From 50aca5cfd1f26555b4a289180f43b2e3bf948f01 Mon Sep 17 00:00:00 2001
From: Can ZHANG <can.zhang@ipfsbit.com>
Date: Wed, 5 Sep 2018 17:58:46 +0800
Subject: [PATCH 1/2] Expose the ability to specify external port when adding
 port map

---
 nat.go    |  3 +++
 natpmp.go | 18 ++++++++++++++++++
 upnp.go   | 18 ++++++++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/nat.go b/nat.go
index 3cf9648..cd1c489 100644
--- a/nat.go
+++ b/nat.go
@@ -30,6 +30,9 @@ type NAT interface {
 	// AddPortMapping maps a port on the local host to an external port.
 	AddPortMapping(protocol string, internalPort int, description string, timeout time.Duration) (mappedExternalPort int, err error)
 
+	AddPortMappingSpecifyExternalPort(protocol string, internalPort, externalPort int,
+		description string, timeout time.Duration) (mappedExternalPort int, err error)
+
 	// DeletePortMapping removes a port mapping.
 	DeletePortMapping(protocol string, internalPort int) (err error)
 }
diff --git a/natpmp.go b/natpmp.go
index 395a5dd..6cc7e83 100644
--- a/natpmp.go
+++ b/natpmp.go
@@ -105,6 +105,24 @@ func (n *natpmpNAT) AddPortMapping(protocol string, internalPort int, descriptio
 	return 0, err
 }
 
+func (n *natpmpNAT) AddPortMappingSpecifyExternalPort(protocol string, internalPort, externalPort int,
+	description string, timeout time.Duration) (int, error) {
+
+	var (
+		err error
+	)
+
+	timeoutInSeconds := int(timeout / time.Second)
+
+	_, err = n.c.AddPortMapping(protocol, internalPort, externalPort, timeoutInSeconds)
+	if err == nil {
+		n.ports[internalPort] = externalPort
+		return externalPort, nil
+	}
+
+	return 0, err
+}
+
 func (n *natpmpNAT) DeletePortMapping(protocol string, internalPort int) (err error) {
 	delete(n.ports, internalPort)
 	return nil
diff --git a/upnp.go b/upnp.go
index 86d6e9b..b39a5c4 100644
--- a/upnp.go
+++ b/upnp.go
@@ -188,6 +188,24 @@ func (u *upnp_NAT) AddPortMapping(protocol string, internalPort int, description
 	return 0, err
 }
 
+func (u *upnp_NAT) AddPortMappingSpecifyExternalPort(protocol string, internalPort, externalPort int,
+	description string, timeout time.Duration) (int, error) {
+
+	ip, err := u.GetInternalAddress()
+	if err != nil {
+		return 0, nil
+	}
+
+	timeoutInSeconds := uint32(timeout / time.Second)
+
+	err = u.c.AddPortMapping("", uint16(externalPort), mapProtocol(protocol), uint16(internalPort),
+		ip.String(), true, description, timeoutInSeconds)
+	if err != nil {
+		return 0, err
+	}
+	return externalPort, nil
+}
+
 func (u *upnp_NAT) DeletePortMapping(protocol string, internalPort int) error {
 	if externalPort := u.ports[internalPort]; externalPort > 0 {
 		delete(u.ports, internalPort)

From 072b1fd4c5f7a25ef9b05ffdd4645c6140ac518d Mon Sep 17 00:00:00 2001
From: Can ZHANG <can.zhang@ipfsbit.com>
Date: Wed, 5 Sep 2018 17:59:10 +0800
Subject: [PATCH 2/2] Add comments and fix test

---
 _examples/nat-tester.go | 2 +-
 nat.go                  | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/_examples/nat-tester.go b/_examples/nat-tester.go
index f2f3bc9..542f719 100644
--- a/_examples/nat-tester.go
+++ b/_examples/nat-tester.go
@@ -52,7 +52,7 @@ func main() {
 		}
 	}()
 
-	defer nat.DeletePortMapping("txp", 3080)
+	defer nat.DeletePortMapping("tcp", 3080)
 
 	http.ListenAndServe(":3080", http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
 		rw.Header().Set("Content-Type", "text/plain")
diff --git a/nat.go b/nat.go
index cd1c489..613b610 100644
--- a/nat.go
+++ b/nat.go
@@ -30,6 +30,7 @@ type NAT interface {
 	// AddPortMapping maps a port on the local host to an external port.
 	AddPortMapping(protocol string, internalPort int, description string, timeout time.Duration) (mappedExternalPort int, err error)
 
+	// AddPortMappingSpecifyExternalPort maps a port on the local host to a specified external port.
 	AddPortMappingSpecifyExternalPort(protocol string, internalPort, externalPort int,
 		description string, timeout time.Duration) (mappedExternalPort int, err error)