Backend: fix IPv6 address parsing erroneous (#28585)

* Backend: Fix parsing of client IP address

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

pkg/infra/network/address.go

@@ -0,0 +1,44 @@
+package network
+
+import (
+	"fmt"
+	"net"
+	"regexp"
+)
+
+var reIPv4AndPort = regexp.MustCompile(`^(\d+\.\d+\.\d+\.\d+):\d+$`)
+
+// An IPv6 address/port pair can consist of the IP address enclosed in square brackets followed by a colon and
+// a port, although the colon/port component is actually optional in practice (e.g., we may receive [::1], where
+// we should just strip off the square brackets).
+var reIPv6AndPort = regexp.MustCompile(`^\[(.+)\](:\d+)?$`)
+
+// GetIPFromAddress tries to get an IPv4 or IPv6 address from a host address, potentially including a port.
+func GetIPFromAddress(input string) (net.IP, error) {
+	if a := net.ParseIP(input); len(a) > 0 {
+		return a, nil
+	}
+
+	err := fmt.Errorf("not a valid IP address or IP address/port pair: %q", input)
+
+	// It could potentially be an IP address/port pair
+	var addr string
+	ms := reIPv4AndPort.FindStringSubmatch(input)
+	if len(ms) == 0 {
+		ms := reIPv6AndPort.FindStringSubmatch(input)
+		if len(ms) == 0 {
+			return nil, err
+		}
+
+		addr = ms[1]
+	} else {
+		// Strip off port
+		addr = ms[1]
+	}
+
+	if a := net.ParseIP(addr); len(a) > 0 {
+		return a, nil
+	}
+
+	return nil, err
+}