88 lines
1.7 KiB
Go
88 lines
1.7 KiB
Go
package buffer
|
|
|
|
import (
|
|
"errors"
|
|
"io"
|
|
)
|
|
|
|
var (
|
|
FullError = errors.New("Buffer is full")
|
|
)
|
|
|
|
// Reads as much data
|
|
func readInto(rd io.Reader, p []byte) (n int, err error) {
|
|
var nr int
|
|
for n < len(p) {
|
|
nr, err = rd.Read(p[n:])
|
|
n += nr
|
|
if err != nil {
|
|
return
|
|
}
|
|
}
|
|
return
|
|
}
|
|
|
|
// A circular buffer on top of a byte-array
|
|
// NOTE: It does not implement the Write() method, it implements ReadFrom()
|
|
// to avoid copies
|
|
type Circular struct {
|
|
buf []byte // the bytes
|
|
size int // == len(buf)
|
|
head int // index of the next byte to read
|
|
tail int // index of the last byte available to read
|
|
}
|
|
|
|
// Returns a new circular buffer of the given size
|
|
func NewCircular(size int) *Circular {
|
|
return &Circular{
|
|
buf: make([]byte, size+1),
|
|
size: size + 1,
|
|
}
|
|
}
|
|
|
|
// Copy data from the given reader into the buffer
|
|
// Any errors encountered while reading are returned EXCEPT io.EOF.
|
|
// If the reader fills the buffer, it returns buffer.FullError
|
|
func (c *Circular) ReadFrom(rd io.Reader) (n int, err error) {
|
|
// IF:
|
|
// [---H+++T--]
|
|
if c.tail >= c.head {
|
|
n, err = readInto(rd, c.buf[c.tail:])
|
|
c.tail = (c.tail + n) % c.size
|
|
if err == io.EOF {
|
|
return n, nil
|
|
} else if err != nil {
|
|
return
|
|
}
|
|
}
|
|
|
|
// NOW:
|
|
// [T---H++++] or [++T--H+++]
|
|
n2, err := readInto(rd, c.buf[c.tail:c.head])
|
|
n += n2
|
|
c.tail += n2
|
|
if err == nil {
|
|
err = FullError
|
|
} else if err == io.EOF {
|
|
err = nil
|
|
}
|
|
return
|
|
}
|
|
|
|
// Read data out of the buffer. This never fails but may
|
|
// return n==0 if there is no data to be read
|
|
func (c *Circular) Read(p []byte) (n int, err error) {
|
|
if c.head > c.tail {
|
|
n = copy(p, c.buf[c.head:])
|
|
c.head = (c.head + n) % c.size
|
|
if c.head != 0 {
|
|
return
|
|
}
|
|
}
|
|
|
|
n2 := copy(p[n:], c.buf[c.head:c.tail])
|
|
n += n2
|
|
c.head += n2
|
|
return
|
|
}
|