tor/controller: add tor version number check

In this commit, we add a check for the Tor server's version number to
ensure it supports creating v3 onion services through its control port.

tor/controller_test.go

@@ -0,0 +1,68 @@
+package tor
+
+import "testing"
+
+// TestParseTorVersion is a series of tests for different version strings that
+// check the correctness of determining whether they support creating v3 onion
+// services through Tor control's port.
+func TestParseTorVersion(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		version string
+		valid   bool
+	}{
+		{
+			version: "0.3.3.6",
+			valid:   true,
+		},
+		{
+			version: "0.3.3.7",
+			valid:   true,
+		},
+		{
+			version: "0.3.4.6",
+			valid:   true,
+		},
+		{
+			version: "0.4.3.6",
+			valid:   true,
+		},
+		{
+			version: "1.3.3.6",
+			valid:   true,
+		},
+		{
+			version: "0.3.3.6-rc",
+			valid:   true,
+		},
+		{
+			version: "0.3.3.7-rc",
+			valid:   true,
+		},
+		{
+			version: "0.3.3.5-rc",
+			valid:   false,
+		},
+		{
+			version: "0.3.3.5",
+			valid:   false,
+		},
+		{
+			version: "0.3.2.6",
+			valid:   false,
+		},
+		{
+			version: "0.1.3.6",
+			valid:   false,
+		},
+	}
+
+	for i, test := range tests {
+		err := supportsV3(test.version)
+		if test.valid != (err == nil) {
+			t.Fatalf("test %d with version string %v failed: %v", i,
+				test.version, err)
+		}
+	}
+}