// Package ioutil contains various constructs for io operations.
package ioutil
import (
"io"
)
// An function alias type that implements io.Writer.
type WriterFunc func([]byte) (int, error)
// Delegates the call to the WriterFunc while implementing io.Writer.
func (w WriterFunc) Write(b []byte) (int, error) {
return w(b)
}
// An function alias type that implements io.Reader.
type ReaderFunc func([]byte) (int, error)
// Delegates the call to the WriterFunc while implementing io.Reader.
func (r ReaderFunc) Read(b []byte) (int, error) {
return r(b)
}
// Reads a single byte from the provided io.Reader
func ReadByte(reader io.Reader) (byte, error) {
var (
arr [1]byte
err error
)
_, err = reader.Read(arr[:])
return arr[0], err
}
// Returns a writer that delegates calls to Write(...) while ensuring
// that it is never called with less bytes than the specified amount.
//
// Calls with fewer bytes are buffered while a call with a nil slice
// causes the buffer to be flushed to the underlying writer.
func SizedWriter(writer io.Writer, size int) io.Writer {
var sw sizedWriter
sw.writer = writer
sw.buffer = make([]byte, 0, size)
sw.size = size
return &sw
}
type sizedWriter struct {
writer io.Writer
buffer []byte
size int
}
func (sw *sizedWriter) Write(input []byte) (int, error) {
var (
count int
err error
)
// Flush the buffer when called with no bytes to write
if input == nil {
// Call the writer with whatever we have in store..
count, err = sw.writer.Write(sw.buffer)
// Advance the buffer
sw.buffer = sw.buffer[:copy(sw.buffer, sw.buffer[count:])]
return 0, err
}
// Delegate to the writer if the size is right
if len(sw.buffer) == 0 && len(input) >= sw.size {
reduced := (len(input) / sw.size) * sw.size
count, err = sw.writer.Write(input[:reduced])
if count < reduced || err != nil {
return count, err
}
// Stage any remaining data in the buffer
sw.buffer = append(sw.buffer, input[count:]...)
return len(input), nil
}
// Append data to the buffer
count = copy(sw.buffer[len(sw.buffer):sw.size], input)
sw.buffer = sw.buffer[:len(sw.buffer)+count]
// Return if we don't have enough bytes to write
if len(sw.buffer) < sw.size {
return len(input), nil
}
// Flush the buffer as it is filled
_, err = sw.Write(nil)
if err != nil {
return count, err
}
// Handle the rest of the input
return sw.Write(input[count:])
}
// Returns a reader that delegates calls to Read(...) while ensuring
// that the output buffer is never smaller than the required size
// and is downsized to a multiple of the required size if larger.
func SizedReader(reader io.Reader, size int) io.Reader {
var sr sizedReader
sr.reader = reader
sr.buffer = make([]byte, size)
sr.size, sr.from, sr.to = size, 0, 0
return &sr
}
type sizedReader struct {
reader io.Reader
buffer []byte
from, to, size int
}
func (sr *sizedReader) Read(output []byte) (int, error) {
var (
count int
err error
)
start:
// Reply with the buffered data if there is any
if sr.to > 0 {
count = copy(output, sr.buffer[sr.from:sr.to])
// Advance the data in the buffer
sr.from += count
// Check whether we have reached the end of the buffer
if sr.from == sr.to {
// Reset the buffer
sr.from, sr.to = 0, 0
return count, err
}
// Do not propagate an error until the buffer is exhausted
return count, nil
}
// Delegate if the buffer is empty and the destination buffer is large enough
if len(output) >= sr.size {
return sr.reader.Read(output[:(len(output)/sr.size)*sr.size])
}
// Perform a read into the buffer
count, err = sr.reader.Read(sr.buffer)
// Size the buffer down to the read data size
// and restart if we have successfully read some bytes
sr.from, sr.to = 0, count
if sr.to > 0 {
goto start
}
// Returning on err/misbehaving noop reader
return 0, err
}