[#17] Implement audit logging

- Add README entry for audit logging
- On login log the redirection target
- Do not log empty headers
- Log login errors into AuditLog
- Fix: Wrong length error is a sign for no Yubikey OTP
- Add missing dependencies
- [#17] Implement audit logging

closes #17

Signed-off-by: Knut Ahlers <knut@ahlers.me>

Gopkg.lock

@@ -3,116 +3,171 @@
 
 [[projects]]
   branch = "master"
+  digest = "1:697c67f85d787be755efeb03461cb252e6c06d021fb67ac269242922f39035f2"
   name = "github.com/GeertJohan/yubigo"
   packages = ["."]
+  pruneopts = ""
   revision = "b1764f04aa9ba3c98a15084e7e13c1a69753e1da"
 
 [[projects]]
+  digest = "1:8483940c8f4bd6dab88903250941fef7773494c86e765734dc3459d61dbc1444"
   name = "github.com/Luzifer/go_helpers"
   packages = ["str"]
+  pruneopts = ""
   revision = "8fdddb7041fe962e750caa553a0714f94e261c4a"
   version = "v2.3.1"
 
 [[projects]]
+  digest = "1:58eb28a3287fe7633eed58de6aa0449a2d937dc03f06f201fcef3994c4795d08"
   name = "github.com/Luzifer/rconfig"
   packages = ["."]
+  pruneopts = ""
   revision = "7aef1d393c1e2d0758901853b59981c7adc67c7e"
   version = "v1.2.0"
 
 [[projects]]
   branch = "master"
+  digest = "1:b7eb152b61f41f0c9bcb6cf1187e1470a91d5e01d1e08f8b7bfd722578851720"
   name = "github.com/flosch/pongo2"
   packages = ["."]
+  pruneopts = ""
   revision = "1f4be1efe3b3529b7e58861f75d70120a9567dc4"
 
 [[projects]]
+  digest = "1:20ed7daa9b3b38b6d1d39b48ab3fd31122be5419461470d0c28de3e121c93ecf"
   name = "github.com/gorilla/context"
   packages = ["."]
+  pruneopts = ""
   revision = "1ea25387ff6f684839d82767c1733ff4d4d15d0a"
   version = "v1.1"
 
 [[projects]]
+  digest = "1:1ff3509899d1357b533eefcc4be703aa4b8b690370de9bce65389aad226acf3c"
   name = "github.com/gorilla/securecookie"
   packages = ["."]
+  pruneopts = ""
   revision = "667fe4e3466a040b780561fe9b51a83a3753eefc"
   version = "v1.1"
 
 [[projects]]
+  digest = "1:bfb5530b06be15a20de32e6c946eddc2d81693980c79205bcda3bd37fe1a931c"
   name = "github.com/gorilla/sessions"
   packages = ["."]
+  pruneopts = ""
   revision = "ca9ada44574153444b00d3fd9c8559e4cc95f896"
   version = "v1.1"
 
 [[projects]]
   branch = "master"
+  digest = "1:d989aa073a1e7f56cfe080f90c2f6c5acf8d6a2ab07cc9d6d0b65b836bc70e10"
   name = "github.com/jda/go-crowd"
   packages = ["."]
+  pruneopts = ""
   revision = "415c27e65cd496563601465cfe630d4b3245d70f"
 
 [[projects]]
   branch = "master"
+  digest = "1:b38a66184fb38b517900ab365f43557ea7e4efe36f939e2fcb53ec0aa92b29c5"
   name = "github.com/juju/errors"
   packages = ["."]
+  pruneopts = ""
   revision = "c7d06af17c68cd34c835053720b21f6549d9b0ee"
 
 [[projects]]
+  digest = "1:7365acd48986e205ccb8652cc746f09c8b7876030d53710ea6ef7d0bd0dcd7ca"
+  name = "github.com/pkg/errors"
+  packages = ["."]
+  pruneopts = ""
+  revision = "645ef00459ed84a119197bfb8d8205042c6df63d"
+  version = "v0.8.0"
+
+[[projects]]
+  digest = "1:42a42c4bc67bed17f40fddf0f24d4403e25e7b96488456cf4248e6d16659d370"
   name = "github.com/sirupsen/logrus"
   packages = ["."]
+  pruneopts = ""
   revision = "d682213848ed68c0a260ca37d6dd5ace8423f5ba"
   version = "v1.0.4"
 
 [[projects]]
+  digest = "1:261bc565833ef4f02121450d74eb88d5ae4bd74bfe5d0e862cddb8550ec35000"
   name = "github.com/spf13/pflag"
   packages = ["."]
+  pruneopts = ""
   revision = "e57e3eeb33f795204c1ca35f56c44f83227c6e66"
   version = "v1.0.0"
 
 [[projects]]
   branch = "master"
+  digest = "1:febc7d7c1a817016b83441742910a3eab682d5c64613fcd91fde7ca06107ea49"
   name = "golang.org/x/crypto"
   packages = [
     "bcrypt",
     "blowfish",
-    "ssh/terminal"
+    "ssh/terminal",
   ]
+  pruneopts = ""
   revision = "1875d0a70c90e57f11972aefd42276df65e895b9"
 
 [[projects]]
   branch = "master"
+  digest = "1:7a77d5b443b8e08a7d8ec3e4bc9ac636599be22668a12fdd01fb478e9b2ed4fa"
   name = "golang.org/x/sys"
   packages = [
     "unix",
-    "windows"
+    "windows",
   ]
+  pruneopts = ""
   revision = "ff2a66f350cefa5c93a634eadb5d25bb60c85a9c"
 
 [[projects]]
+  digest = "1:3cad99e0d1f94b8c162787c12e59d0a0b9df1ef75590eb145cdd625479091efe"
   name = "gopkg.in/asn1-ber.v1"
   packages = ["."]
+  pruneopts = ""
   revision = "379148ca0225df7a432012b8df0355c2a2063ac0"
   version = "v1.2"
 
 [[projects]]
+  digest = "1:367baf06b7dbd0ef0bbdd785f6a79f929c96b0c18e9d3b29c0eed1ac3f5db133"
   name = "gopkg.in/ldap.v2"
   packages = ["."]
+  pruneopts = ""
   revision = "bb7a9ca6e4fbc2129e3db588a34bc970ffe811a9"
   version = "v2.5.1"
 
 [[projects]]
   branch = "v2"
+  digest = "1:8012e3289c36d514a961b9b9a7576324a105c6eee7df346d92afd071cf79f97c"
   name = "gopkg.in/validator.v2"
   packages = ["."]
+  pruneopts = ""
   revision = "460c83432a98c35224a6fe352acf8b23e067ad06"
 
 [[projects]]
   branch = "v2"
+  digest = "1:4b4e5848dfe7f316f95f754df071bebfb40cf4482da62e17e7e1aebdf11f4918"
   name = "gopkg.in/yaml.v2"
   packages = ["."]
+  pruneopts = ""
   revision = "d670f9405373e636a5a2765eea47fac0c9bc91a4"
 
 [solve-meta]
   analyzer-name = "dep"
   analyzer-version = 1
-  inputs-digest = "62f32b4a6ee3a3e10d11f49265d37af10218b5ca992552f010f544cb8b03cd58"
+  input-imports = [
+    "github.com/GeertJohan/yubigo",
+    "github.com/Luzifer/go_helpers/str",
+    "github.com/Luzifer/rconfig",
+    "github.com/flosch/pongo2",
+    "github.com/gorilla/context",
+    "github.com/gorilla/sessions",
+    "github.com/jda/go-crowd",
+    "github.com/pkg/errors",
+    "github.com/sirupsen/logrus",
+    "golang.org/x/crypto/bcrypt",
+    "gopkg.in/ldap.v2",
+    "gopkg.in/yaml.v2",
+  ]
   solver-name = "gps-cdcl"
   solver-version = 1

Gopkg.toml

@@ -51,3 +51,7 @@
 [[constraint]]
   branch = "v2"
   name = "gopkg.in/yaml.v2"
+
+[[constraint]]
+  name = "github.com/pkg/errors"
+  version = "0.8.0"

README.md

@@ -119,6 +119,27 @@ listen:
 
 Pay attention if you are running the docker container you need to change the IP to `0.0.0.0` to expose the port in the container. If you miss this the service will not be available.
 
+### Main configuration: Audit Logging
+
+nginx-sso can be configured to write an audit log which for example can be used to detect brute-force attacks on passwords. By default the audit logging is disabled and gets enabled by providing `targets` in the `audit_log` section of the config.
+
+Due to the fact we do have several credential providers the `login` and `logout` events do not contain an username. The username is only known in requests the user is doing after their login so the `access_denied` and `validate` events contains it.
+
+```yaml
+audit_log:
+  targets:
+    - fd://stdout
+    - file:///var/log/nginx-sso/audit.jsonl
+  events: ['access_denied', 'login_success', 'login_failure', 'logout', 'validate']
+  headers: ['x-origin-uri']
+  trusted_ip_headers: ["X-Forwarded-For", "RemoteAddr", "X-Real-IP"]
+```
+
+- `targets` - required - Supported targets are `fd://stdout`, `fd://stderr` or any `file://...` URI
+- `events` - required - All supported events are listed above in the example. Pay attention `validate` is a quite verbose event
+- `headers` - optional - List of headers to include into the log entry (for details about the headers see the ACL section below)
+- `trusted_ip_headers` - optional - List of headers to use for reading the real IP the request is coming from (defaults see example above)
+
 ### Main configuration: ACL
 
 The rules of the ACL are the most complex part of the configuration and you should take your time to make this bullet-proof. If you mess up you're probably are getting complaints from your users because the default policy applied is to `deny` all access. So in the end you are configuring a white-list here.

audit.go

@@ -0,0 +1,135 @@
+package main
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/url"
+	"os"
+	"path"
+	"strings"
+	"sync"
+
+	"github.com/pkg/errors"
+
+	"github.com/Luzifer/go_helpers/str"
+)
+
+type auditEvent string
+
+const (
+	auditEventAccessDenied            = "access_denied"
+	auditEventLoginFailure            = "login_failure"
+	auditEventLoginSuccess auditEvent = "login_success"
+	auditEventLogout                  = "logout"
+	auditEventValidate                = "validate"
+)
+
+type auditLogger struct {
+	Targets          []string `yaml:"targets"`
+	Events           []string `yaml:"events"`
+	Headers          []string `yaml:"headers"`
+	TrustedIPHeaders []string `yaml:"trusted_ip_headers"`
+
+	lock sync.Mutex
+}
+
+func (a *auditLogger) Log(event auditEvent, r *http.Request, extraFields map[string]string) error {
+	if len(a.Targets) == 0 {
+		return nil
+	}
+
+	if !str.StringInSlice(string(event), a.Events) {
+		return nil
+	}
+
+	// Ensure order of logs, prevent file operation collisions
+	a.lock.Lock()
+	defer a.lock.Unlock()
+
+	// Compile log event
+	evt := map[string]interface{}{}
+	evt["event_type"] = event
+	evt["remote_addr"] = a.findIP(r)
+
+	if extraFields != nil {
+		for k, v := range extraFields {
+			evt[k] = v
+		}
+	}
+
+	headers := map[string]string{}
+	for _, k := range a.Headers {
+		if v := r.Header.Get(k); v != "" {
+			headers[k] = v
+		}
+	}
+
+	evt["headers"] = headers
+
+	// Submit event to all specified targets
+	for _, target := range a.Targets {
+		if err := a.submitLog(target, evt); err != nil {
+			return errors.Wrapf(err, "Could not submit log to target %q", target)
+		}
+	}
+
+	return nil
+}
+
+func (a *auditLogger) findIP(r *http.Request) string {
+	remoteAddr := strings.SplitN(r.RemoteAddr, ":", 2)[0]
+
+	for _, hdr := range a.TrustedIPHeaders {
+		if value := r.Header.Get(hdr); value != "" {
+			return strings.SplitN(value, ",", 2)[0]
+		}
+	}
+
+	return remoteAddr
+}
+
+func (a *auditLogger) submitLog(target string, event map[string]interface{}) error {
+	u, err := url.Parse(target)
+	if err != nil {
+		return errors.Wrap(err, "Unable to parse target")
+	}
+
+	switch u.Scheme {
+	case "fd":
+		return a.submitLogFileDescriptor(u.Host, event)
+	case "file":
+		return a.submitLogFile(u.Path, event)
+	default:
+		return errors.Errorf("Unsupported target scheme %q", u.Scheme)
+	}
+}
+
+func (a *auditLogger) submitLogFile(filename string, event map[string]interface{}) error {
+	if err := os.MkdirAll(path.Dir(filename), 0600); err != nil {
+		return errors.Wrap(err, "Unable to create required paths")
+	}
+
+	f, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0600)
+	if err != nil {
+		return errors.Wrap(err, "Unable to open audit file")
+	}
+	defer f.Close()
+
+	return json.NewEncoder(f).Encode(event)
+}
+
+func (a *auditLogger) submitLogFileDescriptor(descriptor string, event map[string]interface{}) error {
+	var w io.Writer
+
+	switch descriptor {
+	case "stdout":
+		w = os.Stdout
+	case "stderr":
+		w = os.Stderr
+	default:
+		return errors.Errorf("Unsupported file descriptor %q", descriptor)
+	}
+
+	return errors.Wrap(json.NewEncoder(w).Encode(event), "Unable to marshal event")
+}

auth_yubikey.go

@@ -5,8 +5,9 @@ import (
 	"strings"
 
 	"github.com/GeertJohan/yubigo"
-	"github.com/Luzifer/go_helpers/str"
 	yaml "gopkg.in/yaml.v2"
+
+	"github.com/Luzifer/go_helpers/str"
 )
 
 func init() {
@@ -97,7 +98,7 @@ func (a authYubikey) Login(res http.ResponseWriter, r *http.Request) error {
 	}
 
 	_, ok, err := yubiAuth.Verify(keyInput)
-	if err != nil {
+	if err != nil && !strings.Contains(err.Error(), "OTP has wrong length.") {
 		return err
 	}
 

config.yaml

@@ -19,6 +19,14 @@ listen:
   addr: "127.0.0.1"
   port: 8082
 
+audit_log:
+  targets:
+    - fd://stdout
+    - file:///var/log/nginx-sso/audit.jsonl
+  events: ['access_denied', 'login_success', 'login_failure', 'logout', 'validate']
+  headers: ['x-origin-uri']
+  trusted_ip_headers: ["X-Forwarded-For", "RemoteAddr", "X-Real-IP"]
+
 acl:
   rule_sets:
   - rules:

main.go

@@ -10,17 +10,19 @@ import (
 	"path"
 	"syscall"
 
-	"github.com/Luzifer/rconfig"
 	"github.com/flosch/pongo2"
 	"github.com/gorilla/context"
 	"github.com/gorilla/sessions"
 	log "github.com/sirupsen/logrus"
 	yaml "gopkg.in/yaml.v2"
+
+	"github.com/Luzifer/rconfig"
 )
 
 type mainConfig struct {
-	ACL    acl `yaml:"acl"`
+	ACL      acl         `yaml:"acl"`
-	Cookie struct {
+	AuditLog auditLogger `yaml:"audit_log"`
+	Cookie   struct {
 		Domain  string `yaml:"domain"`
 		AuthKey string `yaml:"authentication_key"`
 		Expire  int    `yaml:"expire"`
@@ -38,7 +40,7 @@ type mainConfig struct {
 	} `yaml:"login"`
 }
 
-func (m mainConfig) GetSessionOpts() *sessions.Options {
+func (m *mainConfig) GetSessionOpts() *sessions.Options {
 	return &sessions.Options{
 		Path:     "/",
 		Domain:   m.Cookie.Domain,
@@ -83,6 +85,8 @@ func init() {
 	mainCfg.Cookie.Expire = 3600
 	mainCfg.Listen.Addr = "127.0.0.1"
 	mainCfg.Listen.Port = 8082
+	mainCfg.AuditLog.TrustedIPHeaders = []string{"X-Forwarded-For", "RemoteAddr", "X-Real-IP"}
+	mainCfg.AuditLog.Headers = []string{"x-origin-url"}
 }
 
 func loadConfiguration() error {
@@ -139,14 +143,18 @@ func handleAuthRequest(res http.ResponseWriter, r *http.Request) {
 
 	switch err {
 	case errNoValidUserFound:
+		mainCfg.AuditLog.Log(auditEventValidate, r, map[string]string{"result": "no valid user found"})
 		http.Error(res, "No valid user found", http.StatusUnauthorized)
 
 	case nil:
 		if !mainCfg.ACL.HasAccess(user, groups, r) {
+			mainCfg.AuditLog.Log(auditEventAccessDenied, r, map[string]string{"username": user})
 			http.Error(res, "Access denied for this resource", http.StatusForbidden)
 			return
 		}
 
+		mainCfg.AuditLog.Log(auditEventValidate, r, map[string]string{"result": "valid user found", "username": user})
+
 		res.Header().Set("X-Username", user)
 		res.WriteHeader(http.StatusOK)
 
@@ -163,16 +171,28 @@ func handleLoginRequest(res http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	auditFields := map[string]string{
+		"go": r.FormValue("go"),
+	}
+
 	if r.Method == "POST" {
 		err := loginUser(res, r)
 		switch err {
 		case errNoValidUserFound:
+			auditFields["reason"] = "invalid credentials"
+			mainCfg.AuditLog.Log(auditEventLoginFailure, r, auditFields)
 			http.Redirect(res, r, "/login?go="+url.QueryEscape(r.FormValue("go")), http.StatusFound)
 			return
+
 		case nil:
+			mainCfg.AuditLog.Log(auditEventLoginSuccess, r, auditFields)
 			http.Redirect(res, r, r.FormValue("go"), http.StatusFound)
 			return
+
 		default:
+			auditFields["reason"] = "error"
+			auditFields["error"] = err.Error()
+			mainCfg.AuditLog.Log(auditEventLoginFailure, r, auditFields)
 			log.WithError(err).Error("Login failed with unexpected error")
 			http.Redirect(res, r, "/login?go="+url.QueryEscape(r.FormValue("go")), http.StatusFound)
 			return
@@ -191,6 +211,7 @@ func handleLoginRequest(res http.ResponseWriter, r *http.Request) {
 }
 
 func handleLogoutRequest(res http.ResponseWriter, r *http.Request) {
+	mainCfg.AuditLog.Log(auditEventLogout, r, nil)
 	if err := logoutUser(res, r); err != nil {
 		log.WithError(err).Error("Failed to logout user")
 		http.Error(res, "Something went wrong", http.StatusInternalServerError)

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

vendor/github.com/pkg/errors/.travis.yml

@@ -0,0 +1,11 @@
+language: go
+go_import_path: github.com/pkg/errors
+go:
+  - 1.4.3
+  - 1.5.4
+  - 1.6.2
+  - 1.7.1
+  - tip
+
+script:
+  - go test -v ./...

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.

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)
+
+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.
+
+## Licence
+
+BSD-2-Clause

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

vendor/github.com/pkg/errors/bench_test.go

@@ -0,0 +1,59 @@
+// +build go1.7
+
+package errors
+
+import (
+	"fmt"
+	"testing"
+
+	stderrors "errors"
+)
+
+func noErrors(at, depth int) error {
+	if at >= depth {
+		return stderrors.New("no error")
+	}
+	return noErrors(at+1, depth)
+}
+func yesErrors(at, depth int) error {
+	if at >= depth {
+		return New("ye error")
+	}
+	return yesErrors(at+1, depth)
+}
+
+func BenchmarkErrors(b *testing.B) {
+	var toperr error
+	type run struct {
+		stack int
+		std   bool
+	}
+	runs := []run{
+		{10, false},
+		{10, true},
+		{100, false},
+		{100, true},
+		{1000, false},
+		{1000, true},
+	}
+	for _, r := range runs {
+		part := "pkg/errors"
+		if r.std {
+			part = "errors"
+		}
+		name := fmt.Sprintf("%s-stack-%d", part, r.stack)
+		b.Run(name, func(b *testing.B) {
+			var err error
+			f := yesErrors
+			if r.std {
+				f = noErrors
+			}
+			b.ReportAllocs()
+			for i := 0; i < b.N; i++ {
+				err = f(0, r.stack)
+			}
+			b.StopTimer()
+			toperr = err
+		})
+	}
+}

vendor/github.com/pkg/errors/errors.go

@@ -0,0 +1,269 @@
+// Package errors provides simple error handling primitives.
+//
+// The traditional error handling idiom in Go is roughly akin to
+//
+//     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 by recording a stack trace at the point Wrap is called,
+// and 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 of annotating
+// an error with a stack trace and an 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 which 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
+//     }
+//
+// causer interface is not exported by this package, but is considered a part
+// of stable public API.
+//
+// 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
+//     }
+//
+// Where errors.StackTrace 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)
+//             }
+//     }
+//
+// stackTracer interface is not exported by this package, but is considered a part
+// of stable public API.
+//
+// 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 call, 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,
+	}
+}
+
+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
+}

vendor/github.com/pkg/errors/errors_test.go

@@ -0,0 +1,226 @@
+package errors
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"reflect"
+	"testing"
+)
+
+func TestNew(t *testing.T) {
+	tests := []struct {
+		err  string
+		want error
+	}{
+		{"", fmt.Errorf("")},
+		{"foo", fmt.Errorf("foo")},
+		{"foo", New("foo")},
+		{"string with format specifiers: %v", errors.New("string with format specifiers: %v")},
+	}
+
+	for _, tt := range tests {
+		got := New(tt.err)
+		if got.Error() != tt.want.Error() {
+			t.Errorf("New.Error(): got: %q, want %q", got, tt.want)
+		}
+	}
+}
+
+func TestWrapNil(t *testing.T) {
+	got := Wrap(nil, "no error")
+	if got != nil {
+		t.Errorf("Wrap(nil, \"no error\"): got %#v, expected nil", got)
+	}
+}
+
+func TestWrap(t *testing.T) {
+	tests := []struct {
+		err     error
+		message string
+		want    string
+	}{
+		{io.EOF, "read error", "read error: EOF"},
+		{Wrap(io.EOF, "read error"), "client error", "client error: read error: EOF"},
+	}
+
+	for _, tt := range tests {
+		got := Wrap(tt.err, tt.message).Error()
+		if got != tt.want {
+			t.Errorf("Wrap(%v, %q): got: %v, want %v", tt.err, tt.message, got, tt.want)
+		}
+	}
+}
+
+type nilError struct{}
+
+func (nilError) Error() string { return "nil error" }
+
+func TestCause(t *testing.T) {
+	x := New("error")
+	tests := []struct {
+		err  error
+		want error
+	}{{
+		// nil error is nil
+		err:  nil,
+		want: nil,
+	}, {
+		// explicit nil error is nil
+		err:  (error)(nil),
+		want: nil,
+	}, {
+		// typed nil is nil
+		err:  (*nilError)(nil),
+		want: (*nilError)(nil),
+	}, {
+		// uncaused error is unaffected
+		err:  io.EOF,
+		want: io.EOF,
+	}, {
+		// caused error returns cause
+		err:  Wrap(io.EOF, "ignored"),
+		want: io.EOF,
+	}, {
+		err:  x, // return from errors.New
+		want: x,
+	}, {
+		WithMessage(nil, "whoops"),
+		nil,
+	}, {
+		WithMessage(io.EOF, "whoops"),
+		io.EOF,
+	}, {
+		WithStack(nil),
+		nil,
+	}, {
+		WithStack(io.EOF),
+		io.EOF,
+	}}
+
+	for i, tt := range tests {
+		got := Cause(tt.err)
+		if !reflect.DeepEqual(got, tt.want) {
+			t.Errorf("test %d: got %#v, want %#v", i+1, got, tt.want)
+		}
+	}
+}
+
+func TestWrapfNil(t *testing.T) {
+	got := Wrapf(nil, "no error")
+	if got != nil {
+		t.Errorf("Wrapf(nil, \"no error\"): got %#v, expected nil", got)
+	}
+}
+
+func TestWrapf(t *testing.T) {
+	tests := []struct {
+		err     error
+		message string
+		want    string
+	}{
+		{io.EOF, "read error", "read error: EOF"},
+		{Wrapf(io.EOF, "read error without format specifiers"), "client error", "client error: read error without format specifiers: EOF"},
+		{Wrapf(io.EOF, "read error with %d format specifier", 1), "client error", "client error: read error with 1 format specifier: EOF"},
+	}
+
+	for _, tt := range tests {
+		got := Wrapf(tt.err, tt.message).Error()
+		if got != tt.want {
+			t.Errorf("Wrapf(%v, %q): got: %v, want %v", tt.err, tt.message, got, tt.want)
+		}
+	}
+}
+
+func TestErrorf(t *testing.T) {
+	tests := []struct {
+		err  error
+		want string
+	}{
+		{Errorf("read error without format specifiers"), "read error without format specifiers"},
+		{Errorf("read error with %d format specifier", 1), "read error with 1 format specifier"},
+	}
+
+	for _, tt := range tests {
+		got := tt.err.Error()
+		if got != tt.want {
+			t.Errorf("Errorf(%v): got: %q, want %q", tt.err, got, tt.want)
+		}
+	}
+}
+
+func TestWithStackNil(t *testing.T) {
+	got := WithStack(nil)
+	if got != nil {
+		t.Errorf("WithStack(nil): got %#v, expected nil", got)
+	}
+}
+
+func TestWithStack(t *testing.T) {
+	tests := []struct {
+		err  error
+		want string
+	}{
+		{io.EOF, "EOF"},
+		{WithStack(io.EOF), "EOF"},
+	}
+
+	for _, tt := range tests {
+		got := WithStack(tt.err).Error()
+		if got != tt.want {
+			t.Errorf("WithStack(%v): got: %v, want %v", tt.err, got, tt.want)
+		}
+	}
+}
+
+func TestWithMessageNil(t *testing.T) {
+	got := WithMessage(nil, "no error")
+	if got != nil {
+		t.Errorf("WithMessage(nil, \"no error\"): got %#v, expected nil", got)
+	}
+}
+
+func TestWithMessage(t *testing.T) {
+	tests := []struct {
+		err     error
+		message string
+		want    string
+	}{
+		{io.EOF, "read error", "read error: EOF"},
+		{WithMessage(io.EOF, "read error"), "client error", "client error: read error: EOF"},
+	}
+
+	for _, tt := range tests {
+		got := WithMessage(tt.err, tt.message).Error()
+		if got != tt.want {
+			t.Errorf("WithMessage(%v, %q): got: %q, want %q", tt.err, tt.message, got, tt.want)
+		}
+	}
+
+}
+
+// errors.New, etc values are not expected to be compared by value
+// but the change in errors#27 made them incomparable. Assert that
+// various kinds of errors have a functional equality operator, even
+// if the result of that equality is always false.
+func TestErrorEquality(t *testing.T) {
+	vals := []error{
+		nil,
+		io.EOF,
+		errors.New("EOF"),
+		New("EOF"),
+		Errorf("EOF"),
+		Wrap(io.EOF, "EOF"),
+		Wrapf(io.EOF, "EOF%d", 2),
+		WithMessage(nil, "whoops"),
+		WithMessage(io.EOF, "whoops"),
+		WithStack(io.EOF),
+		WithStack(nil),
+	}
+
+	for i := range vals {
+		for j := range vals {
+			_ = vals[i] == vals[j] // mustn't panic
+		}
+	}
+}

vendor/github.com/pkg/errors/example_test.go

@@ -0,0 +1,205 @@
+package errors_test
+
+import (
+	"fmt"
+
+	"github.com/pkg/errors"
+)
+
+func ExampleNew() {
+	err := errors.New("whoops")
+	fmt.Println(err)
+
+	// Output: whoops
+}
+
+func ExampleNew_printf() {
+	err := errors.New("whoops")
+	fmt.Printf("%+v", err)
+
+	// Example output:
+	// whoops
+	// github.com/pkg/errors_test.ExampleNew_printf
+	//         /home/dfc/src/github.com/pkg/errors/example_test.go:17
+	// testing.runExample
+	//         /home/dfc/go/src/testing/example.go:114
+	// testing.RunExamples
+	//         /home/dfc/go/src/testing/example.go:38
+	// testing.(*M).Run
+	//         /home/dfc/go/src/testing/testing.go:744
+	// main.main
+	//         /github.com/pkg/errors/_test/_testmain.go:106
+	// runtime.main
+	//         /home/dfc/go/src/runtime/proc.go:183
+	// runtime.goexit
+	//         /home/dfc/go/src/runtime/asm_amd64.s:2059
+}
+
+func ExampleWithMessage() {
+	cause := errors.New("whoops")
+	err := errors.WithMessage(cause, "oh noes")
+	fmt.Println(err)
+
+	// Output: oh noes: whoops
+}
+
+func ExampleWithStack() {
+	cause := errors.New("whoops")
+	err := errors.WithStack(cause)
+	fmt.Println(err)
+
+	// Output: whoops
+}
+
+func ExampleWithStack_printf() {
+	cause := errors.New("whoops")
+	err := errors.WithStack(cause)
+	fmt.Printf("%+v", err)
+
+	// Example Output:
+	// whoops
+	// github.com/pkg/errors_test.ExampleWithStack_printf
+	//         /home/fabstu/go/src/github.com/pkg/errors/example_test.go:55
+	// testing.runExample
+	//         /usr/lib/go/src/testing/example.go:114
+	// testing.RunExamples
+	//         /usr/lib/go/src/testing/example.go:38
+	// testing.(*M).Run
+	//         /usr/lib/go/src/testing/testing.go:744
+	// main.main
+	//         github.com/pkg/errors/_test/_testmain.go:106
+	// runtime.main
+	//         /usr/lib/go/src/runtime/proc.go:183
+	// runtime.goexit
+	//         /usr/lib/go/src/runtime/asm_amd64.s:2086
+	// github.com/pkg/errors_test.ExampleWithStack_printf
+	//         /home/fabstu/go/src/github.com/pkg/errors/example_test.go:56
+	// testing.runExample
+	//         /usr/lib/go/src/testing/example.go:114
+	// testing.RunExamples
+	//         /usr/lib/go/src/testing/example.go:38
+	// testing.(*M).Run
+	//         /usr/lib/go/src/testing/testing.go:744
+	// main.main
+	//         github.com/pkg/errors/_test/_testmain.go:106
+	// runtime.main
+	//         /usr/lib/go/src/runtime/proc.go:183
+	// runtime.goexit
+	//         /usr/lib/go/src/runtime/asm_amd64.s:2086
+}
+
+func ExampleWrap() {
+	cause := errors.New("whoops")
+	err := errors.Wrap(cause, "oh noes")
+	fmt.Println(err)
+
+	// Output: oh noes: whoops
+}
+
+func fn() error {
+	e1 := errors.New("error")
+	e2 := errors.Wrap(e1, "inner")
+	e3 := errors.Wrap(e2, "middle")
+	return errors.Wrap(e3, "outer")
+}
+
+func ExampleCause() {
+	err := fn()
+	fmt.Println(err)
+	fmt.Println(errors.Cause(err))
+
+	// Output: outer: middle: inner: error
+	// error
+}
+
+func ExampleWrap_extended() {
+	err := fn()
+	fmt.Printf("%+v\n", err)
+
+	// Example output:
+	// error
+	// github.com/pkg/errors_test.fn
+	//         /home/dfc/src/github.com/pkg/errors/example_test.go:47
+	// github.com/pkg/errors_test.ExampleCause_printf
+	//         /home/dfc/src/github.com/pkg/errors/example_test.go:63
+	// testing.runExample
+	//         /home/dfc/go/src/testing/example.go:114
+	// testing.RunExamples
+	//         /home/dfc/go/src/testing/example.go:38
+	// testing.(*M).Run
+	//         /home/dfc/go/src/testing/testing.go:744
+	// main.main
+	//         /github.com/pkg/errors/_test/_testmain.go:104
+	// runtime.main
+	//         /home/dfc/go/src/runtime/proc.go:183
+	// runtime.goexit
+	//         /home/dfc/go/src/runtime/asm_amd64.s:2059
+	// github.com/pkg/errors_test.fn
+	// 	  /home/dfc/src/github.com/pkg/errors/example_test.go:48: inner
+	// github.com/pkg/errors_test.fn
+	//        /home/dfc/src/github.com/pkg/errors/example_test.go:49: middle
+	// github.com/pkg/errors_test.fn
+	//      /home/dfc/src/github.com/pkg/errors/example_test.go:50: outer
+}
+
+func ExampleWrapf() {
+	cause := errors.New("whoops")
+	err := errors.Wrapf(cause, "oh noes #%d", 2)
+	fmt.Println(err)
+
+	// Output: oh noes #2: whoops
+}
+
+func ExampleErrorf_extended() {
+	err := errors.Errorf("whoops: %s", "foo")
+	fmt.Printf("%+v", err)
+
+	// Example output:
+	// whoops: foo
+	// github.com/pkg/errors_test.ExampleErrorf
+	//         /home/dfc/src/github.com/pkg/errors/example_test.go:101
+	// testing.runExample
+	//         /home/dfc/go/src/testing/example.go:114
+	// testing.RunExamples
+	//         /home/dfc/go/src/testing/example.go:38
+	// testing.(*M).Run
+	//         /home/dfc/go/src/testing/testing.go:744
+	// main.main
+	//         /github.com/pkg/errors/_test/_testmain.go:102
+	// runtime.main
+	//         /home/dfc/go/src/runtime/proc.go:183
+	// runtime.goexit
+	//         /home/dfc/go/src/runtime/asm_amd64.s:2059
+}
+
+func Example_stackTrace() {
+	type stackTracer interface {
+		StackTrace() errors.StackTrace
+	}
+
+	err, ok := errors.Cause(fn()).(stackTracer)
+	if !ok {
+		panic("oops, err does not implement stackTracer")
+	}
+
+	st := err.StackTrace()
+	fmt.Printf("%+v", st[0:2]) // top two frames
+
+	// Example output:
+	// github.com/pkg/errors_test.fn
+	//	/home/dfc/src/github.com/pkg/errors/example_test.go:47
+	// github.com/pkg/errors_test.Example_stackTrace
+	//	/home/dfc/src/github.com/pkg/errors/example_test.go:127
+}
+
+func ExampleCause_printf() {
+	err := errors.Wrap(func() error {
+		return func() error {
+			return errors.Errorf("hello %s", fmt.Sprintf("world"))
+		}()
+	}(), "failed")
+
+	fmt.Printf("%v", err)
+
+	// Output: failed: hello world
+}

vendor/github.com/pkg/errors/format_test.go

@@ -0,0 +1,535 @@
+package errors
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"regexp"
+	"strings"
+	"testing"
+)
+
+func TestFormatNew(t *testing.T) {
+	tests := []struct {
+		error
+		format string
+		want   string
+	}{{
+		New("error"),
+		"%s",
+		"error",
+	}, {
+		New("error"),
+		"%v",
+		"error",
+	}, {
+		New("error"),
+		"%+v",
+		"error\n" +
+			"github.com/pkg/errors.TestFormatNew\n" +
+			"\t.+/github.com/pkg/errors/format_test.go:26",
+	}, {
+		New("error"),
+		"%q",
+		`"error"`,
+	}}
+
+	for i, tt := range tests {
+		testFormatRegexp(t, i, tt.error, tt.format, tt.want)
+	}
+}
+
+func TestFormatErrorf(t *testing.T) {
+	tests := []struct {
+		error
+		format string
+		want   string
+	}{{
+		Errorf("%s", "error"),
+		"%s",
+		"error",
+	}, {
+		Errorf("%s", "error"),
+		"%v",
+		"error",
+	}, {
+		Errorf("%s", "error"),
+		"%+v",
+		"error\n" +
+			"github.com/pkg/errors.TestFormatErrorf\n" +
+			"\t.+/github.com/pkg/errors/format_test.go:56",
+	}}
+
+	for i, tt := range tests {
+		testFormatRegexp(t, i, tt.error, tt.format, tt.want)
+	}
+}
+
+func TestFormatWrap(t *testing.T) {
+	tests := []struct {
+		error
+		format string
+		want   string
+	}{{
+		Wrap(New("error"), "error2"),
+		"%s",
+		"error2: error",
+	}, {
+		Wrap(New("error"), "error2"),
+		"%v",
+		"error2: error",
+	}, {
+		Wrap(New("error"), "error2"),
+		"%+v",
+		"error\n" +
+			"github.com/pkg/errors.TestFormatWrap\n" +
+			"\t.+/github.com/pkg/errors/format_test.go:82",
+	}, {
+		Wrap(io.EOF, "error"),
+		"%s",
+		"error: EOF",
+	}, {
+		Wrap(io.EOF, "error"),
+		"%v",
+		"error: EOF",
+	}, {
+		Wrap(io.EOF, "error"),
+		"%+v",
+		"EOF\n" +
+			"error\n" +
+			"github.com/pkg/errors.TestFormatWrap\n" +
+			"\t.+/github.com/pkg/errors/format_test.go:96",
+	}, {
+		Wrap(Wrap(io.EOF, "error1"), "error2"),
+		"%+v",
+		"EOF\n" +
+			"error1\n" +
+			"github.com/pkg/errors.TestFormatWrap\n" +
+			"\t.+/github.com/pkg/errors/format_test.go:103\n",
+	}, {
+		Wrap(New("error with space"), "context"),
+		"%q",
+		`"context: error with space"`,
+	}}
+
+	for i, tt := range tests {
+		testFormatRegexp(t, i, tt.error, tt.format, tt.want)
+	}
+}
+
+func TestFormatWrapf(t *testing.T) {
+	tests := []struct {
+		error
+		format string
+		want   string
+	}{{
+		Wrapf(io.EOF, "error%d", 2),
+		"%s",
+		"error2: EOF",
+	}, {
+		Wrapf(io.EOF, "error%d", 2),
+		"%v",
+		"error2: EOF",
+	}, {
+		Wrapf(io.EOF, "error%d", 2),
+		"%+v",
+		"EOF\n" +
+			"error2\n" +
+			"github.com/pkg/errors.TestFormatWrapf\n" +
+			"\t.+/github.com/pkg/errors/format_test.go:134",
+	}, {
+		Wrapf(New("error"), "error%d", 2),
+		"%s",
+		"error2: error",
+	}, {
+		Wrapf(New("error"), "error%d", 2),
+		"%v",
+		"error2: error",
+	}, {
+		Wrapf(New("error"), "error%d", 2),
+		"%+v",
+		"error\n" +
+			"github.com/pkg/errors.TestFormatWrapf\n" +
+			"\t.+/github.com/pkg/errors/format_test.go:149",
+	}}
+
+	for i, tt := range tests {
+		testFormatRegexp(t, i, tt.error, tt.format, tt.want)
+	}
+}
+
+func TestFormatWithStack(t *testing.T) {
+	tests := []struct {
+		error
+		format string
+		want   []string
+	}{{
+		WithStack(io.EOF),
+		"%s",
+		[]string{"EOF"},
+	}, {
+		WithStack(io.EOF),
+		"%v",
+		[]string{"EOF"},
+	}, {
+		WithStack(io.EOF),
+		"%+v",
+		[]string{"EOF",
+			"github.com/pkg/errors.TestFormatWithStack\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:175"},
+	}, {
+		WithStack(New("error")),
+		"%s",
+		[]string{"error"},
+	}, {
+		WithStack(New("error")),
+		"%v",
+		[]string{"error"},
+	}, {
+		WithStack(New("error")),
+		"%+v",
+		[]string{"error",
+			"github.com/pkg/errors.TestFormatWithStack\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:189",
+			"github.com/pkg/errors.TestFormatWithStack\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:189"},
+	}, {
+		WithStack(WithStack(io.EOF)),
+		"%+v",
+		[]string{"EOF",
+			"github.com/pkg/errors.TestFormatWithStack\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:197",
+			"github.com/pkg/errors.TestFormatWithStack\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:197"},
+	}, {
+		WithStack(WithStack(Wrapf(io.EOF, "message"))),
+		"%+v",
+		[]string{"EOF",
+			"message",
+			"github.com/pkg/errors.TestFormatWithStack\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:205",
+			"github.com/pkg/errors.TestFormatWithStack\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:205",
+			"github.com/pkg/errors.TestFormatWithStack\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:205"},
+	}, {
+		WithStack(Errorf("error%d", 1)),
+		"%+v",
+		[]string{"error1",
+			"github.com/pkg/errors.TestFormatWithStack\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:216",
+			"github.com/pkg/errors.TestFormatWithStack\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:216"},
+	}}
+
+	for i, tt := range tests {
+		testFormatCompleteCompare(t, i, tt.error, tt.format, tt.want, true)
+	}
+}
+
+func TestFormatWithMessage(t *testing.T) {
+	tests := []struct {
+		error
+		format string
+		want   []string
+	}{{
+		WithMessage(New("error"), "error2"),
+		"%s",
+		[]string{"error2: error"},
+	}, {
+		WithMessage(New("error"), "error2"),
+		"%v",
+		[]string{"error2: error"},
+	}, {
+		WithMessage(New("error"), "error2"),
+		"%+v",
+		[]string{
+			"error",
+			"github.com/pkg/errors.TestFormatWithMessage\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:244",
+			"error2"},
+	}, {
+		WithMessage(io.EOF, "addition1"),
+		"%s",
+		[]string{"addition1: EOF"},
+	}, {
+		WithMessage(io.EOF, "addition1"),
+		"%v",
+		[]string{"addition1: EOF"},
+	}, {
+		WithMessage(io.EOF, "addition1"),
+		"%+v",
+		[]string{"EOF", "addition1"},
+	}, {
+		WithMessage(WithMessage(io.EOF, "addition1"), "addition2"),
+		"%v",
+		[]string{"addition2: addition1: EOF"},
+	}, {
+		WithMessage(WithMessage(io.EOF, "addition1"), "addition2"),
+		"%+v",
+		[]string{"EOF", "addition1", "addition2"},
+	}, {
+		Wrap(WithMessage(io.EOF, "error1"), "error2"),
+		"%+v",
+		[]string{"EOF", "error1", "error2",
+			"github.com/pkg/errors.TestFormatWithMessage\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:272"},
+	}, {
+		WithMessage(Errorf("error%d", 1), "error2"),
+		"%+v",
+		[]string{"error1",
+			"github.com/pkg/errors.TestFormatWithMessage\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:278",
+			"error2"},
+	}, {
+		WithMessage(WithStack(io.EOF), "error"),
+		"%+v",
+		[]string{
+			"EOF",
+			"github.com/pkg/errors.TestFormatWithMessage\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:285",
+			"error"},
+	}, {
+		WithMessage(Wrap(WithStack(io.EOF), "inside-error"), "outside-error"),
+		"%+v",
+		[]string{
+			"EOF",
+			"github.com/pkg/errors.TestFormatWithMessage\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:293",
+			"inside-error",
+			"github.com/pkg/errors.TestFormatWithMessage\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:293",
+			"outside-error"},
+	}}
+
+	for i, tt := range tests {
+		testFormatCompleteCompare(t, i, tt.error, tt.format, tt.want, true)
+	}
+}
+
+func TestFormatGeneric(t *testing.T) {
+	starts := []struct {
+		err  error
+		want []string
+	}{
+		{New("new-error"), []string{
+			"new-error",
+			"github.com/pkg/errors.TestFormatGeneric\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:315"},
+		}, {Errorf("errorf-error"), []string{
+			"errorf-error",
+			"github.com/pkg/errors.TestFormatGeneric\n" +
+				"\t.+/github.com/pkg/errors/format_test.go:319"},
+		}, {errors.New("errors-new-error"), []string{
+			"errors-new-error"},
+		},
+	}
+
+	wrappers := []wrapper{
+		{
+			func(err error) error { return WithMessage(err, "with-message") },
+			[]string{"with-message"},
+		}, {
+			func(err error) error { return WithStack(err) },
+			[]string{
+				"github.com/pkg/errors.(func·002|TestFormatGeneric.func2)\n\t" +
+					".+/github.com/pkg/errors/format_test.go:333",
+			},
+		}, {
+			func(err error) error { return Wrap(err, "wrap-error") },
+			[]string{
+				"wrap-error",
+				"github.com/pkg/errors.(func·003|TestFormatGeneric.func3)\n\t" +
+					".+/github.com/pkg/errors/format_test.go:339",
+			},
+		}, {
+			func(err error) error { return Wrapf(err, "wrapf-error%d", 1) },
+			[]string{
+				"wrapf-error1",
+				"github.com/pkg/errors.(func·004|TestFormatGeneric.func4)\n\t" +
+					".+/github.com/pkg/errors/format_test.go:346",
+			},
+		},
+	}
+
+	for s := range starts {
+		err := starts[s].err
+		want := starts[s].want
+		testFormatCompleteCompare(t, s, err, "%+v", want, false)
+		testGenericRecursive(t, err, want, wrappers, 3)
+	}
+}
+
+func testFormatRegexp(t *testing.T, n int, arg interface{}, format, want string) {
+	got := fmt.Sprintf(format, arg)
+	gotLines := strings.SplitN(got, "\n", -1)
+	wantLines := strings.SplitN(want, "\n", -1)
+
+	if len(wantLines) > len(gotLines) {
+		t.Errorf("test %d: wantLines(%d) > gotLines(%d):\n got: %q\nwant: %q", n+1, len(wantLines), len(gotLines), got, want)
+		return
+	}
+
+	for i, w := range wantLines {
+		match, err := regexp.MatchString(w, gotLines[i])
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !match {
+			t.Errorf("test %d: line %d: fmt.Sprintf(%q, err):\n got: %q\nwant: %q", n+1, i+1, format, got, want)
+		}
+	}
+}
+
+var stackLineR = regexp.MustCompile(`\.`)
+
+// parseBlocks parses input into a slice, where:
+//  - incase entry contains a newline, its a stacktrace
+//  - incase entry contains no newline, its a solo line.
+//
+// Detecting stack boundaries only works incase the WithStack-calls are
+// to be found on the same line, thats why it is optionally here.
+//
+// Example use:
+//
+// for _, e := range blocks {
+//   if strings.ContainsAny(e, "\n") {
+//     // Match as stack
+//   } else {
+//     // Match as line
+//   }
+// }
+//
+func parseBlocks(input string, detectStackboundaries bool) ([]string, error) {
+	var blocks []string
+
+	stack := ""
+	wasStack := false
+	lines := map[string]bool{} // already found lines
+
+	for _, l := range strings.Split(input, "\n") {
+		isStackLine := stackLineR.MatchString(l)
+
+		switch {
+		case !isStackLine && wasStack:
+			blocks = append(blocks, stack, l)
+			stack = ""
+			lines = map[string]bool{}
+		case isStackLine:
+			if wasStack {
+				// Detecting two stacks after another, possible cause lines match in
+				// our tests due to WithStack(WithStack(io.EOF)) on same line.
+				if detectStackboundaries {
+					if lines[l] {
+						if len(stack) == 0 {
+							return nil, errors.New("len of block must not be zero here")
+						}
+
+						blocks = append(blocks, stack)
+						stack = l
+						lines = map[string]bool{l: true}
+						continue
+					}
+				}
+
+				stack = stack + "\n" + l
+			} else {
+				stack = l
+			}
+			lines[l] = true
+		case !isStackLine && !wasStack:
+			blocks = append(blocks, l)
+		default:
+			return nil, errors.New("must not happen")
+		}
+
+		wasStack = isStackLine
+	}
+
+	// Use up stack
+	if stack != "" {
+		blocks = append(blocks, stack)
+	}
+	return blocks, nil
+}
+
+func testFormatCompleteCompare(t *testing.T, n int, arg interface{}, format string, want []string, detectStackBoundaries bool) {
+	gotStr := fmt.Sprintf(format, arg)
+
+	got, err := parseBlocks(gotStr, detectStackBoundaries)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if len(got) != len(want) {
+		t.Fatalf("test %d: fmt.Sprintf(%s, err) -> wrong number of blocks: got(%d) want(%d)\n got: %s\nwant: %s\ngotStr: %q",
+			n+1, format, len(got), len(want), prettyBlocks(got), prettyBlocks(want), gotStr)
+	}
+
+	for i := range got {
+		if strings.ContainsAny(want[i], "\n") {
+			// Match as stack
+			match, err := regexp.MatchString(want[i], got[i])
+			if err != nil {
+				t.Fatal(err)
+			}
+			if !match {
+				t.Fatalf("test %d: block %d: fmt.Sprintf(%q, err):\ngot:\n%q\nwant:\n%q\nall-got:\n%s\nall-want:\n%s\n",
+					n+1, i+1, format, got[i], want[i], prettyBlocks(got), prettyBlocks(want))
+			}
+		} else {
+			// Match as message
+			if got[i] != want[i] {
+				t.Fatalf("test %d: fmt.Sprintf(%s, err) at block %d got != want:\n got: %q\nwant: %q", n+1, format, i+1, got[i], want[i])
+			}
+		}
+	}
+}
+
+type wrapper struct {
+	wrap func(err error) error
+	want []string
+}
+
+func prettyBlocks(blocks []string, prefix ...string) string {
+	var out []string
+
+	for _, b := range blocks {
+		out = append(out, fmt.Sprintf("%v", b))
+	}
+
+	return "   " + strings.Join(out, "\n   ")
+}
+
+func testGenericRecursive(t *testing.T, beforeErr error, beforeWant []string, list []wrapper, maxDepth int) {
+	if len(beforeWant) == 0 {
+		panic("beforeWant must not be empty")
+	}
+	for _, w := range list {
+		if len(w.want) == 0 {
+			panic("want must not be empty")
+		}
+
+		err := w.wrap(beforeErr)
+
+		// Copy required cause append(beforeWant, ..) modified beforeWant subtly.
+		beforeCopy := make([]string, len(beforeWant))
+		copy(beforeCopy, beforeWant)
+
+		beforeWant := beforeCopy
+		last := len(beforeWant) - 1
+		var want []string
+
+		// Merge two stacks behind each other.
+		if strings.ContainsAny(beforeWant[last], "\n") && strings.ContainsAny(w.want[0], "\n") {
+			want = append(beforeWant[:last], append([]string{beforeWant[last] + "((?s).*)" + w.want[0]}, w.want[1:]...)...)
+		} else {
+			want = append(beforeWant, w.want...)
+		}
+
+		testFormatCompleteCompare(t, maxDepth, err, "%+v", want, false)
+		if maxDepth > 0 {
+			testGenericRecursive(t, err, want, list, maxDepth-1)
+		}
+	}
+}

vendor/github.com/pkg/errors/stack.go

@@ -0,0 +1,178 @@
+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   path of source file relative to the compile time GOPATH
+//    %+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
+
+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:]
+}
+
+func trimGOPATH(name, file string) string {
+	// Here we want to get the source file path relative to the compile time
+	// GOPATH. As of Go 1.6.x there is no direct way to know the compiled
+	// GOPATH at runtime, but we can infer the number of path segments in the
+	// GOPATH. We note that fn.Name() returns the function name qualified by
+	// the import path, which does not include the GOPATH. Thus we can trim
+	// segments from the beginning of the file path until the number of path
+	// separators remaining is one more than the number of path separators in
+	// the function name. For example, given:
+	//
+	//    GOPATH     /home/user
+	//    file       /home/user/src/pkg/sub/file.go
+	//    fn.Name()  pkg/sub.Type.Method
+	//
+	// We want to produce:
+	//
+	//    pkg/sub/file.go
+	//
+	// From this we can easily see that fn.Name() has one less path separator
+	// than our desired output. We count separators from the end of the file
+	// path until it finds two more than in the function name and then move
+	// one character forward to preserve the initial path segment without a
+	// leading separator.
+	const sep = "/"
+	goal := strings.Count(name, sep) + 2
+	i := len(file)
+	for n := 0; n < goal; n++ {
+		i = strings.LastIndex(file[:i], sep)
+		if i == -1 {
+			// not enough separators found, set i so that the slice expression
+			// below leaves file unmodified
+			i = -len(sep)
+			break
+		}
+	}
+	// get back to 0 or trim the leading separator
+	file = file[i+len(sep):]
+	return file
+}

vendor/github.com/pkg/errors/stack_test.go

@@ -0,0 +1,292 @@
+package errors
+
+import (
+	"fmt"
+	"runtime"
+	"testing"
+)
+
+var initpc, _, _, _ = runtime.Caller(0)
+
+func TestFrameLine(t *testing.T) {
+	var tests = []struct {
+		Frame
+		want int
+	}{{
+		Frame(initpc),
+		9,
+	}, {
+		func() Frame {
+			var pc, _, _, _ = runtime.Caller(0)
+			return Frame(pc)
+		}(),
+		20,
+	}, {
+		func() Frame {
+			var pc, _, _, _ = runtime.Caller(1)
+			return Frame(pc)
+		}(),
+		28,
+	}, {
+		Frame(0), // invalid PC
+		0,
+	}}
+
+	for _, tt := range tests {
+		got := tt.Frame.line()
+		want := tt.want
+		if want != got {
+			t.Errorf("Frame(%v): want: %v, got: %v", uintptr(tt.Frame), want, got)
+		}
+	}
+}
+
+type X struct{}
+
+func (x X) val() Frame {
+	var pc, _, _, _ = runtime.Caller(0)
+	return Frame(pc)
+}
+
+func (x *X) ptr() Frame {
+	var pc, _, _, _ = runtime.Caller(0)
+	return Frame(pc)
+}
+
+func TestFrameFormat(t *testing.T) {
+	var tests = []struct {
+		Frame
+		format string
+		want   string
+	}{{
+		Frame(initpc),
+		"%s",
+		"stack_test.go",
+	}, {
+		Frame(initpc),
+		"%+s",
+		"github.com/pkg/errors.init\n" +
+			"\t.+/github.com/pkg/errors/stack_test.go",
+	}, {
+		Frame(0),
+		"%s",
+		"unknown",
+	}, {
+		Frame(0),
+		"%+s",
+		"unknown",
+	}, {
+		Frame(initpc),
+		"%d",
+		"9",
+	}, {
+		Frame(0),
+		"%d",
+		"0",
+	}, {
+		Frame(initpc),
+		"%n",
+		"init",
+	}, {
+		func() Frame {
+			var x X
+			return x.ptr()
+		}(),
+		"%n",
+		`\(\*X\).ptr`,
+	}, {
+		func() Frame {
+			var x X
+			return x.val()
+		}(),
+		"%n",
+		"X.val",
+	}, {
+		Frame(0),
+		"%n",
+		"",
+	}, {
+		Frame(initpc),
+		"%v",
+		"stack_test.go:9",
+	}, {
+		Frame(initpc),
+		"%+v",
+		"github.com/pkg/errors.init\n" +
+			"\t.+/github.com/pkg/errors/stack_test.go:9",
+	}, {
+		Frame(0),
+		"%v",
+		"unknown:0",
+	}}
+
+	for i, tt := range tests {
+		testFormatRegexp(t, i, tt.Frame, tt.format, tt.want)
+	}
+}
+
+func TestFuncname(t *testing.T) {
+	tests := []struct {
+		name, want string
+	}{
+		{"", ""},
+		{"runtime.main", "main"},
+		{"github.com/pkg/errors.funcname", "funcname"},
+		{"funcname", "funcname"},
+		{"io.copyBuffer", "copyBuffer"},
+		{"main.(*R).Write", "(*R).Write"},
+	}
+
+	for _, tt := range tests {
+		got := funcname(tt.name)
+		want := tt.want
+		if got != want {
+			t.Errorf("funcname(%q): want: %q, got %q", tt.name, want, got)
+		}
+	}
+}
+
+func TestTrimGOPATH(t *testing.T) {
+	var tests = []struct {
+		Frame
+		want string
+	}{{
+		Frame(initpc),
+		"github.com/pkg/errors/stack_test.go",
+	}}
+
+	for i, tt := range tests {
+		pc := tt.Frame.pc()
+		fn := runtime.FuncForPC(pc)
+		file, _ := fn.FileLine(pc)
+		got := trimGOPATH(fn.Name(), file)
+		testFormatRegexp(t, i, got, "%s", tt.want)
+	}
+}
+
+func TestStackTrace(t *testing.T) {
+	tests := []struct {
+		err  error
+		want []string
+	}{{
+		New("ooh"), []string{
+			"github.com/pkg/errors.TestStackTrace\n" +
+				"\t.+/github.com/pkg/errors/stack_test.go:172",
+		},
+	}, {
+		Wrap(New("ooh"), "ahh"), []string{
+			"github.com/pkg/errors.TestStackTrace\n" +
+				"\t.+/github.com/pkg/errors/stack_test.go:177", // this is the stack of Wrap, not New
+		},
+	}, {
+		Cause(Wrap(New("ooh"), "ahh")), []string{
+			"github.com/pkg/errors.TestStackTrace\n" +
+				"\t.+/github.com/pkg/errors/stack_test.go:182", // this is the stack of New
+		},
+	}, {
+		func() error { return New("ooh") }(), []string{
+			`github.com/pkg/errors.(func·009|TestStackTrace.func1)` +
+				"\n\t.+/github.com/pkg/errors/stack_test.go:187", // this is the stack of New
+			"github.com/pkg/errors.TestStackTrace\n" +
+				"\t.+/github.com/pkg/errors/stack_test.go:187", // this is the stack of New's caller
+		},
+	}, {
+		Cause(func() error {
+			return func() error {
+				return Errorf("hello %s", fmt.Sprintf("world"))
+			}()
+		}()), []string{
+			`github.com/pkg/errors.(func·010|TestStackTrace.func2.1)` +
+				"\n\t.+/github.com/pkg/errors/stack_test.go:196", // this is the stack of Errorf
+			`github.com/pkg/errors.(func·011|TestStackTrace.func2)` +
+				"\n\t.+/github.com/pkg/errors/stack_test.go:197", // this is the stack of Errorf's caller
+			"github.com/pkg/errors.TestStackTrace\n" +
+				"\t.+/github.com/pkg/errors/stack_test.go:198", // this is the stack of Errorf's caller's caller
+		},
+	}}
+	for i, tt := range tests {
+		x, ok := tt.err.(interface {
+			StackTrace() StackTrace
+		})
+		if !ok {
+			t.Errorf("expected %#v to implement StackTrace() StackTrace", tt.err)
+			continue
+		}
+		st := x.StackTrace()
+		for j, want := range tt.want {
+			testFormatRegexp(t, i, st[j], "%+v", want)
+		}
+	}
+}
+
+func stackTrace() StackTrace {
+	const depth = 8
+	var pcs [depth]uintptr
+	n := runtime.Callers(1, pcs[:])
+	var st stack = pcs[0:n]
+	return st.StackTrace()
+}
+
+func TestStackTraceFormat(t *testing.T) {
+	tests := []struct {
+		StackTrace
+		format string
+		want   string
+	}{{
+		nil,
+		"%s",
+		`\[\]`,
+	}, {
+		nil,
+		"%v",
+		`\[\]`,
+	}, {
+		nil,
+		"%+v",
+		"",
+	}, {
+		nil,
+		"%#v",
+		`\[\]errors.Frame\(nil\)`,
+	}, {
+		make(StackTrace, 0),
+		"%s",
+		`\[\]`,
+	}, {
+		make(StackTrace, 0),
+		"%v",
+		`\[\]`,
+	}, {
+		make(StackTrace, 0),
+		"%+v",
+		"",
+	}, {
+		make(StackTrace, 0),
+		"%#v",
+		`\[\]errors.Frame{}`,
+	}, {
+		stackTrace()[:2],
+		"%s",
+		`\[stack_test.go stack_test.go\]`,
+	}, {
+		stackTrace()[:2],
+		"%v",
+		`\[stack_test.go:225 stack_test.go:272\]`,
+	}, {
+		stackTrace()[:2],
+		"%+v",
+		"\n" +
+			"github.com/pkg/errors.stackTrace\n" +
+			"\t.+/github.com/pkg/errors/stack_test.go:225\n" +
+			"github.com/pkg/errors.TestStackTraceFormat\n" +
+			"\t.+/github.com/pkg/errors/stack_test.go:276",
+	}, {
+		stackTrace()[:2],
+		"%#v",
+		`\[\]errors.Frame{stack_test.go:225, stack_test.go:284}`,
+	}}
+
+	for i, tt := range tests {
+		testFormatRegexp(t, i, tt.StackTrace, tt.format, tt.want)
+	}
+}