// 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 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 buffer []byte = make([]byte, 0, size)
var write WriterFunc
write = func(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 = writer.Write(buffer)
// Advance the buffer
buffer = buffer[:copy(buffer, buffer[count:])]
return 0, err
}
// Delegate to the writer if the size is right
if len(buffer) == 0 && len(input) >= size {
reduced := (len(input) / size) * size
count, err = writer.Write(input[:reduced])
if count < reduced || err != nil {
return count, err
}
// Stage any remaining data in the buffer
buffer = append(buffer, input[count:]...)
return len(input), nil
}
// Append data to the buffer
count = copy(buffer[len(buffer):size], input)
buffer = buffer[:len(buffer)+count]
// Return if we don't have enough bytes to write
if len(buffer) < size {
return len(input), nil
}
// Flush the buffer as it is filled
_, err = write(nil)
if err != nil {
return count, err
}
// Handle the rest of the input
return write(input[count:])
}
return write
}
// 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 (
count int
err error
)
start:
// Reply with the buffered data if there is any
if len(buffer) > 0 {
count = copy(output, buffer)
// Advance the data in the buffer
buffer = buffer[:copy(buffer, buffer[count:])]
// Return count and error if we have read the whole buffer
if len(buffer) == 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) >= size {
return reader.Read(output[:(len(output)/size)*size])
}
// Perform a read into the buffer
count, 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[:count]
if len(buffer) > 0 {
goto start
}
// Returning on err/misbehaving noop reader
return 0, err
})
}