consistent error handling

Make the error handling consistent by:

* Using github.com/pkg/errors to wrap errors before returning.
* Having consistent format specifiers for logs.
* Using `fmt.Errorf()` for non-wrapping errors.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

14 files changed, 601 insertions, 23 deletions

diff --git a/go.mod b/go.mod
index aaccba6..b14fd95 100644
--- a/go.mod
+++ b/go.mod
@@ -8,6 +8,7 @@ require (
 	github.com/coreos/go-iptables v0.4.2
 	github.com/onsi/ginkgo v1.10.1
 	github.com/onsi/gomega v1.7.0
+	github.com/pkg/errors v0.8.1
 	github.com/sirupsen/logrus v1.4.2
 	github.com/vishvananda/netlink v1.0.0
 	golang.org/x/sys v0.0.0-20190916202348-b4ddaad3f8a3
diff --git a/go.sum b/go.sum
index adc328b..39bb8e5 100644
--- a/go.sum
+++ b/go.sum
@@ -40,6 +40,8 @@ github.com/onsi/ginkgo v1.10.1/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+
 github.com/onsi/gomega v0.0.0-20151007035656-2152b45fa28a/go.mod h1:C1qb7wdrVGGVU+Z6iS04AVkA3Q65CEZX59MT0QO5uiA=
 github.com/onsi/gomega v1.7.0 h1:XPnZz8VVBHjVsy1vzJmRwIcSwiUO+JFfrv/xGiigmME=
 github.com/onsi/gomega v1.7.0/go.mod h1:ex+gbHU/CVuBBDIJjb2X0qEXbFg53c61hWP/1CpauHY=
+github.com/pkg/errors v0.8.1 h1:iURUrRGxPUNPdy5/HRSm+Yj6okJ6UtLINN0Q9M4+h3I=
+github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/safchain/ethtool v0.0.0-20190326074333-42ed695e3de8/go.mod h1:Z0q5wiBQGYcxhMZ6gUqHn6pYNLypFAvaL3UvgZLR0U4=
 github.com/sirupsen/logrus v1.0.6/go.mod h1:pMByvHTf9Beacp5x1UXfOR9xyW/9antXMhjMPG0dEzc=
diff --git a/plugins/meta/dnsname/files.go b/plugins/meta/dnsname/files.go
index c74bae4..c0f1ee8 100644
--- a/plugins/meta/dnsname/files.go
+++ b/plugins/meta/dnsname/files.go
@@ -95,7 +95,7 @@ func appendToFile(path, podname string, ips []*net.IPNet) error {
 	}
 	defer func() {
 		if err := f.Close(); err != nil {
-			logrus.Errorf("failed to close file '%s': %q", path, err)
+			logrus.Errorf("failed to close file %q: %v", path, err)
 		}
 	}()
 	for _, ip := range ips {
@@ -127,7 +127,7 @@ func removeFromFile(path, podname string) (bool, error) {
 	}
 	defer func() {
 		if err := f.Close(); err != nil {
-			logrus.Errorf("unable to close '%s': %q", backup, err)
+			logrus.Errorf("unable to close %q: %v", backup, err)
 		}
 	}()
 
@@ -164,7 +164,7 @@ func removeFromFile(path, podname string) (bool, error) {
 // renameFile renames a file to backup
 func renameFile(oldpath, newpath string) {
 	if renameError := os.Rename(oldpath, newpath); renameError != nil {
-		logrus.Errorf("unable to restore '%s' to '%s': %q", oldpath, newpath, renameError)
+		logrus.Errorf("unable to restore %q to %q: %v", oldpath, newpath, renameError)
 	}
 }
 
@@ -178,7 +178,7 @@ func writeFile(path string, content []string) (int, error) {
 	}
 	defer func() {
 		if err := f.Close(); err != nil {
-			logrus.Errorf("unable to close '%s': %q", path, err)
+			logrus.Errorf("unable to close %q: %v", path, err)
 		}
 	}()
 
diff --git a/plugins/meta/dnsname/main.go b/plugins/meta/dnsname/main.go
index b84f2da..8630480 100644
--- a/plugins/meta/dnsname/main.go
+++ b/plugins/meta/dnsname/main.go
@@ -28,7 +28,6 @@ package main
 
 import (
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -40,6 +39,7 @@ import (
 	"github.com/containernetworking/cni/pkg/types/current"
 	"github.com/containernetworking/cni/pkg/version"
 	bv "github.com/containernetworking/plugins/pkg/utils/buildversion"
+	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 )
 
@@ -49,7 +49,7 @@ func cmdAdd(args *skel.CmdArgs) error {
 	}
 	netConf, result, podname, err := parseConfig(args.StdinData, args.Args)
 	if err != nil {
-		return fmt.Errorf("failed to parse config: %v", err)
+		return errors.Wrap(err, "failed to parse config")
 	}
 	if netConf.PrevResult == nil {
 		return fmt.Errorf("must be called as chained plugin")
@@ -80,7 +80,7 @@ func cmdAdd(args *skel.CmdArgs) error {
 	}
 	defer func() {
 		if err := lock.release(); err != nil {
-			logrus.Errorf("unable to release lock for '%s': %q", dnsNameConf.AddOnHostsFile, err)
+			logrus.Errorf("unable to release lock for %q: %v", dnsNameConf.AddOnHostsFile, err)
 		}
 	}()
 	if err := checkForDNSMasqConfFile(dnsNameConf); err != nil {
@@ -110,9 +110,8 @@ func cmdDel(args *skel.CmdArgs) error {
 	}
 	netConf, result, podname, err := parseConfig(args.StdinData, args.Args)
 	if err != nil {
-		return fmt.Errorf("failed to parse config: %v", err)
-	}
-	if result == nil {
+		return errors.Wrap(err, "failed to parse config")
+	} else if result == nil {
 		return nil
 	}
 	dnsNameConf, err := newDNSMasqFile(netConf.DomainName, result.Interfaces[0].Name, netConf.Name)
@@ -130,7 +129,7 @@ func cmdDel(args *skel.CmdArgs) error {
 	defer func() {
 		// if the lock isn't given up by another process
 		if err := lock.release(); err != nil {
-			logrus.Errorf("unable to release lock for '%s': %q", domainBaseDir, err)
+			logrus.Errorf("unable to release lock for %q: %v", domainBaseDir, err)
 		}
 	}()
 	shouldHUP, err := removeFromFile(filepath.Join(domainBaseDir, hostsFileName), podname)
@@ -159,7 +158,7 @@ func cmdCheck(args *skel.CmdArgs) error {
 	}
 	netConf, result, podname, err := parseConfig(args.StdinData, args.Args)
 	if err != nil {
-		return fmt.Errorf("failed to parse config: %v", err)
+		return errors.Wrap(err, "failed to parse config")
 	}
 
 	_ = podname
@@ -183,7 +182,7 @@ func cmdCheck(args *skel.CmdArgs) error {
 	defer func() {
 		// if the lock isn't given up by another process
 		if err := lock.release(); err != nil {
-			logrus.Errorf("unable to release lock for '%s': %q", domainBaseDir, err)
+			logrus.Errorf("unable to release lock for %q: %v", domainBaseDir, err)
 		}
 	}()
 
@@ -194,7 +193,7 @@ func cmdCheck(args *skel.CmdArgs) error {
 
 	// Ensure the dnsmasq instance is running
 	if !isRunning(pid) {
-		return errors.New("dnsmasq instance not running")
+		return fmt.Errorf("dnsmasq instance not running")
 	}
 	// Above will make sure the pidfile exists
 	files, err := ioutil.ReadDir(dnsNameConfPath)
@@ -205,10 +204,10 @@ func cmdCheck(args *skel.CmdArgs) error {
 		conffiles = append(conffiles, f.Name())
 	}
 	if !stringInSlice("addnhosts", conffiles) {
-		return errors.New("addnhost file missing from configuration")
+		return fmt.Errorf("addnhost file missing from configuration")
 	}
 	if !stringInSlice("dnsmasq.conf", conffiles) {
-		return errors.New("dnsmasq.conf file missing from configuration")
+		return fmt.Errorf("dnsmasq.conf file missing from configuration")
 	}
 	return nil
 }
@@ -233,18 +232,18 @@ type podname struct {
 func parseConfig(stdin []byte, args string) (*DNSNameConf, *current.Result, string, error) {
 	conf := DNSNameConf{}
 	if err := json.Unmarshal(stdin, &conf); err != nil {
-		return nil, nil, "", fmt.Errorf("failed to parse network configuration: %v", err)
+		return nil, nil, "", errors.Wrap(err, "failed to parse network configuration")
 	}
 	// Parse previous result.
 	var result *current.Result
 	if conf.RawPrevResult != nil {
 		var err error
 		if err = version.ParsePrevResult(&conf.NetConf); err != nil {
-			return nil, nil, "", fmt.Errorf("could not parse prevResult: %v", err)
+			return nil, nil, "", errors.Wrap(err, "could not parse prevResult")
 		}
 		result, err = current.NewResultFromResult(conf.PrevResult)
 		if err != nil {
-			return nil, nil, "", fmt.Errorf("could not convert result to current version: %v", err)
+			return nil, nil, "", errors.Wrap(err, "could not convert result to current version")
 		}
 	}
 	e := podname{}
diff --git a/plugins/meta/dnsname/result.go b/plugins/meta/dnsname/result.go
index 115f69a..b2e78a1 100644
--- a/plugins/meta/dnsname/result.go
+++ b/plugins/meta/dnsname/result.go
@@ -1,7 +1,7 @@
 package main
 
 import (
-	"errors"
+	"fmt"
 	"net"
 
 	"github.com/containernetworking/cni/pkg/types/current"
@@ -24,7 +24,7 @@ func getIPs(r *current.Result) ([]*net.IPNet, error) {
 			if isInterfaceIndexSandox(*ip.Interface, r) {
 				ips = append(ips, &ip.Address)
 			} else {
-				return nil, errors.New("unable to check if interface has a sandbox due to index being out of range")
+				return nil, fmt.Errorf("unable to check if interface has a sandbox due to index being out of range")
 			}
 		}
 	}
diff --git a/plugins/meta/dnsname/service.go b/plugins/meta/dnsname/service.go
index f569f73..93c4ee3 100644
--- a/plugins/meta/dnsname/service.go
+++ b/plugins/meta/dnsname/service.go
@@ -1,7 +1,6 @@
 package main
 
 import (
-	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -18,7 +17,7 @@ import (
 func newDNSMasqFile(domainName, networkInterface, networkName string) (dnsNameFile, error) {
 	dnsMasqBinary, err := exec.LookPath("dnsmasq")
 	if err != nil {
-		return dnsNameFile{}, errors.New("the dnsmasq cni plugin requires the dnsmasq binary be in PATH")
+		return dnsNameFile{}, fmt.Errorf("the dnsmasq cni plugin requires the dnsmasq binary be in PATH")
 	}
 	masqConf := dnsNameFile{
 		ConfigFile:       makePath(networkName, confFileName),
diff --git a/vendor/github.com/pkg/errors/.gitignore b/vendor/github.com/pkg/errors/.gitignore
new file mode 100644
index 0000000..daf913b
--- /dev/null
+++ b/vendor/github.com/pkg/errors/.gitignore
@@ -0,0 +1,24 @@
+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
+*.test
+*.prof
diff --git a/vendor/github.com/pkg/errors/.travis.yml b/vendor/github.com/pkg/errors/.travis.yml
new file mode 100644
index 0000000..d4b9266
--- /dev/null
+++ b/vendor/github.com/pkg/errors/.travis.yml
@@ -0,0 +1,15 @@
+language: go
+go_import_path: github.com/pkg/errors
+go:
+  - 1.4.x
+  - 1.5.x
+  - 1.6.x
+  - 1.7.x
+  - 1.8.x
+  - 1.9.x
+  - 1.10.x
+  - 1.11.x
+  - tip
+
+script:
+  - go test -v ./...
diff --git a/vendor/github.com/pkg/errors/LICENSE b/vendor/github.com/pkg/errors/LICENSE
new file mode 100644
index 0000000..835ba3e
--- /dev/null
+++ b/vendor/github.com/pkg/errors/LICENSE
@@ -0,0 +1,23 @@
+Copyright (c) 2015, Dave Cheney <dave@cheney.net>
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright notice,
+  this list of conditions and the following disclaimer in the documentation
+  and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/vendor/github.com/pkg/errors/README.md b/vendor/github.com/pkg/errors/README.md
new file mode 100644
index 0000000..6483ba2
--- /dev/null
+++ b/vendor/github.com/pkg/errors/README.md
@@ -0,0 +1,52 @@
+# errors [![Travis-CI](https://travis-ci.org/pkg/errors.svg)](https://travis-ci.org/pkg/errors) [![AppVeyor](https://ci.appveyor.com/api/projects/status/b98mptawhudj53ep/branch/master?svg=true)](https://ci.appveyor.com/project/davecheney/errors/branch/master) [![GoDoc](https://godoc.org/github.com/pkg/errors?status.svg)](http://godoc.org/github.com/pkg/errors) [![Report card](https://goreportcard.com/badge/github.com/pkg/errors)](https://goreportcard.com/report/github.com/pkg/errors) [![Sourcegraph](https://sourcegraph.com/github.com/pkg/errors/-/badge.svg)](https://sourcegraph.com/github.com/pkg/errors?badge)
+
+Package errors provides simple error handling primitives.
+
+`go get github.com/pkg/errors`
+
+The traditional error handling idiom in Go is roughly akin to
+```go
+if err != nil {
+        return err
+}
+```
+which applied recursively up the call stack results in error reports without context or debugging information. The errors package allows programmers to add context to the failure path in their code in a way that does not destroy the original value of the error.
+
+## Adding context to an error
+
+The errors.Wrap function returns a new error that adds context to the original error. For example
+```go
+_, err := ioutil.ReadAll(r)
+if err != nil {
+        return errors.Wrap(err, "read failed")
+}
+```
+## Retrieving the cause of an error
+
+Using `errors.Wrap` constructs a stack of errors, adding context to the preceding error. Depending on the nature of the error it may be necessary to reverse the operation of errors.Wrap to retrieve the original error for inspection. Any error value which implements this interface can be inspected by `errors.Cause`.
+```go
+type causer interface {
+        Cause() error
+}
+```
+`errors.Cause` will recursively retrieve the topmost error which does not implement `causer`, which is assumed to be the original cause. For example:
+```go
+switch err := errors.Cause(err).(type) {
+case *MyError:
+        // handle specifically
+default:
+        // unknown error
+}
+```
+
+[Read the package documentation for more information](https://godoc.org/github.com/pkg/errors).
+
+## Contributing
+
+We welcome pull requests, bug fixes and issue reports. With that said, the bar for adding new symbols to this package is intentionally set high.
+
+Before proposing a change, please discuss your change by raising an issue.
+
+## License
+
+BSD-2-Clause
diff --git a/vendor/github.com/pkg/errors/appveyor.yml b/vendor/github.com/pkg/errors/appveyor.yml
new file mode 100644
index 0000000..a932ead
--- /dev/null
+++ b/vendor/github.com/pkg/errors/appveyor.yml
@@ -0,0 +1,32 @@
+version: build-{build}.{branch}
+
+clone_folder: C:\gopath\src\github.com\pkg\errors
+shallow_clone: true # for startup speed
+
+environment:
+  GOPATH: C:\gopath
+
+platform:
+  - x64
+
+# http://www.appveyor.com/docs/installed-software
+install:
+  # some helpful output for debugging builds
+  - go version
+  - go env
+  # pre-installed MinGW at C:\MinGW is 32bit only
+  # but MSYS2 at C:\msys64 has mingw64
+  - set PATH=C:\msys64\mingw64\bin;%PATH%
+  - gcc --version
+  - g++ --version
+
+build_script:
+  - go install -v ./...
+
+test_script:
+  - set PATH=C:\gopath\bin;%PATH%
+  - go test -v ./...
+
+#artifacts:
+#  - path: '%GOPATH%\bin\*.exe'
+deploy: off
diff --git a/vendor/github.com/pkg/errors/errors.go b/vendor/github.com/pkg/errors/errors.go
new file mode 100644
index 0000000..7421f32
--- /dev/null
+++ b/vendor/github.com/pkg/errors/errors.go
@@ -0,0 +1,282 @@
+// Package errors provides simple error handling primitives.
+//
+// The traditional error handling idiom in Go is roughly akin to
+//
+//     if err != nil {
+//             return err
+//     }
+//
+// which when applied recursively up the call stack results in error reports
+// without context or debugging information. The errors package allows
+// programmers to add context to the failure path in their code in a way
+// that does not destroy the original value of the error.
+//
+// Adding context to an error
+//
+// The errors.Wrap function returns a new error that adds context to the
+// original error by recording a stack trace at the point Wrap is called,
+// together with the supplied message. For example
+//
+//     _, err := ioutil.ReadAll(r)
+//     if err != nil {
+//             return errors.Wrap(err, "read failed")
+//     }
+//
+// If additional control is required, the errors.WithStack and
+// errors.WithMessage functions destructure errors.Wrap into its component
+// operations: annotating an error with a stack trace and with a message,
+// respectively.
+//
+// Retrieving the cause of an error
+//
+// Using errors.Wrap constructs a stack of errors, adding context to the
+// preceding error. Depending on the nature of the error it may be necessary
+// to reverse the operation of errors.Wrap to retrieve the original error
+// for inspection. Any error value which implements this interface
+//
+//     type causer interface {
+//             Cause() error
+//     }
+//
+// can be inspected by errors.Cause. errors.Cause will recursively retrieve
+// the topmost error that does not implement causer, which is assumed to be
+// the original cause. For example:
+//
+//     switch err := errors.Cause(err).(type) {
+//     case *MyError:
+//             // handle specifically
+//     default:
+//             // unknown error
+//     }
+//
+// Although the causer interface is not exported by this package, it is
+// considered a part of its stable public interface.
+//
+// Formatted printing of errors
+//
+// All error values returned from this package implement fmt.Formatter and can
+// be formatted by the fmt package. The following verbs are supported:
+//
+//     %s    print the error. If the error has a Cause it will be
+//           printed recursively.
+//     %v    see %s
+//     %+v   extended format. Each Frame of the error's StackTrace will
+//           be printed in detail.
+//
+// Retrieving the stack trace of an error or wrapper
+//
+// New, Errorf, Wrap, and Wrapf record a stack trace at the point they are
+// invoked. This information can be retrieved with the following interface:
+//
+//     type stackTracer interface {
+//             StackTrace() errors.StackTrace
+//     }
+//
+// The returned errors.StackTrace type is defined as
+//
+//     type StackTrace []Frame
+//
+// The Frame type represents a call site in the stack trace. Frame supports
+// the fmt.Formatter interface that can be used for printing information about
+// the stack trace of this error. For example:
+//
+//     if err, ok := err.(stackTracer); ok {
+//             for _, f := range err.StackTrace() {
+//                     fmt.Printf("%+s:%d", f)
+//             }
+//     }
+//
+// Although the stackTracer interface is not exported by this package, it is
+// considered a part of its stable public interface.
+//
+// See the documentation for Frame.Format for more details.
+package errors
+
+import (
+	"fmt"
+	"io"
+)
+
+// New returns an error with the supplied message.
+// New also records the stack trace at the point it was called.
+func New(message string) error {
+	return &fundamental{
+		msg:   message,
+		stack: callers(),
+	}
+}
+
+// Errorf formats according to a format specifier and returns the string
+// as a value that satisfies error.
+// Errorf also records the stack trace at the point it was called.
+func Errorf(format string, args ...interface{}) error {
+	return &fundamental{
+		msg:   fmt.Sprintf(format, args...),
+		stack: callers(),
+	}
+}
+
+// fundamental is an error that has a message and a stack, but no caller.
+type fundamental struct {
+	msg string
+	*stack
+}
+
+func (f *fundamental) Error() string { return f.msg }
+
+func (f *fundamental) Format(s fmt.State, verb rune) {
+	switch verb {
+	case 'v':
+		if s.Flag('+') {
+			io.WriteString(s, f.msg)
+			f.stack.Format(s, verb)
+			return
+		}
+		fallthrough
+	case 's':
+		io.WriteString(s, f.msg)
+	case 'q':
+		fmt.Fprintf(s, "%q", f.msg)
+	}
+}
+
+// WithStack annotates err with a stack trace at the point WithStack was called.
+// If err is nil, WithStack returns nil.
+func WithStack(err error) error {
+	if err == nil {
+		return nil
+	}
+	return &withStack{
+		err,
+		callers(),
+	}
+}
+
+type withStack struct {
+	error
+	*stack
+}
+
+func (w *withStack) Cause() error { return w.error }
+
+func (w *withStack) Format(s fmt.State, verb rune) {
+	switch verb {
+	case 'v':
+		if s.Flag('+') {
+			fmt.Fprintf(s, "%+v", w.Cause())
+			w.stack.Format(s, verb)
+			return
+		}
+		fallthrough
+	case 's':
+		io.WriteString(s, w.Error())
+	case 'q':
+		fmt.Fprintf(s, "%q", w.Error())
+	}
+}
+
+// Wrap returns an error annotating err with a stack trace
+// at the point Wrap is called, and the supplied message.
+// If err is nil, Wrap returns nil.
+func Wrap(err error, message string) error {
+	if err == nil {
+		return nil
+	}
+	err = &withMessage{
+		cause: err,
+		msg:   message,
+	}
+	return &withStack{
+		err,
+		callers(),
+	}
+}
+
+// Wrapf returns an error annotating err with a stack trace
+// at the point Wrapf is called, and the format specifier.
+// If err is nil, Wrapf returns nil.
+func Wrapf(err error, format string, args ...interface{}) error {
+	if err == nil {
+		return nil
+	}
+	err = &withMessage{
+		cause: err,
+		msg:   fmt.Sprintf(format, args...),
+	}
+	return &withStack{
+		err,
+		callers(),
+	}
+}
+
+// WithMessage annotates err with a new message.
+// If err is nil, WithMessage returns nil.
+func WithMessage(err error, message string) error {
+	if err == nil {
+		return nil
+	}
+	return &withMessage{
+		cause: err,
+		msg:   message,
+	}
+}
+
+// WithMessagef annotates err with the format specifier.
+// If err is nil, WithMessagef returns nil.
+func WithMessagef(err error, format string, args ...interface{}) error {
+	if err == nil {
+		return nil
+	}
+	return &withMessage{
+		cause: err,
+		msg:   fmt.Sprintf(format, args...),
+	}
+}
+
+type withMessage struct {
+	cause error
+	msg   string
+}
+
+func (w *withMessage) Error() string { return w.msg + ": " + w.cause.Error() }
+func (w *withMessage) Cause() error  { return w.cause }
+
+func (w *withMessage) Format(s fmt.State, verb rune) {
+	switch verb {
+	case 'v':
+		if s.Flag('+') {
+			fmt.Fprintf(s, "%+v\n", w.Cause())
+			io.WriteString(s, w.msg)
+			return
+		}
+		fallthrough
+	case 's', 'q':
+		io.WriteString(s, w.Error())
+	}
+}
+
+// Cause returns the underlying cause of the error, if possible.
+// An error value has a cause if it implements the following
+// interface:
+//
+//     type causer interface {
+//            Cause() error
+//     }
+//
+// If the error does not implement Cause, the original error will
+// be returned. If the error is nil, nil will be returned without further
+// investigation.
+func Cause(err error) error {
+	type causer interface {
+		Cause() error
+	}
+
+	for err != nil {
+		cause, ok := err.(causer)
+		if !ok {
+			break
+		}
+		err = cause.Cause()
+	}
+	return err
+}
diff --git a/vendor/github.com/pkg/errors/stack.go b/vendor/github.com/pkg/errors/stack.go
new file mode 100644
index 0000000..2874a04
--- /dev/null
+++ b/vendor/github.com/pkg/errors/stack.go
@@ -0,0 +1,147 @@
+package errors
+
+import (
+	"fmt"
+	"io"
+	"path"
+	"runtime"
+	"strings"
+)
+
+// Frame represents a program counter inside a stack frame.
+type Frame uintptr
+
+// pc returns the program counter for this frame;
+// multiple frames may have the same PC value.
+func (f Frame) pc() uintptr { return uintptr(f) - 1 }
+
+// file returns the full path to the file that contains the
+// function for this Frame's pc.
+func (f Frame) file() string {
+	fn := runtime.FuncForPC(f.pc())
+	if fn == nil {
+		return "unknown"
+	}
+	file, _ := fn.FileLine(f.pc())
+	return file
+}
+
+// line returns the line number of source code of the
+// function for this Frame's pc.
+func (f Frame) line() int {
+	fn := runtime.FuncForPC(f.pc())
+	if fn == nil {
+		return 0
+	}
+	_, line := fn.FileLine(f.pc())
+	return line
+}
+
+// Format formats the frame according to the fmt.Formatter interface.
+//
+//    %s    source file
+//    %d    source line
+//    %n    function name
+//    %v    equivalent to %s:%d
+//
+// Format accepts flags that alter the printing of some verbs, as follows:
+//
+//    %+s   function name and path of source file relative to the compile time
+//          GOPATH separated by \n\t (<funcname>\n\t<path>)
+//    %+v   equivalent to %+s:%d
+func (f Frame) Format(s fmt.State, verb rune) {
+	switch verb {
+	case 's':
+		switch {
+		case s.Flag('+'):
+			pc := f.pc()
+			fn := runtime.FuncForPC(pc)
+			if fn == nil {
+				io.WriteString(s, "unknown")
+			} else {
+				file, _ := fn.FileLine(pc)
+				fmt.Fprintf(s, "%s\n\t%s", fn.Name(), file)
+			}
+		default:
+			io.WriteString(s, path.Base(f.file()))
+		}
+	case 'd':
+		fmt.Fprintf(s, "%d", f.line())
+	case 'n':
+		name := runtime.FuncForPC(f.pc()).Name()
+		io.WriteString(s, funcname(name))
+	case 'v':
+		f.Format(s, 's')
+		io.WriteString(s, ":")
+		f.Format(s, 'd')
+	}
+}
+
+// StackTrace is stack of Frames from innermost (newest) to outermost (oldest).
+type StackTrace []Frame
+
+// Format formats the stack of Frames according to the fmt.Formatter interface.
+//
+//    %s	lists source files for each Frame in the stack
+//    %v	lists the source file and line number for each Frame in the stack
+//
+// Format accepts flags that alter the printing of some verbs, as follows:
+//
+//    %+v   Prints filename, function, and line number for each Frame in the stack.
+func (st StackTrace) Format(s fmt.State, verb rune) {
+	switch verb {
+	case 'v':
+		switch {
+		case s.Flag('+'):
+			for _, f := range st {
+				fmt.Fprintf(s, "\n%+v", f)
+			}
+		case s.Flag('#'):
+			fmt.Fprintf(s, "%#v", []Frame(st))
+		default:
+			fmt.Fprintf(s, "%v", []Frame(st))
+		}
+	case 's':
+		fmt.Fprintf(s, "%s", []Frame(st))
+	}
+}
+
+// stack represents a stack of program counters.
+type stack []uintptr
+
+func (s *stack) Format(st fmt.State, verb rune) {
+	switch verb {
+	case 'v':
+		switch {
+		case st.Flag('+'):
+			for _, pc := range *s {
+				f := Frame(pc)
+				fmt.Fprintf(st, "\n%+v", f)
+			}
+		}
+	}
+}
+
+func (s *stack) StackTrace() StackTrace {
+	f := make([]Frame, len(*s))
+	for i := 0; i < len(f); i++ {
+		f[i] = Frame((*s)[i])
+	}
+	return f
+}
+
+func callers() *stack {
+	const depth = 32
+	var pcs [depth]uintptr
+	n := runtime.Callers(3, pcs[:])
+	var st stack = pcs[0:n]
+	return &st
+}
+
+// funcname removes the path prefix component of a function's name reported by func.Name().
+func funcname(name string) string {
+	i := strings.LastIndex(name, "/")
+	name = name[i+1:]
+	i = strings.Index(name, ".")
+	return name[i+1:]
+}
diff --git a/vendor/modules.txt b/vendor/modules.txt
index 90c8276..8478f28 100644
--- a/vendor/modules.txt
+++ b/vendor/modules.txt
@@ -54,6 +54,8 @@ github.com/onsi/gomega/matchers/support/goraph/bipartitegraph
 github.com/onsi/gomega/matchers/support/goraph/edge
 github.com/onsi/gomega/matchers/support/goraph/node
 github.com/onsi/gomega/matchers/support/goraph/util
+# github.com/pkg/errors v0.8.1
+github.com/pkg/errors
 # github.com/sirupsen/logrus v1.4.2
 github.com/sirupsen/logrus
 # github.com/vishvananda/netlink v1.0.0