Lesson 31 · Parse query parameters

Parse query parameters

The query string carries a handler's inputs as key=value pairs. Today you decode it into a lookup so a handler can read parameters like q and page.

The goal

Parse a raw query string into named parameters a handler can read.

Start here - the target

TO DO

Scenario: Decoding the query string

Giventhe raw query "q=cats&n=2"

Whenit is parsed

Thenthe parameter "q" is "cats" and "n" is "2"

Anda parameter that was not present, like "missing", reads as the empty string

Background

Back in the parsing chapter you split the raw query string off the target but left it as one opaque string. Handlers need it broken up: a query like q=cats&n=2 is a set of key=value pairs joined by &, and a search handler wants q and n individually.

Split on &, then split each pair on its first =. A pair with no = (flag) has an empty value; an absent key reads back empty, mirroring how Headers.Get behaves. Now a handler can offer real behavior — search, pagination, filtering — driven by the URL.

Make it work

params := map[string]string{}
for _, pair := range strings.Split(rawQuery, "&") {
    if pair == "" { continue }
    k, v, _ := strings.Cut(pair, "=") // "a=b" -> "a","b"; "a" -> "a",""
    params[k] = v
}

CheckpointDONE

The query string parses into named parameters a handler can read. Commit.