Encapsulate the Tag type, and have it implement the Stringer interface.

pkg/log/log.go

@@ -171,7 +171,7 @@ const (
 // above.
 type RecordType uint8
 
-func tags() []string {
+func initTags() []string {
 	var tags []string
 	if uint8(C.slt_max()) > ^uint8(0) {
 		panic("SLT__MAX > max uint8")
@@ -188,18 +188,28 @@ func tags() []string {
 }
 
 var (
-	// Tags is an array of strings indexed by the Tag field of a
-	// Record, classifying the Record's contents, as in the second
-	// column of default varnishlog output. Examples are "ReqURL"
-	// for a client request URL and "BerespStatus" for the HTTP
-	// status of a backend response.
-	//
-	// If Tags[i] == "", then no tag exists for index i.
-	Tags     = tags()
+	tags     = initTags()
 	nonprint = regexp.MustCompile("[^[:print:]]")
 	cbMap    = make(map[int]ReadCB)
 )
 
+// A Tag is a classifier for the contents of a Record's payload,
+// corresponding to the second column of default varnishlog
+// output. For a Tag t, t.String() may be "ReqURL" for a client
+// request URL, "BerespStatus" for the HTTP status of a backend
+// response, and so forth.
+type Tag uint8
+
+// String returns the Tag name that appears in the second column of
+// default varnishlog output, such as "ReqHeader" for a client request
+// header, or "BerespHeader" for a backend response header.
+//
+// If t.String() == "", then no tag exists for Tag t. No such tag is
+// generated from log reads.
+func (tag Tag) String() string {
+	return tags[tag]
+}
+
 // A Record in the Varnish log, corresponding to a line of output from
 // the varnishlog utility. Instances of this type are contained in the
 // Tx objects returned by Read() operations, and form the bulk of log
@@ -213,12 +223,11 @@ type Record struct {
 	// backend log, or neither.
 	Type RecordType
 
-	// An index into the Tags array, classifying the contents of
-	// this record, as in the second column of default varnishlog
-	// output. For a Tag t, Tags[t] may be a string such as
-	// "ReqURL" for a client request URL, "BerespStatus" for the
-	// HTTP status of a backend response, and so forth.
-	Tag uint8
+	// A classifier for the contents of this Record's payload. Use
+	// Tag.String() to get tag names such as "ReqURL" or
+	// "BerespHeader" that appear in the second column of default
+	// varnishlog output.
+	Tag Tag
 
 	// The unique ID generated by Varnish for this log
 	// transaction.
@@ -383,14 +392,14 @@ func publish(trans unsafe.Pointer, priv unsafe.Pointer) C.int {
 				break
 			}
 			tag := C.tag(vtx.c)
-			if tag < 0 || int(tag) >= len(Tags) {
+			if tag < 0 || int(tag) >= len(tags) {
 				panic("tag index out of range")
 			}
-			if Tags[tag] == "" {
+			if tags[tag] == "" {
 				panic("unknown tag")
 			}
 			rec := new(Record)
-			rec.Tag = uint8(tag)
+			rec.Tag = Tag(tag)
 			rec.Payload = C.GoStringN(C.cdata(vtx.c), C.len(vtx.c))
 			if C.unsafe(tag) != 0 || C.binary(tag) != 0 {
 				nonprint.ReplaceAllStringFunc(rec.Payload,

pkg/log/log_test.go

@@ -221,8 +221,8 @@ func TestDefaultRead(t *testing.T) {
 					t.Errorf("rec vxid expected=%v got=%v",
 						expRec.vxid, rec.VXID)
 				}
-				if Tags[rec.Tag] != expRec.tag {
-					t.Errorf("rec tag expected=%v got=%v",
+				if rec.Tag.String() != expRec.tag {
+					t.Errorf("rec tag expected=%v got=%s",
 						expRec.tag, rec.Tag)
 				}
 				if rune(rec.Type) != expRec.rectype {