Add TLS arg parsing to ParseDSN().

Factor out the TLS cert handling and add it to `configTLS()` via a
`struct` argument.

conn.go

@@ -703,45 +703,17 @@ func ParseURI(uri string) (ConnConfig, error) {
 		cp.Dial = d.Dial
 	}
 
-	err = configTLS(url.Query().Get("sslmode"), &cp)
+	tlsArgs := configTLSArgs{
+		sslCert:     url.Query().Get("sslcert"),
+		sslKey:      url.Query().Get("sslkey"),
+		sslMode:     url.Query().Get("sslmode"),
+		sslRootCert: url.Query().Get("sslrootcert"),
+	}
+	err = configTLS(tlsArgs, &cp)
 	if err != nil {
 		return cp, err
 	}
 
-	// Extract optional TLS parameters and reconstruct a coherent tls.Config based
-	// on the DSN input.  Reuse the same keywords found in github.com/lib/pq.
-	if cp.TLSConfig != nil {
-		{
-			caCertPool := x509.NewCertPool()
-
-			caPath := url.Query().Get("sslrootcert")
-			caCert, err := ioutil.ReadFile(caPath)
-			if err != nil {
-				return cp, errors.Wrapf(err, "unable to read CA file %q", caPath)
-			}
-
-			if !caCertPool.AppendCertsFromPEM(caCert) {
-				return cp, errors.Wrap(err, "unable to add CA to cert pool")
-			}
-
-			cp.TLSConfig.RootCAs = caCertPool
-			cp.TLSConfig.ClientCAs = caCertPool
-		}
-
-		sslcert := url.Query().Get("sslcert")
-		sslkey := url.Query().Get("sslkey")
-		if (sslcert != "" && sslkey == "") || (sslcert == "" && sslkey != "") {
-			return cp, fmt.Errorf(`both "sslcert" and "sslkey" are required`)
-		}
-
-		cert, err := tls.LoadX509KeyPair(sslcert, sslkey)
-		if err != nil {
-			return cp, errors.Wrap(err, "unable to read cert")
-		}
-
-		cp.TLSConfig.Certificates = []tls.Certificate{cert}
-	}
-
 	ignoreKeys := map[string]struct{}{
 		"connect_timeout": {},
 		"sslcert":         {},
@@ -783,7 +755,7 @@ func ParseDSN(s string) (ConnConfig, error) {
 
 	m := dsnRegexp.FindAllStringSubmatch(s, -1)
 
-	var sslmode string
+	tlsArgs := configTLSArgs{}
 
 	cp.RuntimeParams = make(map[string]string)
 
@@ -804,7 +776,13 @@ func ParseDSN(s string) (ConnConfig, error) {
 		case "dbname":
 			cp.Database = b[2]
 		case "sslmode":
-			sslmode = b[2]
+			tlsArgs.sslMode = b[2]
+		case "sslrootcert":
+			tlsArgs.sslRootCert = b[2]
+		case "sslcert":
+			tlsArgs.sslCert = b[2]
+		case "sslkey":
+			tlsArgs.sslKey = b[2]
 		case "connect_timeout":
 			timeout, err := strconv.ParseInt(b[2], 10, 64)
 			if err != nil {
@@ -818,7 +796,7 @@ func ParseDSN(s string) (ConnConfig, error) {
 		}
 	}
 
-	err := configTLS(sslmode, &cp)
+	err := configTLS(tlsArgs, &cp)
 	if err != nil {
 		return cp, err
 	}
@@ -898,7 +876,7 @@ func ParseEnvLibpq() (ConnConfig, error) {
 
 	sslmode := os.Getenv("PGSSLMODE")
 
-	err := configTLS(sslmode, &cc)
+	err := configTLS(configTLSArgs{sslMode: sslmode}, &cc)
 	if err != nil {
 		return cc, err
 	}
@@ -913,14 +891,27 @@ func ParseEnvLibpq() (ConnConfig, error) {
 	return cc, nil
 }
 
-func configTLS(sslmode string, cc *ConnConfig) error {
+type configTLSArgs struct {
+	sslMode     string
+	sslRootCert string
+	sslCert     string
+	sslKey      string
+}
+
+// configTLS uses lib/pq's TLS parameters to reconstruct a coherent tls.Config.
+// Inputs are parsed out and provided by ParseDSN() or ParseURI().
+func configTLS(args configTLSArgs, cc *ConnConfig) error {
 	// Match libpq default behavior
-	if sslmode == "" {
-		sslmode = "prefer"
+	if args.sslMode == "" {
+		args.sslMode = "prefer"
 	}
 
-	switch sslmode {
+	switch args.sslMode {
 	case "disable":
+		cc.UseFallbackTLS = false
+		cc.TLSConfig = nil
+		cc.FallbackTLSConfig = nil
+		return nil
 	case "allow":
 		cc.UseFallbackTLS = true
 		cc.FallbackTLSConfig = &tls.Config{InsecureSkipVerify: true}
@@ -938,6 +929,37 @@ func configTLS(sslmode string, cc *ConnConfig) error {
 		return errors.New("sslmode is invalid")
 	}
 
+	{
+		caCertPool := x509.NewCertPool()
+
+		caPath := args.sslRootCert
+		caCert, err := ioutil.ReadFile(caPath)
+		if err != nil {
+			return errors.Wrapf(err, "unable to read CA file %q", caPath)
+		}
+
+		if !caCertPool.AppendCertsFromPEM(caCert) {
+			return errors.Wrap(err, "unable to add CA to cert pool")
+		}
+
+		cc.TLSConfig.RootCAs = caCertPool
+		cc.TLSConfig.ClientCAs = caCertPool
+	}
+
+	sslcert := args.sslCert
+	sslkey := args.sslKey
+
+	if (sslcert != "" && sslkey == "") || (sslcert == "" && sslkey != "") {
+		return fmt.Errorf(`both "sslcert" and "sslkey" are required`)
+	}
+
+	cert, err := tls.LoadX509KeyPair(sslcert, sslkey)
+	if err != nil {
+		return errors.Wrap(err, "unable to read cert")
+	}
+
+	cc.TLSConfig.Certificates = []tls.Certificate{cert}
+
 	return nil
 }