metadata: add Copy method, fix old methods

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

metadata/metadata.go

@@ -9,7 +9,7 @@ import (
 
 var (
 	// HeaderTopic is the header name that contains topic name
-	HeaderTopic = "Micro-Topic"
+	//	HeaderTopic = "Micro-Topic"
 	// HeaderContentType specifies content type of message
 	HeaderContentType = "Content-Type"
 	// HeaderEndpoint specifies endpoint in service
@@ -68,15 +68,7 @@ func (md Metadata) Iterator() *Iterator {
 }
 
 func (md Metadata) MustGet(key string) string {
-	// fast path
-	val, ok := md[key]
-	if !ok {
-		// slow path
-		val, ok = md[textproto.CanonicalMIMEHeaderKey(key)]
-		if !ok {
-			val, ok = md[strings.ToLower(key)]
-		}
-	}
+	val, ok := md.Get(key)
 	if !ok {
 		panic("missing metadata key")
 	}
@@ -119,11 +111,18 @@ func (md Metadata) Del(keys ...string) {
 	}
 }
 
+// Copy makes a copy of the metadata
+func (md Metadata) CopyTo(dst Metadata) {
+	for k, v := range md {
+		dst[k] = v
+	}
+}
+
 // Copy makes a copy of the metadata
 func Copy(md Metadata, exclude ...string) Metadata {
 	nmd := New(len(md))
-	for key, val := range md {
-		nmd.Set(key, val)
+	for k, v := range md {
+		nmd[k] = v
 	}
 	nmd.Del(exclude...)
 	return nmd
@@ -147,7 +146,7 @@ func Merge(omd Metadata, mmd Metadata, overwrite bool) Metadata {
 		case ok && !overwrite:
 			continue
 		case val != "":
-			nmd.Set(key, val)
+			nmd[key] = val
 		case ok && val == "":
 			nmd.Del(key)
 		}
@@ -161,6 +160,8 @@ func Pairs(kv ...string) (Metadata, bool) {
 		return nil, false
 	}
 	md := New(len(kv) / 2)
-	md.Set(kv...)
+	for idx := 0; idx < len(kv); idx += 2 {
+		md[kv[idx]] = kv[idx+1]
+	}
 	return md, true
 }

semconv/metadata.go

@@ -0,0 +1,18 @@
+package semconv
+
+var (
+	// HeaderTopic is the header name that contains topic name
+	HeaderTopic = "Micro-Topic"
+	// HeaderContentType specifies content type of message
+	HeaderContentType = "Content-Type"
+	// HeaderEndpoint specifies endpoint in service
+	HeaderEndpoint = "Micro-Endpoint"
+	// HeaderService specifies service
+	HeaderService = "Micro-Service"
+	// HeaderTimeout specifies timeout of operation
+	HeaderTimeout = "Micro-Timeout"
+	// HeaderAuthorization specifies Authorization header
+	HeaderAuthorization = "Authorization"
+	// HeaderXRequestID specifies request id
+	HeaderXRequestID = "X-Request-Id"
+)