caddyhttp: Add uuid to access logs when used (#5859)

caddyconfig/httpcaddyfile/shorthands.go

@@ -64,6 +64,7 @@ func placeholderShorthands() []string {
 		"{remote_port}", "{http.request.remote.port}",
 		"{scheme}", "{http.request.scheme}",
 		"{uri}", "{http.request.uri}",
+		"{uuid}", "{http.request.uuid}",
 		"{tls_cipher}", "{http.request.tls.cipher_suite}",
 		"{tls_version}", "{http.request.tls.version}",
 		"{tls_client_fingerprint}", "{http.request.tls.client.fingerprint}",

modules/caddyhttp/logging.go

@@ -151,6 +151,18 @@ func (e *ExtraLogFields) Add(field zap.Field) {
 	e.fields = append(e.fields, field)
 }
 
+// Set sets a field in the list of extra fields to log.
+// If the field already exists, it is replaced.
+func (e *ExtraLogFields) Set(field zap.Field) {
+	for i := range e.fields {
+		if e.fields[i].Key == field.Key {
+			e.fields[i] = field
+			return
+		}
+	}
+	e.fields = append(e.fields, field)
+}
+
 const (
 	// Variable name used to indicate that this request
 	// should be omitted from the access logs

modules/caddyhttp/replacer.go

@@ -40,6 +40,7 @@ import (
 	"time"
 
 	"github.com/google/uuid"
+	"go.uber.org/zap"
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/modules/caddytls"
@@ -157,9 +158,17 @@ func addHTTPVarsToReplacer(repl *caddy.Replacer, req *http.Request, w http.Respo
 			case "http.request.duration_ms":
 				start := GetVar(req.Context(), "start_time").(time.Time)
 				return time.Since(start).Seconds() * 1e3, true // multiply seconds to preserve decimal (see #4666)
+
 			case "http.request.uuid":
+				// fetch the UUID for this request
 				id := GetVar(req.Context(), "uuid").(*requestID)
+
+				// set it to this request's access log
+				extra := req.Context().Value(ExtraLogFieldsCtxKey).(*ExtraLogFields)
+				extra.Set(zap.String("uuid", id.String()))
+
 				return id.String(), true
+
 			case "http.request.body":
 				if req.Body == nil {
 					return "", true