buf = growSlice(b.buf[b.off:], b.off+n) 143 } 144 // Restore b.off and len(b.buf). 145 b.off = 0 146 b.buf = b.buf[:m+n] 147 return m 148 } 149 150 // Grow grows the buffer's capacity, if necessary, to guarantee space for 151 // another n bytes. After Grow(n), at least n bytes can be written to the 152 // buffer without another allocation. 153 // If n is negative, Grow will panic. 154 // If the buffer can't grow it will panic with ErrTooLarge. 155 func (b *Buffer) Grow(n int) { 156 if n < 0 { 157 panic("bytes.Buffer.Grow: negative count") 158 } 159 m := b.grow(n) 160 b.buf = b.buf[:m] 161 } 162 163 // Write appends the contents of p to the buffer, growing the buffer as 164 // needed. The return value n is the length of p; err is always nil. If the 165 // buffer becomes too large, Write will panic with ErrTooLarge. 166 func (b *Buffer) Write(p []byte) (n int, err error) { 167 b.lastRead = opInvalid 168 m, ok := b.tryGrowByReslice(len(p)) 169 if !ok { 170 m = b.grow(len(p)) 171 } 172 return copy(b.buf[m:], p), nil 173 } 174 175 // WriteString appends the contents of s to the buffer, growing the buffer as 176 // needed. The return value n is the length of s; err is always nil. If the 177 // buffer becomes too large, WriteString will panic with ErrTooLarge. 178 func (b *Buffer) WriteString(s string) (n int, err error) { 179 b.lastRead = opInvalid 180 m, ok := b.tryGrowByReslice(len(s)) 181 if !ok { 182 m = b.grow(len(s)) 183 } 184 return copy(b.buf[m:], s), nil 185 } 186 187 // MinRead is the minimum slice size passed to a Read call by 188 // Buffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond 189 // what is required to hold the contents of r, ReadFrom will not grow the 190 // underlying buffer. 191 const MinRead = 512 192 193 // ReadFrom reads data from r until EOF and appends it to the buffer, growing 194 // the buffer as needed. The return value n is the number of bytes read. Any 195 // error except io.EOF encountered during the read is also returned. If the 196 // buffer becomes too large, ReadFrom will panic with ErrTooLarge. 197 func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) { 198 b.lastRead = opInvalid 199 for { 200 i := b.grow(MinRead) 201 b.buf = b.buf[:i] 202 m, e := r.Read(b.buf[i:cap(b.buf)]) 203 if m < 0 { 204 panic(errNegativeRead) 205 } 206 207 b.buf = b.buf[:i+m] 208 n += int64(m) 209 if e == io.EOF { 210 return n, nil // e is EOF, so return nil explicitly 211 } 212 if e != nil { 213 return n, e 214 } 215 } 216 } 217 218 // growSlice grows b by n, preserving the original content of b. 219 // If the allocation fails, it panics with ErrTooLarge. 220 func growSlice(b []byte, n int) []byte { 221 defer func() { 222 if recover() != nil { 223 panic(ErrTooLarge) 224 } 225 }() 226 // TODO(http://golang.org/issue/51462): We should rely on the append-make 227 // pattern so that the compiler can call runtime.growslice. For example: 228 // return append(b, make([]byte, n)...) 229 // This avoids unnecessary zero-ing of the first len(b) bytes of the 230 // allocated slice, but this pattern causes b to escape onto the heap. 231 // 232 // Instead use the append-make pattern with a nil slice to ensure that 233 // we allocate buffers rounded up to the closest size class. 234 c := len(b) + n // ensure enough space for n elements 235 if c < 2*cap(b) { 236 // The growth rate has historically always been 2x. In the future, 237 // we could rely purely on append to determine the growth rate. 238 c = 2 * cap(b) 239 } 240 b2 := append([]byte(nil), make([]byte, c)...) 241 copy(b2, b) 242 return b2[:len(b)] 243 } 244 245 // WriteTo writes data to w until the buffer is drained or an error occurs. 246 // The return value n is the number of bytes written; it always fits into an 247 // int, but it is int64 to match the io.WriterTo interface. Any error 248 // encountered during the write is also returned. 249 func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) { 250 b.lastRead = opInvalid 251 if nBytes := b.Len(); nBytes > 0 { 252 m, e := w.Write(b.buf[b.off:]) 253 if m > nBytes { 254 panic("bytes.Buffer.WriteTo: invalid Write count") 255 } 256 b.off += m 257 n = int64(m) 258 if e != nil { 259 return n, e 260 } 261 // all bytes should have been written, by definition of 262 // Write method in io.Writer 263 if m != nBytes { 264 return n, io.ErrShortWrite 265 } 266 } 267 // Buffer is now empty; reset. 268 b.Reset() 269 return n, nil 270 } 271 272 // WriteByte appends the byte c to the buffer, growing the buffer as needed. 273 // The returned error is always nil, but is included to match bufio.Writer's 274 // WriteByte. If the buffer becomes too large, WriteByte will panic with 275 // ErrTooLarge. 276 func (b *Buffer) WriteByte(c byte) error { 277 b.lastRead = opInvalid 278 m, ok := b.tryGrowByReslice(1) 279 if !ok { 280 m = b.grow(1) 281 } 282 b.buf[m] = c 283 return nil 284 } 285 286 // WriteRune appends the UTF-8 encoding of Unicode code point r to the 287 // buffer, returning its length and an error, which is always nil but is 288 // included to match bufio.Writer's WriteRune. The buffer is grown as needed; 289 // if it becomes too large, WriteRune will panic with ErrTooLarge. 290 func (b *Buffer) WriteRune(r rune) (n int, err error) { 291 // Compare as uint32 to correctly handle negative runes. 292 if uint32(r) < utf8.RuneSelf { 293 b.WriteByte(byte(r)) 294 return 1, nil 295 } 296 b.lastRead = opInvalid 297 m, ok := b.tryGrowByReslice(utf8.UTFMax) 298 if !ok { 299 m = b.grow(utf8.UTFMax) 300 } 301 n = utf8.EncodeRune(b.buf[m:m+utf8.UTFMax], r) 302 b.buf = b.buf[:m+n] 303 return n, nil 304 } 305 306 // Read reads the next len(p) bytes from the buffer or until the buffer 307 // is drained. The return value n is the number of bytes read. If the 308 // buffer has no data to return, err is io.EOF (unless len(p) is zero); 309 // otherwise it is nil. 310 func (b *Buffer) Read(p []byte) (n int, err error) { 311 b.lastRead = opInvalid 312 if b.empty() { 313 // Buffer is empty, reset to recover space. 314 b.Reset() 315 if len(p) == 0 { 316 return 0, nil 317 } 318 return 0, io.EOF 319 } 320 n = copy(p, b.buf[b.off:]) 321 b.off += n 322 if n > 0 { 323 b.lastRead = opRead 324 } 325 return n, nil 326 } 327 328 // Next returns a slice containing the next n bytes from the buffer, 329 // advancing the buffer as if the bytes had been returned by Read. 330 // If there are fewer than n bytes in the buffer, Next returns the entire buffer. 331 // The slice is only valid until the next call to a read or write method. 332 func (b *Buffer) Next(n int) []byte { 333 b.lastRead = opInvalid 334 m := b.Len() 335 if n > m { 336 n = m 337 } 338 data := b.buf[b.off : b.off+n] 339 b.off += n 340 if n > 0 { 341 b.lastRead = opRead 342 } 343 return data 344 } 345 346 // ReadByte reads and returns the next byte from the buffer. 347 // If no byte is available, it returns error io.EOF. 348 func (b *Buffer) ReadByte() (byte, error) { 349 if b.empty() { 350 // Buffer is empty, reset to recover space. 351 b.Reset() 352 return 0, io.EOF 353 } 354 c := b.buf[b.off] 355 b.off++ 356 b.lastRead = opRead 357 return c, nil 358 } 359 360 // ReadRune reads and returns the next UTF-8-encoded 361 // Unicode code point from the buffer. 362 // If no bytes are available, the error returned is io.EOF. 363 // If the bytes are an erroneous UTF-8 encoding, it 364 // consumes one byte and returns U+FFFD, 1. 365 func (b *Buffer) ReadRune() (r rune, size int, err error) { 366 if b.empty() { 367 // Buffer is empty, reset to recover space. 368 b.Reset() 369 return 0, 0, io.EOF 370 } 371 c := b.buf[b.off] 372 if c < utf8.RuneSelf { 373 b.off++ 374 b.lastRead = opReadRune1 375 return rune(c), 1, nil 376 } 377 r, n := utf8.DecodeRune(b.buf[b.off:]) 378 b.off += n 379 b.lastRead = readOp(n) 380 return r, n, nil 381 } 382 383 // UnreadRune unreads the last rune returned by ReadRune. 384 // If the most recent read or write operation on the buffer was 385 // not a successful ReadRune, UnreadRune returns an error. (In this regard 386 // it is stricter than UnreadByte, which will unread the last byte 387 // from any read operation.) 388 func (b *Buffer) UnreadRune() error { 389 if b.lastRead <= opInvalid { 390 return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune") 391 } 392 if b.off >= int(b.lastRead) { 393 b.off -= int(b.lastRead) 394 } 395 b.lastRead = opInvalid 396 return nil 397 } 398 399 var errUnreadByte = errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read") 400 401 // UnreadByte unreads the last byte returned by the most recent successful 402 // read operation that read at least one byte. If a write has happened since 403 // the last read, if the last read returned an error, or if the read read zero 404 // bytes, UnreadByte returns an error. 405 func (b *Buffer) UnreadByte() error { 406 if b.lastRead == opInvalid { 407 return errUnreadByte 408 } 409 b.lastRead = opInvalid 410 if b.off > 0 { 411 b.off-- 412 } 413 return nil 414 } 415 416 // ReadBytes reads until the first occurrence of delim in the input, 417 // returning a slice containing the data up to and including the delimiter. 418 // If ReadBytes encounters an error before finding a delimiter, 419 // it returns the data read before the error and the error itself (often io.EOF). 420 // ReadBytes returns err != nil if and only if the returned data does not end in 421 // delim. 422 func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) { 423 slice, err := b.readSlice(delim) 424 // return a copy of slice. The buffer's backing array may 425 // be overwritten by later calls. 426 line = append(line, slice...) 427 return line, err 428 } 429 430 // readSlice is like ReadBytes but returns a reference to internal buffer data. 431 func (b *Buffer) readSlice(delim byte) (line []byte, err error) { 432 i := IndexByte(b.buf[b.off:], delim) 433 end := b.off + i + 1 434 if i < 0 { 435 end = len(b.buf) 436 err = io.EOF 437 } 438 line = b.buf[b.off:end] 439 b.off = end 440 b.lastRead = opRead 441 return line, err 442 } 443 444 // ReadString reads until the first occurrence of delim in the input, 445 // returning a string containing the data up to and including the delimiter. 446 // If ReadString encounters an error before finding a delimiter, 447 // it returns the data read before the error and the error itself (often io.EOF). 448 // ReadString returns err != nil if and only if the returned data does not end 449 // in delim. 450 func (b *Buffer) ReadString(delim byte) (line string, err error) { 451 slice, err := b.readSlice(delim) 452 return string(slice), err 453 } 454 455 // NewBuffer creates and initializes a new Buffer using buf as its 456 // initial contents. The new Buffer takes ownership of buf, and the 457 // caller should not use buf after this call. NewBuffer is intended to 458 // prepare a Buffer to read existing data. It can also be used to set 459 // the initial size of the internal buffer for writing. To do that, 460 // buf should have the desired capacity but a length of zero. 461 // 462 // In most cases, new(Buffer) (or just declaring a Buffer variable) is 463 // sufficient to initialize a Buffer. 464 func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} } 465 466 // NewBufferString creates and initializes a new Buffer using string s as its 467 // initial contents. It is intended to prepare a buffer to read an existing 468 // string. 469 // 470 // In most cases, new(Buffer) (or just declaring a Buffer variable) is 471 // sufficient to initialize a Buffer. 472 func NewBufferString(s string) *Buffer { 473 return &Buffer{buf: []byte(s)} 474 } 475