ARROW-5109: [Go] implement reading binary/string arrays from Arrow file

Author: Sebastien Binet <binet@cern.ch>

Closes #4155 from sbinet/issue-5109 and squashes the following commits:

f276be7 <Sebastien Binet> ARROW-5109:  implement reading binary/string arrays from Arrow file

Author: sbinet

go/arrow/ipc/file_reader.go

@@ -361,6 +361,9 @@ func (ctx *arrayLoaderContext) loadArray(dt arrow.DataType) array.Interface {
 		*arrow.Float32Type, *arrow.Float64Type:
 		return ctx.loadPrimitive(dt)
 
+	case *arrow.BinaryType, *arrow.StringType:
+		return ctx.loadBinary(dt)
+
 	default:
 		panic(errors.Errorf("array type %T not handled yet", dt))
 	}
@@ -409,6 +412,16 @@ func (ctx *arrayLoaderContext) loadPrimitive(dt arrow.DataType) array.Interface
 	return array.MakeFromData(data)
 }
 
+func (ctx *arrayLoaderContext) loadBinary(dt arrow.DataType) array.Interface {
+	field, buffers := ctx.loadCommon(3)
+	buffers = append(buffers, ctx.buffer(), ctx.buffer())
+
+	data := array.NewData(dt, int(field.Length()), buffers, nil, int(field.NullCount()), 0)
+	defer data.Release()
+
+	return array.MakeFromData(data)
+}
+
 func readDictionary(meta *memory.Buffer, types dictTypeMap, r ReadAtSeeker) (int64, array.Interface, error) {
 	//	msg := flatbuf.GetRootAsMessage(meta.Bytes(), 0)
 	//	var dictBatch flatbuf.DictionaryBatch