Lesson 38 · Parse Set-Cookie - Build an HTTP Client

Parse Set-Cookie

Servers hand out cookies with the Set-Cookie header, a name-value pair plus attributes. Today you parse one into its parts, the first step toward a cookie jar.

The goal

Parse a Set-Cookie value into the cookie name, value, and its attributes.

Start here - the target

TO DO

Scenario: Parsing a Set-Cookie header

Giventhe Set-Cookie value "sid=abc123; Path=/; Domain=example.com"

Whenit is parsed

Thenthe cookie name is "sid", the value is "abc123", the Path attribute is "/" and the Domain attribute is "example.com"

Andthe first "key=value" pair is the cookie itself; the remaining semicolon-separated parts are attributes

Background

A cookie is how a server keeps state across requests: it sends Set-Cookie with a name=value pair, and the client is expected to send that pair back on later requests. The header carries attributes too - Path, Domain, Expires, HttpOnly - separated by semicolons. The structure is regular: the first semicolon-separated part is the cookie’s name=value, and each part after it is an attribute (a key=value, or a bare flag).

So sid=abc123; Path=/; Domain=example.com parses to a cookie named sid with value abc123, plus Path and Domain attributes. Today just parse the structure; the attributes are captured but the jar you build next stores cookies by name and value. Full attribute semantics - path and domain matching, expiry - are a place this teaching client deliberately keeps simple.

Make it work

// split the value on ";". the FIRST part is "name=value" (the
// cookie). each remaining part is an attribute, itself "key=value"
// (or a bare flag like "HttpOnly"). trim spaces around each part.
type Cookie struct { Name, Value string; Attrs map[string]string }
func parseSetCookie(v string) Cookie { /* first pair + attributes */ }

CheckpointDONE

You can parse a Set-Cookie header into a cookie with its attributes. Commit and stop here.