io.Reader is a Go interface for streaming incoming data. Its Read method fills a byte slice supplied by the caller and reports how many bytes it read and any error. section 5.2.3
type Reader interface {
Read(p []byte) (n int, err error)
}
The interface has one method: callers provide the destination buffer, while the Reader reports the transferred byte count and error. section 5.2.3
This caller-managed design avoids allocating a new slice for every read. Reusing a preallocated buffer limits memory use, especially when processing large or size-limited streams. section 5.2.3
Streaming an HTTP response
An HTTP response body is a Reader, so its bytes can be processed incrementally. Reading it with io.ReadAll stores the complete body in memory and may allocate repeatedly; streaming is preferable when only the downloaded size matters. section 7.3.3
Practice the interface by:
- Satisfying Reader with a type that reads from a []byte. section 7.7
- Passing that Reader to Copy alongside a Writer that counts bytes. section 7.7
