// 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 will delegate calls to Read(...) while ensuring // that the output buffer will never be smaller than the required size func MinReader(reader io.Reader, size int) io.Reader { var buffer []byte = make([]byte, 0, size) return ReaderFunc(func(output []byte) (readCount int, e error) { var ( bufferLength int = len(buffer) err error ) start: // Reply with the buffered data if there is any if bufferLength > 0 { readCount = copy(output, buffer) if readCount < bufferLength { // Advance the data in the buffer buffer = buffer[:copy(buffer, buffer[:readCount])] } else { // Clear the buffer buffer = buffer[:0] } // Stage any error for returning e, err = err, nil return readCount, e } // Delegate if the buffer is empty and the destination buffer is large enough if len(output) >= size { return reader.Read(output) } // Extend the buffer up to the desired size and perform a Read buffer = buffer[:size] readCount, err = reader.Read(buffer) // Size the buffer down to the read data size and restart buffer = buffer[:readCount] bufferLength = len(buffer) goto start }) }