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 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. 30type 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. 34const ( 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. 44var ErrTooLarge = errors.New("bytes.Buffer: too large") 45var errNegativeRead = errors.New("bytes.Buffer: reader returned negative count from Read") 46 47const 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. 54func (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. 60func (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. 69func (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()). 73func (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. 77func (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. 82func (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). 97func (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. 106func (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. 117func (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 // Not enough space anywhere, we need to allocate. 142 buf := makeSlice(2*c + n) 143 copy(buf, b.buf[b.off:]) 144 b.buf = buf 145 } 146 // Restore b.off and len(b.buf). 147 b.off = 0 148 b.buf = b.buf[:m+n] 149 return m 150} 151 152// 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. 157func (b *Buffer) Grow(n int) { 158 if n < 0 { 159 panic("bytes.Buffer.Grow: negative count") 160 } 161 m := b.grow(n) 162 b.buf = b.buf[:m] 163} 164 165// 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. 168func (b *Buffer) Write(p []byte) (n int, err error) { 169 b.lastRead = opInvalid 170 m, ok := b.tryGrowByReslice(len(p)) 171 if !ok { 172 m = b.grow(len(p)) 173 } 174 return copy(b.buf[m:], p), nil 175} 176 177// 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. 180func (b *Buffer) WriteString(s string) (n int, err error) { 181 b.lastRead = opInvalid 182 m, ok := b.tryGrowByReslice(len(s)) 183 if !ok { 184 m = b.grow(len(s)) 185 } 186 return copy(b.buf[m:], s), nil 187} 188 189// 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. 193const MinRead = 512 194 195// 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. 199func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) { 200 b.lastRead = opInvalid 201 for { 202 i := b.grow(MinRead) 203 b.buf = b.buf[:i] 204 m, e := r.Read(b.buf[i:cap(b.buf)]) 205 if m < 0 { 206 panic(errNegativeRead) 207 } 208 209 b.buf = b.buf[:i+m] 210 n += int64(m) 211 if e == io.EOF { 212 return n, nil // e is EOF, so return nil explicitly 213 } 214 if e != nil { 215 return n, e 216 } 217 } 218} 219 220// makeSlice allocates a slice of size n. If the allocation fails, it panics 221// with ErrTooLarge. 222func makeSlice(n int) []byte { 223 // If the make fails, give a known error. 224 defer func() { 225 if recover() != nil { 226 panic(ErrTooLarge) 227 } 228 }() 229 return make([]byte, n) 230} 231 232// 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. 236func (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:]) 240 if m > nBytes { 241 panic("bytes.Buffer.WriteTo: invalid Write count") 242 } 243 b.off += m 244 n = int64(m) 245 if e != nil { 246 return n, e 247 } 248 // all bytes should have been written, by definition of 249 // Write method in io.Writer 250 if m != nBytes { 251 return n, io.ErrShortWrite 252 } 253 } 254 // Buffer is now empty; reset. 255 b.Reset() 256 return n, nil 257} 258 259// 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 262// ErrTooLarge. 263func (b *Buffer) WriteByte(c byte) error { 264 b.lastRead = opInvalid 265 m, ok := b.tryGrowByReslice(1) 266 if !ok { 267 m = b.grow(1) 268 } 269 b.buf[m] = c 270 return nil 271} 272 273// 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. 277func (b *Buffer) WriteRune(r rune) (n int, err error) { 278 if r < utf8.RuneSelf { 279 b.WriteByte(byte(r)) 280 return 1, nil 281 } 282 b.lastRead = opInvalid 283 m, ok := b.tryGrowByReslice(utf8.UTFMax) 284 if !ok { 285 m = b.grow(utf8.UTFMax) 286 } 287 n = utf8.EncodeRune(b.buf[m:m+utf8.UTFMax], r) 288 b.buf = b.buf[:m+n] 289 return n, nil 290} 291 292// Read reads the next len(p) bytes from the buffer or until the buffer 293// is drained. The return value n is the number of bytes read. If the 294// buffer has no data to return, err is io.EOF (unless len(p) is zero); 295// otherwise it is nil. 296func (b *Buffer) Read(p []byte) (n int, err error) { 297 b.lastRead = opInvalid 298 if b.empty() { 299 // Buffer is empty, reset to recover space. 300 b.Reset() 301 if len(p) == 0 { 302 return 0, nil 303 } 304 return 0, io.EOF 305 } 306 n = copy(p, b.buf[b.off:]) 307 b.off += n 308 if n > 0 { 309 b.lastRead = opRead 310 } 311 return n, nil 312} 313 314// Next returns a slice containing the next n bytes from the buffer, 315// advancing the buffer as if the bytes had been returned by Read. 316// If there are fewer than n bytes in the buffer, Next returns the entire buffer. 317// The slice is only valid until the next call to a read or write method. 318func (b *Buffer) Next(n int) []byte { 319 b.lastRead = opInvalid 320 m := b.Len() 321 if n > m { 322 n = m 323 } 324 data := b.buf[b.off : b.off+n] 325 b.off += n 326 if n > 0 { 327 b.lastRead = opRead 328 } 329 return data 330} 331 332// ReadByte reads and returns the next byte from the buffer. 333// If no byte is available, it returns error io.EOF. 334func (b *Buffer) ReadByte() (byte, error) { 335 if b.empty() { 336 // Buffer is empty, reset to recover space. 337 b.Reset() 338 return 0, io.EOF 339 } 340 c := b.buf[b.off] 341 b.off++ 342 b.lastRead = opRead 343 return c, nil 344} 345 346// ReadRune reads and returns the next UTF-8-encoded 347// Unicode code point from the buffer. 348// If no bytes are available, the error returned is io.EOF. 349// If the bytes are an erroneous UTF-8 encoding, it 350// consumes one byte and returns U+FFFD, 1. 351func (b *Buffer) ReadRune() (r rune, size int, err error) { 352 if b.empty() { 353 // Buffer is empty, reset to recover space. 354 b.Reset() 355 return 0, 0, io.EOF 356 } 357 c := b.buf[b.off] 358 if c < utf8.RuneSelf { 359 b.off++ 360 b.lastRead = opReadRune1 361 return rune(c), 1, nil 362 } 363 r, n := utf8.DecodeRune(b.buf[b.off:]) 364 b.off += n 365 b.lastRead = readOp(n) 366 return r, n, nil 367} 368 369// UnreadRune unreads the last rune returned by ReadRune. 370// If the most recent read or write operation on the buffer was 371// not a successful ReadRune, UnreadRune returns an error. (In this regard 372// it is stricter than UnreadByte, which will unread the last byte 373// from any read operation.) 374func (b *Buffer) UnreadRune() error { 375 if b.lastRead <= opInvalid { 376 return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune") 377 } 378 if b.off >= int(b.lastRead) { 379 b.off -= int(b.lastRead) 380 } 381 b.lastRead = opInvalid 382 return nil 383} 384 385var errUnreadByte = errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read") 386 387// UnreadByte unreads the last byte returned by the most recent successful 388// read operation that read at least one byte. If a write has happened since 389// the last read, if the last read returned an error, or if the read read zero 390// bytes, UnreadByte returns an error. 391func (b *Buffer) UnreadByte() error { 392 if b.lastRead == opInvalid { 393 return errUnreadByte 394 } 395 b.lastRead = opInvalid 396 if b.off > 0 { 397 b.off-- 398 } 399 return nil 400} 401 402// ReadBytes reads until the first occurrence of delim in the input, 403// returning a slice containing the data up to and including the delimiter. 404// If ReadBytes encounters an error before finding a delimiter, 405// it returns the data read before the error and the error itself (often io.EOF). 406// ReadBytes returns err != nil if and only if the returned data does not end in 407// delim. 408func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) { 409 slice, err := b.readSlice(delim) 410 // return a copy of slice. The buffer's backing array may 411 // be overwritten by later calls. 412 line = append(line, slice...) 413 return line, err 414} 415 416// readSlice is like ReadBytes but returns a reference to internal buffer data. 417func (b *Buffer) readSlice(delim byte) (line []byte, err error) { 418 i := IndexByte(b.buf[b.off:], delim) 419 end := b.off + i + 1 420 if i < 0 { 421 end = len(b.buf) 422 err = io.EOF 423 } 424 line = b.buf[b.off:end] 425 b.off = end 426 b.lastRead = opRead 427 return line, err 428} 429 430// ReadString reads until the first occurrence of delim in the input, 431// returning a string containing the data up to and including the delimiter. 432// If ReadString encounters an error before finding a delimiter, 433// it returns the data read before the error and the error itself (often io.EOF). 434// ReadString returns err != nil if and only if the returned data does not end 435// in delim. 436func (b *Buffer) ReadString(delim byte) (line string, err error) { 437 slice, err := b.readSlice(delim) 438 return string(slice), err 439} 440 441// NewBuffer creates and initializes a new Buffer using buf as its 442// initial contents. The new Buffer takes ownership of buf, and the 443// caller should not use buf after this call. NewBuffer is intended to 444// prepare a Buffer to read existing data. It can also be used to set 445// the initial size of the internal buffer for writing. To do that, 446// buf should have the desired capacity but a length of zero. 447// 448// In most cases, new(Buffer) (or just declaring a Buffer variable) is 449// sufficient to initialize a Buffer. 450func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} } 451 452// NewBufferString creates and initializes a new Buffer using string s as its 453// initial contents. It is intended to prepare a buffer to read an existing 454// string. 455// 456// In most cases, new(Buffer) (or just declaring a Buffer variable) is 457// sufficient to initialize a Buffer. 458func NewBufferString(s string) *Buffer { 459 return &Buffer{buf: []byte(s)} 460} 461