Add CreateByteVector function to Go's builder

This function gets around the inefficiency of populating a [ubyte] vector
byte by byte. Since ubyte vectors are probably the most commonly used type
of generic byte buffer, this seems like a worthwhile thing to create a
fast path for.

Benchmarks show a 6x improvement in throughput on x64.

There is a new test verifying the functionality of the function.

Change-Id: I82e0228ae0f815dd7ea89bf168b8c1925f3ce0d7

go/builder.go

@@ -259,6 +259,18 @@ func (b *Builder) CreateString(s string) UOffsetT {
 	return b.EndVector(len(x))
 }
 
+// CreateByteVector writes a ubyte vector
+func (b *Builder) CreateByteVector(v []byte) UOffsetT {
+	b.Prep(int(SizeUOffsetT), len(v)*SizeByte)
+
+	l := UOffsetT(len(v))
+
+	b.head -= l
+	copy(b.Bytes[b.head:b.head+l], v)
+
+	return b.EndVector(len(v))
+}
+
 func (b *Builder) notNested() {
 	// Check that no other objects are being built while making this
 	// object. If not, panic:

tests/go_test.go

@@ -90,6 +90,9 @@ func TestAll(t *testing.T) {
 	// some sanity checks:
 	CheckDocExample(generated, off, t.Fatalf)
 
+	// Check Builder.CreateByteVector
+	CheckCreateByteVector(t.Fatalf)
+
 	// If the filename of the FlatBuffers file generated by the Java test
 	// is given, check that Go code can read it, and that Go code
 	// generates an identical buffer when used to create the example data:
@@ -1080,6 +1083,25 @@ func CheckDocExample(buf []byte, off flatbuffers.UOffsetT, fail func(string, ...
 	_ = example.MonsterEnd(builder)
 }
 
+func CheckCreateByteVector(fail func(string, ...interface{})) {
+	raw := [30]byte{}
+	for i := 0; i < len(raw); i++ {
+		raw[i] = byte(i)
+	}
+
+	for size := 0; size < len(raw); size++ {
+		b1 := flatbuffers.NewBuilder(0)
+		b2 := flatbuffers.NewBuilder(0)
+		b1.StartVector(1, size, 1)
+		for i := size - 1; i >= 0; i-- {
+			b1.PrependByte(raw[i])
+		}
+		b1.EndVector(size)
+		b2.CreateByteVector(raw[:size])
+		CheckByteEquality(b1.Bytes, b2.Bytes, fail)
+	}
+}
+
 // Include simple random number generator to ensure results will be the
 // same cross platform.
 // http://en.wikipedia.org/wiki/Park%E2%80%93Miller_random_number_generator