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// A Buffer is a variable-sized buffer of bytes with Read and Write methods. 16// The zero value for Buffer is an empty buffer ready to use. 17type Buffer struct { 18 buf []byte // contents are the bytes buf[off : len(buf)] 19 off int // read at &buf[off], write at &buf[len(buf)] 20 bootstrap [64]byte // memory to hold first slice; helps small buffers avoid allocation. 21 lastRead readOp // last read operation, so that Unread* can work correctly. 22 23 // FIXME: it would be advisable to align Buffer to cachelines to avoid false 24 // sharing. 25} 26 27// The readOp constants describe the last action performed on 28// the buffer, so that UnreadRune and UnreadByte can check for 29// invalid usage. opReadRuneX constants are chosen such that 30// converted to int they correspond to the rune size that was read. 31type readOp int8 32 33// Don't use iota for these, as the values need to correspond with the 34// names and comments, which is easier to see when being explicit. 35const ( 36 opRead readOp = -1 // Any other read operation. 37 opInvalid readOp = 0 // Non-read operation. 38 opReadRune1 readOp = 1 // Read rune of size 1. 39 opReadRune2 readOp = 2 // Read rune of size 2. 40 opReadRune3 readOp = 3 // Read rune of size 3. 41 opReadRune4 readOp = 4 // Read rune of size 4. 42) 43 44// ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer. 45var ErrTooLarge = errors.New("bytes.Buffer: too large") 46var errNegativeRead = errors.New("bytes.Buffer: reader returned negative count from Read") 47 48const maxInt = int(^uint(0) >> 1) 49 50// Bytes returns a slice of length b.Len() holding the unread portion of the buffer. 51// The slice is valid for use only until the next buffer modification (that is, 52// only until the next call to a method like Read, Write, Reset, or Truncate). 53// The slice aliases the buffer content at least until the next buffer modification, 54// so immediate changes to the slice will affect the result of future reads. 55func (b *Buffer) Bytes() []byte { return b.buf[b.off:] } 56 57// String returns the contents of the unread portion of the buffer 58// as a string. If the Buffer is a nil pointer, it returns "<nil>". 59// 60// To build strings more efficiently, see the strings.Builder type. 61func (b *Buffer) String() string { 62 if b == nil { 63 // Special case, useful in debugging. 64 return "<nil>" 65 } 66 return string(b.buf[b.off:]) 67} 68 69// empty returns whether the unread portion of the buffer is empty. 70func (b *Buffer) empty() bool { return len(b.buf) <= b.off } 71 72// Len returns the number of bytes of the unread portion of the buffer; 73// b.Len() == len(b.Bytes()). 74func (b *Buffer) Len() int { return len(b.buf) - b.off } 75 76// Cap returns the capacity of the buffer's underlying byte slice, that is, the 77// total space allocated for the buffer's data. 78func (b *Buffer) Cap() int { return cap(b.buf) } 79 80// Truncate discards all but the first n unread bytes from the buffer 81// but continues to use the same allocated storage. 82// It panics if n is negative or greater than the length of the buffer. 83func (b *Buffer) Truncate(n int) { 84 if n == 0 { 85 b.Reset() 86 return 87 } 88 b.lastRead = opInvalid 89 if n < 0 || n > b.Len() { 90 panic("bytes.Buffer: truncation out of range") 91 } 92 b.buf = b.buf[:b.off+n] 93} 94 95// Reset resets the buffer to be empty, 96// but it retains the underlying storage for use by future writes. 97// Reset is the same as Truncate(0). 98func (b *Buffer) Reset() { 99 b.buf = b.buf[:0] 100 b.off = 0 101 b.lastRead = opInvalid 102} 103 104// tryGrowByReslice is a inlineable version of grow for the fast-case where the 105// internal buffer only needs to be resliced. 106// It returns the index where bytes should be written and whether it succeeded. 107func (b *Buffer) tryGrowByReslice(n int) (int, bool) { 108 if l := len(b.buf); n <= cap(b.buf)-l { 109 b.buf = b.buf[:l+n] 110 return l, true 111 } 112 return 0, false 113} 114 115// grow grows the buffer to guarantee space for n more bytes. 116// It returns the index where bytes should be written. 117// If the buffer can't grow it will panic with ErrTooLarge. 118func (b *Buffer) grow(n int) int { 119 m := b.Len() 120 // If buffer is empty, reset to recover space. 121 if m == 0 && b.off != 0 { 122 b.Reset() 123 } 124 // Try to grow by means of a reslice. 125 if i, ok := b.tryGrowByReslice(n); ok { 126 return i 127 } 128 // Check if we can make use of bootstrap array. 129 if b.buf == nil && n <= len(b.bootstrap) { 130 b.buf = b.bootstrap[:n] 131 return 0 132 } 133 c := cap(b.buf) 134 if n <= c/2-m { 135 // We can slide things down instead of allocating a new 136 // slice. We only need m+n <= c to slide, but 137 // we instead let capacity get twice as large so we 138 // don't spend all our time copying. 139 copy(b.buf, b.buf[b.off:]) 140 } else if c > maxInt-c-n { 141 panic(ErrTooLarge) 142 } else { 143 // Not enough space anywhere, we need to allocate. 144 buf := makeSlice(2*c + n) 145 copy(buf, b.buf[b.off:]) 146 b.buf = buf 147 } 148 // Restore b.off and len(b.buf). 149 b.off = 0 150 b.buf = b.buf[:m+n] 151 return m 152} 153 154// Grow grows the buffer's capacity, if necessary, to guarantee space for 155// another n bytes. After Grow(n), at least n bytes can be written to the 156// buffer without another allocation. 157// If n is negative, Grow will panic. 158// If the buffer can't grow it will panic with ErrTooLarge. 159func (b *Buffer) Grow(n int) { 160 if n < 0 { 161 panic("bytes.Buffer.Grow: negative count") 162 } 163 m := b.grow(n) 164 b.buf = b.buf[:m] 165} 166 167// Write appends the contents of p to the buffer, growing the buffer as 168// needed. The return value n is the length of p; err is always nil. If the 169// buffer becomes too large, Write will panic with ErrTooLarge. 170func (b *Buffer) Write(p []byte) (n int, err error) { 171 b.lastRead = opInvalid 172 m, ok := b.tryGrowByReslice(len(p)) 173 if !ok { 174 m = b.grow(len(p)) 175 } 176 return copy(b.buf[m:], p), nil 177} 178 179// WriteString appends the contents of s to the buffer, growing the buffer as 180// needed. The return value n is the length of s; err is always nil. If the 181// buffer becomes too large, WriteString will panic with ErrTooLarge. 182func (b *Buffer) WriteString(s string) (n int, err error) { 183 b.lastRead = opInvalid 184 m, ok := b.tryGrowByReslice(len(s)) 185 if !ok { 186 m = b.grow(len(s)) 187 } 188 return copy(b.buf[m:], s), nil 189} 190 191// MinRead is the minimum slice size passed to a Read call by 192// Buffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond 193// what is required to hold the contents of r, ReadFrom will not grow the 194// underlying buffer. 195const MinRead = 512 196 197// ReadFrom reads data from r until EOF and appends it to the buffer, growing 198// the buffer as needed. The return value n is the number of bytes read. Any 199// error except io.EOF encountered during the read is also returned. If the 200// buffer becomes too large, ReadFrom will panic with ErrTooLarge. 201func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) { 202 b.lastRead = opInvalid 203 for { 204 i := b.grow(MinRead) 205 m, e := r.Read(b.buf[i:cap(b.buf)]) 206 if m < 0 { 207 panic(errNegativeRead) 208 } 209 210 b.buf = b.buf[:i+m] 211 n += int64(m) 212 if e == io.EOF { 213 return n, nil // e is EOF, so return nil explicitly 214 } 215 if e != nil { 216 return n, e 217 } 218 } 219} 220 221// makeSlice allocates a slice of size n. If the allocation fails, it panics 222// with ErrTooLarge. 223func makeSlice(n int) []byte { 224 // If the make fails, give a known error. 225 defer func() { 226 if recover() != nil { 227 panic(ErrTooLarge) 228 } 229 }() 230 return make([]byte, n) 231} 232 233// WriteTo writes data to w until the buffer is drained or an error occurs. 234// The return value n is the number of bytes written; it always fits into an 235// int, but it is int64 to match the io.WriterTo interface. Any error 236// encountered during the write is also returned. 237func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) { 238 b.lastRead = opInvalid 239 if nBytes := b.Len(); nBytes > 0 { 240 m, e := w.Write(b.buf[b.off:]) 241 if m > nBytes { 242 panic("bytes.Buffer.WriteTo: invalid Write count") 243 } 244 b.off += m 245 n = int64(m) 246 if e != nil { 247 return n, e 248 } 249 // all bytes should have been written, by definition of 250 // Write method in io.Writer 251 if m != nBytes { 252 return n, io.ErrShortWrite 253 } 254 } 255 // Buffer is now empty; reset. 256 b.Reset() 257 return n, nil 258} 259 260// WriteByte appends the byte c to the buffer, growing the buffer as needed. 261// The returned error is always nil, but is included to match bufio.Writer's 262// WriteByte. If the buffer becomes too large, WriteByte will panic with 263// ErrTooLarge. 264func (b *Buffer) WriteByte(c byte) error { 265 b.lastRead = opInvalid 266 m, ok := b.tryGrowByReslice(1) 267 if !ok { 268 m = b.grow(1) 269 } 270 b.buf[m] = c 271 return nil 272} 273 274// WriteRune appends the UTF-8 encoding of Unicode code point r to the 275// buffer, returning its length and an error, which is always nil but is 276// included to match bufio.Writer's WriteRune. The buffer is grown as needed; 277// if it becomes too large, WriteRune will panic with ErrTooLarge. 278func (b *Buffer) WriteRune(r rune) (n int, err error) { 279 if r < utf8.RuneSelf { 280 b.WriteByte(byte(r)) 281 return 1, nil 282 } 283 b.lastRead = opInvalid 284 m, ok := b.tryGrowByReslice(utf8.UTFMax) 285 if !ok { 286 m = b.grow(utf8.UTFMax) 287 } 288 n = utf8.EncodeRune(b.buf[m:m+utf8.UTFMax], r) 289 b.buf = b.buf[:m+n] 290 return n, nil 291} 292 293// 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. 297func (b *Buffer) Read(p []byte) (n int, err error) { 298 b.lastRead = opInvalid 299 if b.empty() { 300 // Buffer is empty, reset to recover space. 301 b.Reset() 302 if len(p) == 0 { 303 return 0, nil 304 } 305 return 0, io.EOF 306 } 307 n = copy(p, b.buf[b.off:]) 308 b.off += n 309 if n > 0 { 310 b.lastRead = opRead 311 } 312 return n, nil 313} 314 315// 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. 319func (b *Buffer) Next(n int) []byte { 320 b.lastRead = opInvalid 321 m := b.Len() 322 if n > m { 323 n = m 324 } 325 data := b.buf[b.off : b.off+n] 326 b.off += n 327 if n > 0 { 328 b.lastRead = opRead 329 } 330 return data 331} 332 333// ReadByte reads and returns the next byte from the buffer. 334// If no byte is available, it returns error io.EOF. 335func (b *Buffer) ReadByte() (byte, error) { 336 if b.empty() { 337 // Buffer is empty, reset to recover space. 338 b.Reset() 339 return 0, io.EOF 340 } 341 c := b.buf[b.off] 342 b.off++ 343 b.lastRead = opRead 344 return c, nil 345} 346 347// 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. 352func (b *Buffer) ReadRune() (r rune, size int, err error) { 353 if b.empty() { 354 // Buffer is empty, reset to recover space. 355 b.Reset() 356 return 0, 0, io.EOF 357 } 358 c := b.buf[b.off] 359 if c < utf8.RuneSelf { 360 b.off++ 361 b.lastRead = opReadRune1 362 return rune(c), 1, nil 363 } 364 r, n := utf8.DecodeRune(b.buf[b.off:]) 365 b.off += n 366 b.lastRead = readOp(n) 367 return r, n, nil 368} 369 370// 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.) 375func (b *Buffer) UnreadRune() error { 376 if b.lastRead <= opInvalid { 377 return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune") 378 } 379 if b.off >= int(b.lastRead) { 380 b.off -= int(b.lastRead) 381 } 382 b.lastRead = opInvalid 383 return nil 384} 385 386// UnreadByte unreads the last byte returned by the most recent successful 387// read operation that read at least one byte. If a write has happened since 388// the last read, if the last read returned an error, or if the read read zero 389// bytes, UnreadByte returns an error. 390func (b *Buffer) UnreadByte() error { 391 if b.lastRead == opInvalid { 392 return errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read") 393 } 394 b.lastRead = opInvalid 395 if b.off > 0 { 396 b.off-- 397 } 398 return nil 399} 400 401// ReadBytes reads until the first occurrence of delim in the input, 402// returning a slice containing the data up to and including the delimiter. 403// If ReadBytes encounters an error before finding a delimiter, 404// it returns the data read before the error and the error itself (often io.EOF). 405// ReadBytes returns err != nil if and only if the returned data does not end in 406// delim. 407func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) { 408 slice, err := b.readSlice(delim) 409 // return a copy of slice. The buffer's backing array may 410 // be overwritten by later calls. 411 line = append(line, slice...) 412 return line, err 413} 414 415// readSlice is like ReadBytes but returns a reference to internal buffer data. 416func (b *Buffer) readSlice(delim byte) (line []byte, err error) { 417 i := IndexByte(b.buf[b.off:], delim) 418 end := b.off + i + 1 419 if i < 0 { 420 end = len(b.buf) 421 err = io.EOF 422 } 423 line = b.buf[b.off:end] 424 b.off = end 425 b.lastRead = opRead 426 return line, err 427} 428 429// ReadString reads until the first occurrence of delim in the input, 430// returning a string containing the data up to and including the delimiter. 431// If ReadString encounters an error before finding a delimiter, 432// it returns the data read before the error and the error itself (often io.EOF). 433// ReadString returns err != nil if and only if the returned data does not end 434// in delim. 435func (b *Buffer) ReadString(delim byte) (line string, err error) { 436 slice, err := b.readSlice(delim) 437 return string(slice), err 438} 439 440// NewBuffer creates and initializes a new Buffer using buf as its 441// initial contents. The new Buffer takes ownership of buf, and the 442// caller should not use buf after this call. NewBuffer is intended to 443// prepare a Buffer to read existing data. It can also be used to size 444// the internal buffer for writing. To do that, buf should have the 445// desired capacity but a length of zero. 446// 447// In most cases, new(Buffer) (or just declaring a Buffer variable) is 448// sufficient to initialize a Buffer. 449func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} } 450 451// NewBufferString creates and initializes a new Buffer using string s as its 452// initial contents. It is intended to prepare a buffer to read an existing 453// string. 454// 455// In most cases, new(Buffer) (or just declaring a Buffer variable) is 456// sufficient to initialize a Buffer. 457func NewBufferString(s string) *Buffer { 458 return &Buffer{buf: []byte(s)} 459} 460