diff --git a/go.mod b/go.mod
index 89f343aa..5d75e67a 100644
--- a/go.mod
+++ b/go.mod
@@ -9,7 +9,7 @@ require (
 	golang.org/x/net v0.29.0
 	golang.org/x/sync v0.8.0
 	google.golang.org/grpc v1.66.0
-	google.golang.org/grpc/cmd/protoc-gen-go-grpc v1.3.0
+	google.golang.org/grpc/cmd/protoc-gen-go-grpc v1.4.0
 	google.golang.org/protobuf v1.34.2
 )
 
diff --git a/go.sum b/go.sum
index d75c5d4e..1a5ca3a6 100644
--- a/go.sum
+++ b/go.sum
@@ -53,8 +53,8 @@ google.golang.org/genproto/googleapis/rpc v0.0.0-20240903143218-8af14fe29dc1 h1:
 google.golang.org/genproto/googleapis/rpc v0.0.0-20240903143218-8af14fe29dc1/go.mod h1:UqMtugtsSgubUsoxbuAoiCXvqvErP7Gf0so0mK9tHxU=
 google.golang.org/grpc v1.66.0 h1:DibZuoBznOxbDQxRINckZcUvnCEvrW9pcWIE2yF9r1c=
 google.golang.org/grpc v1.66.0/go.mod h1:s3/l6xSSCURdVfAnL+TqCNMyTDAGN6+lZeVxnZR128Y=
-google.golang.org/grpc/cmd/protoc-gen-go-grpc v1.3.0 h1:rNBFJjBCOgVr9pWD7rs/knKL4FRTKgpZmsRfV214zcA=
-google.golang.org/grpc/cmd/protoc-gen-go-grpc v1.3.0/go.mod h1:Dk1tviKTvMCz5tvh7t+fh94dhmQVHuCt2OzJB3CTW9Y=
+google.golang.org/grpc/cmd/protoc-gen-go-grpc v1.4.0 h1:9SxA29VM43MF5Z9dQu694wmY5t8E/Gxr7s+RSxiIDmc=
+google.golang.org/grpc/cmd/protoc-gen-go-grpc v1.4.0/go.mod h1:yZOK5zhQMiALmuweVdIVoQPa6eIJyXn2B9g5dJDhqX4=
 google.golang.org/protobuf v1.34.2 h1:6xV6lTsCfpGD21XK49h7MhtcApnLqkfYgPcdHftf6hg=
 google.golang.org/protobuf v1.34.2/go.mod h1:qYOHts0dSfpeUzUFpOMr/WGzszTmLH+DiWniOlNbLDw=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
diff --git a/pkg/apis/proto/sourcetransform/v1/transform.pb.go b/pkg/apis/proto/sourcetransform/v1/transform.pb.go
index 479247d9..e851979e 100644
--- a/pkg/apis/proto/sourcetransform/v1/transform.pb.go
+++ b/pkg/apis/proto/sourcetransform/v1/transform.pb.go
@@ -22,22 +22,18 @@ const (
 	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
 )
 
-// *
-// SourceTransformerRequest represents a request element.
-type SourceTransformRequest struct {
+// Handshake message between client and server to indicate the start of transmission.
+type Handshake struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
 	unknownFields protoimpl.UnknownFields
 
-	Keys      []string               `protobuf:"bytes,1,rep,name=keys,proto3" json:"keys,omitempty"`
-	Value     []byte                 `protobuf:"bytes,2,opt,name=value,proto3" json:"value,omitempty"`
-	EventTime *timestamppb.Timestamp `protobuf:"bytes,3,opt,name=event_time,json=eventTime,proto3" json:"event_time,omitempty"`
-	Watermark *timestamppb.Timestamp `protobuf:"bytes,4,opt,name=watermark,proto3" json:"watermark,omitempty"`
-	Headers   map[string]string      `protobuf:"bytes,5,rep,name=headers,proto3" json:"headers,omitempty" protobuf_key:"bytes,1,opt,name=key,proto3" protobuf_val:"bytes,2,opt,name=value,proto3"`
+	// Required field indicating the start of transmission.
+	Sot bool `protobuf:"varint,1,opt,name=sot,proto3" json:"sot,omitempty"`
 }
 
-func (x *SourceTransformRequest) Reset() {
-	*x = SourceTransformRequest{}
+func (x *Handshake) Reset() {
+	*x = Handshake{}
 	if protoimpl.UnsafeEnabled {
 		mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[0]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
@@ -45,13 +41,13 @@ func (x *SourceTransformRequest) Reset() {
 	}
 }
 
-func (x *SourceTransformRequest) String() string {
+func (x *Handshake) String() string {
 	return protoimpl.X.MessageStringOf(x)
 }
 
-func (*SourceTransformRequest) ProtoMessage() {}
+func (*Handshake) ProtoMessage() {}
 
-func (x *SourceTransformRequest) ProtoReflect() protoreflect.Message {
+func (x *Handshake) ProtoReflect() protoreflect.Message {
 	mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[0]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
@@ -63,42 +59,71 @@ func (x *SourceTransformRequest) ProtoReflect() protoreflect.Message {
 	return mi.MessageOf(x)
 }
 
-// Deprecated: Use SourceTransformRequest.ProtoReflect.Descriptor instead.
-func (*SourceTransformRequest) Descriptor() ([]byte, []int) {
+// Deprecated: Use Handshake.ProtoReflect.Descriptor instead.
+func (*Handshake) Descriptor() ([]byte, []int) {
 	return file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDescGZIP(), []int{0}
 }
 
-func (x *SourceTransformRequest) GetKeys() []string {
+func (x *Handshake) GetSot() bool {
 	if x != nil {
-		return x.Keys
+		return x.Sot
 	}
-	return nil
+	return false
 }
 
-func (x *SourceTransformRequest) GetValue() []byte {
-	if x != nil {
-		return x.Value
+// *
+// SourceTransformerRequest represents a request element.
+type SourceTransformRequest struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Request   *SourceTransformRequest_Request `protobuf:"bytes,1,opt,name=request,proto3" json:"request,omitempty"`
+	Handshake *Handshake                      `protobuf:"bytes,2,opt,name=handshake,proto3,oneof" json:"handshake,omitempty"`
+}
+
+func (x *SourceTransformRequest) Reset() {
+	*x = SourceTransformRequest{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[1]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
 	}
-	return nil
 }
 
-func (x *SourceTransformRequest) GetEventTime() *timestamppb.Timestamp {
-	if x != nil {
-		return x.EventTime
+func (x *SourceTransformRequest) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*SourceTransformRequest) ProtoMessage() {}
+
+func (x *SourceTransformRequest) ProtoReflect() protoreflect.Message {
+	mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[1]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
 	}
-	return nil
+	return mi.MessageOf(x)
 }
 
-func (x *SourceTransformRequest) GetWatermark() *timestamppb.Timestamp {
+// Deprecated: Use SourceTransformRequest.ProtoReflect.Descriptor instead.
+func (*SourceTransformRequest) Descriptor() ([]byte, []int) {
+	return file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDescGZIP(), []int{1}
+}
+
+func (x *SourceTransformRequest) GetRequest() *SourceTransformRequest_Request {
 	if x != nil {
-		return x.Watermark
+		return x.Request
 	}
 	return nil
 }
 
-func (x *SourceTransformRequest) GetHeaders() map[string]string {
+func (x *SourceTransformRequest) GetHandshake() *Handshake {
 	if x != nil {
-		return x.Headers
+		return x.Handshake
 	}
 	return nil
 }
@@ -111,12 +136,16 @@ type SourceTransformResponse struct {
 	unknownFields protoimpl.UnknownFields
 
 	Results []*SourceTransformResponse_Result `protobuf:"bytes,1,rep,name=results,proto3" json:"results,omitempty"`
+	// This ID is used to refer the responses to the request it corresponds to.
+	Id string `protobuf:"bytes,2,opt,name=id,proto3" json:"id,omitempty"`
+	// Handshake message between client and server to indicate the start of transmission.
+	Handshake *Handshake `protobuf:"bytes,3,opt,name=handshake,proto3,oneof" json:"handshake,omitempty"`
 }
 
 func (x *SourceTransformResponse) Reset() {
 	*x = SourceTransformResponse{}
 	if protoimpl.UnsafeEnabled {
-		mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[1]
+		mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[2]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		ms.StoreMessageInfo(mi)
 	}
@@ -129,7 +158,7 @@ func (x *SourceTransformResponse) String() string {
 func (*SourceTransformResponse) ProtoMessage() {}
 
 func (x *SourceTransformResponse) ProtoReflect() protoreflect.Message {
-	mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[1]
+	mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[2]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -142,7 +171,7 @@ func (x *SourceTransformResponse) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use SourceTransformResponse.ProtoReflect.Descriptor instead.
 func (*SourceTransformResponse) Descriptor() ([]byte, []int) {
-	return file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDescGZIP(), []int{1}
+	return file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDescGZIP(), []int{2}
 }
 
 func (x *SourceTransformResponse) GetResults() []*SourceTransformResponse_Result {
@@ -152,6 +181,20 @@ func (x *SourceTransformResponse) GetResults() []*SourceTransformResponse_Result
 	return nil
 }
 
+func (x *SourceTransformResponse) GetId() string {
+	if x != nil {
+		return x.Id
+	}
+	return ""
+}
+
+func (x *SourceTransformResponse) GetHandshake() *Handshake {
+	if x != nil {
+		return x.Handshake
+	}
+	return nil
+}
+
 // *
 // ReadyResponse is the health check result.
 type ReadyResponse struct {
@@ -165,7 +208,7 @@ type ReadyResponse struct {
 func (x *ReadyResponse) Reset() {
 	*x = ReadyResponse{}
 	if protoimpl.UnsafeEnabled {
-		mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[2]
+		mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[3]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		ms.StoreMessageInfo(mi)
 	}
@@ -178,7 +221,7 @@ func (x *ReadyResponse) String() string {
 func (*ReadyResponse) ProtoMessage() {}
 
 func (x *ReadyResponse) ProtoReflect() protoreflect.Message {
-	mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[2]
+	mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[3]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -191,7 +234,7 @@ func (x *ReadyResponse) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use ReadyResponse.ProtoReflect.Descriptor instead.
 func (*ReadyResponse) Descriptor() ([]byte, []int) {
-	return file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDescGZIP(), []int{2}
+	return file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDescGZIP(), []int{3}
 }
 
 func (x *ReadyResponse) GetReady() bool {
@@ -201,6 +244,94 @@ func (x *ReadyResponse) GetReady() bool {
 	return false
 }
 
+type SourceTransformRequest_Request struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Keys      []string               `protobuf:"bytes,1,rep,name=keys,proto3" json:"keys,omitempty"`
+	Value     []byte                 `protobuf:"bytes,2,opt,name=value,proto3" json:"value,omitempty"`
+	EventTime *timestamppb.Timestamp `protobuf:"bytes,3,opt,name=event_time,json=eventTime,proto3" json:"event_time,omitempty"`
+	Watermark *timestamppb.Timestamp `protobuf:"bytes,4,opt,name=watermark,proto3" json:"watermark,omitempty"`
+	Headers   map[string]string      `protobuf:"bytes,5,rep,name=headers,proto3" json:"headers,omitempty" protobuf_key:"bytes,1,opt,name=key,proto3" protobuf_val:"bytes,2,opt,name=value,proto3"`
+	// This ID is used to uniquely identify a transform request
+	Id string `protobuf:"bytes,6,opt,name=id,proto3" json:"id,omitempty"`
+}
+
+func (x *SourceTransformRequest_Request) Reset() {
+	*x = SourceTransformRequest_Request{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[4]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *SourceTransformRequest_Request) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*SourceTransformRequest_Request) ProtoMessage() {}
+
+func (x *SourceTransformRequest_Request) ProtoReflect() protoreflect.Message {
+	mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[4]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use SourceTransformRequest_Request.ProtoReflect.Descriptor instead.
+func (*SourceTransformRequest_Request) Descriptor() ([]byte, []int) {
+	return file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDescGZIP(), []int{1, 0}
+}
+
+func (x *SourceTransformRequest_Request) GetKeys() []string {
+	if x != nil {
+		return x.Keys
+	}
+	return nil
+}
+
+func (x *SourceTransformRequest_Request) GetValue() []byte {
+	if x != nil {
+		return x.Value
+	}
+	return nil
+}
+
+func (x *SourceTransformRequest_Request) GetEventTime() *timestamppb.Timestamp {
+	if x != nil {
+		return x.EventTime
+	}
+	return nil
+}
+
+func (x *SourceTransformRequest_Request) GetWatermark() *timestamppb.Timestamp {
+	if x != nil {
+		return x.Watermark
+	}
+	return nil
+}
+
+func (x *SourceTransformRequest_Request) GetHeaders() map[string]string {
+	if x != nil {
+		return x.Headers
+	}
+	return nil
+}
+
+func (x *SourceTransformRequest_Request) GetId() string {
+	if x != nil {
+		return x.Id
+	}
+	return ""
+}
+
 type SourceTransformResponse_Result struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
@@ -215,7 +346,7 @@ type SourceTransformResponse_Result struct {
 func (x *SourceTransformResponse_Result) Reset() {
 	*x = SourceTransformResponse_Result{}
 	if protoimpl.UnsafeEnabled {
-		mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[4]
+		mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[6]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		ms.StoreMessageInfo(mi)
 	}
@@ -228,7 +359,7 @@ func (x *SourceTransformResponse_Result) String() string {
 func (*SourceTransformResponse_Result) ProtoMessage() {}
 
 func (x *SourceTransformResponse_Result) ProtoReflect() protoreflect.Message {
-	mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[4]
+	mi := &file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[6]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -241,7 +372,7 @@ func (x *SourceTransformResponse_Result) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use SourceTransformResponse_Result.ProtoReflect.Descriptor instead.
 func (*SourceTransformResponse_Result) Descriptor() ([]byte, []int) {
-	return file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDescGZIP(), []int{1, 0}
+	return file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDescGZIP(), []int{2, 0}
 }
 
 func (x *SourceTransformResponse_Result) GetKeys() []string {
@@ -283,63 +414,83 @@ var file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDesc = []byte{
 	0x65, 0x2f, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x62, 0x75, 0x66, 0x2f, 0x74, 0x69, 0x6d, 0x65, 0x73,
 	0x74, 0x61, 0x6d, 0x70, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x1a, 0x1b, 0x67, 0x6f, 0x6f, 0x67,
 	0x6c, 0x65, 0x2f, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x62, 0x75, 0x66, 0x2f, 0x65, 0x6d, 0x70, 0x74,
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+	0x79, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x22, 0x1d, 0x0a, 0x09, 0x48, 0x61, 0x6e, 0x64, 0x73,
+	0x68, 0x61, 0x6b, 0x65, 0x12, 0x10, 0x0a, 0x03, 0x73, 0x6f, 0x74, 0x18, 0x01, 0x20, 0x01, 0x28,
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+	0x61, 0x72, 0x6b, 0x18, 0x04, 0x20, 0x01, 0x28, 0x0b, 0x32, 0x1a, 0x2e, 0x67, 0x6f, 0x6f, 0x67,
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 }
 
 var (
@@ -354,31 +505,36 @@ func file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDescGZIP() []byte
 	return file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDescData
 }
 
-var file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes = make([]protoimpl.MessageInfo, 5)
+var file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes = make([]protoimpl.MessageInfo, 7)
 var file_pkg_apis_proto_sourcetransform_v1_transform_proto_goTypes = []any{
-	(*SourceTransformRequest)(nil),         // 0: sourcetransformer.v1.SourceTransformRequest
-	(*SourceTransformResponse)(nil),        // 1: sourcetransformer.v1.SourceTransformResponse
-	(*ReadyResponse)(nil),                  // 2: sourcetransformer.v1.ReadyResponse
-	nil,                                    // 3: sourcetransformer.v1.SourceTransformRequest.HeadersEntry
-	(*SourceTransformResponse_Result)(nil), // 4: sourcetransformer.v1.SourceTransformResponse.Result
-	(*timestamppb.Timestamp)(nil),          // 5: google.protobuf.Timestamp
-	(*emptypb.Empty)(nil),                  // 6: google.protobuf.Empty
+	(*Handshake)(nil),                      // 0: sourcetransformer.v1.Handshake
+	(*SourceTransformRequest)(nil),         // 1: sourcetransformer.v1.SourceTransformRequest
+	(*SourceTransformResponse)(nil),        // 2: sourcetransformer.v1.SourceTransformResponse
+	(*ReadyResponse)(nil),                  // 3: sourcetransformer.v1.ReadyResponse
+	(*SourceTransformRequest_Request)(nil), // 4: sourcetransformer.v1.SourceTransformRequest.Request
+	nil,                                    // 5: sourcetransformer.v1.SourceTransformRequest.Request.HeadersEntry
+	(*SourceTransformResponse_Result)(nil), // 6: sourcetransformer.v1.SourceTransformResponse.Result
+	(*timestamppb.Timestamp)(nil),          // 7: google.protobuf.Timestamp
+	(*emptypb.Empty)(nil),                  // 8: google.protobuf.Empty
 }
 var file_pkg_apis_proto_sourcetransform_v1_transform_proto_depIdxs = []int32{
-	5, // 0: sourcetransformer.v1.SourceTransformRequest.event_time:type_name -> google.protobuf.Timestamp
-	5, // 1: sourcetransformer.v1.SourceTransformRequest.watermark:type_name -> google.protobuf.Timestamp
-	3, // 2: sourcetransformer.v1.SourceTransformRequest.headers:type_name -> sourcetransformer.v1.SourceTransformRequest.HeadersEntry
-	4, // 3: sourcetransformer.v1.SourceTransformResponse.results:type_name -> sourcetransformer.v1.SourceTransformResponse.Result
-	5, // 4: sourcetransformer.v1.SourceTransformResponse.Result.event_time:type_name -> google.protobuf.Timestamp
-	0, // 5: sourcetransformer.v1.SourceTransform.SourceTransformFn:input_type -> sourcetransformer.v1.SourceTransformRequest
-	6, // 6: sourcetransformer.v1.SourceTransform.IsReady:input_type -> google.protobuf.Empty
-	1, // 7: sourcetransformer.v1.SourceTransform.SourceTransformFn:output_type -> sourcetransformer.v1.SourceTransformResponse
-	2, // 8: sourcetransformer.v1.SourceTransform.IsReady:output_type -> sourcetransformer.v1.ReadyResponse
-	7, // [7:9] is the sub-list for method output_type
-	5, // [5:7] is the sub-list for method input_type
-	5, // [5:5] is the sub-list for extension type_name
-	5, // [5:5] is the sub-list for extension extendee
-	0, // [0:5] is the sub-list for field type_name
+	4,  // 0: sourcetransformer.v1.SourceTransformRequest.request:type_name -> sourcetransformer.v1.SourceTransformRequest.Request
+	0,  // 1: sourcetransformer.v1.SourceTransformRequest.handshake:type_name -> sourcetransformer.v1.Handshake
+	6,  // 2: sourcetransformer.v1.SourceTransformResponse.results:type_name -> sourcetransformer.v1.SourceTransformResponse.Result
+	0,  // 3: sourcetransformer.v1.SourceTransformResponse.handshake:type_name -> sourcetransformer.v1.Handshake
+	7,  // 4: sourcetransformer.v1.SourceTransformRequest.Request.event_time:type_name -> google.protobuf.Timestamp
+	7,  // 5: sourcetransformer.v1.SourceTransformRequest.Request.watermark:type_name -> google.protobuf.Timestamp
+	5,  // 6: sourcetransformer.v1.SourceTransformRequest.Request.headers:type_name -> sourcetransformer.v1.SourceTransformRequest.Request.HeadersEntry
+	7,  // 7: sourcetransformer.v1.SourceTransformResponse.Result.event_time:type_name -> google.protobuf.Timestamp
+	1,  // 8: sourcetransformer.v1.SourceTransform.SourceTransformFn:input_type -> sourcetransformer.v1.SourceTransformRequest
+	8,  // 9: sourcetransformer.v1.SourceTransform.IsReady:input_type -> google.protobuf.Empty
+	2,  // 10: sourcetransformer.v1.SourceTransform.SourceTransformFn:output_type -> sourcetransformer.v1.SourceTransformResponse
+	3,  // 11: sourcetransformer.v1.SourceTransform.IsReady:output_type -> sourcetransformer.v1.ReadyResponse
+	10, // [10:12] is the sub-list for method output_type
+	8,  // [8:10] is the sub-list for method input_type
+	8,  // [8:8] is the sub-list for extension type_name
+	8,  // [8:8] is the sub-list for extension extendee
+	0,  // [0:8] is the sub-list for field type_name
 }
 
 func init() { file_pkg_apis_proto_sourcetransform_v1_transform_proto_init() }
@@ -388,7 +544,7 @@ func file_pkg_apis_proto_sourcetransform_v1_transform_proto_init() {
 	}
 	if !protoimpl.UnsafeEnabled {
 		file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[0].Exporter = func(v any, i int) any {
-			switch v := v.(*SourceTransformRequest); i {
+			switch v := v.(*Handshake); i {
 			case 0:
 				return &v.state
 			case 1:
@@ -400,7 +556,7 @@ func file_pkg_apis_proto_sourcetransform_v1_transform_proto_init() {
 			}
 		}
 		file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[1].Exporter = func(v any, i int) any {
-			switch v := v.(*SourceTransformResponse); i {
+			switch v := v.(*SourceTransformRequest); i {
 			case 0:
 				return &v.state
 			case 1:
@@ -412,6 +568,18 @@ func file_pkg_apis_proto_sourcetransform_v1_transform_proto_init() {
 			}
 		}
 		file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[2].Exporter = func(v any, i int) any {
+			switch v := v.(*SourceTransformResponse); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[3].Exporter = func(v any, i int) any {
 			switch v := v.(*ReadyResponse); i {
 			case 0:
 				return &v.state
@@ -424,6 +592,18 @@ func file_pkg_apis_proto_sourcetransform_v1_transform_proto_init() {
 			}
 		}
 		file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[4].Exporter = func(v any, i int) any {
+			switch v := v.(*SourceTransformRequest_Request); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[6].Exporter = func(v any, i int) any {
 			switch v := v.(*SourceTransformResponse_Result); i {
 			case 0:
 				return &v.state
@@ -436,13 +616,15 @@ func file_pkg_apis_proto_sourcetransform_v1_transform_proto_init() {
 			}
 		}
 	}
+	file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[1].OneofWrappers = []any{}
+	file_pkg_apis_proto_sourcetransform_v1_transform_proto_msgTypes[2].OneofWrappers = []any{}
 	type x struct{}
 	out := protoimpl.TypeBuilder{
 		File: protoimpl.DescBuilder{
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: file_pkg_apis_proto_sourcetransform_v1_transform_proto_rawDesc,
 			NumEnums:      0,
-			NumMessages:   5,
+			NumMessages:   7,
 			NumExtensions: 0,
 			NumServices:   1,
 		},
diff --git a/pkg/apis/proto/sourcetransform/v1/transform.proto b/pkg/apis/proto/sourcetransform/v1/transform.proto
index 8885db08..7eec50c9 100644
--- a/pkg/apis/proto/sourcetransform/v1/transform.proto
+++ b/pkg/apis/proto/sourcetransform/v1/transform.proto
@@ -11,21 +11,35 @@ service SourceTransform {
   // SourceTransformFn applies a function to each request element.
   // In addition to map function, SourceTransformFn also supports assigning a new event time to response.
   // SourceTransformFn can be used only at source vertex by source data transformer.
-  rpc SourceTransformFn(SourceTransformRequest) returns (SourceTransformResponse);
+  rpc SourceTransformFn(stream SourceTransformRequest) returns (stream SourceTransformResponse);
 
   // IsReady is the heartbeat endpoint for gRPC.
   rpc IsReady(google.protobuf.Empty) returns (ReadyResponse);
 }
 
+/*
+ * Handshake message between client and server to indicate the start of transmission.
+ */
+ message Handshake {
+  // Required field indicating the start of transmission.
+  bool sot = 1;
+}
+
 /**
  * SourceTransformerRequest represents a request element.
  */
 message SourceTransformRequest {
-  repeated string keys = 1;
-  bytes value = 2;
-  google.protobuf.Timestamp event_time = 3;
-  google.protobuf.Timestamp watermark = 4;
-  map<string, string> headers = 5;
+  message Request {
+    repeated string keys = 1;
+    bytes value = 2;
+    google.protobuf.Timestamp event_time = 3;
+    google.protobuf.Timestamp watermark = 4;
+    map<string, string> headers = 5;
+    // This ID is used to uniquely identify a transform request
+    string id = 6;
+  }
+  Request request = 1;
+  optional Handshake handshake = 2;
 }
 
 /**
@@ -39,6 +53,10 @@ message SourceTransformResponse {
     repeated string tags = 4;
   }
   repeated Result results = 1;
+  // This ID is used to refer the responses to the request it corresponds to.
+  string id = 2;
+  // Handshake message between client and server to indicate the start of transmission.
+  optional Handshake handshake = 3;
 }
 
 /**
diff --git a/pkg/apis/proto/sourcetransform/v1/transform_grpc.pb.go b/pkg/apis/proto/sourcetransform/v1/transform_grpc.pb.go
index 9fd6bd4a..52995c34 100644
--- a/pkg/apis/proto/sourcetransform/v1/transform_grpc.pb.go
+++ b/pkg/apis/proto/sourcetransform/v1/transform_grpc.pb.go
@@ -31,7 +31,7 @@ type SourceTransformClient interface {
 	// SourceTransformFn applies a function to each request element.
 	// In addition to map function, SourceTransformFn also supports assigning a new event time to response.
 	// SourceTransformFn can be used only at source vertex by source data transformer.
-	SourceTransformFn(ctx context.Context, in *SourceTransformRequest, opts ...grpc.CallOption) (*SourceTransformResponse, error)
+	SourceTransformFn(ctx context.Context, opts ...grpc.CallOption) (SourceTransform_SourceTransformFnClient, error)
 	// IsReady is the heartbeat endpoint for gRPC.
 	IsReady(ctx context.Context, in *emptypb.Empty, opts ...grpc.CallOption) (*ReadyResponse, error)
 }
@@ -44,14 +44,36 @@ func NewSourceTransformClient(cc grpc.ClientConnInterface) SourceTransformClient
 	return &sourceTransformClient{cc}
 }
 
-func (c *sourceTransformClient) SourceTransformFn(ctx context.Context, in *SourceTransformRequest, opts ...grpc.CallOption) (*SourceTransformResponse, error) {
+func (c *sourceTransformClient) SourceTransformFn(ctx context.Context, opts ...grpc.CallOption) (SourceTransform_SourceTransformFnClient, error) {
 	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
-	out := new(SourceTransformResponse)
-	err := c.cc.Invoke(ctx, SourceTransform_SourceTransformFn_FullMethodName, in, out, cOpts...)
+	stream, err := c.cc.NewStream(ctx, &SourceTransform_ServiceDesc.Streams[0], SourceTransform_SourceTransformFn_FullMethodName, cOpts...)
 	if err != nil {
 		return nil, err
 	}
-	return out, nil
+	x := &sourceTransformSourceTransformFnClient{ClientStream: stream}
+	return x, nil
+}
+
+type SourceTransform_SourceTransformFnClient interface {
+	Send(*SourceTransformRequest) error
+	Recv() (*SourceTransformResponse, error)
+	grpc.ClientStream
+}
+
+type sourceTransformSourceTransformFnClient struct {
+	grpc.ClientStream
+}
+
+func (x *sourceTransformSourceTransformFnClient) Send(m *SourceTransformRequest) error {
+	return x.ClientStream.SendMsg(m)
+}
+
+func (x *sourceTransformSourceTransformFnClient) Recv() (*SourceTransformResponse, error) {
+	m := new(SourceTransformResponse)
+	if err := x.ClientStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
 }
 
 func (c *sourceTransformClient) IsReady(ctx context.Context, in *emptypb.Empty, opts ...grpc.CallOption) (*ReadyResponse, error) {
@@ -71,7 +93,7 @@ type SourceTransformServer interface {
 	// SourceTransformFn applies a function to each request element.
 	// In addition to map function, SourceTransformFn also supports assigning a new event time to response.
 	// SourceTransformFn can be used only at source vertex by source data transformer.
-	SourceTransformFn(context.Context, *SourceTransformRequest) (*SourceTransformResponse, error)
+	SourceTransformFn(SourceTransform_SourceTransformFnServer) error
 	// IsReady is the heartbeat endpoint for gRPC.
 	IsReady(context.Context, *emptypb.Empty) (*ReadyResponse, error)
 	mustEmbedUnimplementedSourceTransformServer()
@@ -81,8 +103,8 @@ type SourceTransformServer interface {
 type UnimplementedSourceTransformServer struct {
 }
 
-func (UnimplementedSourceTransformServer) SourceTransformFn(context.Context, *SourceTransformRequest) (*SourceTransformResponse, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method SourceTransformFn not implemented")
+func (UnimplementedSourceTransformServer) SourceTransformFn(SourceTransform_SourceTransformFnServer) error {
+	return status.Errorf(codes.Unimplemented, "method SourceTransformFn not implemented")
 }
 func (UnimplementedSourceTransformServer) IsReady(context.Context, *emptypb.Empty) (*ReadyResponse, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method IsReady not implemented")
@@ -100,22 +122,30 @@ func RegisterSourceTransformServer(s grpc.ServiceRegistrar, srv SourceTransformS
 	s.RegisterService(&SourceTransform_ServiceDesc, srv)
 }
 
-func _SourceTransform_SourceTransformFn_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
-	in := new(SourceTransformRequest)
-	if err := dec(in); err != nil {
+func _SourceTransform_SourceTransformFn_Handler(srv interface{}, stream grpc.ServerStream) error {
+	return srv.(SourceTransformServer).SourceTransformFn(&sourceTransformSourceTransformFnServer{ServerStream: stream})
+}
+
+type SourceTransform_SourceTransformFnServer interface {
+	Send(*SourceTransformResponse) error
+	Recv() (*SourceTransformRequest, error)
+	grpc.ServerStream
+}
+
+type sourceTransformSourceTransformFnServer struct {
+	grpc.ServerStream
+}
+
+func (x *sourceTransformSourceTransformFnServer) Send(m *SourceTransformResponse) error {
+	return x.ServerStream.SendMsg(m)
+}
+
+func (x *sourceTransformSourceTransformFnServer) Recv() (*SourceTransformRequest, error) {
+	m := new(SourceTransformRequest)
+	if err := x.ServerStream.RecvMsg(m); err != nil {
 		return nil, err
 	}
-	if interceptor == nil {
-		return srv.(SourceTransformServer).SourceTransformFn(ctx, in)
-	}
-	info := &grpc.UnaryServerInfo{
-		Server:     srv,
-		FullMethod: SourceTransform_SourceTransformFn_FullMethodName,
-	}
-	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
-		return srv.(SourceTransformServer).SourceTransformFn(ctx, req.(*SourceTransformRequest))
-	}
-	return interceptor(ctx, in, info, handler)
+	return m, nil
 }
 
 func _SourceTransform_IsReady_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
@@ -143,15 +173,18 @@ var SourceTransform_ServiceDesc = grpc.ServiceDesc{
 	ServiceName: "sourcetransformer.v1.SourceTransform",
 	HandlerType: (*SourceTransformServer)(nil),
 	Methods: []grpc.MethodDesc{
-		{
-			MethodName: "SourceTransformFn",
-			Handler:    _SourceTransform_SourceTransformFn_Handler,
-		},
 		{
 			MethodName: "IsReady",
 			Handler:    _SourceTransform_IsReady_Handler,
 		},
 	},
-	Streams:  []grpc.StreamDesc{},
+	Streams: []grpc.StreamDesc{
+		{
+			StreamName:    "SourceTransformFn",
+			Handler:       _SourceTransform_SourceTransformFn_Handler,
+			ServerStreams: true,
+			ClientStreams: true,
+		},
+	},
 	Metadata: "pkg/apis/proto/sourcetransform/v1/transform.proto",
 }
diff --git a/pkg/apis/proto/sourcetransform/v1/transformmock/transformmock.go b/pkg/apis/proto/sourcetransform/v1/transformmock/transformmock.go
index fbc66555..8b347d06 100644
--- a/pkg/apis/proto/sourcetransform/v1/transformmock/transformmock.go
+++ b/pkg/apis/proto/sourcetransform/v1/transformmock/transformmock.go
@@ -58,21 +58,21 @@ func (mr *MockSourceTransformClientMockRecorder) IsReady(arg0, arg1 interface{},
 }
 
 // SourceTransformFn mocks base method.
-func (m *MockSourceTransformClient) SourceTransformFn(arg0 context.Context, arg1 *v1.SourceTransformRequest, arg2 ...grpc.CallOption) (*v1.SourceTransformResponse, error) {
+func (m *MockSourceTransformClient) SourceTransformFn(arg0 context.Context, arg1 ...grpc.CallOption) (v1.SourceTransform_SourceTransformFnClient, error) {
 	m.ctrl.T.Helper()
-	varargs := []interface{}{arg0, arg1}
-	for _, a := range arg2 {
+	varargs := []interface{}{arg0}
+	for _, a := range arg1 {
 		varargs = append(varargs, a)
 	}
 	ret := m.ctrl.Call(m, "SourceTransformFn", varargs...)
-	ret0, _ := ret[0].(*v1.SourceTransformResponse)
+	ret0, _ := ret[0].(v1.SourceTransform_SourceTransformFnClient)
 	ret1, _ := ret[1].(error)
 	return ret0, ret1
 }
 
 // SourceTransformFn indicates an expected call of SourceTransformFn.
-func (mr *MockSourceTransformClientMockRecorder) SourceTransformFn(arg0, arg1 interface{}, arg2 ...interface{}) *gomock.Call {
+func (mr *MockSourceTransformClientMockRecorder) SourceTransformFn(arg0 interface{}, arg1 ...interface{}) *gomock.Call {
 	mr.mock.ctrl.T.Helper()
-	varargs := append([]interface{}{arg0, arg1}, arg2...)
+	varargs := append([]interface{}{arg0}, arg1...)
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "SourceTransformFn", reflect.TypeOf((*MockSourceTransformClient)(nil).SourceTransformFn), varargs...)
 }
diff --git a/pkg/sourcetransformer/examples/event_time_filter/go.mod b/pkg/sourcetransformer/examples/event_time_filter/go.mod
index d8c44a3a..c91400a8 100644
--- a/pkg/sourcetransformer/examples/event_time_filter/go.mod
+++ b/pkg/sourcetransformer/examples/event_time_filter/go.mod
@@ -15,6 +15,7 @@ require (
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/rogpeppe/go-internal v1.11.0 // indirect
 	golang.org/x/net v0.29.0 // indirect
+	golang.org/x/sync v0.8.0 // indirect
 	golang.org/x/sys v0.25.0 // indirect
 	golang.org/x/text v0.18.0 // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20240903143218-8af14fe29dc1 // indirect
diff --git a/pkg/sourcetransformer/examples/event_time_filter/go.sum b/pkg/sourcetransformer/examples/event_time_filter/go.sum
index 47607cf0..15b67493 100644
--- a/pkg/sourcetransformer/examples/event_time_filter/go.sum
+++ b/pkg/sourcetransformer/examples/event_time_filter/go.sum
@@ -15,6 +15,8 @@ github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsT
 github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
 golang.org/x/net v0.29.0 h1:5ORfpBpCs4HzDYoodCDBbwHzdR5UrLBZ3sOnUJmFoHo=
 golang.org/x/net v0.29.0/go.mod h1:gLkgy8jTGERgjzMic6DS9+SP0ajcu6Xu3Orq/SpETg0=
+golang.org/x/sync v0.8.0 h1:3NFvSEYkUoMifnESzZl15y791HH1qU2xm6eCJU5ZPXQ=
+golang.org/x/sync v0.8.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
 golang.org/x/sys v0.25.0 h1:r+8e+loiHxRqhXVl6ML1nO3l1+oFoWbnlu2Ehimmi34=
 golang.org/x/sys v0.25.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/text v0.18.0 h1:XvMDiNzPAl0jr17s6W9lcaIhGUfUORdGCNsuLmPG224=
diff --git a/pkg/sourcetransformer/examples/event_time_filter/impl/filter_test.go b/pkg/sourcetransformer/examples/event_time_filter/impl/filter_test.go
index fb8b5b06..2ddd5cd7 100644
--- a/pkg/sourcetransformer/examples/event_time_filter/impl/filter_test.go
+++ b/pkg/sourcetransformer/examples/event_time_filter/impl/filter_test.go
@@ -23,6 +23,10 @@ func (d beforeYear2022Datum) Watermark() time.Time {
 	return time.Now()
 }
 
+func (d beforeYear2022Datum) Headers() map[string]string {
+	return map[string]string{}
+}
+
 type withinYear2022Datum struct{}
 
 func (d withinYear2022Datum) ID() string {
@@ -39,6 +43,9 @@ func (d withinYear2022Datum) EventTime() time.Time {
 func (d withinYear2022Datum) Watermark() time.Time {
 	return time.Now()
 }
+func (d withinYear2022Datum) Headers() map[string]string {
+	return map[string]string{}
+}
 
 type afterYear2022Datum struct{}
 
@@ -52,6 +59,9 @@ func (d afterYear2022Datum) EventTime() time.Time {
 func (d afterYear2022Datum) Watermark() time.Time {
 	return time.Now()
 }
+func (d afterYear2022Datum) Headers() map[string]string {
+	return map[string]string{}
+}
 
 func Test_FilterEventTime(t *testing.T) {
 	testKeys := []string{"test-key"}
diff --git a/pkg/sourcetransformer/service.go b/pkg/sourcetransformer/service.go
index 1651f825..bbd91f19 100644
--- a/pkg/sourcetransformer/service.go
+++ b/pkg/sourcetransformer/service.go
@@ -2,9 +2,16 @@ package sourcetransformer
 
 import (
 	"context"
+	"errors"
+	"fmt"
+	"io"
 	"log"
 	"runtime/debug"
 
+	"golang.org/x/sync/errgroup"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+
 	"google.golang.org/protobuf/types/known/emptypb"
 	"google.golang.org/protobuf/types/known/timestamppb"
 
@@ -31,10 +38,12 @@ func (fs *Service) IsReady(context.Context, *emptypb.Empty) (*v1.ReadyResponse,
 	return &v1.ReadyResponse{Ready: true}, nil
 }
 
+var errTransformerPanic = errors.New("transformer function panicked")
+
 // SourceTransformFn applies a function to each request element.
 // In addition to map function, SourceTransformFn also supports assigning a new event time to response.
 // SourceTransformFn can be used only at source vertex by source data transformer.
-func (fs *Service) SourceTransformFn(ctx context.Context, d *v1.SourceTransformRequest) (*v1.SourceTransformResponse, error) {
+func (fs *Service) SourceTransformFn(stream v1.SourceTransform_SourceTransformFnServer) error {
 	// handle panic
 	defer func() {
 		if r := recover(); r != nil {
@@ -42,19 +51,105 @@ func (fs *Service) SourceTransformFn(ctx context.Context, d *v1.SourceTransformR
 			fs.shutdownCh <- struct{}{}
 		}
 	}()
-	var hd = NewHandlerDatum(d.GetValue(), d.EventTime.AsTime(), d.Watermark.AsTime(), d.Headers)
-	messageTs := fs.Transformer.Transform(ctx, d.GetKeys(), hd)
-	var results []*v1.SourceTransformResponse_Result
-	for _, m := range messageTs.Items() {
-		results = append(results, &v1.SourceTransformResponse_Result{
-			EventTime: timestamppb.New(m.EventTime()),
-			Keys:      m.Keys(),
-			Value:     m.Value(),
-			Tags:      m.Tags(),
+
+	req, err := stream.Recv()
+	if err != nil {
+		return fmt.Errorf("reading handshake message from stream: %w", err)
+	}
+
+	if req.Handshake == nil || !req.Handshake.Sot {
+		return fmt.Errorf("invalid handshake message: %+v", req)
+	}
+
+	handshakeResponse := &v1.SourceTransformResponse{
+		Handshake: &v1.Handshake{
+			Sot: true,
+		},
+	}
+	if err := stream.Send(handshakeResponse); err != nil {
+		return fmt.Errorf("sending handshake response to client over gRPC stream: %w", err)
+	}
+
+	ctx := stream.Context()
+	// We depend on grpContext to cancel all goroutines, since it will be automatically closed when the first function returns a non-nil error.
+	// This error will be caught later with grp.Wait()
+	grp, grpCtx := errgroup.WithContext(ctx)
+
+	senderCh := make(chan *v1.SourceTransformResponse, 500) // FIXME: identify the right buffer size
+	// goroutine to send the response to the stream
+	grp.Go(func() error {
+		for {
+			var resp *v1.SourceTransformResponse
+			select {
+			case <-grpCtx.Done():
+				return grpCtx.Err()
+			case resp = <-senderCh:
+			}
+			if err := stream.Send(resp); err != nil {
+				return fmt.Errorf("failed to send response to client: %w", err)
+			}
+		}
+	})
+
+outer:
+	for {
+		// Stop reading new messages when we are shutting down
+		select {
+		case <-grpCtx.Done():
+			// If the context was cancelled while this loop is running, it will be caught and returned in one of the errgroup's goroutines.
+			break outer
+		default:
+		}
+
+		d, err := stream.Recv()
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				break
+			}
+			return err
+		}
+
+		req := d.Request
+		grp.Go(func() (err error) {
+			defer func() {
+				if r := recover(); r != nil {
+					log.Printf("Panic inside source transform handler: %v %v", r, string(debug.Stack()))
+					// We only listen for 1 message on the shutdown channel. If multiple requests panic, only the first one will succeed.
+					// The one that succeds returns the errTransformerPanic. This causes grpCtx to be cancelled.
+					select {
+					case fs.shutdownCh <- struct{}{}:
+					case <-grpCtx.Done():
+					}
+					err = errTransformerPanic
+				}
+			}()
+			var hd = NewHandlerDatum(req.GetValue(), req.EventTime.AsTime(), req.Watermark.AsTime(), req.Headers)
+			messageTs := fs.Transformer.Transform(grpCtx, req.GetKeys(), hd)
+			var results []*v1.SourceTransformResponse_Result
+			for _, m := range messageTs.Items() {
+				results = append(results, &v1.SourceTransformResponse_Result{
+					EventTime: timestamppb.New(m.EventTime()),
+					Keys:      m.Keys(),
+					Value:     m.Value(),
+					Tags:      m.Tags(),
+				})
+			}
+			resp := &v1.SourceTransformResponse{
+				Results: results,
+				Id:      req.GetId(),
+			}
+			select {
+			case senderCh <- resp:
+			case <-grpCtx.Done():
+				return grpCtx.Err()
+			}
+			return nil
 		})
 	}
-	responseList := &v1.SourceTransformResponse{
-		Results: results,
+
+	if err := grp.Wait(); err != nil {
+		statusErr := status.Errorf(codes.Internal, err.Error())
+		return statusErr
 	}
-	return responseList, nil
+	return nil
 }
diff --git a/pkg/sourcetransformer/service_test.go b/pkg/sourcetransformer/service_test.go
index d57d937e..79449c9a 100644
--- a/pkg/sourcetransformer/service_test.go
+++ b/pkg/sourcetransformer/service_test.go
@@ -2,28 +2,83 @@ package sourcetransformer
 
 import (
 	"context"
-	"reflect"
+	"errors"
+	"fmt"
+	"net"
 	"testing"
 	"time"
 
-	"google.golang.org/protobuf/types/known/timestamppb"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials/insecure"
+	"google.golang.org/grpc/status"
+	"google.golang.org/grpc/test/bufconn"
 
-	stpb "github.com/numaproj/numaflow-go/pkg/apis/proto/sourcetransform/v1"
+	proto "github.com/numaproj/numaflow-go/pkg/apis/proto/sourcetransform/v1"
+	"google.golang.org/protobuf/types/known/timestamppb"
 )
 
+func newTestServer(t *testing.T, register func(server *grpc.Server)) *grpc.ClientConn {
+	lis := bufconn.Listen(1024 * 1024)
+	t.Cleanup(func() {
+		_ = lis.Close()
+	})
+
+	server := grpc.NewServer()
+	t.Cleanup(func() {
+		server.Stop()
+	})
+
+	register(server)
+
+	errChan := make(chan error, 1)
+	go func() {
+		// t.Fatal should only be called from the goroutine running the test
+		if err := server.Serve(lis); err != nil {
+			errChan <- err
+		}
+	}()
+
+	dialer := func(context.Context, string) (net.Conn, error) {
+		return lis.Dial()
+	}
+
+	conn, err := grpc.NewClient("passthrough://", grpc.WithContextDialer(dialer), grpc.WithTransportCredentials(insecure.NewCredentials()))
+	t.Cleanup(func() {
+		_ = conn.Close()
+	})
+	if err != nil {
+		t.Fatalf("Creating new gRPC client connection: %v", err)
+	}
+
+	var grpcServerErr error
+	select {
+	case grpcServerErr = <-errChan:
+	case <-time.After(500 * time.Millisecond):
+		grpcServerErr = errors.New("gRPC server didn't start in 500ms")
+	}
+	if err != nil {
+		t.Fatalf("Failed to start gRPC server: %v", grpcServerErr)
+	}
+
+	return conn
+}
+
+var testTime = time.Date(2021, 8, 15, 14, 30, 45, 100, time.Local)
+
 func TestService_sourceTransformFn(t *testing.T) {
 	type args struct {
 		ctx context.Context
-		d   *stpb.SourceTransformRequest
+		d   *proto.SourceTransformRequest
 	}
 
-	testTime := time.Date(2021, 8, 15, 14, 30, 45, 100, time.Local)
 	tests := []struct {
 		name    string
 		handler SourceTransformer
 		args    args
-		want    *stpb.SourceTransformResponse
-		wantErr bool
+		want    *proto.SourceTransformResponse
 	}{
 		{
 			name: "sourceTransform_fn_forward_msg",
@@ -33,15 +88,17 @@ func TestService_sourceTransformFn(t *testing.T) {
 			}),
 			args: args{
 				ctx: context.Background(),
-				d: &stpb.SourceTransformRequest{
-					Keys:      []string{"client"},
-					Value:     []byte(`test`),
-					EventTime: timestamppb.New(time.Time{}),
-					Watermark: timestamppb.New(time.Time{}),
+				d: &proto.SourceTransformRequest{
+					Request: &proto.SourceTransformRequest_Request{
+						Keys:      []string{"client"},
+						Value:     []byte(`test`),
+						EventTime: timestamppb.New(time.Time{}),
+						Watermark: timestamppb.New(time.Time{}),
+					},
 				},
 			},
-			want: &stpb.SourceTransformResponse{
-				Results: []*stpb.SourceTransformResponse_Result{
+			want: &proto.SourceTransformResponse{
+				Results: []*proto.SourceTransformResponse_Result{
 					{
 						EventTime: timestamppb.New(testTime),
 						Keys:      []string{"client_test"},
@@ -49,7 +106,6 @@ func TestService_sourceTransformFn(t *testing.T) {
 					},
 				},
 			},
-			wantErr: false,
 		},
 		{
 			name: "sourceTransform_fn_forward_msg_forward_to_all",
@@ -59,22 +115,23 @@ func TestService_sourceTransformFn(t *testing.T) {
 			}),
 			args: args{
 				ctx: context.Background(),
-				d: &stpb.SourceTransformRequest{
-					Keys:      []string{"client"},
-					Value:     []byte(`test`),
-					EventTime: timestamppb.New(time.Time{}),
-					Watermark: timestamppb.New(time.Time{}),
+				d: &proto.SourceTransformRequest{
+					Request: &proto.SourceTransformRequest_Request{
+						Keys:      []string{"client"},
+						Value:     []byte(`test`),
+						EventTime: timestamppb.New(time.Time{}),
+						Watermark: timestamppb.New(time.Time{}),
+					},
 				},
 			},
-			want: &stpb.SourceTransformResponse{
-				Results: []*stpb.SourceTransformResponse_Result{
+			want: &proto.SourceTransformResponse{
+				Results: []*proto.SourceTransformResponse_Result{
 					{
 						EventTime: timestamppb.New(testTime),
 						Value:     []byte(`test`),
 					},
 				},
 			},
-			wantErr: false,
 		},
 		{
 			name: "sourceTransform_fn_forward_msg_drop_msg",
@@ -83,42 +140,159 @@ func TestService_sourceTransformFn(t *testing.T) {
 			}),
 			args: args{
 				ctx: context.Background(),
-				d: &stpb.SourceTransformRequest{
-					Keys:      []string{"client"},
-					Value:     []byte(`test`),
-					EventTime: timestamppb.New(time.Time{}),
-					Watermark: timestamppb.New(time.Time{}),
+				d: &proto.SourceTransformRequest{
+					Request: &proto.SourceTransformRequest_Request{
+						Keys:      []string{"client"},
+						Value:     []byte(`test`),
+						EventTime: timestamppb.New(time.Time{}),
+						Watermark: timestamppb.New(time.Time{}),
+					},
 				},
 			},
-			want: &stpb.SourceTransformResponse{
-				Results: []*stpb.SourceTransformResponse_Result{
+			want: &proto.SourceTransformResponse{
+				Results: []*proto.SourceTransformResponse_Result{
 					{
 						EventTime: timestamppb.New(testTime),
 						Tags:      []string{DROP},
-						Value:     []byte{},
+						Value:     nil,
 					},
 				},
 			},
-			wantErr: false,
 		},
 	}
+
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			fs := &Service{
+			svc := &Service{
 				Transformer: tt.handler,
 			}
-			// here's a trick for testing:
-			// because we are not using gRPC, we directly set a new incoming ctx
-			// instead of the regular outgoing context in the real gRPC connection.
-			ctx := context.Background()
-			got, err := fs.SourceTransformFn(ctx, tt.args.d)
-			if (err != nil) != tt.wantErr {
-				t.Errorf("SourceTransformFn() error = %v, wantErr %v", err, tt.wantErr)
-				return
-			}
-			if !reflect.DeepEqual(got, tt.want) {
-				t.Errorf("SourceTransformFn() got = %v, want %v", got, tt.want)
-			}
+
+			conn := newTestServer(t, func(server *grpc.Server) {
+				proto.RegisterSourceTransformServer(server, svc)
+			})
+
+			client := proto.NewSourceTransformClient(conn)
+			stream, err := client.SourceTransformFn(context.Background())
+			require.NoError(t, err, "Creating stream")
+
+			doHandshake(t, stream)
+
+			err = stream.Send(tt.args.d)
+			require.NoError(t, err, "Sending message over the stream")
+
+			got, err := stream.Recv()
+			require.NoError(t, err, "Receiving message from the stream")
+
+			assert.Equal(t, got.Results, tt.want.Results)
 		})
 	}
 }
+
+func doHandshake(t *testing.T, stream proto.SourceTransform_SourceTransformFnClient) {
+	t.Helper()
+	handshakeReq := &proto.SourceTransformRequest{
+		Handshake: &proto.Handshake{Sot: true},
+	}
+	err := stream.Send(handshakeReq)
+	require.NoError(t, err, "Sending handshake request to the stream")
+
+	handshakeResp, err := stream.Recv()
+	require.NoError(t, err, "Receiving handshake response")
+
+	require.Empty(t, handshakeResp.Results, "Invalid handshake response")
+	require.Empty(t, handshakeResp.Id, "Invalid handshake response")
+	require.NotNil(t, handshakeResp.Handshake, "Invalid handshake response")
+	require.True(t, handshakeResp.Handshake.Sot, "Invalid handshake response")
+}
+
+func TestService_SourceTransformFn_Multiple_Messages(t *testing.T) {
+	svc := &Service{
+		Transformer: SourceTransformFunc(func(ctx context.Context, keys []string, datum Datum) Messages {
+			msg := datum.Value()
+			return MessagesBuilder().Append(NewMessage(msg, testTime).WithKeys([]string{keys[0] + "_test"}))
+		}),
+	}
+	conn := newTestServer(t, func(server *grpc.Server) {
+		proto.RegisterSourceTransformServer(server, svc)
+	})
+
+	client := proto.NewSourceTransformClient(conn)
+	stream, err := client.SourceTransformFn(context.Background())
+	require.NoError(t, err, "Creating stream")
+
+	doHandshake(t, stream)
+
+	const msgCount = 10
+	for i := 0; i < msgCount; i++ {
+		msg := proto.SourceTransformRequest{
+			Request: &proto.SourceTransformRequest_Request{
+				Keys:      []string{"client"},
+				Value:     []byte(fmt.Sprintf("test_%d", i)),
+				EventTime: timestamppb.New(time.Time{}),
+				Watermark: timestamppb.New(time.Time{}),
+			},
+		}
+		err = stream.Send(&msg)
+		require.NoError(t, err, "Sending message over the stream")
+	}
+	err = stream.CloseSend()
+	require.NoError(t, err, "Closing the send direction of the stream")
+
+	expectedResults := make([][]*proto.SourceTransformResponse_Result, msgCount)
+	for i := 0; i < msgCount; i++ {
+		expectedResults[i] = []*proto.SourceTransformResponse_Result{
+			{
+				EventTime: timestamppb.New(testTime),
+				Keys:      []string{"client_test"},
+				Value:     []byte(fmt.Sprintf("test_%d", i)),
+			},
+		}
+	}
+
+	results := make([][]*proto.SourceTransformResponse_Result, msgCount)
+	for i := 0; i < msgCount; i++ {
+		got, err := stream.Recv()
+		require.NoError(t, err, "Receiving message from the stream")
+		results[i] = got.Results
+	}
+	require.ElementsMatch(t, results, expectedResults)
+}
+
+func TestService_SourceTransformFn_Panic(t *testing.T) {
+	svc := &Service{
+		Transformer: SourceTransformFunc(func(ctx context.Context, keys []string, datum Datum) Messages {
+			panic("transformer panicked")
+		}),
+		// panic in the transformer causes the server to send a shutdown signal to shutdownCh channel.
+		// The function that errgroup runs in a goroutine will be blocked until this shutdown signal is received somewhere else.
+		// Since we don't listen for shutdown signal in the tests, we use buffered channel to unblock the server function.
+		shutdownCh: make(chan<- struct{}, 1),
+	}
+	conn := newTestServer(t, func(server *grpc.Server) {
+		proto.RegisterSourceTransformServer(server, svc)
+	})
+
+	client := proto.NewSourceTransformClient(conn)
+	stream, err := client.SourceTransformFn(context.Background())
+	require.NoError(t, err, "Creating stream")
+
+	doHandshake(t, stream)
+
+	msg := proto.SourceTransformRequest{
+		Request: &proto.SourceTransformRequest_Request{
+			Keys:      []string{"client"},
+			Value:     []byte("test"),
+			EventTime: timestamppb.New(time.Time{}),
+			Watermark: timestamppb.New(time.Time{}),
+		},
+	}
+	err = stream.Send(&msg)
+	require.NoError(t, err, "Sending message over the stream")
+	err = stream.CloseSend()
+	require.NoError(t, err, "Closing the send direction of the stream")
+	_, err = stream.Recv()
+	require.Error(t, err, "Expected error while receiving message from the stream")
+	gotStatus, _ := status.FromError(err)
+	expectedStatus := status.Convert(status.Errorf(codes.Internal, errTransformerPanic.Error()))
+	require.Equal(t, expectedStatus, gotStatus)
+}