Cleanup ParseHostOrFile (#2100)

Create plugin/pkg/transport that holds the transport related functions.
This needed to be a new pkg to prevent cyclic import errors.

This cleans up a bunch of duplicated code in core/dnsserver that also
tried to parse a transport (now all done in transport.Parse).

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/pkg/transport/transport.go

@@ -0,0 +1,49 @@
+package transport
+
+import (
+	"strings"
+)
+
+// Parse returns the transport defined in s and a string where the
+// transport prefix is removed (if there was any). If no transport is defined
+// we default to TransportDNS
+func Parse(s string) (transport string, addr string) {
+	switch {
+	case strings.HasPrefix(s, TLS+"://"):
+		s = s[len(TLS+"://"):]
+		return TLS, s
+
+	case strings.HasPrefix(s, DNS+"://"):
+		s = s[len(DNS+"://"):]
+		return DNS, s
+
+	case strings.HasPrefix(s, GRPC+"://"):
+		s = s[len(GRPC+"://"):]
+		return GRPC, s
+
+	case strings.HasPrefix(s, HTTPS+"://"):
+		s = s[len(HTTPS+"://"):]
+
+		return HTTPS, s
+	}
+
+	return DNS, s
+}
+
+// Supported transports.
+const (
+	DNS   = "dns"
+	TLS   = "tls"
+	GRPC  = "grpc"
+	HTTPS = "https"
+)
+
+// Port numbers for the various protocols
+const (
+	// TLSPort is the default port for DNS-over-TLS.
+	TLSPort = "853"
+	// GRPCPort is the default port for DNS-over-gRPC.
+	GRPCPort = "443"
+	// HTTPSPort is the default port for DNS-over-HTTPS.
+	HTTPSPort = "443"
+)

plugin/pkg/transport/transport_test.go

@@ -0,0 +1,21 @@
+package transport
+
+import "testing"
+
+func TestParse(t *testing.T) {
+	for i, test := range []struct {
+		input    string
+		expected string
+	}{
+		{"dns://.:53", DNS},
+		{"2003::1/64.:53", DNS},
+		{"grpc://example.org:1443 ", GRPC},
+		{"tls://example.org ", TLS},
+		{"https://example.org ", HTTPS},
+	} {
+		actual, _ := Parse(test.input)
+		if actual != test.expected {
+			t.Errorf("Test %d: Expected %s but got %s", i, test.expected, actual)
+		}
+	}
+}