Settings code: one file per daemon (closes #227)

internal/config now keeps waf's settings in waf.go and rproxy's in
rproxy.go. config.go keeps what both read: the package doc,
SWW_COMMAND, the environment reader, listen addresses, sizes and
netblock lists. The app URL reader and the default trusted proxies,
which only rproxy uses, move to rproxy.go. config_test.go becomes
waf_test.go, beside rproxy_test.go. Code is moved, not changed.

Model: opus-5-5

internal/config/rproxy.go

@@ -48,7 +48,17 @@ type RProxy struct {
 	settings []slog.Attr
 }
 
+// defaultUpstreamURL is the default of SWRP_UPSTREAM_URL.
+const defaultUpstreamURL = "http://127.0.0.1:8081"
+
+// privateRanges are the private address ranges, the default trusted
+// proxies.
+const privateRanges = "10.0.0.0/8,172.16.0.0/12,192.168.0.0/16"
+
 var (
+	errNotUpstreamURL = errors.New(
+		"is not a URL with only a scheme, a host and an optional port, " +
+			"such as http://127.0.0.1:8081")
 	errNeedsWAFBackend = errors.New(
 		"is required: it is waf's URL, such as http://waf:8080")
 	errNotDisposition  = errors.New("is not allow or deny")
@@ -124,6 +134,14 @@ func (c *RProxy) LogValue() slog.Value {
 	return slog.GroupValue(c.settings...)
 }
 
+// appURL reads a setting that is the app's URL.
+func (e *environment) appURL(name, defaultValue string) *url.URL {
+	upstream, err := parseUpstreamURL(e.value(name, defaultValue))
+	e.check(name, err)
+
+	return upstream
+}
+
 // wafBackend reads the setting that is waf's URL, which must be set.
 func (e *environment) wafBackend(name string) *url.URL {
 	value := e.value(name, "")
@@ -190,3 +208,32 @@ func parseMilliseconds(value string) (time.Duration, bool) {
 
 	return time.Duration(n) * time.Millisecond, true
 }
+
+// parseUpstreamURL reads the app's URL: http or https, a host and an
+// optional port from 1 to 65535, and nothing else, since the request's
+// own path and query go to the app unchanged.
+func parseUpstreamURL(value string) (*url.URL, error) {
+	upstream, err := url.Parse(value)
+	if err != nil {
+		return nil, fmt.Errorf("%q %w", value, errNotUpstreamURL)
+	}
+
+	onlySchemeAndHost := (upstream.Scheme == "http" || upstream.Scheme == "https") &&
+		upstream.Hostname() != "" && upstream.User == nil &&
+		upstream.Opaque == "" &&
+		(upstream.Path == "" || upstream.Path == "/") &&
+		upstream.RawQuery == "" &&
+		upstream.Fragment == ""
+	if !onlySchemeAndHost {
+		return nil, fmt.Errorf("%q %w", value, errNotUpstreamURL)
+	}
+
+	if upstream.Port() != "" {
+		port, err := strconv.ParseUint(upstream.Port(), 10, 16)
+		if err != nil || port == 0 {
+			return nil, fmt.Errorf("%q %w", value, errNotUpstreamURL)
+		}
+	}
+
+	return upstream, nil
+}