Function buildQueryString

modules/caddyhttp/rewrite/rewrite.go:336–396

buildQueryString takes an input query string and performs replacements on each component, returning the resulting query string. This function appends duplicate keys rather than replaces.

(qs string, repl *caddy.Replacer)

// the resulting query string. This function appends
// duplicate keys rather than replaces.
func buildQueryString(qs string, repl *caddy.Replacer) string {
	var sb strings.Builder

	// first component must be key, which is the same
	// as if we just wrote a value in previous iteration
	wroteVal := true

	for len(qs) > 0 {
		// determine the end of this component, which will be at
		// the next equal sign or ampersand, whichever comes first
		nextEq, nextAmp := strings.Index(qs, "="), strings.Index(qs, "&")
		ampIsNext := nextAmp >= 0 && (nextAmp < nextEq || nextEq < 0)
		end := len(qs) // assume no delimiter remains...
		if ampIsNext {
			end = nextAmp // ...unless ampersand is first...
		} else if nextEq >= 0 && (nextEq < nextAmp || nextAmp < 0) {
			end = nextEq // ...or unless equal is first.
		}

		// consume the component and write the result
		comp := qs[:end]
		comp, _ = repl.ReplaceFunc(comp, func(name string, val any) (any, error) {
			if name == "http.request.uri.query" && wroteVal {
				return val, nil // already escaped
			}
			var valStr string
			switch v := val.(type) {
			case string:
				valStr = v
			case fmt.Stringer:
				valStr = v.String()
			case int:
				valStr = strconv.Itoa(v)
			default:
				valStr = fmt.Sprintf("%+v", v)
			}
			return url.QueryEscape(valStr), nil
		})
		if end < len(qs) {
			end++ // consume delimiter
		}
		qs = qs[end:]

		// if previous iteration wrote a value,
		// that means we are writing a key
		if wroteVal {
			if sb.Len() > 0 && len(comp) > 0 {
				sb.WriteRune('&')
			}
		} else {
			sb.WriteRune('=')
		}
		sb.WriteString(comp)

		// remember for the next iteration that we just wrote a value,
		// which means the next iteration MUST write a key
		wroteVal = ampIsNext
	}