Compat: Treat already attached networks as a no-op

Applies only to containers in created state. Maintain error in running state.

Signed-off-by: Jason T. Greene <[email protected]>

libpod/networking_linux.go

@@ -1357,6 +1357,11 @@ func (c *Container) NetworkConnect(nameOrID, netName string, netOpts types.PerNe
 	}
 
 	if err := c.runtime.state.NetworkConnect(c, netName, netOpts); err != nil {
+		// Docker compat: treat requests to attach already attached networks as a no-op, ignoring opts
+		if errors.Is(err, define.ErrNetworkExists) && c.ensureState(define.ContainerStateConfigured) {
+			return nil
+		}
+
 		return err
 	}
 	c.newNetworkEvent(events.NetworkConnect, netName)

test/e2e/network_connect_disconnect_test.go

@@ -157,7 +157,7 @@ var _ = Describe("Podman network connect and disconnect", func() {
 		Expect(con.ErrorToString()).To(ContainSubstring(`"slirp4netns" is not supported: invalid network mode`))
 	})
 
-	It("podman connect on a container that already is connected to the network should error", func() {
+	It("podman connect on a container that already is connected to the network should error after init", func() {
 		netName := "aliasTest" + stringid.GenerateNonCryptoID()
 		session := podmanTest.Podman([]string{"network", "create", netName})
 		session.WaitWithDefaultTimeout()
@@ -177,7 +177,15 @@ var _ = Describe("Podman network connect and disconnect", func() {
 
 		con := podmanTest.Podman([]string{"network", "connect", netName, "test"})
 		con.WaitWithDefaultTimeout()
-		Expect(con).Should(ExitWithError())
+		Expect(con).Should(Exit(0))
+
+		init := podmanTest.Podman([]string{"init", "test"})
+		init.WaitWithDefaultTimeout()
+		Expect(init).Should(Exit(0))
+
+		con2 := podmanTest.Podman([]string{"network", "connect", netName, "test"})
+		con2.WaitWithDefaultTimeout()
+		Expect(con2).Should(ExitWithError())
 	})
 
 	It("podman network connect", func() {