mreo ui

internal/httpattr/httpattr.go

@@ -0,0 +1,136 @@
+// Package httpattr collapses the many attribute spellings used for "which
+// HTTP endpoint was this" (OTel stable semconv, legacy semconv, nginx, Go
+// net/http, browser RUM) into one Endpoint, so spans from different
+// instrumentations can be compared and joined.
+package httpattr
+
+import (
+	"net/url"
+	"strings"
+)
+
+// Endpoint is the normalized identity of one HTTP request.
+type Endpoint struct {
+	Method string // upper-case, e.g. "GET"
+	Host   string // host without port, lower-case; "" if unknown
+	Path   string // concrete path, no query/fragment, no trailing slash
+	Route  string // instrumentation-provided template ("/orders/:id"), may be ""
+}
+
+// Key is the join key between a client-side (RUM) request and a server-side
+// span: method plus the concrete path. Route is deliberately not part of it -
+// a browser only knows the concrete URL.
+func (e Endpoint) Key() string {
+	if e.Path == "" {
+		return ""
+	}
+	return e.Method + " " + e.Path
+}
+
+// Lookup returns the first non-empty value among keys.
+type Lookup func(keys ...string) string
+
+// Extract reads an Endpoint out of span/log attributes.
+//
+// Sources, in order of preference:
+//
+//	method: http.request.method, http.method
+//	path:   url.path, http.target (path+query), url.full, http.url
+//	host:   server.address, http.host, net.host.name, url.full/http.url host
+//	route:  http.route
+//
+// nginx's OTel module emits the stable keys; older nginx/Go/Java agents emit
+// http.target/http.url; browsers only know url.full (absolute or relative).
+func Extract(get Lookup) Endpoint {
+	e := Endpoint{
+		Method: strings.ToUpper(get("http.request.method", "http.method")),
+		Route:  get("http.route"),
+	}
+	e.Host = stripPort(strings.ToLower(get("server.address", "http.host", "net.host.name", "server.host")))
+	if p := get("url.path"); p != "" {
+		e.Path = CleanPath(p)
+	} else if t := get("http.target"); t != "" {
+		e.Path = CleanPath(t)
+	}
+	if full := get("url.full", "http.url"); full != "" {
+		host, path := SplitURL(full)
+		if e.Path == "" {
+			e.Path = path
+		}
+		if e.Host == "" {
+			e.Host = host
+		}
+	}
+	// Some instrumentations report the router mount ("/") as the route.
+	if e.Route == "/" && e.Path != "" && e.Path != "/" {
+		e.Route = ""
+	}
+	return e
+}
+
+// SplitURL splits an absolute or relative URL into (host without port, clean path).
+func SplitURL(raw string) (host, path string) {
+	u, err := url.Parse(raw)
+	if err != nil {
+		return "", CleanPath(raw)
+	}
+	return stripPort(strings.ToLower(u.Host)), CleanPath(u.Path)
+}
+
+// CleanPath drops query/fragment and a trailing slash, and guarantees a
+// leading slash. "" stays "".
+func CleanPath(p string) string {
+	if i := strings.IndexAny(p, "?#"); i >= 0 {
+		p = p[:i]
+	}
+	p = strings.TrimSpace(p)
+	if p == "" {
+		return ""
+	}
+	if !strings.HasPrefix(p, "/") {
+		p = "/" + p
+	}
+	if len(p) > 1 {
+		p = strings.TrimRight(p, "/")
+		if p == "" {
+			p = "/"
+		}
+	}
+	return p
+}
+
+// StripPrefix removes a reverse-proxy mount prefix (e.g. nginx
+// `location /api/ { proxy_pass http://backend/; }` makes the browser see
+// /api/orders while the backend sees /orders). The longest matching prefix wins.
+func StripPrefix(path string, prefixes []string) string {
+	best := ""
+	for _, p := range prefixes {
+		p = CleanPath(p)
+		if p == "" || p == "/" {
+			continue
+		}
+		if (path == p || strings.HasPrefix(path, p+"/")) && len(p) > len(best) {
+			best = p
+		}
+	}
+	if best == "" {
+		return path
+	}
+	if rest := path[len(best):]; rest != "" {
+		return rest
+	}
+	return "/"
+}
+
+func stripPort(host string) string {
+	if strings.HasPrefix(host, "[") { // IPv6 literal
+		if i := strings.Index(host, "]"); i > 0 {
+			return host[:i+1]
+		}
+		return host
+	}
+	if i := strings.LastIndexByte(host, ':'); i >= 0 {
+		return host[:i]
+	}
+	return host
+}

internal/httpattr/httpattr_test.go

@@ -0,0 +1,49 @@
+package httpattr
+
+import "testing"
+
+func lookup(m map[string]string) Lookup {
+	return func(keys ...string) string {
+		for _, k := range keys {
+			if v := m[k]; v != "" {
+				return v
+			}
+		}
+		return ""
+	}
+}
+
+func TestExtractVariants(t *testing.T) {
+	cases := []struct {
+		name  string
+		attrs map[string]string
+		want  string
+	}{
+		{"stable semconv", map[string]string{"http.request.method": "get", "url.path": "/api/orders/"}, "GET /api/orders"},
+		{"legacy nginx target", map[string]string{"http.method": "GET", "http.target": "/api/orders?x=1"}, "GET /api/orders"},
+		{"go http.url", map[string]string{"http.method": "POST", "http.url": "https://shop.example.com:8443/api/cart?a=b"}, "POST /api/cart"},
+		{"browser url.full", map[string]string{"http.request.method": "GET", "url.full": "https://shop.example.com/api/orders#x"}, "GET /api/orders"},
+		{"relative url.full", map[string]string{"http.request.method": "GET", "url.full": "api/orders"}, "GET /api/orders"},
+	}
+	for _, c := range cases {
+		if got := Extract(lookup(c.attrs)).Key(); got != c.want {
+			t.Errorf("%s: got %q want %q", c.name, got, c.want)
+		}
+	}
+}
+
+func TestExtractHostAndMountRoute(t *testing.T) {
+	e := Extract(lookup(map[string]string{"http.route": "/", "url.path": "/x", "server.address": "API.example.com:443"}))
+	if e.Host != "api.example.com" || e.Route != "" {
+		t.Fatalf("got %+v", e)
+	}
+}
+
+func TestStripPrefix(t *testing.T) {
+	p := []string{"/api", "/api/v2"}
+	for in, want := range map[string]string{"/api/orders": "/orders", "/api/v2/orders": "/orders", "/api": "/", "/apix": "/apix", "/other": "/other"} {
+		if got := StripPrefix(in, p); got != want {
+			t.Errorf("%s: got %q want %q", in, got, want)
+		}
+	}
+}