// 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 // and will be downsized to a multiple of the required size if larger func BlockReader(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 }) }