mirror of
https://github.com/go-gitea/gitea
synced 2024-12-23 17:14:27 +00:00
384 lines
9.2 KiB
Go
384 lines
9.2 KiB
Go
// 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 arbitrary 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 {
|
|
if r.n < len(r.data) {
|
|
r.data = r.data[:copy(r.data[0:], r.data[r.n:])]
|
|
} else {
|
|
r.data = r.data[:0]
|
|
}
|
|
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
|
|
} else if a > 0 && r.state == io.EOF {
|
|
// discard the io.EOF if we read more than 0 bytes.
|
|
// the next call to Read should return io.EOF again.
|
|
r.state = nil
|
|
}
|
|
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 analogous 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 we have data in the buffer, just
|
|
// return that.
|
|
if r.buffered() != 0 {
|
|
x := copy(b, r.data[r.n:])
|
|
r.n += x
|
|
return x, nil
|
|
}
|
|
var n int
|
|
// we have no buffered data; determine
|
|
// whether or not to buffer or call
|
|
// the underlying reader directly
|
|
if len(b) >= cap(r.data) {
|
|
n, r.state = r.r.Read(b)
|
|
} else {
|
|
r.more()
|
|
n = copy(b, r.data)
|
|
r.n = n
|
|
}
|
|
if n == 0 {
|
|
return 0, r.err()
|
|
}
|
|
return n, nil
|
|
}
|
|
|
|
// 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 n int // read into b
|
|
var nn int // scratch
|
|
l := len(b)
|
|
// either read buffered data,
|
|
// or read directly for the underlying
|
|
// buffer, or fetch more buffered data.
|
|
for n < l && r.state == nil {
|
|
if r.buffered() != 0 {
|
|
nn = copy(b[n:], r.data[r.n:])
|
|
n += nn
|
|
r.n += nn
|
|
} else if l-n > cap(r.data) {
|
|
nn, r.state = r.r.Read(b[n:])
|
|
n += nn
|
|
} else {
|
|
r.more()
|
|
}
|
|
}
|
|
if n < l {
|
|
return n, r.noEOF()
|
|
}
|
|
return n, 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
|
|
}
|