Fix streaming only via first interface candidate

7 files changed, 68 insertions, 81 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5661bf7..b90ce16 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,9 +6,16 @@ The format is based on [Keep a Changelog][keep-a-changelog], and this project
 adheres to [Semantic Versioning][semantic-versioning].
 
 
+## [Unreleased][unreleased]
+
+### Fixed
+
+- streaming only via first network interface candidate
+
+
 ## [Version 0.1.4][0.1.4] - 2024-11-10
 
-## Fixed
+### Fixed
 
 - possible time offsets between soundboxes after longer time
 
diff --git a/soundbox/interfaces.go b/soundbox/interfaces.go
deleted file mode 100644
index 04839c7..0000000
--- a/soundbox/interfaces.go
+++ /dev/null
@@ -1,39 +0,0 @@
-package soundbox
-
-import (
-	"fmt"
-	"net"
-)
-
-// getInterface is a function guessing which interface should be used for
-// soundbox streaming. This is required since soundbox relies on communication
-// via IPv6 link-local addresses which require a specified interface to allow
-// communication. This function returns the first interface it finds which is
-// up and has a link-local address assigned.
-func getInterface() (net.Interface, error) {
-	all, err := net.Interfaces()
-	if err != nil {
-		return net.Interface{}, err
-	}
-
-	for _, iface := range all {
-		if iface.Flags&net.FlagUp == 0 {
-			continue
-		}
-		addresses, err := iface.Addrs()
-		if err != nil {
-			return net.Interface{}, err
-		}
-		for _, addr := range addresses {
-			ip, _, err := net.ParseCIDR(addr.String())
-			if err != nil {
-				return net.Interface{}, err
-			}
-			if ip.IsLinkLocalUnicast() {
-				return iface, nil
-			}
-		}
-	}
-
-	return net.Interface{}, fmt.Errorf("No interface found for soundbox streaming")
-}
diff --git a/soundbox/ipv6.go b/soundbox/ipv6.go
deleted file mode 100644
index 355e233..0000000
--- a/soundbox/ipv6.go
+++ /dev/null
@@ -1,19 +0,0 @@
-package soundbox
-
-import (
-	"fmt"
-	"net"
-)
-
-// toLinkLocal converts a MAC address to the corresponding IPv6 link-local
-// address.
-func toLinkLocal(ha net.HardwareAddr) (net.IP, error) {
-	switch len(ha) {
-	case 6:
-		ip := net.IP{0xfe, 0x80, 0, 0, 0, 0, 0, 0,
-			ha[0] ^ 0b10, ha[1], ha[2], 0xff, 0xfe, ha[3], ha[4], ha[5]}
-		return ip, nil
-	default:
-		return nil, fmt.Errorf("Only IEEE 802 MAC-48 addresses supported")
-	}
-}
diff --git a/soundbox/network.go b/soundbox/network.go
new file mode 100644
index 0000000..6e7acea
--- /dev/null
+++ b/soundbox/network.go
@@ -0,0 +1,58 @@
+package soundbox
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"time"
+)
+
+const dialTimeoutSeconds = 3
+
+// toLinkLocal converts a MAC address to the corresponding IPv6 link-local
+// address.
+func toLinkLocal(ha net.HardwareAddr) (net.IP, error) {
+	switch len(ha) {
+	case 6:
+		ip := net.IP{0xfe, 0x80, 0, 0, 0, 0, 0, 0,
+			ha[0] ^ 0b10, ha[1], ha[2], 0xff, 0xfe, ha[3], ha[4], ha[5]}
+		return ip, nil
+	default:
+		return nil, fmt.Errorf("Only IEEE 802 MAC-48 addresses supported")
+	}
+}
+
+func dialContext(ctx context.Context, ha net.HardwareAddr) (net.Conn, error) {
+	ip, err := toLinkLocal(ha)
+	if err != nil {
+		return nil, err
+	}
+
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	c := make(chan net.Conn)
+	dialContext, cancel := context.WithTimeout(ctx, dialTimeoutSeconds * time.Second)
+	defer cancel()
+	for _, iface := range ifaces {
+		go func() {
+			var d net.Dialer
+			conn, err := d.DialContext(
+				ctx,
+				"tcp6",
+				fmt.Sprintf("[%s%%%s]:%d", ip, iface.Name, streamingPort),
+			)
+			if err == nil {
+				c <- conn
+			}
+		}()
+	}
+	select {
+	case conn := <-c:
+		return conn, nil
+	case <-dialContext.Done():
+		return nil, fmt.Errorf("Could not dial TCP connection to %v on port %d on any interface.", ha, streamingPort)
+	}
+}
diff --git a/soundbox/ipv6_test.go b/soundbox/network_test.go
index 93ac489..93ac489 100644
--- a/soundbox/ipv6_test.go
+++ b/soundbox/network_test.go
diff --git a/soundbox/stream.go b/soundbox/url.go
index 910523d..4ad9908 100644
--- a/soundbox/stream.go
+++ b/soundbox/url.go
@@ -3,7 +3,6 @@ package soundbox
 import (
 	"context"
 	"errors"
-	"fmt"
 	"io"
 	"net"
 	"os/exec"
@@ -22,28 +21,9 @@ const writeTimeout = 1 * time.Second
 // devices. The devices are referenced via their MAC addresses given by the
 // targets argument. The ctx argument is passed to cancel the streaming.
 func StreamURLContext(ctx context.Context, url string, targets []net.HardwareAddr) error {
-	iface, err := getInterface()
-	if err != nil {
-		return err
-	}
-
-	ips := make([]net.IP, 0)
-	for _, target := range targets {
-		ip, err := toLinkLocal(target)
-		if err != nil {
-			return err
-		}
-		ips = append(ips, ip)
-	}
-
 	conns := make([]net.Conn, 0)
-	for _, ip := range ips {
-		var d net.Dialer
-		conn, err := d.DialContext(
-			ctx,
-			"tcp6",
-			fmt.Sprintf("[%s%%%s]:%d", ip, iface.Name, streamingPort),
-		)
+	for _, target := range targets {
+		conn, err := dialContext(ctx, target)
 		if err != nil {
 			return err
 		}
diff --git a/soundbox/stream_test.go b/soundbox/url_test.go
index 41907ad..41907ad 100644
--- a/soundbox/stream_test.go
+++ b/soundbox/url_test.go