log: 'except' subdirective to skip logging certain requests (#2028)

* proof of concept

* Initial implementation with debug code

* Tidy up debug code

* remove unneeded import

* removed extra line

* Move ShouldLog function to rule entry Logger type

* add tests for ShouldLog

* Added tests for log exceptions

* Fix logic

* fix govet fail for test

* Updates requested for code clarity

* Update requested for style

* log: Minor style tweaks to logic of log exceptions

caddyhttp/httpserver/logger.go

@@ -44,6 +44,7 @@ type Logger struct {
 	V4ipMask     net.IPMask
 	V6ipMask     net.IPMask
 	IPMaskExists bool
+	Exceptions   []string
 }
 
 // NewTestLogger creates logger suitable for testing purposes
@@ -84,6 +85,17 @@ func (l Logger) MaskIP(ip string) string {
 
 }
 
+// ShouldLog returns true if the path is not exempted from
+// being logged (i.e. it is not found in l.Exceptions).
+func (l Logger) ShouldLog(path string) bool {
+	for _, exc := range l.Exceptions {
+		if Path(path).Matches(exc) {
+			return false
+		}
+	}
+	return true
+}
+
 // Attach binds logger Start and Close functions to
 // controller's OnStartup and OnShutdown hooks.
 func (l *Logger) Attach(controller *caddy.Controller) {