Add key lookup support for tables in Go (#7644)

* Add support for key lookup for tables in Go

* Run clang format

* Run go fmt on tests

* Remove TODO in tests

* Update LookupByKey API

* Update LookupByKey API

* Don't use resolvePointer in expectEq

* Use generated getters instead of reading values directly from buffer

* Fix typo

Co-authored-by: Derek Bailey <derekbailey@google.com>

go/builder.go

@@ -1,5 +1,7 @@
 package flatbuffers
 
+import "sort"
+
 // Builder is a state machine for creating FlatBuffer objects.
 // Use a Builder to construct object(s) starting from leaf nodes.
 //
@@ -315,6 +317,25 @@ func (b *Builder) EndVector(vectorNumElems int) UOffsetT {
 	return b.Offset()
 }
 
+// CreateVectorOfTables serializes slice of table offsets into a vector.
+func (b *Builder) CreateVectorOfTables(offsets []UOffsetT) UOffsetT {
+	b.assertNotNested()
+	b.StartVector(4, len(offsets), 4)
+	for i := len(offsets) - 1; i >= 0; i-- {
+		b.PrependUOffsetT(offsets[i])
+	}
+	return b.EndVector(len(offsets))
+}
+
+type KeyCompare func(o1, o2 UOffsetT, buf []byte) bool
+
+func (b *Builder) CreateVectorOfSortedTables(offsets []UOffsetT, keyCompare KeyCompare) UOffsetT {
+	sort.Slice(offsets, func(i, j int) bool {
+		return keyCompare(offsets[i], offsets[j], b.Bytes)
+	})
+	return b.CreateVectorOfTables(offsets)
+}
+
 // CreateSharedString Checks if the string is already written
 // to the buffer before calling CreateString
 func (b *Builder) CreateSharedString(s string) UOffsetT {

go/lib.go

@@ -23,3 +23,8 @@ func GetSizePrefixedRootAs(buf []byte, offset UOffsetT, fb FlatBuffer) {
 func GetSizePrefix(buf []byte, offset UOffsetT) uint32 {
 	return GetUint32(buf[offset:])
 }
+
+// GetIndirectOffset retrives the relative offset in the provided buffer stored at `offset`.
+func GetIndirectOffset(buf []byte, offset UOffsetT) UOffsetT {
+	return offset + GetUOffsetT(buf[offset:])
+}