Lesson 03 · Read a CRLF-terminated line

Read a CRLF-terminated line

HTTP is a line-based text protocol, and every line ends with a carriage-return plus line-feed. Today you read one such line off a connection, the primitive the whole parser is built from.

The goal

Read one CRLF-terminated line from a stream and return it with the trailing CRLF removed.

Start here - the target

TO DO

Scenario: Reading a single request line

Givena stream holding "GET / HTTP/1.1\r\nHost: example.com\r\n"

Whenyou read one line

Thenyou get "GET / HTTP/1.1" with no trailing "\r\n"

Andthe next read begins at "Host: example.com"

Background

HTTP framing is built on lines separated by \r\n (carriage return, then line feed — often written CRLF). The request line, every header, and the blank line that ends the header block are all CRLF-terminated. So the first tool you need is “read up to the next line feed, then strip the line ending.”

Wrap the connection in a buffered reader and keep using that same reader for the rest of the request. It remembers its position, so after you pull off one line the next read naturally continues with the following bytes — exactly what you need to read a request line and then its headers.

Make it work

r := bufio.NewReader(conn) // buffered so the next read continues where this left off
line, err := r.ReadString('\n') // includes the \n
line = strings.TrimRight(line, "\r\n") // drop the CR and LF

CheckpointDONE

You can pull one CRLF line off a stream, leaving the rest intact. Commit.