/usr/share/gocode/src/github.com/philhofer/fwd/reader.go is in golang-github-philhofer-fwd-dev 0.0~git20151005.0.8fd9a4b-1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 | // The `fwd` package provides a buffered reader
// and writer. Each has methods that help improve
// the encoding/decoding performance of some binary
// protocols.
//
// The `fwd.Writer` and `fwd.Reader` type provide similar
// functionality to their counterparts in `bufio`, plus
// a few extra utility methods that simplify read-ahead
// and write-ahead. I wrote this package to improve serialization
// performance for http://github.com/tinylib/msgp,
// where it provided about a 2x speedup over `bufio` for certain
// workloads. However, care must be taken to understand the semantics of the
// extra methods provided by this package, as they allow
// the user to access and manipulate the buffer memory
// directly.
//
// The extra methods for `fwd.Reader` are `Peek`, `Skip`
// and `Next`. `(*fwd.Reader).Peek`, unlike `(*bufio.Reader).Peek`,
// will re-allocate the read buffer in order to accommodate arbitrarily
// large read-ahead. `(*fwd.Reader).Skip` skips the next `n` bytes
// in the stream, and uses the `io.Seeker` interface if the underlying
// stream implements it. `(*fwd.Reader).Next` returns a slice pointing
// to the next `n` bytes in the read buffer (like `Peek`), but also
// increments the read position. This allows users to process streams
// in aribtrary block sizes without having to manage appropriately-sized
// slices. Additionally, obviating the need to copy the data from the
// buffer to another location in memory can improve performance dramatically
// in CPU-bound applications.
//
// `fwd.Writer` only has one extra method, which is `(*fwd.Writer).Next`, which
// returns a slice pointing to the next `n` bytes of the writer, and increments
// the write position by the length of the returned slice. This allows users
// to write directly to the end of the buffer.
//
package fwd
import "io"
const (
// DefaultReaderSize is the default size of the read buffer
DefaultReaderSize = 2048
// minimum read buffer; straight from bufio
minReaderSize = 16
)
// NewReader returns a new *Reader that reads from 'r'
func NewReader(r io.Reader) *Reader {
return NewReaderSize(r, DefaultReaderSize)
}
// NewReaderSize returns a new *Reader that
// reads from 'r' and has a buffer size 'n'
func NewReaderSize(r io.Reader, n int) *Reader {
rd := &Reader{
r: r,
data: make([]byte, 0, max(minReaderSize, n)),
}
if s, ok := r.(io.Seeker); ok {
rd.rs = s
}
return rd
}
// Reader is a buffered look-ahead reader
type Reader struct {
r io.Reader // underlying reader
// data[n:len(data)] is buffered data; data[len(data):cap(data)] is free buffer space
data []byte // data
n int // read offset
state error // last read error
// if the reader past to NewReader was
// also an io.Seeker, this is non-nil
rs io.Seeker
}
// Reset resets the underlying reader
// and the read buffer.
func (r *Reader) Reset(rd io.Reader) {
r.r = rd
r.data = r.data[0:0]
r.n = 0
r.state = nil
if s, ok := rd.(io.Seeker); ok {
r.rs = s
} else {
r.rs = nil
}
}
// more() does one read on the underlying reader
func (r *Reader) more() {
// move data backwards so that
// the read offset is 0; this way
// we can supply the maximum number of
// bytes to the reader
if r.n != 0 {
r.data = r.data[:copy(r.data[0:], r.data[r.n:])]
r.n = 0
}
var a int
a, r.state = r.r.Read(r.data[len(r.data):cap(r.data)])
if a == 0 && r.state == nil {
r.state = io.ErrNoProgress
return
}
r.data = r.data[:len(r.data)+a]
}
// pop error
func (r *Reader) err() (e error) {
e, r.state = r.state, nil
return
}
// pop error; EOF -> io.ErrUnexpectedEOF
func (r *Reader) noEOF() (e error) {
e, r.state = r.state, nil
if e == io.EOF {
e = io.ErrUnexpectedEOF
}
return
}
// buffered bytes
func (r *Reader) buffered() int { return len(r.data) - r.n }
// Buffered returns the number of bytes currently in the buffer
func (r *Reader) Buffered() int { return len(r.data) - r.n }
// BufferSize returns the total size of the buffer
func (r *Reader) BufferSize() int { return cap(r.data) }
// Peek returns the next 'n' buffered bytes,
// reading from the underlying reader if necessary.
// It will only return a slice shorter than 'n' bytes
// if it also returns an error. Peek does not advance
// the reader. EOF errors are *not* returned as
// io.ErrUnexpectedEOF.
func (r *Reader) Peek(n int) ([]byte, error) {
// in the degenerate case,
// we may need to realloc
// (the caller asked for more
// bytes than the size of the buffer)
if cap(r.data) < n {
old := r.data[r.n:]
r.data = make([]byte, n+r.buffered())
r.data = r.data[:copy(r.data, old)]
r.n = 0
}
// keep filling until
// we hit an error or
// read enough bytes
for r.buffered() < n && r.state == nil {
r.more()
}
// we must have hit an error
if r.buffered() < n {
return r.data[r.n:], r.err()
}
return r.data[r.n : r.n+n], nil
}
// Skip moves the reader forward 'n' bytes.
// Returns the number of bytes skipped and any
// errors encountered. It is analagous to Seek(n, 1).
// If the underlying reader implements io.Seeker, then
// that method will be used to skip forward.
//
// If the reader encounters
// an EOF before skipping 'n' bytes, it
// returns io.ErrUnexpectedEOF. If the
// underlying reader implements io.Seeker, then
// those rules apply instead. (Many implementations
// will not return `io.EOF` until the next call
// to Read.)
func (r *Reader) Skip(n int) (int, error) {
// fast path
if r.buffered() >= n {
r.n += n
return n, nil
}
// use seeker implementation
// if we can
if r.rs != nil {
return r.skipSeek(n)
}
// loop on filling
// and then erasing
o := n
for r.buffered() < n && r.state == nil {
r.more()
// we can skip forward
// up to r.buffered() bytes
step := min(r.buffered(), n)
r.n += step
n -= step
}
// at this point, n should be
// 0 if everything went smoothly
return o - n, r.noEOF()
}
// Next returns the next 'n' bytes in the stream.
// Unlike Peek, Next advances the reader position.
// The returned bytes point to the same
// data as the buffer, so the slice is
// only valid until the next reader method call.
// An EOF is considered an unexpected error.
// If an the returned slice is less than the
// length asked for, an error will be returned,
// and the reader position will not be incremented.
func (r *Reader) Next(n int) ([]byte, error) {
// in case the buffer is too small
if cap(r.data) < n {
old := r.data[r.n:]
r.data = make([]byte, n+r.buffered())
r.data = r.data[:copy(r.data, old)]
r.n = 0
}
// fill at least 'n' bytes
for r.buffered() < n && r.state == nil {
r.more()
}
if r.buffered() < n {
return r.data[r.n:], r.noEOF()
}
out := r.data[r.n : r.n+n]
r.n += n
return out, nil
}
// skipSeek uses the io.Seeker to seek forward.
// only call this function when n > r.buffered()
func (r *Reader) skipSeek(n int) (int, error) {
o := r.buffered()
// first, clear buffer
n -= o
r.n = 0
r.data = r.data[:0]
// then seek forward remaning bytes
i, err := r.rs.Seek(int64(n), 1)
return int(i) + o, err
}
// Read implements `io.Reader`
func (r *Reader) Read(b []byte) (int, error) {
if len(b) <= r.buffered() {
x := copy(b, r.data[r.n:])
r.n += x
return x, nil
}
r.more()
if r.buffered() > 0 {
x := copy(b, r.data[r.n:])
r.n += x
return x, nil
}
// io.Reader is supposed to return
// 0 read bytes on error
return 0, r.err()
}
// ReadFull attempts to read len(b) bytes into
// 'b'. It returns the number of bytes read into
// 'b', and an error if it does not return len(b).
// EOF is considered an unexpected error.
func (r *Reader) ReadFull(b []byte) (int, error) {
var x int
l := len(b)
for x < l {
if r.buffered() == 0 {
r.more()
}
c := copy(b[x:], r.data[r.n:])
x += c
r.n += c
if r.state != nil {
return x, r.noEOF()
}
}
return x, nil
}
// ReadByte implements `io.ByteReader`
func (r *Reader) ReadByte() (byte, error) {
for r.buffered() < 1 && r.state == nil {
r.more()
}
if r.buffered() < 1 {
return 0, r.err()
}
b := r.data[r.n]
r.n++
return b, nil
}
// WriteTo implements `io.WriterTo`
func (r *Reader) WriteTo(w io.Writer) (int64, error) {
var (
i int64
ii int
err error
)
// first, clear buffer
if r.buffered() > 0 {
ii, err = w.Write(r.data[r.n:])
i += int64(ii)
if err != nil {
return i, err
}
r.data = r.data[0:0]
r.n = 0
}
for r.state == nil {
// here we just do
// 1:1 reads and writes
r.more()
if r.buffered() > 0 {
ii, err = w.Write(r.data)
i += int64(ii)
if err != nil {
return i, err
}
r.data = r.data[0:0]
r.n = 0
}
}
if r.state != io.EOF {
return i, r.err()
}
return i, nil
}
func min(a int, b int) int {
if a < b {
return a
}
return b
}
func max(a int, b int) int {
if a < b {
return b
}
return a
}
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