errors: Support multierr and pkg/errors' causer

error.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2016 Uber Technologies, Inc.
+// Copyright (c) 2017 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

error_test.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2016 Uber Technologies, Inc.
+// Copyright (c) 2017 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

zapcore/error.go

@@ -0,0 +1,128 @@
+// Copyright (c) 2017 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 zapcore
+
+import (
+	"fmt"
+	"sync"
+)
+
+// Encodes the given error into fields of an object. A field with the given
+// name is added for the error message.
+//
+// If the error implements fmt.Formatter, a field with the name ${key}Verbose
+// is also added with the full verbose error message.
+//
+// Finally, if the error implements errorGroup (from go.uber.org/multierr) or
+// causer (from github.com/pkg/errors), a ${key}Causes field is added with an
+// array of objects containing the errors this error was comprised of.
+//
+//  {
+//    "error": err.Error(),
+//    "errorVerbose": fmt.Sprintf("%+v", err),
+//    "errorCauses": [
+//      ...
+//    ],
+//  }
+func encodeError(key string, err error, enc ObjectEncoder) error {
+	basic := err.Error()
+	enc.AddString(key, basic)
+
+	if fancy, ok := err.(fmt.Formatter); ok {
+		verbose := fmt.Sprintf("%+v", fancy)
+		if verbose != basic {
+			// This is a rich error type, like those produced by
+			// github.com/pkg/errors.
+			enc.AddString(key+"Verbose", verbose)
+		}
+	}
+
+	switch e := err.(type) {
+	case errorGroup:
+		return enc.AddArray(key+"Causes", errArray(e.Errors()))
+	case causer:
+		el := newErrArrayElem(e.Cause())
+		err := enc.AddArray(key+"Causes", el)
+		el.Free()
+		return err
+	}
+
+	return nil
+}
+
+type errorGroup interface {
+	// Provides read-only access to the underlying list of errors, preferably
+	// without causing any allocs.
+	Errors() []error
+}
+
+type causer interface {
+	// Provides access to the error that caused this error.
+	Cause() error
+}
+
+// Note that errArry and errArrayElem are very similar to the version
+// implemented in the top-level error.go file. We can't re-use this because
+// that would require exporting errArray as part of the zapcore API.
+
+// Encodes a list of errors using the standard error encoding logic.
+type errArray []error
+
+func (errs errArray) MarshalLogArray(arr ArrayEncoder) error {
+	for i := range errs {
+		if errs[i] == nil {
+			continue
+		}
+
+		el := newErrArrayElem(errs[i])
+		arr.AppendObject(el)
+		el.Free()
+	}
+	return nil
+}
+
+var _errArrayElemPool = sync.Pool{New: func() interface{} {
+	return &errArrayElem{}
+}}
+
+// Encodes any error into a {"error": ...} re-using the same errors logic.
+//
+// May be passed in place of an array to build a single-element array.
+type errArrayElem struct{ err error }
+
+func newErrArrayElem(err error) *errArrayElem {
+	e := _errArrayElemPool.Get().(*errArrayElem)
+	e.err = err
+	return e
+}
+
+func (e *errArrayElem) MarshalLogArray(arr ArrayEncoder) error {
+	return arr.AppendObject(e)
+}
+
+func (e *errArrayElem) MarshalLogObject(enc ObjectEncoder) error {
+	return encodeError("error", e.err, enc)
+}
+
+func (e *errArrayElem) Free() {
+	e.err = nil
+	_errArrayElemPool.Put(e)
+}