Added support for marshalling subgraph to protocol buffers

1. Added subgraph.proto file which has the message structure.
2. Added ToProtocolBuffer method which converts a subgraph to protocol buffer.

query/protocolbuffer/subgraph.pb.go

+// Code generated by protoc-gen-go.
+// source: subgraph.proto
+// DO NOT EDIT!
+
+/*
+Package protocolbuffer is a generated protocol buffer package.
+
+It is generated from these files:
+	subgraph.proto
+
+It has these top-level messages:
+	UidList
+	Result
+	SubGraph
+*/
+package protocolbuffer
+
+import proto "github.com/golang/protobuf/proto"
+import fmt "fmt"
+import math "math"
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ = proto.Marshal
+var _ = fmt.Errorf
+var _ = math.Inf
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the proto package it is being compiled against.
+const _ = proto.ProtoPackageIsVersion1
+
+type UidList struct {
+	Uids []uint64 `protobuf:"fixed64,1,rep,packed,name=uids" json:"uids,omitempty"`
+}
+
+func (m *UidList) Reset()                    { *m = UidList{} }
+func (m *UidList) String() string            { return proto.CompactTextString(m) }
+func (*UidList) ProtoMessage()               {}
+func (*UidList) Descriptor() ([]byte, []int) { return fileDescriptor0, []int{0} }
+
+type Result struct {
+	Values    [][]byte   `protobuf:"bytes,1,rep,name=values,proto3" json:"values,omitempty"`
+	Uidmatrix []*UidList `protobuf:"bytes,2,rep,name=uidmatrix" json:"uidmatrix,omitempty"`
+}
+
+func (m *Result) Reset()                    { *m = Result{} }
+func (m *Result) String() string            { return proto.CompactTextString(m) }
+func (*Result) ProtoMessage()               {}
+func (*Result) Descriptor() ([]byte, []int) { return fileDescriptor0, []int{1} }
+
+func (m *Result) GetUidmatrix() []*UidList {
+	if m != nil {
+		return m.Uidmatrix
+	}
+	return nil
+}
+
+type SubGraph struct {
+	Attr     string      `protobuf:"bytes,1,opt,name=attr" json:"attr,omitempty"`
+	Children []*SubGraph `protobuf:"bytes,2,rep,name=children" json:"children,omitempty"`
+	Result   *Result     `protobuf:"bytes,3,opt,name=result" json:"result,omitempty"`
+}
+
+func (m *SubGraph) Reset()                    { *m = SubGraph{} }
+func (m *SubGraph) String() string            { return proto.CompactTextString(m) }
+func (*SubGraph) ProtoMessage()               {}
+func (*SubGraph) Descriptor() ([]byte, []int) { return fileDescriptor0, []int{2} }
+
+func (m *SubGraph) GetChildren() []*SubGraph {
+	if m != nil {
+		return m.Children
+	}
+	return nil
+}
+
+func (m *SubGraph) GetResult() *Result {
+	if m != nil {
+		return m.Result
+	}
+	return nil
+}
+
+func init() {
+	proto.RegisterType((*UidList)(nil), "protocolbuffer.UidList")
+	proto.RegisterType((*Result)(nil), "protocolbuffer.Result")
+	proto.RegisterType((*SubGraph)(nil), "protocolbuffer.SubGraph")
+}
+
+var fileDescriptor0 = []byte{
+	// 212 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x09, 0x6e, 0x88, 0x02, 0xff, 0xe2, 0xe2, 0x2b, 0x2e, 0x4d, 0x4a,
+	0x2f, 0x4a, 0x2c, 0xc8, 0xd0, 0x2b, 0x28, 0xca, 0x2f, 0xc9, 0x17, 0xe2, 0x03, 0x53, 0xc9, 0xf9,
+	0x39, 0x49, 0xa5, 0x69, 0x69, 0xa9, 0x45, 0x4a, 0x8a, 0x5c, 0xec, 0xa1, 0x99, 0x29, 0x3e, 0x99,
+	0xc5, 0x25, 0x42, 0x62, 0x5c, 0x2c, 0xa5, 0x99, 0x29, 0xc5, 0x12, 0x8c, 0x0a, 0xcc, 0x1a, 0x6c,
+	0x4e, 0x4c, 0x02, 0x8c, 0x41, 0x60, 0xbe, 0x52, 0x38, 0x17, 0x5b, 0x50, 0x6a, 0x71, 0x69, 0x0e,
+	0x48, 0x05, 0x5b, 0x59, 0x62, 0x4e, 0x69, 0x2a, 0x44, 0x0d, 0x4f, 0x10, 0x94, 0x27, 0x64, 0xca,
+	0xc5, 0x09, 0x54, 0x99, 0x9b, 0x58, 0x52, 0x94, 0x59, 0x21, 0xc1, 0x04, 0x94, 0xe2, 0x36, 0x12,
+	0xd7, 0x43, 0xb5, 0x48, 0x0f, 0x6a, 0x4b, 0x10, 0x42, 0xa5, 0x52, 0x0b, 0x23, 0x17, 0x47, 0x70,
+	0x69, 0x92, 0x3b, 0xc8, 0x79, 0x42, 0x42, 0x5c, 0x2c, 0x89, 0x25, 0x25, 0x45, 0x40, 0x93, 0x19,
+	0x35, 0x38, 0x83, 0xc0, 0x6c, 0x21, 0x13, 0x2e, 0x8e, 0xe4, 0x8c, 0xcc, 0x9c, 0x94, 0xa2, 0xd4,
+	0x3c, 0xa8, 0xb1, 0x12, 0xe8, 0xc6, 0xc2, 0xf4, 0x07, 0xc1, 0x55, 0x0a, 0xe9, 0x71, 0xb1, 0x15,
+	0x81, 0xdd, 0x2b, 0xc1, 0x0c, 0x34, 0x8b, 0xdb, 0x48, 0x0c, 0x5d, 0x0f, 0xc4, 0x37, 0x41, 0x50,
+	0x55, 0x49, 0x6c, 0x60, 0x69, 0x63, 0x40, 0x00, 0x00, 0x00, 0xff, 0xff, 0xfd, 0x1f, 0xc8, 0xb1,
+	0x2b, 0x01, 0x00, 0x00,
+}

query/protocolbuffer/subgraph.proto

+syntax="proto3";
+package protocolbuffer;
+
+message UidList {
+  repeated fixed64 uids = 1 [packed=true];;
+}
+
+message Result {
+  repeated bytes values = 1;
+  repeated UidList uidmatrix = 2;
+}
+
+message SubGraph {
+  string attr = 1;
+  repeated SubGraph children = 2; //Each node can have multiple children
+  Result result = 3;
+}
\ No newline at end of file

query/query.go

@@ -26,9 +26,11 @@ import (
 	"github.com/Sirupsen/logrus"
 	"github.com/dgraph-io/dgraph/gql"
 	"github.com/dgraph-io/dgraph/posting"
+	"github.com/dgraph-io/dgraph/query/protocolbuffer"
 	"github.com/dgraph-io/dgraph/task"
 	"github.com/dgraph-io/dgraph/worker"
 	"github.com/dgraph-io/dgraph/x"
+	"github.com/golang/protobuf/proto"
 	"github.com/google/flatbuffers/go"
 )
 
@@ -251,6 +253,70 @@ func (g *SubGraph) ToJson(l *Latency) (js []byte, rerr error) {
 	return json.Marshal(r)
 }
 
+func preTraverse(g *SubGraph) (sg *protocolbuffer.SubGraph, rerr error) {
+	sg = &protocolbuffer.SubGraph{}
+	sg.Attr = g.Attr
+
+	ro := flatbuffers.GetUOffsetT(g.result)
+	r := new(task.Result)
+	r.Init(g.result, ro)
+
+	var ul task.UidList
+	result := &protocolbuffer.Result{}
+	for i := 0; i < r.UidmatrixLength(); i++ {
+		if ok := r.Uidmatrix(&ul, i); !ok {
+			return sg, fmt.Errorf("While parsing UidList")
+		}
+		uidList := &protocolbuffer.UidList{}
+		for j := 0; j < ul.UidsLength(); j++ {
+			uid := ul.Uids(j)
+			uidList.Uids = append(uidList.Uids, uid)
+		}
+		result.Uidmatrix = append(result.Uidmatrix, uidList)
+	}
+
+	var tv task.Value
+	for i := 0; i < r.ValuesLength(); i++ {
+		if ok := r.Values(&tv, i); !ok {
+			return sg, fmt.Errorf("While parsing value")
+		}
+		var ival interface{}
+		if err := posting.ParseValue(&ival, tv.ValBytes()); err != nil {
+			return sg, err
+		}
+		if ival == nil {
+			continue
+		}
+		result.Values = append(result.Values, []byte(ival.(string)))
+	}
+
+	sg.Result = result
+
+	for _, child := range g.Children {
+		childSg, err := preTraverse(child)
+		if err != nil {
+			x.Err(glog, err).Error("Error while traversal")
+			return sg, err
+		}
+		sg.Children = append(sg.Children, childSg)
+	}
+	return sg, nil
+}
+
+func (g *SubGraph) ToProtocolBuffer() (pb []byte, rerr error) {
+	sg, err := preTraverse(g)
+	if err != nil {
+		x.Err(glog, err).Error("Error while traversal")
+		return pb, err
+	}
+	pb, err = proto.Marshal(sg)
+	if err != nil {
+		x.Err(glog, err).Error("Error while marshalling to protocol buffer")
+		return pb, err
+	}
+	return pb, nil
+}
+
 func treeCopy(gq *gql.GraphQuery, sg *SubGraph) {
 	for _, gchild := range gq.Children {
 		dst := new(SubGraph)

query/query_test.go

@@ -26,10 +26,12 @@ import (
 	"github.com/dgraph-io/dgraph/commit"
 	"github.com/dgraph-io/dgraph/gql"
 	"github.com/dgraph-io/dgraph/posting"
+	"github.com/dgraph-io/dgraph/query/protocolbuffer"
 	"github.com/dgraph-io/dgraph/store"
 	"github.com/dgraph-io/dgraph/task"
 	"github.com/dgraph-io/dgraph/worker"
 	"github.com/dgraph-io/dgraph/x"
+	"github.com/golang/protobuf/proto"
 	"github.com/google/flatbuffers/go"
 )
 
@@ -319,3 +321,79 @@ func TestToJson(t *testing.T) {
 	}
 	fmt.Printf(string(js))
 }
+
+func TestToProtocolBuffer(t *testing.T) {
+	dir, _ := populateGraph(t)
+	defer os.RemoveAll(dir)
+
+	query := `
+		{
+			me(_uid_:0x01) {
+				name
+				gender
+				status
+				friend {
+					name
+				}
+			}
+		}
+	`
+
+	gq, _, err := gql.Parse(query)
+	if err != nil {
+		t.Error(err)
+	}
+	sg, err := ToSubGraph(gq)
+	if err != nil {
+		t.Error(err)
+	}
+
+	ch := make(chan error)
+	go ProcessGraph(sg, ch)
+	err = <-ch
+	if err != nil {
+		t.Error(err)
+	}
+
+	pb, err := sg.ToProtocolBuffer()
+	if err != nil {
+		t.Error(err)
+	}
+
+	// Unmarshalling to a protocol buffer subgraph for testing
+	usg := &protocolbuffer.SubGraph{}
+	err = proto.Unmarshal(pb, usg)
+	if err != nil {
+		t.Error(err)
+	}
+
+	if len(usg.Children) != 4 {
+		t.Errorf("Expected len 4. Got: %v", usg.Children)
+	}
+	child := usg.Children[0]
+	if child.Attr != "name" {
+		t.Errorf("Expected attr name. Got: %v", child.Attr)
+	}
+	if string(child.Result.Values[0]) != "Michonne" {
+		t.Errorf("Expected value Michonne. Got %v", string(child.Result.Values[0]))
+	}
+	child = usg.Children[3]
+	if child.Attr != "friend" {
+		t.Errorf("Expected attr friend. Got: %v", child.Attr)
+	}
+	uids := child.Result.Uidmatrix[0].Uids
+	if uids[0] != 23 || uids[1] != 24 || uids[2] != 25 || uids[3] != 31 || uids[4] != 101 {
+		t.Errorf("Friend ids don't match")
+	}
+	// To check for name of friends
+	child = child.Children[0]
+	if child.Attr != "name" {
+		t.Errorf("Expected attr friend. Got: %v", child.Attr)
+	}
+
+	names := child.Result.Values
+
+	if string(names[0]) != "Rick Grimes" || string(names[1]) != "Glenn Rhee" || string(names[2]) != "Daryl Dixon" || string(names[3]) != "Andrea" {
+		t.Errorf("Names don't match")
+	}
+}