// 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)
}
// 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 buffer []byte = make([]byte, 0, size)
return ReaderFunc(func(output []byte) (int, error) {
var (
readCount int
err error
)
start:
// Reply with the buffered data if there is any
if len(buffer) > 0 {
readCount = copy(output, buffer)
// Advance the data in the buffer
buffer = buffer[:copy(buffer, buffer[readCount:])]
// Return count and error if we have read the whole buffer
if len(buffer) == 0 {
return readCount, err
}
// Do not propagate an error until the buffer is exhausted
return readCount, nil
}
// Delegate if the buffer is empty and the destination buffer is large enough
if len(output) >= size {
return reader.Read(output[:(len(output)/size)*size])
}
// Perform a read into the buffer
readCount, err = reader.Read(buffer[:size])
// Size the buffer down to the read data size
// and restart if we have successfully read some bytes
buffer = buffer[:readCount]
if len(buffer) > 0 {
goto start
}
// Returning on err/misbehaving noop reader
return 0, err
})
}