diff --git a/api/services/control/control.pb.go b/api/services/control/control.pb.go
index 45ca3194e..c0862fcc0 100644
--- a/api/services/control/control.pb.go
+++ b/api/services/control/control.pb.go
@@ -19,6 +19,7 @@
 		Vertex
 		VertexStatus
 		VertexLog
+		BytesMessage
 */
 package moby_buildkit_v1
 
@@ -121,6 +122,7 @@ type SolveRequest struct {
 	Definition    [][]byte          `protobuf:"bytes,2,rep,name=Definition" json:"Definition,omitempty"`
 	Exporter      string            `protobuf:"bytes,3,opt,name=Exporter,proto3" json:"Exporter,omitempty"`
 	ExporterAttrs map[string]string `protobuf:"bytes,4,rep,name=ExporterAttrs" json:"ExporterAttrs,omitempty" protobuf_key:"bytes,1,opt,name=key,proto3" protobuf_val:"bytes,2,opt,name=value,proto3"`
+	Session       string            `protobuf:"bytes,5,opt,name=Session,proto3" json:"Session,omitempty"`
 }
 
 func (m *SolveRequest) Reset()                    { *m = SolveRequest{} }
@@ -156,6 +158,13 @@ func (m *SolveRequest) GetExporterAttrs() map[string]string {
 	return nil
 }
 
+func (m *SolveRequest) GetSession() string {
+	if m != nil {
+		return m.Session
+	}
+	return ""
+}
+
 type SolveResponse struct {
 	Vtx []*Vertex `protobuf:"bytes,1,rep,name=vtx" json:"vtx,omitempty"`
 }
@@ -369,6 +378,22 @@ func (m *VertexLog) GetMsg() []byte {
 	return nil
 }
 
+type BytesMessage struct {
+	Data []byte `protobuf:"bytes,1,opt,name=data,proto3" json:"data,omitempty"`
+}
+
+func (m *BytesMessage) Reset()                    { *m = BytesMessage{} }
+func (m *BytesMessage) String() string            { return proto.CompactTextString(m) }
+func (*BytesMessage) ProtoMessage()               {}
+func (*BytesMessage) Descriptor() ([]byte, []int) { return fileDescriptorControl, []int{10} }
+
+func (m *BytesMessage) GetData() []byte {
+	if m != nil {
+		return m.Data
+	}
+	return nil
+}
+
 func init() {
 	proto.RegisterType((*DiskUsageRequest)(nil), "moby.buildkit.v1.DiskUsageRequest")
 	proto.RegisterType((*DiskUsageResponse)(nil), "moby.buildkit.v1.DiskUsageResponse")
@@ -380,6 +405,7 @@ func init() {
 	proto.RegisterType((*Vertex)(nil), "moby.buildkit.v1.Vertex")
 	proto.RegisterType((*VertexStatus)(nil), "moby.buildkit.v1.VertexStatus")
 	proto.RegisterType((*VertexLog)(nil), "moby.buildkit.v1.VertexLog")
+	proto.RegisterType((*BytesMessage)(nil), "moby.buildkit.v1.BytesMessage")
 }
 
 // Reference imports to suppress errors if they are not otherwise used.
@@ -396,6 +422,7 @@ type ControlClient interface {
 	DiskUsage(ctx context.Context, in *DiskUsageRequest, opts ...grpc.CallOption) (*DiskUsageResponse, error)
 	Solve(ctx context.Context, in *SolveRequest, opts ...grpc.CallOption) (*SolveResponse, error)
 	Status(ctx context.Context, in *StatusRequest, opts ...grpc.CallOption) (Control_StatusClient, error)
+	Session(ctx context.Context, opts ...grpc.CallOption) (Control_SessionClient, error)
 }
 
 type controlClient struct {
@@ -456,12 +483,44 @@ func (x *controlStatusClient) Recv() (*StatusResponse, error) {
 	return m, nil
 }
 
+func (c *controlClient) Session(ctx context.Context, opts ...grpc.CallOption) (Control_SessionClient, error) {
+	stream, err := grpc.NewClientStream(ctx, &_Control_serviceDesc.Streams[1], c.cc, "/moby.buildkit.v1.Control/Session", opts...)
+	if err != nil {
+		return nil, err
+	}
+	x := &controlSessionClient{stream}
+	return x, nil
+}
+
+type Control_SessionClient interface {
+	Send(*BytesMessage) error
+	Recv() (*BytesMessage, error)
+	grpc.ClientStream
+}
+
+type controlSessionClient struct {
+	grpc.ClientStream
+}
+
+func (x *controlSessionClient) Send(m *BytesMessage) error {
+	return x.ClientStream.SendMsg(m)
+}
+
+func (x *controlSessionClient) Recv() (*BytesMessage, error) {
+	m := new(BytesMessage)
+	if err := x.ClientStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
 // Server API for Control service
 
 type ControlServer interface {
 	DiskUsage(context.Context, *DiskUsageRequest) (*DiskUsageResponse, error)
 	Solve(context.Context, *SolveRequest) (*SolveResponse, error)
 	Status(*StatusRequest, Control_StatusServer) error
+	Session(Control_SessionServer) error
 }
 
 func RegisterControlServer(s *grpc.Server, srv ControlServer) {
@@ -525,6 +584,32 @@ func (x *controlStatusServer) Send(m *StatusResponse) error {
 	return x.ServerStream.SendMsg(m)
 }
 
+func _Control_Session_Handler(srv interface{}, stream grpc.ServerStream) error {
+	return srv.(ControlServer).Session(&controlSessionServer{stream})
+}
+
+type Control_SessionServer interface {
+	Send(*BytesMessage) error
+	Recv() (*BytesMessage, error)
+	grpc.ServerStream
+}
+
+type controlSessionServer struct {
+	grpc.ServerStream
+}
+
+func (x *controlSessionServer) Send(m *BytesMessage) error {
+	return x.ServerStream.SendMsg(m)
+}
+
+func (x *controlSessionServer) Recv() (*BytesMessage, error) {
+	m := new(BytesMessage)
+	if err := x.ServerStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
 var _Control_serviceDesc = grpc.ServiceDesc{
 	ServiceName: "moby.buildkit.v1.Control",
 	HandlerType: (*ControlServer)(nil),
@@ -544,6 +629,12 @@ var _Control_serviceDesc = grpc.ServiceDesc{
 			Handler:       _Control_Status_Handler,
 			ServerStreams: true,
 		},
+		{
+			StreamName:    "Session",
+			Handler:       _Control_Session_Handler,
+			ServerStreams: true,
+			ClientStreams: true,
+		},
 	},
 	Metadata: "control.proto",
 }
@@ -697,6 +788,12 @@ func (m *SolveRequest) MarshalTo(dAtA []byte) (int, error) {
 			i += copy(dAtA[i:], v)
 		}
 	}
+	if len(m.Session) > 0 {
+		dAtA[i] = 0x2a
+		i++
+		i = encodeVarintControl(dAtA, i, uint64(len(m.Session)))
+		i += copy(dAtA[i:], m.Session)
+	}
 	return i, nil
 }
 
@@ -1006,6 +1103,30 @@ func (m *VertexLog) MarshalTo(dAtA []byte) (int, error) {
 	return i, nil
 }
 
+func (m *BytesMessage) Marshal() (dAtA []byte, err error) {
+	size := m.Size()
+	dAtA = make([]byte, size)
+	n, err := m.MarshalTo(dAtA)
+	if err != nil {
+		return nil, err
+	}
+	return dAtA[:n], nil
+}
+
+func (m *BytesMessage) MarshalTo(dAtA []byte) (int, error) {
+	var i int
+	_ = i
+	var l int
+	_ = l
+	if len(m.Data) > 0 {
+		dAtA[i] = 0xa
+		i++
+		i = encodeVarintControl(dAtA, i, uint64(len(m.Data)))
+		i += copy(dAtA[i:], m.Data)
+	}
+	return i, nil
+}
+
 func encodeFixed64Control(dAtA []byte, offset int, v uint64) int {
 	dAtA[offset] = uint8(v)
 	dAtA[offset+1] = uint8(v >> 8)
@@ -1095,6 +1216,10 @@ func (m *SolveRequest) Size() (n int) {
 			n += mapEntrySize + 1 + sovControl(uint64(mapEntrySize))
 		}
 	}
+	l = len(m.Session)
+	if l > 0 {
+		n += 1 + l + sovControl(uint64(l))
+	}
 	return n
 }
 
@@ -1232,6 +1357,16 @@ func (m *VertexLog) Size() (n int) {
 	return n
 }
 
+func (m *BytesMessage) Size() (n int) {
+	var l int
+	_ = l
+	l = len(m.Data)
+	if l > 0 {
+		n += 1 + l + sovControl(uint64(l))
+	}
+	return n
+}
+
 func sovControl(x uint64) (n int) {
 	for {
 		n++
@@ -1746,6 +1881,35 @@ func (m *SolveRequest) Unmarshal(dAtA []byte) error {
 				m.ExporterAttrs[mapkey] = mapvalue
 			}
 			iNdEx = postIndex
+		case 5:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field Session", wireType)
+			}
+			var stringLen uint64
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowControl
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				stringLen |= (uint64(b) & 0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			intStringLen := int(stringLen)
+			if intStringLen < 0 {
+				return ErrInvalidLengthControl
+			}
+			postIndex := iNdEx + intStringLen
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			m.Session = string(dAtA[iNdEx:postIndex])
+			iNdEx = postIndex
 		default:
 			iNdEx = preIndex
 			skippy, err := skipControl(dAtA[iNdEx:])
@@ -2752,6 +2916,87 @@ func (m *VertexLog) Unmarshal(dAtA []byte) error {
 	}
 	return nil
 }
+func (m *BytesMessage) Unmarshal(dAtA []byte) error {
+	l := len(dAtA)
+	iNdEx := 0
+	for iNdEx < l {
+		preIndex := iNdEx
+		var wire uint64
+		for shift := uint(0); ; shift += 7 {
+			if shift >= 64 {
+				return ErrIntOverflowControl
+			}
+			if iNdEx >= l {
+				return io.ErrUnexpectedEOF
+			}
+			b := dAtA[iNdEx]
+			iNdEx++
+			wire |= (uint64(b) & 0x7F) << shift
+			if b < 0x80 {
+				break
+			}
+		}
+		fieldNum := int32(wire >> 3)
+		wireType := int(wire & 0x7)
+		if wireType == 4 {
+			return fmt.Errorf("proto: BytesMessage: wiretype end group for non-group")
+		}
+		if fieldNum <= 0 {
+			return fmt.Errorf("proto: BytesMessage: illegal tag %d (wire type %d)", fieldNum, wire)
+		}
+		switch fieldNum {
+		case 1:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field Data", wireType)
+			}
+			var byteLen int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowControl
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				byteLen |= (int(b) & 0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if byteLen < 0 {
+				return ErrInvalidLengthControl
+			}
+			postIndex := iNdEx + byteLen
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			m.Data = append(m.Data[:0], dAtA[iNdEx:postIndex]...)
+			if m.Data == nil {
+				m.Data = []byte{}
+			}
+			iNdEx = postIndex
+		default:
+			iNdEx = preIndex
+			skippy, err := skipControl(dAtA[iNdEx:])
+			if err != nil {
+				return err
+			}
+			if skippy < 0 {
+				return ErrInvalidLengthControl
+			}
+			if (iNdEx + skippy) > l {
+				return io.ErrUnexpectedEOF
+			}
+			iNdEx += skippy
+		}
+	}
+
+	if iNdEx > l {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}
 func skipControl(dAtA []byte) (n int, err error) {
 	l := len(dAtA)
 	iNdEx := 0
@@ -2860,55 +3105,57 @@ var (
 func init() { proto.RegisterFile("control.proto", fileDescriptorControl) }
 
 var fileDescriptorControl = []byte{
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+	0xcf, 0x80, 0xe8, 0x23, 0xcf, 0x3c, 0x1c, 0xe8, 0x3e, 0x00, 0x9f, 0x01, 0xed, 0x1f, 0xa7, 0xbe,
+	0xe6, 0xd2, 0x96, 0xeb, 0x93, 0x67, 0xd6, 0xbf, 0x99, 0x9d, 0xf9, 0xcd, 0x9f, 0x85, 0x83, 0x29,
+	0x2b, 0x24, 0x67, 0x79, 0xbc, 0xe4, 0x4c, 0x32, 0x72, 0xb8, 0x60, 0x93, 0x75, 0x3c, 0x29, 0xb3,
+	0x7c, 0x36, 0xcf, 0x64, 0xbc, 0x7a, 0x1c, 0x3e, 0x4c, 0x33, 0xf9, 0xbc, 0x9c, 0xc4, 0x53, 0xb6,
+	0x38, 0x4a, 0x59, 0xca, 0x8e, 0x34, 0x70, 0x52, 0x5e, 0x68, 0x4d, 0x2b, 0x5a, 0x32, 0x0e, 0xc2,
+	0x5e, 0xca, 0x58, 0x9a, 0xe3, 0x4b, 0x94, 0xcc, 0x16, 0x28, 0x64, 0xb2, 0x58, 0x1a, 0x40, 0x44,
+	0xe0, 0x70, 0x9c, 0x89, 0xf9, 0x33, 0x91, 0xa4, 0x48, 0xf1, 0xa7, 0x12, 0x85, 0x8c, 0x4e, 0xe1,
+	0xfd, 0xda, 0x99, 0x58, 0xb2, 0x42, 0x20, 0xf9, 0x1c, 0x7c, 0x8e, 0x53, 0xc6, 0x67, 0x81, 0xd3,
+	0xf7, 0x06, 0xfb, 0xc3, 0x8f, 0xe2, 0x57, 0x63, 0x8b, 0xad, 0x81, 0x02, 0x51, 0x0b, 0x8e, 0x12,
+	0xd8, 0xaf, 0x1d, 0x93, 0x7b, 0xe0, 0x9e, 0x8c, 0x03, 0xa7, 0xef, 0x0c, 0xda, 0xd4, 0x3d, 0x19,
+	0x93, 0x00, 0x9a, 0x67, 0xa5, 0x4c, 0x26, 0x39, 0x06, 0x6e, 0xdf, 0x19, 0xb4, 0x68, 0xa5, 0x92,
+	0x0f, 0x60, 0xef, 0xa4, 0x78, 0x26, 0x30, 0xf0, 0xf4, 0xb9, 0x51, 0x08, 0x81, 0xc6, 0x79, 0xf6,
+	0x33, 0x06, 0x8d, 0xbe, 0x33, 0xf0, 0xa8, 0x96, 0xa3, 0x5f, 0x5d, 0xe8, 0x9c, 0xb3, 0x7c, 0x55,
+	0xc5, 0x4f, 0x0e, 0xc1, 0xa3, 0x78, 0x61, 0x6f, 0x51, 0x22, 0xe9, 0x02, 0x8c, 0xf1, 0x22, 0x2b,
+	0x32, 0x99, 0xb1, 0x22, 0x70, 0xfb, 0xde, 0xa0, 0x43, 0x6b, 0x27, 0x24, 0x84, 0xd6, 0x93, 0xcb,
+	0x25, 0xe3, 0x12, 0xb9, 0xbe, 0xaf, 0x4d, 0x37, 0x3a, 0xf9, 0x11, 0x0e, 0x2a, 0xf9, 0x1b, 0x29,
+	0xb9, 0x08, 0x1a, 0x3a, 0xff, 0xc7, 0xdb, 0xf9, 0xd7, 0x83, 0x88, 0x6f, 0xd8, 0x3c, 0x29, 0x24,
+	0x5f, 0xd3, 0x9b, 0x7e, 0x54, 0xee, 0xe7, 0x28, 0x84, 0x8a, 0x68, 0x4f, 0xdf, 0x59, 0xa9, 0xe1,
+	0xd7, 0x40, 0xb6, 0xcd, 0x55, 0x5a, 0x73, 0x5c, 0x57, 0x69, 0xcd, 0x71, 0xad, 0x38, 0x5a, 0x25,
+	0x79, 0x69, 0xb8, 0x6b, 0x53, 0xa3, 0x1c, 0xbb, 0x5f, 0x38, 0xd1, 0x97, 0x70, 0x60, 0xa3, 0xb1,
+	0xe5, 0x7b, 0x00, 0xde, 0x4a, 0x5e, 0xda, 0xda, 0x05, 0xdb, 0xb1, 0xff, 0x80, 0x5c, 0xe2, 0x25,
+	0x55, 0xa0, 0xe8, 0x63, 0x38, 0x38, 0x97, 0x89, 0x2c, 0xc5, 0x4e, 0x42, 0xa3, 0xdf, 0x1c, 0xb8,
+	0x57, 0x61, 0xec, 0x0d, 0x9f, 0x41, 0x6b, 0xa5, 0x9d, 0xa0, 0x78, 0xe3, 0x35, 0x1b, 0x24, 0x39,
+	0x86, 0x96, 0xd0, 0x7e, 0x50, 0xe8, 0xba, 0xec, 0x0f, 0xbb, 0xbb, 0xac, 0xec, 0x7d, 0x1b, 0x3c,
+	0x39, 0x82, 0x46, 0xce, 0x52, 0x11, 0x78, 0xda, 0xee, 0xc3, 0x5d, 0x76, 0xdf, 0xb3, 0x94, 0x6a,
+	0x60, 0x74, 0xe5, 0x82, 0x6f, 0xce, 0xc8, 0x29, 0xf8, 0xb3, 0x2c, 0x45, 0x21, 0x4d, 0x56, 0xa3,
+	0xe1, 0x8b, 0xab, 0xde, 0x7b, 0x7f, 0x5d, 0xf5, 0x1e, 0xd4, 0xe6, 0x8b, 0x2d, 0xb1, 0x50, 0xf3,
+	0x98, 0x64, 0x05, 0x72, 0x71, 0x94, 0xb2, 0x87, 0xc6, 0x24, 0x1e, 0xeb, 0x0f, 0xb5, 0x1e, 0x94,
+	0xaf, 0xac, 0x58, 0x96, 0xd2, 0x64, 0x70, 0x47, 0x5f, 0xc6, 0x83, 0x6a, 0xf0, 0x22, 0x59, 0xa0,
+	0xed, 0x42, 0x2d, 0x93, 0xfb, 0xe0, 0x4f, 0x93, 0xe9, 0x73, 0x9c, 0xe9, 0xb6, 0x6f, 0x51, 0xab,
+	0x91, 0x63, 0x68, 0x0a, 0x99, 0x70, 0x89, 0x33, 0xdd, 0x40, 0xfb, 0xc3, 0x30, 0x36, 0xe3, 0x1e,
+	0x57, 0xe3, 0x1e, 0x3f, 0xad, 0xc6, 0x7d, 0xd4, 0xf8, 0xe5, 0xef, 0x9e, 0x43, 0x2b, 0x03, 0xf2,
+	0x15, 0xb4, 0xa7, 0x6c, 0xb1, 0xcc, 0x51, 0x59, 0xfb, 0x6f, 0x69, 0xfd, 0xd2, 0x44, 0xb5, 0x1e,
+	0x72, 0xce, 0x78, 0xd0, 0x34, 0xad, 0xa7, 0x95, 0xe8, 0x5f, 0x17, 0x3a, 0xf5, 0x62, 0x6d, 0xcd,
+	0xfb, 0x29, 0xf8, 0xa6, 0xf4, 0xa6, 0x65, 0xef, 0x46, 0x95, 0xf1, 0x70, 0x2b, 0x55, 0x01, 0x34,
+	0xa7, 0x25, 0xe7, 0x58, 0x48, 0xbb, 0x22, 0x2a, 0x55, 0x05, 0x2c, 0x99, 0x4c, 0x72, 0x4d, 0x95,
+	0x47, 0x8d, 0x42, 0x46, 0xd0, 0xde, 0x6c, 0xc4, 0xb7, 0xa0, 0xa1, 0xa5, 0xc2, 0x35, 0x54, 0x6c,
+	0xcc, 0xea, 0x65, 0x68, 0xbe, 0x53, 0x19, 0x5a, 0xff, 0xbb, 0x0c, 0xd1, 0xef, 0x0e, 0xb4, 0x37,
+	0x5d, 0x5e, 0x63, 0xd7, 0x79, 0x67, 0x76, 0x6f, 0x30, 0xe3, 0xde, 0x8d, 0x99, 0xfb, 0xe0, 0x0b,
+	0xc9, 0x31, 0x59, 0xe8, 0x1a, 0x79, 0xd4, 0x6a, 0x6a, 0x9f, 0x2c, 0x44, 0xaa, 0x2b, 0xd4, 0xa1,
+	0x4a, 0x8c, 0x22, 0xe8, 0x8c, 0xd6, 0x12, 0xc5, 0x19, 0x0a, 0xf5, 0x5a, 0xa8, 0xda, 0xce, 0x12,
+	0x99, 0xe8, 0x3c, 0x3a, 0x54, 0xcb, 0xc3, 0x3f, 0x5c, 0x68, 0x7e, 0x6b, 0x9e, 0x47, 0xf2, 0x14,
+	0xda, 0x9b, 0x27, 0x8a, 0x44, 0xdb, 0x93, 0xff, 0xea, 0x9b, 0x16, 0x7e, 0xf2, 0x5a, 0x8c, 0x5d,
+	0x61, 0xdf, 0xc1, 0x9e, 0xde, 0x9a, 0xa4, 0xfb, 0xfa, 0xe5, 0x1e, 0xf6, 0x76, 0xfe, 0xb7, 0x9e,
+	0xce, 0xc0, 0xb7, 0x13, 0x70, 0x1b, 0xb4, 0xbe, 0x5c, 0xc3, 0xfe, 0x6e, 0x80, 0x71, 0xf6, 0xc8,
+	0x21, 0x67, 0x9b, 0xa7, 0xe2, 0xb6, 0xd0, 0xea, 0xcc, 0x85, 0x6f, 0xf8, 0x3f, 0x70, 0x1e, 0x39,
+	0xa3, 0xce, 0x8b, 0xeb, 0xae, 0xf3, 0xe7, 0x75, 0xd7, 0xf9, 0xe7, 0xba, 0xeb, 0x4c, 0x7c, 0x5d,
+	0xce, 0x4f, 0xff, 0x0b, 0x00, 0x00, 0xff, 0xff, 0xc9, 0xc1, 0x1a, 0x81, 0x7c, 0x08, 0x00, 0x00,
 }
diff --git a/api/services/control/control.proto b/api/services/control/control.proto
index d4ad20748..4a4af389b 100644
--- a/api/services/control/control.proto
+++ b/api/services/control/control.proto
@@ -13,6 +13,7 @@ service Control {
 	rpc DiskUsage(DiskUsageRequest) returns (DiskUsageResponse);
 	rpc Solve(SolveRequest) returns (SolveResponse);
 	rpc Status(StatusRequest) returns (stream StatusResponse);
+	rpc Session(stream BytesMessage) returns (stream BytesMessage);
 }
 
 message DiskUsageRequest {
@@ -34,6 +35,7 @@ message SolveRequest {
 	repeated bytes Definition = 2; // TODO: remove repeated
 	string Exporter = 3;
 	map<string, string> ExporterAttrs = 4;
+	string Session = 5;
 }
 
 message SolveResponse {
@@ -78,3 +80,7 @@ message VertexLog {
 	int64 stream = 3;
 	bytes msg = 4;
 }
+
+message BytesMessage {
+	bytes data = 1;
+}
\ No newline at end of file
diff --git a/client/client_test.go b/client/client_test.go
index dadf6f8f1..3b07ef679 100644
--- a/client/client_test.go
+++ b/client/client_test.go
@@ -106,6 +106,6 @@ func testBuildMultiMount(t *testing.T, address string) {
 	err = llb.WriteTo(dt, buf)
 	assert.Nil(t, err)
 
-	err = c.Solve(context.TODO(), buf, nil, "", nil)
+	err = c.Solve(context.TODO(), buf, nil, "", nil, "")
 	assert.Nil(t, err)
 }
diff --git a/client/llb/llb.go b/client/llb/llb.go
index 65605baaf..aa1736b00 100644
--- a/client/llb/llb.go
+++ b/client/llb/llb.go
@@ -78,6 +78,18 @@ func Scratch() *State {
 	return s
 }
 
+func Local(name string) *State {
+	return Source("local://" + name)
+}
+
+type LocalOption func(*source)
+
+func SessionID(id string) LocalOption {
+	return func(s *source) {
+		s.attrs[pb.AttrLocalSessionID] = id
+	}
+}
+
 type exec struct {
 	meta   Meta
 	mounts []*mount
diff --git a/client/local.go b/client/local.go
new file mode 100644
index 000000000..25c977079
--- /dev/null
+++ b/client/local.go
@@ -0,0 +1,5 @@
+package client
+
+func getSharedKey(dir string) (string, error) {
+	return dir, nil // not implemented
+}
diff --git a/client/solve.go b/client/solve.go
index a9cbf144d..4b71d5187 100644
--- a/client/solve.go
+++ b/client/solve.go
@@ -5,15 +5,29 @@ import (
 	"crypto/rand"
 	"encoding/hex"
 	"io"
+	"os"
+	"path/filepath"
+	"strings"
 	"time"
 
+	"github.com/Sirupsen/logrus"
 	controlapi "github.com/moby/buildkit/api/services/control"
 	"github.com/moby/buildkit/client/llb"
+	"github.com/moby/buildkit/session"
+	"github.com/moby/buildkit/session/filesync"
+	"github.com/moby/buildkit/session/grpchijack"
+	"github.com/moby/buildkit/solver/pb"
 	"github.com/pkg/errors"
 	"golang.org/x/sync/errgroup"
 )
 
-func (c *Client) Solve(ctx context.Context, r io.Reader, statusChan chan *SolveStatus, exporter string, exporterAttrs map[string]string) error {
+func (c *Client) Solve(ctx context.Context, r io.Reader, statusChan chan *SolveStatus, exporter string, exporterAttrs map[string]string, localDir string) error {
+	defer func() {
+		if statusChan != nil {
+			close(statusChan)
+		}
+	}()
+
 	def, err := llb.ReadFrom(r)
 	if err != nil {
 		return errors.Wrap(err, "failed to parse input")
@@ -23,10 +37,34 @@ func (c *Client) Solve(ctx context.Context, r io.Reader, statusChan chan *SolveS
 		return errors.New("invalid empty definition")
 	}
 
+	if err := validateLocals(def, localDir); err != nil {
+		return err
+	}
+
 	ref := generateID()
 	eg, ctx := errgroup.WithContext(ctx)
 
 	statusContext, cancelStatus := context.WithCancel(context.Background())
+	defer cancelStatus()
+
+	sharedKey, err := getSharedKey(localDir)
+	if err != nil {
+		return errors.Wrap(err, "failed to get build shared key")
+	}
+	s, err := session.NewSession(filepath.Base(localDir), sharedKey)
+	if err != nil {
+		return errors.Wrap(err, "failed to create session")
+	}
+
+	if localDir != "" {
+		_, dir, _ := parseLocalDir(localDir)
+		workdirProvider := filesync.NewFSSyncProvider(dir, nil)
+		s.Allow(workdirProvider)
+	}
+
+	eg.Go(func() error {
+		return s.Run(ctx, grpchijack.Dialer(c.controlClient()))
+	})
 
 	eg.Go(func() error {
 		defer func() { // make sure the Status ends cleanly on build errors
@@ -34,12 +72,15 @@ func (c *Client) Solve(ctx context.Context, r io.Reader, statusChan chan *SolveS
 				<-time.After(3 * time.Second)
 				cancelStatus()
 			}()
+			logrus.Debugf("stopping session")
+			s.Close()
 		}()
 		_, err = c.controlClient().Solve(ctx, &controlapi.SolveRequest{
 			Ref:           ref,
 			Definition:    def,
 			Exporter:      exporter,
 			ExporterAttrs: exporterAttrs,
+			Session:       s.UUID(),
 		})
 		if err != nil {
 			return errors.Wrap(err, "failed to solve")
@@ -100,12 +141,6 @@ func (c *Client) Solve(ctx context.Context, r io.Reader, statusChan chan *SolveS
 		}
 	})
 
-	defer func() {
-		if statusChan != nil {
-			close(statusChan)
-		}
-	}()
-
 	return eg.Wait()
 }
 
@@ -116,3 +151,44 @@ func generateID() string {
 	}
 	return hex.EncodeToString(b)
 }
+
+func validateLocals(defs [][]byte, localDir string) error {
+	k, _, err := parseLocalDir(localDir)
+	if err != nil {
+		return err
+	}
+	for _, dt := range defs {
+		var op pb.Op
+		if err := (&op).Unmarshal(dt); err != nil {
+			return errors.Wrap(err, "failed to parse llb proto op")
+		}
+		if src := op.GetSource(); src != nil {
+			if strings.HasPrefix(src.Identifier, "local://") { // TODO: just make a type property
+				name := strings.TrimPrefix(src.Identifier, "local://")
+				if name != k {
+					return errors.Errorf("local directory %s not enabled", name)
+				}
+			}
+		}
+	}
+	return nil
+}
+
+func parseLocalDir(str string) (string, string, error) {
+	if str == "" {
+		return "", "", nil
+	}
+	parts := strings.SplitN(str, "=", 2)
+	if len(parts) != 2 {
+		return "", "", errors.Errorf("invalid local indentifier %q, need name=dir", str)
+	}
+	fi, err := os.Stat(parts[1])
+	if err != nil {
+		return "", "", errors.Wrapf(err, "could not find %s", parts[1])
+	}
+	if !fi.IsDir() {
+		return "", "", errors.Errorf("%s not a directory", parts[1])
+	}
+	return parts[0], parts[1], nil
+
+}
diff --git a/cmd/buildctl/build.go b/cmd/buildctl/build.go
index 06b2adf80..6e597ea32 100644
--- a/cmd/buildctl/build.go
+++ b/cmd/buildctl/build.go
@@ -33,6 +33,10 @@ var buildCommand = cli.Command{
 			Name:  "no-progress",
 			Usage: "Don't show interactive progress",
 		},
+		cli.StringFlag{
+			Name:  "local",
+			Usage: "Allow build access to the local directory",
+		},
 	},
 }
 
@@ -61,7 +65,7 @@ func build(clicontext *cli.Context) error {
 	}
 
 	eg.Go(func() error {
-		return c.Solve(ctx, os.Stdin, ch, clicontext.String("exporter"), exporterAttrs)
+		return c.Solve(ctx, os.Stdin, ch, clicontext.String("exporter"), exporterAttrs, clicontext.String("local"))
 	})
 
 	eg.Go(func() error {
diff --git a/control/control.go b/control/control.go
index 51e9618b1..95e214db9 100644
--- a/control/control.go
+++ b/control/control.go
@@ -1,11 +1,14 @@
 package control
 
 import (
+	"github.com/Sirupsen/logrus"
 	"github.com/containerd/containerd/snapshot"
 	controlapi "github.com/moby/buildkit/api/services/control"
 	"github.com/moby/buildkit/cache"
 	"github.com/moby/buildkit/client"
 	"github.com/moby/buildkit/exporter"
+	"github.com/moby/buildkit/session"
+	"github.com/moby/buildkit/session/grpchijack"
 	"github.com/moby/buildkit/solver"
 	"github.com/moby/buildkit/source"
 	"github.com/moby/buildkit/worker"
@@ -22,6 +25,7 @@ type Opt struct {
 	SourceManager    *source.Manager
 	InstructionCache solver.InstructionCache
 	Exporters        map[string]exporter.Exporter
+	SessionManager   *session.Manager
 }
 
 type Controller struct { // TODO: ControlService
@@ -83,6 +87,8 @@ func (c *Controller) Solve(ctx context.Context, req *controlapi.SolveRequest) (*
 		}
 	}
 
+	ctx = session.NewContext(ctx, req.Session)
+
 	if err := c.solver.Solve(ctx, req.Ref, v, expi); err != nil {
 		return nil, err
 	}
@@ -147,3 +153,12 @@ func (c *Controller) Status(req *controlapi.StatusRequest, stream controlapi.Con
 
 	return eg.Wait()
 }
+
+func (c *Controller) Session(stream controlapi.Control_SessionServer) error {
+	logrus.Debugf("session started")
+	conn, opts := grpchijack.Hijack(stream)
+	defer conn.Close()
+	err := c.opt.SessionManager.HandleConn(stream.Context(), conn, opts)
+	logrus.Debugf("session finished: %v", err)
+	return err
+}
diff --git a/control/control_default.go b/control/control_default.go
index a313fe0c3..ab21bfaff 100644
--- a/control/control_default.go
+++ b/control/control_default.go
@@ -14,10 +14,12 @@ import (
 	"github.com/moby/buildkit/cache/metadata"
 	"github.com/moby/buildkit/exporter"
 	imageexporter "github.com/moby/buildkit/exporter/containerimage"
+	"github.com/moby/buildkit/session"
 	"github.com/moby/buildkit/snapshot/blobmapping"
 	"github.com/moby/buildkit/source"
 	"github.com/moby/buildkit/source/containerimage"
 	"github.com/moby/buildkit/source/git"
+	"github.com/moby/buildkit/source/local"
 )
 
 const keyImageExporter = "image"
@@ -85,6 +87,20 @@ func defaultControllerOpts(root string, pd pullDeps) (*Opt, error) {
 
 	sm.Register(gs)
 
+	sessm, err := session.NewManager()
+	if err != nil {
+		return nil, err
+	}
+
+	ss, err := local.NewSource(local.Opt{
+		SessionManager: sessm,
+		CacheAccessor:  cm,
+	})
+	if err != nil {
+		return nil, err
+	}
+	sm.Register(ss)
+
 	exporters := map[string]exporter.Exporter{}
 
 	imageExporter, err := imageexporter.New(imageexporter.Opt{
@@ -105,5 +121,6 @@ func defaultControllerOpts(root string, pd pullDeps) (*Opt, error) {
 		SourceManager:    sm,
 		InstructionCache: ic,
 		Exporters:        exporters,
+		SessionManager:   sessm,
 	}, nil
 }
diff --git a/session/context.go b/session/context.go
new file mode 100644
index 000000000..4f10f30c1
--- /dev/null
+++ b/session/context.go
@@ -0,0 +1,22 @@
+package session
+
+import "context"
+
+type contextKeyT string
+
+var contextKey = contextKeyT("buildkit/session-uuid")
+
+func NewContext(ctx context.Context, uuid string) context.Context {
+	if uuid != "" {
+		return context.WithValue(ctx, contextKey, uuid)
+	}
+	return ctx
+}
+
+func FromContext(ctx context.Context) string {
+	v := ctx.Value(contextKey)
+	if v == nil {
+		return ""
+	}
+	return v.(string)
+}
diff --git a/session/filesync/diffcopy.go b/session/filesync/diffcopy.go
index 533847acd..ab5c549aa 100644
--- a/session/filesync/diffcopy.go
+++ b/session/filesync/diffcopy.go
@@ -3,10 +3,9 @@ package filesync
 import (
 	"time"
 
-	"google.golang.org/grpc"
-
 	"github.com/Sirupsen/logrus"
 	"github.com/tonistiigi/fsutil"
+	"google.golang.org/grpc"
 )
 
 func sendDiffCopy(stream grpc.Stream, dir string, includes, excludes []string, progress progressCb) error {
diff --git a/session/filesync/filesync.go b/session/filesync/filesync.go
index fe4d00a72..2a1ea365a 100644
--- a/session/filesync/filesync.go
+++ b/session/filesync/filesync.go
@@ -1,6 +1,7 @@
 package filesync
 
 import (
+	"fmt"
 	"os"
 	"strings"
 
@@ -177,6 +178,8 @@ func FSSync(ctx context.Context, c session.Caller, opt FSSendRequestOpt) error {
 			return err
 		}
 		stream = cc
+	default:
+		panic(fmt.Sprintf("invalid protocol: %q", pr.name))
 	}
 
 	return pr.recvFn(stream, opt.DestDir, opt.CacheUpdater)
diff --git a/session/grpchijack/dial.go b/session/grpchijack/dial.go
new file mode 100644
index 000000000..c820bb9a1
--- /dev/null
+++ b/session/grpchijack/dial.go
@@ -0,0 +1,123 @@
+package grpchijack
+
+import (
+	"net"
+	"strings"
+	"sync"
+	"time"
+
+	controlapi "github.com/moby/buildkit/api/services/control"
+	"github.com/moby/buildkit/session"
+	"golang.org/x/net/context"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/metadata"
+)
+
+var bufPool = sync.Pool{
+	New: func() interface{} {
+		return make([]byte, 32*1<<10)
+	},
+}
+
+func Dialer(api controlapi.ControlClient) session.Dialer {
+	return func(ctx context.Context, proto string, meta map[string][]string) (net.Conn, error) {
+
+		meta = lowerHeaders(meta)
+
+		md := metadata.MD(meta)
+
+		ctx = metadata.NewContext(context.Background(), md)
+
+		stream, err := api.Session(ctx)
+		if err != nil {
+			return nil, err
+		}
+
+		return streamToConn(stream), nil
+	}
+}
+
+func streamToConn(stream grpc.Stream) net.Conn {
+	return &conn{stream: stream, buf: make([]byte, 32*1<<10)}
+}
+
+type conn struct {
+	stream  grpc.Stream
+	buf     []byte
+	lastBuf []byte
+}
+
+func (c *conn) Read(b []byte) (int, error) {
+	if c.lastBuf != nil {
+		n := copy(b, c.lastBuf)
+		c.lastBuf = c.lastBuf[n:]
+		if len(c.lastBuf) == 0 {
+			c.lastBuf = nil
+		}
+		return n, nil
+	}
+	m := new(controlapi.BytesMessage)
+	m.Data = c.buf
+
+	if err := c.stream.RecvMsg(m); err != nil {
+		return 0, err
+	}
+	c.buf = m.Data[:cap(m.Data)]
+
+	n := copy(b, m.Data)
+	if n < len(m.Data) {
+		c.lastBuf = m.Data[n:]
+	}
+
+	return n, nil
+}
+
+func (c *conn) Write(b []byte) (int, error) {
+	m := &controlapi.BytesMessage{Data: b}
+	if err := c.stream.SendMsg(m); err != nil {
+		return 0, err
+	}
+	return len(b), nil
+}
+
+func (s *conn) Close() error {
+	if cs, ok := s.stream.(grpc.ClientStream); ok {
+		return cs.CloseSend()
+	}
+	return nil
+}
+
+func (s *conn) LocalAddr() net.Addr {
+	return dummyAddr{}
+}
+func (s *conn) RemoteAddr() net.Addr {
+	return dummyAddr{}
+}
+func (s *conn) SetDeadline(t time.Time) error {
+	return nil
+}
+func (s *conn) SetReadDeadline(t time.Time) error {
+	return nil
+}
+func (s *conn) SetWriteDeadline(t time.Time) error {
+	return nil
+}
+
+type dummyAddr struct {
+}
+
+func (d dummyAddr) Network() string {
+	return "tcp"
+}
+
+func (d dummyAddr) String() string {
+	return "localhost"
+}
+
+func lowerHeaders(in map[string][]string) map[string][]string {
+	out := map[string][]string{}
+	for k := range in {
+		out[strings.ToLower(k)] = in[k]
+	}
+	return out
+}
diff --git a/session/grpchijack/hijack.go b/session/grpchijack/hijack.go
new file mode 100644
index 000000000..2c9cc81bf
--- /dev/null
+++ b/session/grpchijack/hijack.go
@@ -0,0 +1,13 @@
+package grpchijack
+
+import (
+	"net"
+
+	controlapi "github.com/moby/buildkit/api/services/control"
+	"google.golang.org/grpc/metadata"
+)
+
+func Hijack(stream controlapi.Control_SessionServer) (net.Conn, map[string][]string) {
+	md, _ := metadata.FromContext(stream.Context())
+	return streamToConn(stream), md
+}
diff --git a/session/manager.go b/session/manager.go
index 9523e6f31..e44957fed 100644
--- a/session/manager.go
+++ b/session/manager.go
@@ -102,6 +102,8 @@ func (sm *Manager) handleConn(ctx context.Context, conn net.Conn, opts map[strin
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 
+	opts = canonicalHeaders(opts)
+
 	h := http.Header(opts)
 	uuid := h.Get(headerSessionUUID)
 	name := h.Get(headerSessionName)
@@ -200,3 +202,11 @@ func (c *client) Supports(url string) bool {
 func (c *client) Conn() *grpc.ClientConn {
 	return c.cc
 }
+
+func canonicalHeaders(in map[string][]string) map[string][]string {
+	out := map[string][]string{}
+	for k := range in {
+		out[http.CanonicalHeaderKey(k)] = in[k]
+	}
+	return out
+}
diff --git a/session/session.go b/session/session.go
index 147486a75..d29f6f47a 100644
--- a/session/session.go
+++ b/session/session.go
@@ -92,6 +92,7 @@ func (s *Session) Run(ctx context.Context, dialer Dialer) error {
 // Close closes the session
 func (s *Session) Close() error {
 	if s.cancelCtx != nil && s.done != nil {
+		s.grpcServer.Stop()
 		s.cancelCtx()
 		<-s.done
 	}
diff --git a/solver/pb/attr.go b/solver/pb/attr.go
index 64ac3886d..0e84fe6a4 100644
--- a/solver/pb/attr.go
+++ b/solver/pb/attr.go
@@ -1,3 +1,4 @@
 package pb
 
 const AttrKeepGitDir = "git.keepgitdir"
+const AttrLocalSessionID = "local.session"
diff --git a/solver/source.go b/solver/source.go
index 378aa25fa..e551bf707 100644
--- a/solver/source.go
+++ b/solver/source.go
@@ -42,6 +42,14 @@ func (s *sourceOp) instance(ctx context.Context) (source.SourceInstance, error)
 			}
 		}
 	}
+	if id, ok := id.(*source.LocalIdentifier); ok {
+		for k, v := range s.op.Source.Attrs {
+			switch k {
+			case pb.AttrLocalSessionID:
+				id.SessionID = v
+			}
+		}
+	}
 	src, err := s.sm.Resolve(ctx, id)
 	if err != nil {
 		return nil, err
diff --git a/solver/vertex.go b/solver/vertex.go
index b30b24368..a6cb99280 100644
--- a/solver/vertex.go
+++ b/solver/vertex.go
@@ -83,6 +83,7 @@ func (v *vertex) notifyStarted(ctx context.Context) {
 	defer pw.Close()
 	now := time.Now()
 	v.clientVertex.Started = &now
+	v.clientVertex.Completed = nil
 	pw.Write(v.Digest().String(), v.clientVertex)
 }
 
diff --git a/source/identifier.go b/source/identifier.go
index 926ffb5a9..0bd364188 100644
--- a/source/identifier.go
+++ b/source/identifier.go
@@ -15,6 +15,7 @@ var (
 const (
 	DockerImageScheme = "docker-image"
 	GitScheme         = "git"
+	LocalScheme       = "local"
 )
 
 type Identifier interface {
@@ -33,6 +34,8 @@ func FromString(s string) (Identifier, error) {
 		return NewImageIdentifier(parts[1])
 	case GitScheme:
 		return NewGitIdentifier(parts[1])
+	case LocalScheme:
+		return NewLocalIdentifier(parts[1])
 	default:
 		return nil, errors.Wrapf(errNotFound, "unknown schema %s", parts[0])
 	}
@@ -54,6 +57,19 @@ func NewImageIdentifier(str string) (*ImageIdentifier, error) {
 	return &ImageIdentifier{Reference: ref}, nil
 }
 
-func (i *ImageIdentifier) ID() string {
+func (_ *ImageIdentifier) ID() string {
 	return DockerImageScheme
 }
+
+type LocalIdentifier struct {
+	Name      string
+	SessionID string
+}
+
+func NewLocalIdentifier(str string) (*LocalIdentifier, error) {
+	return &LocalIdentifier{Name: str}, nil
+}
+
+func (_ *LocalIdentifier) ID() string {
+	return LocalScheme
+}
diff --git a/source/local/local.go b/source/local/local.go
new file mode 100644
index 000000000..f95d97713
--- /dev/null
+++ b/source/local/local.go
@@ -0,0 +1,138 @@
+package local
+
+import (
+	"time"
+
+	"github.com/moby/buildkit/cache"
+	"github.com/moby/buildkit/session"
+	"github.com/moby/buildkit/session/filesync"
+	"github.com/moby/buildkit/snapshot"
+	"github.com/moby/buildkit/source"
+	"github.com/pkg/errors"
+	"golang.org/x/net/context"
+)
+
+type Opt struct {
+	SessionManager *session.Manager
+	CacheAccessor  cache.Accessor
+}
+
+func NewSource(opt Opt) (source.Source, error) {
+	ls := &localSource{
+		sm: opt.SessionManager,
+		cm: opt.CacheAccessor,
+	}
+	return ls, nil
+}
+
+type localSource struct {
+	sm *session.Manager
+	cm cache.Accessor
+}
+
+func (ls *localSource) ID() string {
+	return source.LocalScheme
+}
+
+func (ls *localSource) Resolve(ctx context.Context, id source.Identifier) (source.SourceInstance, error) {
+	localIdentifier, ok := id.(*source.LocalIdentifier)
+	if !ok {
+		return nil, errors.Errorf("invalid local identifier %v", id)
+	}
+
+	return &localSourceHandler{
+		src:         *localIdentifier,
+		localSource: ls,
+	}, nil
+}
+
+type localSourceHandler struct {
+	src source.LocalIdentifier
+	*localSource
+}
+
+func (ls *localSourceHandler) CacheKey(ctx context.Context) (string, error) {
+	sessionID := ls.src.SessionID
+
+	if sessionID == "" {
+		uuid := session.FromContext(ctx)
+		if uuid == "" {
+			return "", errors.New("could not access local files without session")
+		}
+		sessionID = uuid
+	}
+
+	return "session:" + ls.src.Name + ":" + sessionID, nil
+}
+
+func (ls *localSourceHandler) Snapshot(ctx context.Context) (out cache.ImmutableRef, retErr error) {
+
+	uuid := session.FromContext(ctx)
+	if uuid == "" {
+		return nil, errors.New("could not access local files without session")
+	}
+
+	timeoutCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	defer cancel()
+
+	caller, err := ls.sm.Get(timeoutCtx, uuid)
+	if err != nil {
+		return nil, err
+	}
+
+	mutable, err := ls.cm.New(ctx, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	defer func() {
+		if retErr != nil && mutable != nil {
+			s, err := mutable.Freeze()
+			if err == nil {
+				go s.Release(context.TODO())
+			}
+		}
+	}()
+
+	mount, err := mutable.Mount(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	lm := snapshot.LocalMounter(mount)
+
+	dest, err := lm.Mount()
+	if err != nil {
+		return nil, err
+	}
+
+	defer func() {
+		if retErr != nil && lm != nil {
+			lm.Unmount()
+		}
+	}()
+
+	opt := filesync.FSSendRequestOpt{
+		IncludePatterns:  nil,
+		OverrideExcludes: false,
+		DestDir:          dest,
+		CacheUpdater:     nil,
+	}
+
+	if err := filesync.FSSync(ctx, caller, opt); err != nil {
+		return nil, err
+	}
+
+	if err := lm.Unmount(); err != nil {
+		return nil, err
+	}
+	lm = nil
+
+	snap, err := mutable.ReleaseAndCommit(ctx)
+	if err != nil {
+		return nil, err
+	}
+	mutable = nil
+
+	return snap, err
+}