Fixes #9 - reacquire previously discovered device by URL.

Some more changes will be required for this to be supported by the dcps
packages.

example/example_test.go

@@ -2,6 +2,7 @@ package example_test
 
 import (
 	"fmt"
+	"net/url"
 	"os"
 
 	"github.com/huin/goupnp"
@@ -60,3 +61,33 @@ func DisplayExternalIPResults(clients []GetExternalIPAddresser, errors []error,
 		}
 	}
 }
+
+func Example_ReuseDiscoveredDevice() {
+	var allMaybeRootDevices []goupnp.MaybeRootDevice
+	for _, urn := range []string{internetgateway1.URN_WANPPPConnection_1, internetgateway1.URN_WANIPConnection_1} {
+		maybeRootDevices, err := goupnp.DiscoverDevices(internetgateway1.URN_WANPPPConnection_1)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Could not discover %s devices: %v\n", urn, err)
+		}
+		allMaybeRootDevices = append(allMaybeRootDevices, maybeRootDevices...)
+	}
+	locations := make([]*url.URL, 0, len(allMaybeRootDevices))
+	fmt.Fprintf(os.Stderr, "Found %d devices:\n", len(allMaybeRootDevices))
+	for _, maybeRootDevice := range allMaybeRootDevices {
+		if maybeRootDevice.Err != nil {
+			fmt.Fprintln(os.Stderr, "  Failed to probe device at ", maybeRootDevice.Location.String())
+		} else {
+			locations = append(locations, maybeRootDevice.Location)
+			fmt.Fprintln(os.Stderr, "  Successfully probed device at ", maybeRootDevice.Location.String())
+		}
+	}
+	fmt.Fprintf(os.Stderr, "Attempt to re-acquire %d devices:\n", len(locations))
+	for _, location := range locations {
+		if _, err := goupnp.DeviceByURL(location); err != nil {
+			fmt.Fprintf(os.Stderr, "  Failed to reacquire device at %s: %v\n", location.String(), err)
+		} else {
+			fmt.Fprintf(os.Stderr, "  Successfully reacquired device at %s\n", location.String())
+		}
+	}
+	// Output:
+}

goupnp.go

@@ -20,6 +20,7 @@ import (
 	"net/http"
 	"net/url"
 	"time"
+
 	"golang.org/x/net/html/charset"
 
 	"github.com/huin/goupnp/httpu"
@@ -36,10 +37,18 @@ func (err ContextError) Error() string {
 	return fmt.Sprintf("%s: %v", err.Context, err.Err)
 }
 
-// MaybeRootDevice contains either a RootDevice or an error.
+// MaybeRootDevice contains either a RootDevice (and URL) or an error.
 type MaybeRootDevice struct {
+	// Set iff Err == nil.
 	Root *RootDevice
-	Err  error
+
+	// The location the device was discovered at. This can be used with
+	// DeviceByURL, assuming the device is still present. A location represents
+	// the discovery of a device, regardless of if there was an error probing it.
+	Location *url.URL
+
+	// Any error encountered probing a discovered device.
+	Err error
 }
 
 // DiscoverDevices attempts to find targets of the given type. This is
@@ -67,30 +76,37 @@ func DiscoverDevices(searchTarget string) ([]MaybeRootDevice, error) {
 			maybe.Err = ContextError{"unexpected bad location from search", err}
 			continue
 		}
-		locStr := loc.String()
+		maybe.Location = loc
-		root := new(RootDevice)
+		if root, err := DeviceByURL(loc); err != nil {
-		if err := requestXml(locStr, DeviceXMLNamespace, root); err != nil {
+			maybe.Err = err
-			maybe.Err = ContextError{fmt.Sprintf("error requesting root device details from %q", locStr), err}
-			continue
-		}
-		var urlBaseStr string
-		if root.URLBaseStr != "" {
-			urlBaseStr = root.URLBaseStr
 		} else {
-			urlBaseStr = locStr
+			maybe.Root = root
 		}
-		urlBase, err := url.Parse(urlBaseStr)
-		if err != nil {
-			maybe.Err = ContextError{fmt.Sprintf("error parsing location URL %q", locStr), err}
-			continue
-		}
-		root.SetURLBase(urlBase)
-		maybe.Root = root
 	}
 
 	return results, nil
 }
 
+func DeviceByURL(loc *url.URL) (*RootDevice, error) {
+	locStr := loc.String()
+	root := new(RootDevice)
+	if err := requestXml(locStr, DeviceXMLNamespace, root); err != nil {
+		return nil, ContextError{fmt.Sprintf("error requesting root device details from %q", locStr), err}
+	}
+	var urlBaseStr string
+	if root.URLBaseStr != "" {
+		urlBaseStr = root.URLBaseStr
+	} else {
+		urlBaseStr = locStr
+	}
+	urlBase, err := url.Parse(urlBaseStr)
+	if err != nil {
+		return nil, ContextError{fmt.Sprintf("error parsing location URL %q", locStr), err}
+	}
+	root.SetURLBase(urlBase)
+	return root, nil
+}
+
 func requestXml(url string, defaultSpace string, doc interface{}) error {
 	timeout := time.Duration(3 * time.Second)
 	client := http.Client{

service_client.go

@@ -2,6 +2,7 @@ package goupnp
 
 import (
 	"fmt"
+
 	"github.com/huin/goupnp/soap"
 )