Io.Reader
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.
Go in Action, Second Edition
io.Reader is the Go interface for reading a stream of bytes into a supplied buffer.
- How it is used
- Decouples input processing from files, standard input, buffers, and other byte sources.
- How deep it goes
- Defines Read’s signature and partial-read behavior, then demonstrates interface compatibility without implementing a custom Reader.
- Examples
- Uses a file-backed word counter and source-independent input for a JSON/XML conversion CLI.
- What you can do after
- Apply it via os.Open and bufio.NewScanner to process a file without coupling scanning logic to the file type.
Go by Example
io.Reader is a Go interface whose Read method fills a caller-provided byte slice with incoming data and reports the amount read and any error.
- How it is used
- Streams response data incrementally while enabling reusable, testable APIs.
- How deep it goes
- Defines the single-method contract, explains caller-managed buffers, and contrasts streaming with io.ReadAll.
- Examples
- Uses HTTP response bodies, byte-slice readers, counting writers, and Copy exercises.
- What you can do after
- Apply it via io.Copy or incremental reads to process streams without retaining complete responses.
100 Go Mistakes and How to Avoid Them
io.Reader is a Go interface for reading bytes from a data source.
- How it is used
- Designs reusable functions that consume bytes from files, strings, buffers, or other implicitly compatible data sources.
- How deep it goes
- Defines the single Read contract, demonstrates generic use and testing, and connects the caller-provided slice to escape analysis.
- Examples
- Uses copySourceToDest with strings.Reader and bytes.Buffer, plus contrasting Read signatures for allocation behavior.
- What you can do after
- Build reusable and testable byte-consuming functions by accepting io.Reader instead of concrete filenames or file types.
Read how 100 Go Mistakes and How to Avoid Them explains io.Reader →
Related concepts
- os.Fileimplemented by · os.File is a Go standard-library type representing an open file or other operating-system file handle and providing associated file operations.
- contractkind of · An API contract is a specification of the operations, data, and behavioral expectations that govern interactions between software components.
- interfacekind of · A software interface is a contract or boundary that specifies the operations, properties, or capabilities through which types or components interact, without requiring a particular implementation.
- bufio.Readerimplemented by · bufio.Reader is a Go buffered reader that wraps an io.Reader and supports efficient incremental and look-ahead reading.
- io.Copyused by · 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.
These guides are generated from the text of Manning books by Manning's knowledge graph and link to the sections they draw on. The full books are available on liveBook and at manning.com.