caddyhttp: General improvements to access logging (#3301)

* httpcaddyfile: Exclude access logs written to files from default log

Even though any logs can just be ignored, most users don't seem to like
configuring an access log to go to a file only to have it doubly appear
in the default log.

Related to:
- #3294
- https://caddy.community/t/v2-logging-format/7642/4?u=matt
- https://caddy.community/t/caddyfile-questions/7651/3?u=matt

* caddyhttp: General improvements to access log controls (fixes #3310)

* caddyhttp: Move log config nil check higher

* Rename LoggerName -> DefaultLoggerName

modules/caddyhttp/server.go

@@ -101,9 +101,9 @@ type Server struct {
 	// client authentication.
 	StrictSNIHost *bool `json:"strict_sni_host,omitempty"`
 
-	// Customizes how access logs are handled in this server. To
-	// minimally enable access logs, simply set this to a non-null,
-	// empty struct.
+	// Enables access logging and configures how access logs are handled
+	// in this server. To minimally enable access logs, simply set this
+	// to a non-null, empty struct.
 	Logs *ServerLogConfig `json:"logs,omitempty"`
 
 	// Enable experimental HTTP/3 support. Note that HTTP/3 is not a
@@ -157,7 +157,7 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		loggableReq,
 	)
 
-	if s.accessLogger != nil {
+	if s.shouldLogRequest(r) {
 		wrec := NewResponseRecorder(w, nil, nil)
 		w = wrec
 
@@ -390,17 +390,52 @@ func (*HTTPErrorConfig) WithError(r *http.Request, err error) *http.Request {
 	return r
 }
 
-// ServerLogConfig describes a server's logging configuration.
+// shouldLogRequest returns true if this request should be logged.
+func (s *Server) shouldLogRequest(r *http.Request) bool {
+	if s.accessLogger == nil || s.Logs == nil {
+		// logging is disabled
+		return false
+	}
+	for _, dh := range s.Logs.SkipHosts {
+		// logging for this particular host is disabled
+		if r.Host == dh {
+			return false
+		}
+	}
+	if _, ok := s.Logs.LoggerNames[r.Host]; ok {
+		// this host is mapped to a particular logger name
+		return true
+	}
+	if s.Logs.SkipUnmappedHosts {
+		// this host is not mapped and thus must not be logged
+		return false
+	}
+	return true
+}
+
+// ServerLogConfig describes a server's logging configuration. If
+// enabled without customization, all requests to this server are
+// logged to the default logger; logger destinations may be
+// customized per-request-host.
 type ServerLogConfig struct {
-	// The logger name for all logs emitted by this server unless
-	// the hostname is found in the LoggerNames (logger_names) map.
-	LoggerName string `json:"log_name,omitempty"`
+	// The default logger name for all logs emitted by this server for
+	// hostnames that are not in the LoggerNames (logger_names) map.
+	DefaultLoggerName string `json:"default_logger_name,omitempty"`
 
 	// LoggerNames maps request hostnames to a custom logger name.
 	// For example, a mapping of "example.com" to "example" would
 	// cause access logs from requests with a Host of example.com
 	// to be emitted by a logger named "http.log.access.example".
 	LoggerNames map[string]string `json:"logger_names,omitempty"`
+
+	// By default, all requests to this server will be logged if
+	// access logging is enabled. This field lists the request
+	// hosts for which access logging should be disabled.
+	SkipHosts []string `json:"skip_hosts,omitempty"`
+
+	// If true, requests to any host not appearing in the
+	// LoggerNames (logger_names) map will not be logged.
+	SkipUnmappedHosts bool `json:"skip_unmapped_hosts,omitempty"`
 }
 
 // wrapLogger wraps logger in a logger named according to user preferences for the given host.
@@ -415,7 +450,7 @@ func (slc ServerLogConfig) getLoggerName(host string) string {
 	if loggerName, ok := slc.LoggerNames[host]; ok {
 		return loggerName
 	}
-	return slc.LoggerName
+	return slc.DefaultLoggerName
 }
 
 // errLogValues inspects err and returns the status code