github.com/MangoDowner/go-gm@v0.0.0-20180818020936-8baa2bd4408c/src/bytes/buffer.go (about) 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 // 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. 17 type 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 lastRead readOp // last read operation, so that Unread* can work correctly. 21 // FIXME: lastRead can fit in a single byte 22 23 // memory to hold first slice; helps small buffers avoid allocation. 24 // FIXME: it would be advisable to align Buffer to cachelines to avoid false 25 // sharing. 26 bootstrap [64]byte 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. 33 type readOp int 34 35 const ( 36 opRead readOp = -1 // Any other read operation. 37 opInvalid = 0 // Non-read operation. 38 opReadRune1 = 1 // Read rune of size 1. 39 opReadRune2 = 2 // Read rune of size 2. 40 opReadRune3 = 3 // Read rune of size 3. 41 opReadRune4 = 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. 45 var ErrTooLarge = errors.New("bytes.Buffer: too large") 46 47 // Bytes returns a slice of length b.Len() holding the unread portion of the buffer. 48 // The slice is valid for use only until the next buffer modification (that is, 49 // only until the next call to a method like Read, Write, Reset, or Truncate). 50 // The slice aliases the buffer content at least until the next buffer modification, 51 // so immediate changes to the slice will affect the result of future reads. 52 func (b *Buffer) Bytes() []byte { return b.buf[b.off:] } 53 54 // String returns the contents of the unread portion of the buffer 55 // as a string. If the Buffer is a nil pointer, it returns "<nil>". 56 func (b *Buffer) String() string { 57 if b == nil { 58 // Special case, useful in debugging. 59 return "<nil>" 60 } 61 return string(b.buf[b.off:]) 62 } 63 64 // Len returns the number of bytes of the unread portion of the buffer; 65 // b.Len() == len(b.Bytes()). 66 func (b *Buffer) Len() int { return len(b.buf) - b.off } 67 68 // Cap returns the capacity of the buffer's underlying byte slice, that is, the 69 // total space allocated for the buffer's data. 70 func (b *Buffer) Cap() int { return cap(b.buf) } 71 72 // Truncate discards all but the first n unread bytes from the buffer 73 // but continues to use the same allocated storage. 74 // It panics if n is negative or greater than the length of the buffer. 75 func (b *Buffer) Truncate(n int) { 76 if n == 0 { 77 b.Reset() 78 return 79 } 80 b.lastRead = opInvalid 81 if n < 0 || n > b.Len() { 82 panic("bytes.Buffer: truncation out of range") 83 } 84 b.buf = b.buf[0 : b.off+n] 85 } 86 87 // Reset resets the buffer to be empty, 88 // but it retains the underlying storage for use by future writes. 89 // Reset is the same as Truncate(0). 90 func (b *Buffer) Reset() { 91 b.buf = b.buf[:0] 92 b.off = 0 93 b.lastRead = opInvalid 94 } 95 96 // tryGrowByReslice is a inlineable version of grow for the fast-case where the 97 // internal buffer only needs to be resliced. 98 // It returns the index where bytes should be written and whether it succeeded. 99 func (b *Buffer) tryGrowByReslice(n int) (int, bool) { 100 if l := len(b.buf); l+n <= cap(b.buf) { 101 b.buf = b.buf[:l+n] 102 return l, true 103 } 104 return 0, false 105 } 106 107 // grow grows the buffer to guarantee space for n more bytes. 108 // It returns the index where bytes should be written. 109 // If the buffer can't grow it will panic with ErrTooLarge. 110 func (b *Buffer) grow(n int) int { 111 m := b.Len() 112 // If buffer is empty, reset to recover space. 113 if m == 0 && b.off != 0 { 114 b.Reset() 115 } 116 // Try to grow by means of a reslice. 117 if i, ok := b.tryGrowByReslice(n); ok { 118 return i 119 } 120 // Check if we can make use of bootstrap array. 121 if b.buf == nil && n <= len(b.bootstrap) { 122 b.buf = b.bootstrap[:n] 123 return 0 124 } 125 if m+n <= cap(b.buf)/2 { 126 // We can slide things down instead of allocating a new 127 // slice. We only need m+n <= cap(b.buf) to slide, but 128 // we instead let capacity get twice as large so we 129 // don't spend all our time copying. 130 copy(b.buf[:], b.buf[b.off:]) 131 } else { 132 // Not enough space anywhere, we need to allocate. 133 buf := makeSlice(2*cap(b.buf) + n) 134 copy(buf, b.buf[b.off:]) 135 b.buf = buf 136 } 137 // Restore b.off and len(b.buf). 138 b.off = 0 139 b.buf = b.buf[:m+n] 140 return m 141 } 142 143 // Grow grows the buffer's capacity, if necessary, to guarantee space for 144 // another n bytes. After Grow(n), at least n bytes can be written to the 145 // buffer without another allocation. 146 // If n is negative, Grow will panic. 147 // If the buffer can't grow it will panic with ErrTooLarge. 148 func (b *Buffer) Grow(n int) { 149 if n < 0 { 150 panic("bytes.Buffer.Grow: negative count") 151 } 152 m := b.grow(n) 153 b.buf = b.buf[0:m] 154 } 155 156 // Write appends the contents of p to the buffer, growing the buffer as 157 // needed. The return value n is the length of p; err is always nil. If the 158 // buffer becomes too large, Write will panic with ErrTooLarge. 159 func (b *Buffer) Write(p []byte) (n int, err error) { 160 b.lastRead = opInvalid 161 m, ok := b.tryGrowByReslice(len(p)) 162 if !ok { 163 m = b.grow(len(p)) 164 } 165 return copy(b.buf[m:], p), nil 166 } 167 168 // WriteString appends the contents of s to the buffer, growing the buffer as 169 // needed. The return value n is the length of s; err is always nil. If the 170 // buffer becomes too large, WriteString will panic with ErrTooLarge. 171 func (b *Buffer) WriteString(s string) (n int, err error) { 172 b.lastRead = opInvalid 173 m, ok := b.tryGrowByReslice(len(s)) 174 if !ok { 175 m = b.grow(len(s)) 176 } 177 return copy(b.buf[m:], s), nil 178 } 179 180 // MinRead is the minimum slice size passed to a Read call by 181 // Buffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond 182 // what is required to hold the contents of r, ReadFrom will not grow the 183 // underlying buffer. 184 const MinRead = 512 185 186 // ReadFrom reads data from r until EOF and appends it to the buffer, growing 187 // the buffer as needed. The return value n is the number of bytes read. Any 188 // error except io.EOF encountered during the read is also returned. If the 189 // buffer becomes too large, ReadFrom will panic with ErrTooLarge. 190 func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) { 191 b.lastRead = opInvalid 192 // If buffer is empty, reset to recover space. 193 if b.off >= len(b.buf) { 194 b.Reset() 195 } 196 for { 197 if free := cap(b.buf) - len(b.buf); free < MinRead { 198 // not enough space at end 199 newBuf := b.buf 200 if b.off+free < MinRead { 201 // not enough space using beginning of buffer; 202 // double buffer capacity 203 newBuf = makeSlice(2*cap(b.buf) + MinRead) 204 } 205 copy(newBuf, b.buf[b.off:]) 206 b.buf = newBuf[:len(b.buf)-b.off] 207 b.off = 0 208 } 209 m, e := r.Read(b.buf[len(b.buf):cap(b.buf)]) 210 b.buf = b.buf[0 : len(b.buf)+m] 211 n += int64(m) 212 if e == io.EOF { 213 break 214 } 215 if e != nil { 216 return n, e 217 } 218 } 219 return n, nil // err is EOF, so return nil explicitly 220 } 221 222 // makeSlice allocates a slice of size n. If the allocation fails, it panics 223 // with ErrTooLarge. 224 func makeSlice(n int) []byte { 225 // If the make fails, give a known error. 226 defer func() { 227 if recover() != nil { 228 panic(ErrTooLarge) 229 } 230 }() 231 return make([]byte, n) 232 } 233 234 // WriteTo writes data to w until the buffer is drained or an error occurs. 235 // The return value n is the number of bytes written; it always fits into an 236 // int, but it is int64 to match the io.WriterTo interface. Any error 237 // encountered during the write is also returned. 238 func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) { 239 b.lastRead = opInvalid 240 if b.off < len(b.buf) { 241 nBytes := b.Len() 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 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. 266 func (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. 280 func (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. 299 func (b *Buffer) Read(p []byte) (n int, err error) { 300 b.lastRead = opInvalid 301 if b.off >= len(b.buf) { 302 // Buffer is empty, reset to recover space. 303 b.Reset() 304 if len(p) == 0 { 305 return 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 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. 321 func (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. 337 func (b *Buffer) ReadByte() (byte, error) { 338 b.lastRead = opInvalid 339 if b.off >= len(b.buf) { 340 // Buffer is empty, reset to recover space. 341 b.Reset() 342 return 0, io.EOF 343 } 344 c := b.buf[b.off] 345 b.off++ 346 b.lastRead = opRead 347 return c, nil 348 } 349 350 // ReadRune reads and returns the next UTF-8-encoded 351 // Unicode code point from the buffer. 352 // If no bytes are available, the error returned is io.EOF. 353 // If the bytes are an erroneous UTF-8 encoding, it 354 // consumes one byte and returns U+FFFD, 1. 355 func (b *Buffer) ReadRune() (r rune, size int, err error) { 356 b.lastRead = opInvalid 357 if b.off >= len(b.buf) { 358 // Buffer is empty, reset to recover space. 359 b.Reset() 360 return 0, 0, io.EOF 361 } 362 c := b.buf[b.off] 363 if c < utf8.RuneSelf { 364 b.off++ 365 b.lastRead = opReadRune1 366 return rune(c), 1, nil 367 } 368 r, n := utf8.DecodeRune(b.buf[b.off:]) 369 b.off += n 370 b.lastRead = readOp(n) 371 return r, n, nil 372 } 373 374 // UnreadRune unreads the last rune returned by ReadRune. 375 // If the most recent read or write operation on the buffer was 376 // not a successful ReadRune, UnreadRune returns an error. (In this regard 377 // it is stricter than UnreadByte, which will unread the last byte 378 // from any read operation.) 379 func (b *Buffer) UnreadRune() error { 380 if b.lastRead <= opInvalid { 381 return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune") 382 } 383 if b.off >= int(b.lastRead) { 384 b.off -= int(b.lastRead) 385 } 386 b.lastRead = opInvalid 387 return nil 388 } 389 390 // UnreadByte unreads the last byte returned by the most recent successful 391 // read operation that read at least one byte. If a write has happened since 392 // the last read, if the last read returned an error, or if the read read zero 393 // bytes, UnreadByte returns an error. 394 func (b *Buffer) UnreadByte() error { 395 if b.lastRead == opInvalid { 396 return errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read") 397 } 398 b.lastRead = opInvalid 399 if b.off > 0 { 400 b.off-- 401 } 402 return nil 403 } 404 405 // ReadBytes reads until the first occurrence of delim in the input, 406 // returning a slice containing the data up to and including the delimiter. 407 // If ReadBytes encounters an error before finding a delimiter, 408 // it returns the data read before the error and the error itself (often io.EOF). 409 // ReadBytes returns err != nil if and only if the returned data does not end in 410 // delim. 411 func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) { 412 slice, err := b.readSlice(delim) 413 // return a copy of slice. The buffer's backing array may 414 // be overwritten by later calls. 415 line = append(line, slice...) 416 return 417 } 418 419 // readSlice is like ReadBytes but returns a reference to internal buffer data. 420 func (b *Buffer) readSlice(delim byte) (line []byte, err error) { 421 i := IndexByte(b.buf[b.off:], delim) 422 end := b.off + i + 1 423 if i < 0 { 424 end = len(b.buf) 425 err = io.EOF 426 } 427 line = b.buf[b.off:end] 428 b.off = end 429 b.lastRead = opRead 430 return line, err 431 } 432 433 // ReadString reads until the first occurrence of delim in the input, 434 // returning a string containing the data up to and including the delimiter. 435 // If ReadString encounters an error before finding a delimiter, 436 // it returns the data read before the error and the error itself (often io.EOF). 437 // ReadString returns err != nil if and only if the returned data does not end 438 // in delim. 439 func (b *Buffer) ReadString(delim byte) (line string, err error) { 440 slice, err := b.readSlice(delim) 441 return string(slice), err 442 } 443 444 // NewBuffer creates and initializes a new Buffer using buf as its 445 // initial contents. The new Buffer takes ownership of buf, and the 446 // caller should not use buf after this call. NewBuffer is intended to 447 // prepare a Buffer to read existing data. It can also be used to size 448 // the internal buffer for writing. To do that, buf should have the 449 // desired capacity but a length of zero. 450 // 451 // In most cases, new(Buffer) (or just declaring a Buffer variable) is 452 // sufficient to initialize a Buffer. 453 func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} } 454 455 // NewBufferString creates and initializes a new Buffer using string s as its 456 // initial contents. It is intended to prepare a buffer to read an existing 457 // string. 458 // 459 // In most cases, new(Buffer) (or just declaring a Buffer variable) is 460 // sufficient to initialize a Buffer. 461 func NewBufferString(s string) *Buffer { 462 return &Buffer{buf: []byte(s)} 463 }