hdf5: add ObjectTypeByIndex to CommonFG

This CL adds a new method to CommonFG, ObjectTypeByIndex, to retrieve the type of an object in
a file or a group, prior to read from storage.

Fixes #77.

Signed-off-by: Sebastien Binet <[email protected]>

Author: sbinet

h5g_group.go

@@ -15,6 +15,37 @@ import (
 	"unsafe"
 )
 
+// GType describes the type of an object inside a Group or File.
+type GType int
+
+const (
+	H5G_UNKNOWN GType = C.H5G_UNKNOWN // Unknown object type
+	H5G_GROUP   GType = C.H5G_GROUP   // Object is a group
+	H5G_DATASET GType = C.H5G_DATASET // Object is a dataset
+	H5G_TYPE    GType = C.H5G_TYPE    // Object is a named data type
+	H5G_LINK    GType = C.H5G_LINK    // Object is a symbolic link
+	H5G_UDLINK  GType = C.H5G_UDLINK  // Object is a user-defined link
+)
+
+func (typ GType) String() string {
+	switch typ {
+	case H5G_UNKNOWN:
+		return "unknown"
+	case H5G_GROUP:
+		return "group"
+	case H5G_DATASET:
+		return "dataset"
+	case H5G_TYPE:
+		return "type"
+	case H5G_LINK:
+		return "link"
+	case H5G_UDLINK:
+		return "udlink"
+	default:
+		return fmt.Sprintf("GType(%d)", int(typ))
+	}
+}
+
 // CommonFG is for methods common to both File and Group
 type CommonFG struct {
 	Identifier
@@ -145,6 +176,17 @@ func (g *CommonFG) ObjectNameByIndex(idx uint) (string, error) {
 	return C.GoString(&name[0]), nil
 }
 
+// ObjectTypeByIndex returns the type of the object at idx.
+func (g *CommonFG) ObjectTypeByIndex(idx uint) (GType, error) {
+	cidx := C.hsize_t(idx)
+	gtyp := GType(C.H5Gget_objtype_by_idx(g.id, cidx))
+	if gtyp < H5G_GROUP {
+		return H5G_UNKNOWN, fmt.Errorf("could not get object type")
+	}
+
+	return gtyp, nil
+}
+
 // CreateTable creates a packet table to store fixed-length packets.
 // The returned table must be closed by the user when it is no longer needed.
 func (g *Group) CreateTable(name string, dtype *Datatype, chunkSize, compression int) (*Table, error) {

h5g_group_test.go

@@ -71,6 +71,18 @@ func TestGroup(t *testing.T) {
 		t.Errorf("wrong number of objects in group: want 1, got %d", nObjs)
 	}
 
+	if name, err := g2.ObjectNameByIndex(0); err != nil {
+		t.Fatalf("could not retrieve object name idx=%d: %+v", 0, err)
+	} else if got, want := name, "baz"; got != want {
+		t.Errorf("invalid name for object idx=%d: got=%q, want=%q", 0, got, want)
+	}
+
+	if typ, err := g2.ObjectTypeByIndex(0); err != nil {
+		t.Fatalf("could not retrieve object type idx=%d: %+v", 0, err)
+	} else if got, want := typ, H5G_GROUP; got != want {
+		t.Errorf("invalid type for object idx=%d: got=%v, want=%v", 0, got, want)
+	}
+
 	err = g1.Close()
 	if err != nil {
 		t.Error(err)