GetArgumentValues: public version of getArgumentValues()

to write custom validation rules, sometimes it want to access field's
argument values, but getArgumentValues() is private.  this creates
public version of getArgumentValues() to access from those validation
rules.

graphql_test.go

@@ -327,3 +327,66 @@ func TestQueryWithCustomRule(t *testing.T) {
 		}
 	}
 }
+
+// TestCustomRuleWithArgs tests graphql.GetArgumentValues() be able to access
+// field's argument values from custom validation rule.
+func TestCustomRuleWithArgs(t *testing.T) {
+	fieldDef, ok := testutil.StarWarsSchema.QueryType().Fields()["human"]
+	if !ok {
+		t.Fatal("can't retrieve \"human\" field definition")
+	}
+
+	// a custom validation rule to extract argument values of "human" field.
+	var actual map[string]interface{}
+	enter := func(p visitor.VisitFuncParams) (string, interface{}) {
+		// only interested in "human" field.
+		fieldNode, ok := p.Node.(*ast.Field)
+		if !ok || fieldNode.Name == nil || fieldNode.Name.Value != "human" {
+			return visitor.ActionNoChange, nil
+		}
+		// extract argument values by graphql.GetArgumentValues().
+		actual = graphql.GetArgumentValues(fieldDef.Args, fieldNode.Arguments, nil)
+		return visitor.ActionNoChange, nil
+	}
+	checkHumanArgs := func(context *graphql.ValidationContext) *graphql.ValidationRuleInstance {
+		return &graphql.ValidationRuleInstance{
+			VisitorOpts: &visitor.VisitorOptions{
+				KindFuncMap: map[string]visitor.NamedVisitFuncs{
+					kinds.Field: {Enter: enter},
+				},
+			},
+		}
+	}
+
+	for _, tc := range []struct {
+		query      string
+		expected   map[string]interface{}
+	}{
+		{
+			`query { human(id: "1000") { name } }`,
+			map[string]interface{}{"id": "1000"},
+		},
+		{
+			`query { human(id: "1002") { name } }`,
+			map[string]interface{}{"id": "1002"},
+		},
+		{
+			`query { human(id: "9999") { name } }`,
+			map[string]interface{}{"id": "9999"},
+		},
+	} {
+		actual = nil
+		params := graphql.Params{
+			Schema:          testutil.StarWarsSchema,
+			RequestString:   tc.query,
+			ValidationRules: append(graphql.SpecifiedRules, checkHumanArgs),
+		}
+		result := graphql.Do(params)
+		if len(result.Errors) > 0 {
+			t.Fatalf("wrong result, unexpected errors: %v", result.Errors)
+		}
+		if !reflect.DeepEqual(actual, tc.expected) {
+			t.Fatalf("unexpected result: want=%+v got=%+v", tc.expected, actual)
+		}
+	}
+}

values.go

@@ -67,6 +67,17 @@ func getArgumentValues(
 	return results
 }
 
+// GetArgumentValues prepares an object map of argument values given a list of
+// argument definitions and list of argument AST nodes.
+//
+// This is an exported version of getArgumentValues(), to ease writing custom
+// validation rules.
+func GetArgumentValues(
+	argDefs []*Argument, argASTs []*ast.Argument,
+	variableValues map[string]interface{}) map[string]interface{} {
+	return getArgumentValues(argDefs, argASTs, variableValues)
+}
+
 // Given a variable definition, and any value of input, return a value which
 // adheres to the variable definition, or throw an error.
 func getVariableValue(schema Schema, definitionAST *ast.VariableDefinition, input interface{}) (interface{}, error) {