metadata: add MustGet func

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

metadata/context.go

@@ -11,6 +11,34 @@ type (
 	mdKey         struct{}
 )
 
+// MustIncomingContext returns metadata from incoming ctx
+// returned metadata shoud not be modified or race condition happens.
+// If metadata not exists panics.
+func MustIncomingContext(ctx context.Context) Metadata {
+	if ctx == nil {
+		panic("missing metadata")
+	}
+	md, ok := ctx.Value(mdIncomingKey{}).(*rawMetadata)
+	if !ok {
+		panic("missing metadata")
+	}
+	return md.md
+}
+
+// MustOutgoingContext returns metadata from outgoing ctx
+// returned metadata shoud not be modified or race condition happens.
+// If metadata not exists panics.
+func MustOutgoingContext(ctx context.Context) Metadata {
+	if ctx == nil {
+		panic("missing metadata")
+	}
+	md, ok := ctx.Value(mdOutgoingKey{}).(*rawMetadata)
+	if !ok {
+		panic("missing metadata")
+	}
+	return md.md
+}
+
 // FromIncomingContext returns metadata from incoming ctx
 // returned metadata shoud not be modified or race condition happens
 func FromIncomingContext(ctx context.Context) (Metadata, bool) {

metadata/metadata.go

@@ -67,6 +67,22 @@ func (md Metadata) Iterator() *Iterator {
 	return iter
 }
 
+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)]
+		}
+	}
+	if !ok {
+		panic("missing metadata key")
+	}
+	return val
+}
+
 // Get returns value from metadata by key
 func (md Metadata) Get(key string) (string, bool) {
 	// fast path