bufioNewReader

bufio.NewReader is a constructor in the Go standard library that returns a new buffered reader wrapping an underlying io.Reader. Its primary purpose is to improve efficiency by buffering input reads, reducing the number of calls to the underlying source such as a file or network connection.

The canonical form is func NewReader(rd io.Reader) *Reader, which creates a Reader with a default internal buffer size of 4096 bytes. For cases where a different buffer size is desired, the package provides func NewReaderSize(rd io.Reader, size int) *Reader. The resulting object is a *bufio.Reader that exposes methods for reading data from the buffered source.

A bufio.Reader fills its internal buffer from the underlying reader as needed. Read copies data from the buffer into the caller’s slice and, if necessary, reads more data from the underlying reader to refill the buffer. The reader also offers higher-level operations such as ReadBytes(delim byte) and ReadString(delim byte), which read until a specified delimiter, and ReadRune or ReadByte for single units. Peek allows inspecting upcoming bytes without advancing the reader, and Buffered reports how many bytes are currently stored in the internal buffer. The Reset method can reassign the reader to a new underlying io.Reader.

Notable limitations include that a bufio.Reader is not safe for concurrent use by multiple goroutines; external synchronization is required if sharing a single reader across goroutines. bufio.NewReader is commonly used to efficiently parse tokens, lines, or records from files, networks, or other streams, especially when small reads are common or when there is a need to minimize system calls.