Break api error handling into a new pkg

pkg/api/errors/errors.go

@@ -0,0 +1,104 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package errors
+
+import (
+	"fmt"
+	"strings"
+)
+
+// ValidationErrorEnum is a type of validation error.
+type ValidationErrorEnum string
+
+// These are known errors of validation.
+const (
+	Invalid      ValidationErrorEnum = "invalid value"
+	NotSupported ValidationErrorEnum = "unsupported value"
+	Duplicate    ValidationErrorEnum = "duplicate value"
+	NotFound     ValidationErrorEnum = "not found"
+)
+
+// ValidationError is an implementation of the 'error' interface, which represents an error of validation.
+type ValidationError struct {
+	Type     ValidationErrorEnum
+	Field    string
+	BadValue interface{}
+}
+
+func (v ValidationError) Error() string {
+	return fmt.Sprintf("%s: %v '%v'", v.Field, v.Type, v.BadValue)
+}
+
+// NewInvalid returns a ValidationError indicating "invalid value".  Use this to
+// report malformed values (e.g. failed regex match) or missing "required" fields.
+func NewInvalid(field string, value interface{}) ValidationError {
+	return ValidationError{Invalid, field, value}
+}
+
+// NewNotSupported returns a ValidationError indicating "unsuported value".  Use
+// this to report valid (as per formatting rules) values that can not be handled
+// (e.g. an enumerated string).
+func NewNotSupported(field string, value interface{}) ValidationError {
+	return ValidationError{NotSupported, field, value}
+}
+
+// NewDuplicate returns a ValidationError indicating "duplicate value".  Use this
+// to report collisions of values that must be unique (e.g. unique IDs).
+func NewDuplicate(field string, value interface{}) ValidationError {
+	return ValidationError{Duplicate, field, value}
+}
+
+// NewNotFound returns a ValidationError indicating "value not found".  Use this
+// to report failure to find a requested value (e.g. looking up an ID).
+func NewNotFound(field string, value interface{}) ValidationError {
+	return ValidationError{NotFound, field, value}
+}
+
+// ErrorList is a collection of errors.  This does not implement the error
+// interface to avoid confusion where an empty ErrorList would still be an
+// error (non-nil).  To produce a single error instance from an ErrorList, use
+// the ToError() method, which will return nil for an empty ErrorList.
+type ErrorList []error
+
+// This helper implements the error interface for ErrorList, but must prevents
+// accidental conversion of ErrorList to error.
+type errorListInternal ErrorList
+
+// Error is part of the error interface.
+func (list errorListInternal) Error() string {
+	if len(list) == 0 {
+		return ""
+	}
+	sl := make([]string, len(list))
+	for i := range list {
+		sl[i] = list[i].Error()
+	}
+	return strings.Join(sl, "; ")
+}
+
+// Deprecated, will be removed soon.
+func (list *ErrorList) Append(errs ...error) {
+	*list = append(*list, errs...)
+}
+
+// ToError converts an ErrorList into a "normal" error, or nil if the list is empty.
+func (list ErrorList) ToError() error {
+	if len(list) == 0 {
+		return nil
+	}
+	return errorListInternal(list)
+}

pkg/api/errors/errors_test.go

@@ -0,0 +1,85 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package errors
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestMakeFuncs(t *testing.T) {
+	testCases := []struct {
+		fn       func() ValidationError
+		expected ValidationErrorEnum
+	}{
+		{
+			func() ValidationError { return NewInvalid("f", "v") },
+			Invalid,
+		},
+		{
+			func() ValidationError { return NewNotSupported("f", "v") },
+			NotSupported,
+		},
+		{
+			func() ValidationError { return NewDuplicate("f", "v") },
+			Duplicate,
+		},
+		{
+			func() ValidationError { return NewNotFound("f", "v") },
+			NotFound,
+		},
+	}
+
+	for _, testCase := range testCases {
+		err := testCase.fn()
+		if err.Type != testCase.expected {
+			t.Errorf("expected Type %q, got %q", testCase.expected, err.Type)
+		}
+	}
+}
+
+func TestErrorList(t *testing.T) {
+	errList := ErrorList{}
+	errList = append(errList, NewInvalid("field", "value"))
+	// The fact that this compiles is the test.
+}
+
+func TestErrorListToError(t *testing.T) {
+	errList := ErrorList{}
+	err := errList.ToError()
+	if err != nil {
+		t.Errorf("expected nil, got %v", err)
+	}
+
+	testCases := []struct {
+		errs     ErrorList
+		expected string
+	}{
+		{ErrorList{fmt.Errorf("abc")}, "abc"},
+		{ErrorList{fmt.Errorf("abc"), fmt.Errorf("123")}, "abc; 123"},
+	}
+	for _, testCase := range testCases {
+		err := testCase.errs.ToError()
+		if err == nil {
+			t.Errorf("expected an error, got nil: ErrorList=%v", testCase)
+			continue
+		}
+		if err.Error() != testCase.expected {
+			t.Errorf("expected %q, got %q", testCase.expected, err.Error())
+		}
+	}
+}