From 8e812b7ac028cce91166207f7cebf02338f92206 Mon Sep 17 00:00:00 2001
From: Alexander Neumann <alexander@bumpern.de>
Date: Tue, 23 Jan 2018 21:40:51 +0100
Subject: [PATCH] errors: Make Cause() unwrap *url.Error

---
 internal/errors/{wrap.go => errors.go} | 35 ++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 5 deletions(-)
 rename internal/errors/{wrap.go => errors.go} (56%)

diff --git a/internal/errors/wrap.go b/internal/errors/errors.go
similarity index 56%
rename from internal/errors/wrap.go
rename to internal/errors/errors.go
index 99d6e88ba..aa2ff6f2b 100644
--- a/internal/errors/wrap.go
+++ b/internal/errors/errors.go
@@ -1,11 +1,10 @@
 package errors
 
-import "github.com/pkg/errors"
+import (
+	"net/url"
 
-// Cause returns the cause of an error.
-func Cause(err error) error {
-	return errors.Cause(err)
-}
+	"github.com/pkg/errors"
+)
 
 // New creates a new error based on message. Wrapped so that this package does
 // not appear in the stack trace.
@@ -22,3 +21,29 @@ var Wrap = errors.Wrap
 // Wrapf returns an error annotating err with the format specifier. If err is
 // nil, Wrapf returns nil.
 var Wrapf = errors.Wrapf
+
+// Cause returns the cause of an error. It will also unwrap certain errors,
+// e.g. *url.Error returned by the net/http client.
+func Cause(err error) error {
+	type Causer interface {
+		Cause() error
+	}
+
+	for {
+		// unwrap *url.Error
+		if urlErr, ok := err.(*url.Error); ok {
+			err = urlErr.Err
+			continue
+		}
+
+		// if err is a Causer, return the cause for this error.
+		if c, ok := err.(Causer); ok {
+			err = c.Cause()
+			continue
+		}
+
+		break
+	}
+
+	return err
+}