From 26f399ddf3405216dd31419f2627fff8f3204616 Mon Sep 17 00:00:00 2001
From: Jessica Frazelle <jess@docker.com>
Date: Thu, 20 Nov 2014 16:07:55 -0800
Subject: [PATCH] Typed errors for iptables chain raw command output. YAYYYYYY.

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)
---
 iptables/iptables.go | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/iptables/iptables.go b/iptables/iptables.go
index 53e6e14..b783347 100644
--- a/iptables/iptables.go
+++ b/iptables/iptables.go
@@ -20,9 +20,9 @@ const (
 )
 
 var (
-	ErrIptablesNotFound = errors.New("Iptables not found")
 	nat                 = []string{"-t", "nat"}
 	supportsXlock       = false
+	ErrIptablesNotFound = errors.New("Iptables not found")
 )
 
 type Chain struct {
@@ -30,6 +30,15 @@ type Chain struct {
 	Bridge string
 }
 
+type ChainError struct {
+	Chain  string
+	Output []byte
+}
+
+func (e *ChainError) Error() string {
+	return fmt.Sprintf("Error iptables %s: %s", e.Chain, string(e.Output))
+}
+
 func init() {
 	supportsXlock = exec.Command("iptables", "--wait", "-L", "-n").Run() == nil
 }
@@ -78,7 +87,7 @@ func (c *Chain) Forward(action Action, ip net.IP, port int, proto, dest_addr str
 		"--to-destination", net.JoinHostPort(dest_addr, strconv.Itoa(dest_port))); err != nil {
 		return err
 	} else if len(output) != 0 {
-		return fmt.Errorf("Error iptables forward: %s", output)
+		return &ChainError{Chain: "FORWARD", Output: output}
 	}
 
 	fAction := action
@@ -94,7 +103,7 @@ func (c *Chain) Forward(action Action, ip net.IP, port int, proto, dest_addr str
 		"-j", "ACCEPT"); err != nil {
 		return err
 	} else if len(output) != 0 {
-		return fmt.Errorf("Error iptables forward: %s", output)
+		return &ChainError{Chain: "FORWARD", Output: output}
 	}
 
 	return nil
@@ -108,7 +117,7 @@ func (c *Chain) Prerouting(action Action, args ...string) error {
 	if output, err := Raw(append(a, "-j", c.Name)...); err != nil {
 		return err
 	} else if len(output) != 0 {
-		return fmt.Errorf("Error iptables prerouting: %s", output)
+		return &ChainError{Chain: "PREROUTING", Output: output}
 	}
 	return nil
 }
@@ -121,7 +130,7 @@ func (c *Chain) Output(action Action, args ...string) error {
 	if output, err := Raw(append(a, "-j", c.Name)...); err != nil {
 		return err
 	} else if len(output) != 0 {
-		return fmt.Errorf("Error iptables output: %s", output)
+		return &ChainError{Chain: "OUTPUT", Output: output}
 	}
 	return nil
 }