Io.Copy
io.Copy is a Go standard-library function that copies bytes from an io.Reader to an io.Writer until input is exhausted or an error occurs.
Go by Example
io.Copy is a Go standard-library function that copies bytes from an io.Reader to an io.Writer and returns the number of bytes copied and any error.
- How it is used
- Counts or transfers streaming data while avoiding full-content buffering, especially when processing HTTP response bodies.
- How deep it goes
- Explains the Reader-to-Writer contract, 32 KB buffering, return values, EOF handling, and CopyBuffer trade-offs.
- Examples
- Uses discarded HTTP downloads, a complete Send helper, configurable buffers, and exercises with custom Reader and Writer implementations.
- What you can do after
- Apply io.Copy to stream HTTP bodies and other I/O sources while measuring transferred bytes and controlling memory use.
Go in Action, Second Edition
io.Copy transfers data from a Reader to a Writer until the input reaches end of file or an error occurs.
- How it is used
- Transfers streams between interchangeable readers and writers for file-copying and data-pipeline operations.
- How deep it goes
- Defines efficient Reader-to-Writer transfer and its EOF-or-error boundary, but defers implementation internals.
- Examples
- Uses file copying, streaming between sources and sinks, and partial-stream copying as practical cases.
- What you can do after
- Apply it via io.Copy to move data between any compatible Reader and Writer.
Related concepts
- io.Readeruses · io.Reader is a Go standard-library interface whose Read method reads bytes into a supplied buffer and reports the number read and any error.
- io.Writeruses · io.Writer is a Go interface whose Write method accepts a byte sequence and returns the number of bytes written and any error.
- bufferinguses · Buffering is the temporary storage of data or work between production and consumption to accommodate differences in processing rates, absorb interruptions, or improve transfer efficiency.
- payloaduses · A payload is the data, code, or other material carried by or attached to a message, token, system, or operation.
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