daemon/links: fix port-sorting with mixed protocols

The intent of this sorting was twofold;

- the "default" port of the container to be the first TCP port (if present)
- consecutive port-mappings with the same protocol to be together so
  that port-ranges would produce an env-var describing the range.

The current sorting would sort TCP ports before UDP (or SCTP) port, but
only if they had the same port-number. This could result in range-detection
incorrectly combining TCP and UDP (or SCTP) ports in the same range.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/links/links.go

@@ -54,11 +54,7 @@ func (l *Link) ToEnv() []string {
 	alias := strings.ReplaceAll(strings.ToUpper(n), "-", "_")
 
 	// sort the ports so that we can bulk the continuous ports together
-	nat.Sort(l.Ports, func(ip, jp nat.Port) bool {
-		// If the two ports have the same number, tcp takes priority
-		// Sort in desc order
-		return ip.Int() < jp.Int() || (ip.Int() == jp.Int() && strings.ToLower(ip.Proto()) == "tcp")
-	})
+	nat.Sort(l.Ports, withTCPPriority)
 
 	for i := 0; i < len(l.Ports); {
 		p := l.Ports[i]
@@ -108,6 +104,23 @@ func (l *Link) ToEnv() []string {
 	return env
 }
 
+// withTCPPriority prioritizes ports using TCP over other protocols before
+// comparing port-number and protocol.
+func withTCPPriority(ip, jp nat.Port) bool {
+	if strings.EqualFold(ip.Proto(), jp.Proto()) {
+		return ip.Int() < jp.Int()
+	}
+
+	if strings.EqualFold(ip.Proto(), "tcp") {
+		return true
+	}
+	if strings.EqualFold(jp.Proto(), "tcp") {
+		return false
+	}
+
+	return strings.ToLower(ip.Proto()) < strings.ToLower(jp.Proto())
+}
+
 func nextContiguous(ports []nat.Port, value int, index int) int {
 	if index+1 == len(ports) {
 		return index

daemon/links/links_test.go

@@ -60,6 +60,35 @@ func TestLinkEnv(t *testing.T) {
 	assert.DeepEqual(t, expectedEnv, actual)
 }
 
+// TestSortPorts verifies that ports are sorted with TCP taking priority,
+// and ports with the same protocol to be sorted by port.
+func TestSortPorts(t *testing.T) {
+	ports := []nat.Port{
+		"6379/tcp",
+		"6376/udp",
+		"6380/tcp",
+		"6376/sctp",
+		"6381/tcp",
+		"6381/udp",
+		"6375/udp",
+		"6375/sctp",
+	}
+
+	expected := []nat.Port{
+		"6379/tcp",
+		"6380/tcp",
+		"6381/tcp",
+		"6375/sctp",
+		"6376/sctp",
+		"6375/udp",
+		"6376/udp",
+		"6381/udp",
+	}
+
+	nat.Sort(ports, withTCPPriority)
+	assert.DeepEqual(t, expected, ports)
+}
+
 func TestLinkMultipleEnv(t *testing.T) {
 	actual := EnvVars("172.0.17.3", "172.0.17.2", "/db/docker", []string{"PASSWORD=gordon"}, nat.PortSet{
 		"6379/tcp": struct{}{},