Add BLOB support to scalar functions

- Add DUCKDB_TYPE_BLOB case to vector_set_value_at()
- Uses same API as VARCHAR: duckdb_vector_assign_string_element_len()
- Update type validation to allow :blob
- Add test_scalar_function_blob_return_type test
- Sort allowed types alphabetically in validation

Author: suketa

ext/duckdb/scalar_function.c

@@ -251,6 +251,14 @@ static void vector_set_value_at(duckdb_vector vector, duckdb_logical_type elemen
             duckdb_vector_assign_string_element_len(vector, index, str_ptr, str_len);
             break;
         }
+        case DUCKDB_TYPE_BLOB: {
+            // BLOB uses same API as VARCHAR, but expects binary data
+            VALUE str = rb_obj_as_string(value);
+            const char *str_ptr = StringValuePtr(str);
+            idx_t str_len = RSTRING_LEN(str);
+            duckdb_vector_assign_string_element_len(vector, index, str_ptr, str_len);
+            break;
+        }
         default:
             rb_raise(rb_eArgError, "Unsupported return type for scalar function");
             break;

lib/duckdb/scalar_function.rb

@@ -4,7 +4,7 @@ module DuckDB
   # DuckDB::ScalarFunction encapsulates DuckDB's scalar function
   class ScalarFunction
     # Sets the return type for the scalar function.
-    # Currently supports BOOLEAN, INTEGER, BIGINT, FLOAT, DOUBLE, and VARCHAR types.
+    # Currently supports BOOLEAN, INTEGER, BIGINT, FLOAT, DOUBLE, VARCHAR, and BLOB types.
     #
     # @param logical_type [DuckDB::LogicalType] the return type
     # @return [DuckDB::ScalarFunction] self
@@ -13,9 +13,9 @@ def return_type=(logical_type)
       raise DuckDB::Error, 'logical_type must be a DuckDB::LogicalType' unless logical_type.is_a?(DuckDB::LogicalType)
 
       # Check if the type is supported
-      unless %i[boolean integer bigint float double varchar].include?(logical_type.type)
+      unless %i[bigint blob boolean double float integer varchar].include?(logical_type.type)
         raise DuckDB::Error,
-              'Only BOOLEAN, INTEGER, BIGINT, FLOAT, DOUBLE, and VARCHAR return types are currently supported'
+              'Only BIGINT, BLOB, BOOLEAN, DOUBLE, FLOAT, INTEGER, and VARCHAR return types are currently supported'
       end
 
       _set_return_type(logical_type)

test/duckdb_test/scalar_function_test.rb

@@ -231,5 +231,25 @@ def test_scalar_function_varchar_return_type # rubocop:disable Metrics/MethodLen
 
       assert_equal [['Hello, Alice!'], ['Hello, Bob!']], result.to_a
     end
+
+    def test_scalar_function_blob_return_type # rubocop:disable Metrics/AbcSize, Metrics/MethodLength
+      @con.execute('SET threads=1')
+      @con.execute('CREATE TABLE test_table (data BLOB)')
+      @con.execute("INSERT INTO test_table VALUES ('\\x01\\x02\\x03'::BLOB), ('\\xAA\\xBB\\xCC'::BLOB)")
+
+      sf = DuckDB::ScalarFunction.new
+      sf.name = 'add_prefix'
+      sf.add_parameter(DuckDB::LogicalType.new(18)) # BLOB (type ID 18)
+      sf.return_type = DuckDB::LogicalType.new(18) # BLOB
+      sf.set_function { |data| DuckDB::Blob.new("\xFF".b + data) }
+
+      @con.register_scalar_function(sf)
+      result = @con.execute('SELECT add_prefix(data) FROM test_table ORDER BY data')
+      rows = result.to_a
+
+      assert_equal 2, rows.size
+      assert_equal "\xFF\x01\x02\x03".b, rows[0][0]
+      assert_equal "\xFF\xAA\xBB\xCC".b, rows[1][0]
+    end
   end
 end