Add utility for wrapping multiple errors

pkg/multierror/multierror.go

@@ -0,0 +1,61 @@
+// Copyright (c) 2016 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package multierror
+
+import (
+	"fmt"
+	"strings"
+)
+
+// Wrap takes a slice of errors and returns a single error that encapsulates
+// those underlying errors. If the slice is nil or empty it returns nil.
+// If the slice only contains a single element, that error is returned directly.
+// When more than one error is wrapped, the Error() string is a concatenation
+// of the Error() values of all underlying errors.
+func Wrap(errs []error) error {
+	return multiError(errs).flatten()
+}
+
+// multiError bundles several errors together into a single error.
+type multiError []error
+
+// flatten returns either: nil, the only error, or the multiError instance itself
+// if there are 0, 1, or more errors in the slice respectively.
+func (errors multiError) flatten() error {
+	switch len(errors) {
+	case 0:
+		return nil
+	case 1:
+		return errors[0]
+	default:
+		return errors
+	}
+}
+
+// Error returns a string like "[e1, e2, ...]" where each eN is the Error() of
+// each error in the slice.
+func (errors multiError) Error() string {
+	parts := make([]string, len(errors))
+	for i, err := range errors {
+		parts[i] = err.Error()
+	}
+	return fmt.Sprintf("[%s]", strings.Join(parts, ", "))
+}

pkg/multierror/multierror_test.go

@@ -0,0 +1,69 @@
+// Copyright (c) 2016 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package multierror
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func ExampleWrap() {
+	someFunc := func() error {
+		return errors.New("doh")
+	}
+
+	var errs []error
+	for i := 0; i < 2; i++ {
+		if err := someFunc(); err != nil {
+			errs = append(errs, err)
+		}
+		fmt.Println(Wrap(errs).Error())
+	}
+	// Output: doh
+	// [doh, doh]
+}
+
+func TestWrapEmptySlice(t *testing.T) {
+	var errors []error
+	e1 := Wrap(errors)
+	assert.Nil(t, e1)
+	e2 := Wrap([]error{})
+	assert.Nil(t, e2)
+}
+
+func TestWrapSingleError(t *testing.T) {
+	err := errors.New("doh")
+	e1 := Wrap([]error{err})
+	assert.Error(t, e1)
+	assert.Equal(t, err, e1)
+	assert.Equal(t, "doh", e1.Error())
+}
+
+func TestWrapManyErrors(t *testing.T) {
+	err1 := errors.New("ay")
+	err2 := errors.New("caramba")
+	e1 := Wrap([]error{err1, err2})
+	assert.Error(t, e1)
+	assert.Equal(t, "[ay, caramba]", e1.Error())
+}