Very ad hoc Attribute implementation

lib/hdf5.rb

@@ -36,3 +36,4 @@ def search_hdf5lib
 require_relative 'hdf5/file'
 require_relative 'hdf5/group'
 require_relative 'hdf5/dataset'
+require_relative 'hdf5/attribute'

lib/hdf5/attribute.rb

@@ -0,0 +1,60 @@
+module HDF5
+  class Attribute
+    def initialize(dataset_id, attr_name)
+      @dataset_id = dataset_id
+      @attr_name = attr_name
+      @attr_id = FFI.H5Aopen(@dataset_id, @attr_name, 0)
+      raise 'Failed to open attribute' if @attr_id < 0
+    end
+
+    def read
+      type_id = FFI.H5Aget_type(@attr_id)
+      space_id = FFI.H5Aget_space(@attr_id)
+
+      size = FFI.H5Sget_simple_extent_npoints(space_id)
+
+      buffer = \
+        case FFI.H5Tget_class(type_id)
+        when :H5T_INTEGER
+          ::FFI::MemoryPointer.new(:int, size)
+        when :H5T_FLOAT
+          ::FFI::MemoryPointer.new(:double, size)
+        when :H5T_STRING
+          ::FFI::MemoryPointer.new(:pointer, size)
+        else
+          raise 'Unsupported data type'
+        end
+
+      status = FFI.H5Aread(@attr_id, type_id, buffer)
+      raise 'Failed to read attribute' if status < 0
+
+      case FFI.H5Tget_class(type_id)
+      when :H5T_INTEGER
+        buffer.read_array_of_int(size)
+      when :H5T_FLOAT
+        buffer.read_array_of_double(size)
+      when :H5T_STRING
+        buffer.read_pointer.read_string
+      else
+        raise 'Unsupported data type'
+      end
+    end
+
+    def close
+      FFI.H5Aclose(@attr_id)
+    end
+  end
+
+  class AttributeManager
+    def initialize(dataset_id)
+      @dataset_id = dataset_id
+    end
+
+    def [](attr_name)
+      attr = Attribute.new(@dataset_id, attr_name)
+      attr.read
+    ensure
+      attr.close if attr
+    end
+  end
+end

lib/hdf5/dataset.rb

@@ -4,6 +4,10 @@ def initialize(parent_id, name)
       @dataset_id = HDF5::FFI.H5Dopen1(parent_id, name)
     end
 
+    def attrs
+      @attrs ||= AttributeManager.new(@dataset_id)
+    end
+
     def write(data)
       HDF5::FFI.H5Dwrite(@dataset_id, data)
     end

lib/hdf5/file.rb

@@ -43,6 +43,10 @@ def [](name)
       end
     end
 
+    def attrs
+      @attrs ||= AttributeManager.new(@file_id)
+    end
+
     private
 
     def group?(name)

lib/hdf5/group.rb

@@ -34,6 +34,10 @@ def [](name)
       end
     end
 
+    def attrs
+      @attrs ||= AttributeManager.new(@group_id)
+    end
+
     private
 
     def group?(name)