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util.go
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util.go
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package yamux
import (
"io"
"sync"
pool "github.com/libp2p/go-buffer-pool"
)
// asyncSendErr is used to try an async send of an error
func asyncSendErr(ch chan error, err error) {
if ch == nil {
return
}
select {
case ch <- err:
default:
}
}
// asyncNotify is used to signal a waiting goroutine
func asyncNotify(ch chan struct{}) {
select {
case ch <- struct{}{}:
default:
}
}
// min computes the minimum of a set of values
func min(values ...uint32) uint32 {
m := values[0]
for _, v := range values[1:] {
if v < m {
m = v
}
}
return m
}
// The segmented buffer looks like:
//
// | data | empty space |
// < window (10) >
// < len (5) > < cap (5) >
// < pending (4) >
//
// As data is read, the buffer gets updated like so:
//
// | data | empty space |
// < window (8) >
// < len (3) > < cap (5) >
// < pending (4) >
//
// It can then grow as follows (given a "max" of 10):
//
//
// | data | empty space |
// < window (10) >
// < len (3) > < cap (7) >
// < pending (4) >
//
// Data can then be written into the pending space, expanding len, and shrinking
// cap and pending:
//
// | data | empty space |
// < window (10) >
// < len (5) > < cap (5) >
// < pending (2)>
//
type segmentedBuffer struct {
cap uint32
pending uint32
len uint32
bm sync.Mutex
// read position in b[0].
// We must not reslice any of the buffers in b, as we need to put them back into the pool.
readPos int
b [][]byte
}
// NewSegmentedBuffer allocates a ring buffer.
func newSegmentedBuffer(initialCapacity uint32) segmentedBuffer {
return segmentedBuffer{cap: initialCapacity, b: make([][]byte, 0)}
}
// Len is the amount of data in the receive buffer.
func (s *segmentedBuffer) Len() int {
s.bm.Lock()
len := s.len
s.bm.Unlock()
return int(len)
}
// Cap is the remaining capacity in the receive buffer.
//
// Note: this is _not_ the same as go's 'cap' function. The total size of the
// buffer is len+cap.
func (s *segmentedBuffer) Cap() uint32 {
s.bm.Lock()
cap := s.cap
s.bm.Unlock()
return cap
}
// If the space to write into + current buffer size has grown to half of the window size,
// grow up to that max size, and indicate how much additional space was reserved.
func (s *segmentedBuffer) GrowTo(max uint32, force bool) (bool, uint32) {
s.bm.Lock()
defer s.bm.Unlock()
currentWindow := s.cap + s.len
if currentWindow >= max {
return force, 0
}
delta := max - currentWindow
if delta < (max/2) && !force {
return false, 0
}
s.cap += delta
return true, delta
}
func (s *segmentedBuffer) TryReserve(space uint32) bool {
s.bm.Lock()
defer s.bm.Unlock()
if s.cap < s.pending+space {
return false
}
s.pending += space
return true
}
func (s *segmentedBuffer) Read(b []byte) (int, error) {
s.bm.Lock()
defer s.bm.Unlock()
if len(s.b) == 0 {
return 0, io.EOF
}
data := s.b[0][s.readPos:]
n := copy(b, data)
if n == len(data) {
pool.Put(s.b[0])
s.b[0] = nil
s.b = s.b[1:]
s.readPos = 0
} else {
s.readPos += n
}
if n > 0 {
s.len -= uint32(n)
}
return n, nil
}
func (s *segmentedBuffer) Append(input io.Reader, length int) error {
dst := pool.Get(length)
n, err := io.ReadFull(input, dst)
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
s.bm.Lock()
defer s.bm.Unlock()
if n > 0 {
s.len += uint32(n)
s.cap -= uint32(n)
s.pending = s.pending - uint32(length)
s.b = append(s.b, dst[0:n])
}
return err
}