github.com/peggyl/go@v0.0.0-20151008231540-ae315999c2d5/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 runeBytes [utf8.UTFMax]byte // avoid allocation of slice on each WriteByte or Rune 21 bootstrap [64]byte // memory to hold first slice; helps small buffers (Printf) avoid allocation. 22 lastRead readOp // last read operation, so that Unread* can work correctly. 23 } 24 25 // The readOp constants describe the last action performed on 26 // the buffer, so that UnreadRune and UnreadByte can 27 // check for invalid usage. 28 type readOp int 29 30 const ( 31 opInvalid readOp = iota // Non-read operation. 32 opReadRune // Read rune. 33 opRead // Any other read operation. 34 ) 35 36 // ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer. 37 var ErrTooLarge = errors.New("bytes.Buffer: too large") 38 39 // Bytes returns a slice of the contents of the unread portion of the buffer; 40 // len(b.Bytes()) == b.Len(). If the caller changes the contents of the 41 // returned slice, the contents of the buffer will change provided there 42 // are no intervening method calls on the Buffer. 43 func (b *Buffer) Bytes() []byte { return b.buf[b.off:] } 44 45 // String returns the contents of the unread portion of the buffer 46 // as a string. If the Buffer is a nil pointer, it returns "<nil>". 47 func (b *Buffer) String() string { 48 if b == nil { 49 // Special case, useful in debugging. 50 return "<nil>" 51 } 52 return string(b.buf[b.off:]) 53 } 54 55 // Len returns the number of bytes of the unread portion of the buffer; 56 // b.Len() == len(b.Bytes()). 57 func (b *Buffer) Len() int { return len(b.buf) - b.off } 58 59 // Cap returns the capacity of the buffer's underlying byte slice, that is, the 60 // total space allocated for the buffer's data. 61 func (b *Buffer) Cap() int { return cap(b.buf) } 62 63 // Truncate discards all but the first n unread bytes from the buffer. 64 // It panics if n is negative or greater than the length of the buffer. 65 func (b *Buffer) Truncate(n int) { 66 b.lastRead = opInvalid 67 switch { 68 case n < 0 || n > b.Len(): 69 panic("bytes.Buffer: truncation out of range") 70 case n == 0: 71 // Reuse buffer space. 72 b.off = 0 73 } 74 b.buf = b.buf[0 : b.off+n] 75 } 76 77 // Reset resets the buffer so it has no content. 78 // b.Reset() is the same as b.Truncate(0). 79 func (b *Buffer) Reset() { b.Truncate(0) } 80 81 // grow grows the buffer to guarantee space for n more bytes. 82 // It returns the index where bytes should be written. 83 // If the buffer can't grow it will panic with ErrTooLarge. 84 func (b *Buffer) grow(n int) int { 85 m := b.Len() 86 // If buffer is empty, reset to recover space. 87 if m == 0 && b.off != 0 { 88 b.Truncate(0) 89 } 90 if len(b.buf)+n > cap(b.buf) { 91 var buf []byte 92 if b.buf == nil && n <= len(b.bootstrap) { 93 buf = b.bootstrap[0:] 94 } else if m+n <= cap(b.buf)/2 { 95 // We can slide things down instead of allocating a new 96 // slice. We only need m+n <= cap(b.buf) to slide, but 97 // we instead let capacity get twice as large so we 98 // don't spend all our time copying. 99 copy(b.buf[:], b.buf[b.off:]) 100 buf = b.buf[:m] 101 } else { 102 // not enough space anywhere 103 buf = makeSlice(2*cap(b.buf) + n) 104 copy(buf, b.buf[b.off:]) 105 } 106 b.buf = buf 107 b.off = 0 108 } 109 b.buf = b.buf[0 : b.off+m+n] 110 return b.off + m 111 } 112 113 // Grow grows the buffer's capacity, if necessary, to guarantee space for 114 // another n bytes. After Grow(n), at least n bytes can be written to the 115 // buffer without another allocation. 116 // If n is negative, Grow will panic. 117 // If the buffer can't grow it will panic with ErrTooLarge. 118 func (b *Buffer) Grow(n int) { 119 if n < 0 { 120 panic("bytes.Buffer.Grow: negative count") 121 } 122 m := b.grow(n) 123 b.buf = b.buf[0:m] 124 } 125 126 // Write appends the contents of p to the buffer, growing the buffer as 127 // needed. The return value n is the length of p; err is always nil. If the 128 // buffer becomes too large, Write will panic with ErrTooLarge. 129 func (b *Buffer) Write(p []byte) (n int, err error) { 130 b.lastRead = opInvalid 131 m := b.grow(len(p)) 132 return copy(b.buf[m:], p), nil 133 } 134 135 // WriteString appends the contents of s to the buffer, growing the buffer as 136 // needed. The return value n is the length of s; err is always nil. If the 137 // buffer becomes too large, WriteString will panic with ErrTooLarge. 138 func (b *Buffer) WriteString(s string) (n int, err error) { 139 b.lastRead = opInvalid 140 m := b.grow(len(s)) 141 return copy(b.buf[m:], s), nil 142 } 143 144 // MinRead is the minimum slice size passed to a Read call by 145 // Buffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond 146 // what is required to hold the contents of r, ReadFrom will not grow the 147 // underlying buffer. 148 const MinRead = 512 149 150 // ReadFrom reads data from r until EOF and appends it to the buffer, growing 151 // the buffer as needed. The return value n is the number of bytes read. Any 152 // error except io.EOF encountered during the read is also returned. If the 153 // buffer becomes too large, ReadFrom will panic with ErrTooLarge. 154 func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) { 155 b.lastRead = opInvalid 156 // If buffer is empty, reset to recover space. 157 if b.off >= len(b.buf) { 158 b.Truncate(0) 159 } 160 for { 161 if free := cap(b.buf) - len(b.buf); free < MinRead { 162 // not enough space at end 163 newBuf := b.buf 164 if b.off+free < MinRead { 165 // not enough space using beginning of buffer; 166 // double buffer capacity 167 newBuf = makeSlice(2*cap(b.buf) + MinRead) 168 } 169 copy(newBuf, b.buf[b.off:]) 170 b.buf = newBuf[:len(b.buf)-b.off] 171 b.off = 0 172 } 173 m, e := r.Read(b.buf[len(b.buf):cap(b.buf)]) 174 b.buf = b.buf[0 : len(b.buf)+m] 175 n += int64(m) 176 if e == io.EOF { 177 break 178 } 179 if e != nil { 180 return n, e 181 } 182 } 183 return n, nil // err is EOF, so return nil explicitly 184 } 185 186 // makeSlice allocates a slice of size n. If the allocation fails, it panics 187 // with ErrTooLarge. 188 func makeSlice(n int) []byte { 189 // If the make fails, give a known error. 190 defer func() { 191 if recover() != nil { 192 panic(ErrTooLarge) 193 } 194 }() 195 return make([]byte, n) 196 } 197 198 // WriteTo writes data to w until the buffer is drained or an error occurs. 199 // The return value n is the number of bytes written; it always fits into an 200 // int, but it is int64 to match the io.WriterTo interface. Any error 201 // encountered during the write is also returned. 202 func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) { 203 b.lastRead = opInvalid 204 if b.off < len(b.buf) { 205 nBytes := b.Len() 206 m, e := w.Write(b.buf[b.off:]) 207 if m > nBytes { 208 panic("bytes.Buffer.WriteTo: invalid Write count") 209 } 210 b.off += m 211 n = int64(m) 212 if e != nil { 213 return n, e 214 } 215 // all bytes should have been written, by definition of 216 // Write method in io.Writer 217 if m != nBytes { 218 return n, io.ErrShortWrite 219 } 220 } 221 // Buffer is now empty; reset. 222 b.Truncate(0) 223 return 224 } 225 226 // WriteByte appends the byte c to the buffer, growing the buffer as needed. 227 // The returned error is always nil, but is included to match bufio.Writer's 228 // WriteByte. If the buffer becomes too large, WriteByte will panic with 229 // ErrTooLarge. 230 func (b *Buffer) WriteByte(c byte) error { 231 b.lastRead = opInvalid 232 m := b.grow(1) 233 b.buf[m] = c 234 return nil 235 } 236 237 // WriteRune appends the UTF-8 encoding of Unicode code point r to the 238 // buffer, returning its length and an error, which is always nil but is 239 // included to match bufio.Writer's WriteRune. The buffer is grown as needed; 240 // if it becomes too large, WriteRune will panic with ErrTooLarge. 241 func (b *Buffer) WriteRune(r rune) (n int, err error) { 242 if r < utf8.RuneSelf { 243 b.WriteByte(byte(r)) 244 return 1, nil 245 } 246 n = utf8.EncodeRune(b.runeBytes[0:], r) 247 b.Write(b.runeBytes[0:n]) 248 return n, nil 249 } 250 251 // Read reads the next len(p) bytes from the buffer or until the buffer 252 // is drained. The return value n is the number of bytes read. If the 253 // buffer has no data to return, err is io.EOF (unless len(p) is zero); 254 // otherwise it is nil. 255 func (b *Buffer) Read(p []byte) (n int, err error) { 256 b.lastRead = opInvalid 257 if b.off >= len(b.buf) { 258 // Buffer is empty, reset to recover space. 259 b.Truncate(0) 260 if len(p) == 0 { 261 return 262 } 263 return 0, io.EOF 264 } 265 n = copy(p, b.buf[b.off:]) 266 b.off += n 267 if n > 0 { 268 b.lastRead = opRead 269 } 270 return 271 } 272 273 // Next returns a slice containing the next n bytes from the buffer, 274 // advancing the buffer as if the bytes had been returned by Read. 275 // If there are fewer than n bytes in the buffer, Next returns the entire buffer. 276 // The slice is only valid until the next call to a read or write method. 277 func (b *Buffer) Next(n int) []byte { 278 b.lastRead = opInvalid 279 m := b.Len() 280 if n > m { 281 n = m 282 } 283 data := b.buf[b.off : b.off+n] 284 b.off += n 285 if n > 0 { 286 b.lastRead = opRead 287 } 288 return data 289 } 290 291 // ReadByte reads and returns the next byte from the buffer. 292 // If no byte is available, it returns error io.EOF. 293 func (b *Buffer) ReadByte() (c byte, err error) { 294 b.lastRead = opInvalid 295 if b.off >= len(b.buf) { 296 // Buffer is empty, reset to recover space. 297 b.Truncate(0) 298 return 0, io.EOF 299 } 300 c = b.buf[b.off] 301 b.off++ 302 b.lastRead = opRead 303 return c, nil 304 } 305 306 // ReadRune reads and returns the next UTF-8-encoded 307 // Unicode code point from the buffer. 308 // If no bytes are available, the error returned is io.EOF. 309 // If the bytes are an erroneous UTF-8 encoding, it 310 // consumes one byte and returns U+FFFD, 1. 311 func (b *Buffer) ReadRune() (r rune, size int, err error) { 312 b.lastRead = opInvalid 313 if b.off >= len(b.buf) { 314 // Buffer is empty, reset to recover space. 315 b.Truncate(0) 316 return 0, 0, io.EOF 317 } 318 b.lastRead = opReadRune 319 c := b.buf[b.off] 320 if c < utf8.RuneSelf { 321 b.off++ 322 return rune(c), 1, nil 323 } 324 r, n := utf8.DecodeRune(b.buf[b.off:]) 325 b.off += n 326 return r, n, nil 327 } 328 329 // UnreadRune unreads the last rune returned by ReadRune. 330 // If the most recent read or write operation on the buffer was 331 // not a ReadRune, UnreadRune returns an error. (In this regard 332 // it is stricter than UnreadByte, which will unread the last byte 333 // from any read operation.) 334 func (b *Buffer) UnreadRune() error { 335 if b.lastRead != opReadRune { 336 return errors.New("bytes.Buffer: UnreadRune: previous operation was not ReadRune") 337 } 338 b.lastRead = opInvalid 339 if b.off > 0 { 340 _, n := utf8.DecodeLastRune(b.buf[0:b.off]) 341 b.off -= n 342 } 343 return nil 344 } 345 346 // UnreadByte unreads the last byte returned by the most recent 347 // read operation. If write has happened since the last read, UnreadByte 348 // returns an error. 349 func (b *Buffer) UnreadByte() error { 350 if b.lastRead != opReadRune && b.lastRead != opRead { 351 return errors.New("bytes.Buffer: UnreadByte: previous operation was not a read") 352 } 353 b.lastRead = opInvalid 354 if b.off > 0 { 355 b.off-- 356 } 357 return nil 358 } 359 360 // ReadBytes reads until the first occurrence of delim in the input, 361 // returning a slice containing the data up to and including the delimiter. 362 // If ReadBytes encounters an error before finding a delimiter, 363 // it returns the data read before the error and the error itself (often io.EOF). 364 // ReadBytes returns err != nil if and only if the returned data does not end in 365 // delim. 366 func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) { 367 slice, err := b.readSlice(delim) 368 // return a copy of slice. The buffer's backing array may 369 // be overwritten by later calls. 370 line = append(line, slice...) 371 return 372 } 373 374 // readSlice is like ReadBytes but returns a reference to internal buffer data. 375 func (b *Buffer) readSlice(delim byte) (line []byte, err error) { 376 i := IndexByte(b.buf[b.off:], delim) 377 end := b.off + i + 1 378 if i < 0 { 379 end = len(b.buf) 380 err = io.EOF 381 } 382 line = b.buf[b.off:end] 383 b.off = end 384 b.lastRead = opRead 385 return line, err 386 } 387 388 // ReadString reads until the first occurrence of delim in the input, 389 // returning a string containing the data up to and including the delimiter. 390 // If ReadString encounters an error before finding a delimiter, 391 // it returns the data read before the error and the error itself (often io.EOF). 392 // ReadString returns err != nil if and only if the returned data does not end 393 // in delim. 394 func (b *Buffer) ReadString(delim byte) (line string, err error) { 395 slice, err := b.readSlice(delim) 396 return string(slice), err 397 } 398 399 // NewBuffer creates and initializes a new Buffer using buf as its initial 400 // contents. It is intended to prepare a Buffer to read existing data. It 401 // can also be used to size the internal buffer for writing. To do that, 402 // buf should have the desired capacity but a length of zero. 403 // 404 // In most cases, new(Buffer) (or just declaring a Buffer variable) is 405 // sufficient to initialize a Buffer. 406 func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} } 407 408 // NewBufferString creates and initializes a new Buffer using string s as its 409 // initial contents. It is intended to prepare a buffer to read an existing 410 // string. 411 // 412 // In most cases, new(Buffer) (or just declaring a Buffer variable) is 413 // sufficient to initialize a Buffer. 414 func NewBufferString(s string) *Buffer { 415 return &Buffer{buf: []byte(s)} 416 }