net/url: permit colons in the host of postgresql:// URLs

PostgreSQL's postgresql:// URL scheme permits a comma-separated list of
host:ports to appear in the host subcomponent:
https://www.postgresql.org/docs/11/libpq-connect.html#LIBPQ-MULTIPLE-HOSTS

While this is not compliant with RFC 3986, it's something we've accepted
for a long time. Continue to accept colons in the host when the URL
scheme is "postgresql".

Fixes #75859

Change-Id: Iaa2e82b0be11d8e034e10dd7f4d6070039acfa2c
Reviewed-on: https://go-review.googlesource.com/c/go/+/722300
Reviewed-by: Roland Shoemaker <roland@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sean Liao <sean@liao.dev>

src/net/url/url.go

@@ -489,7 +489,7 @@ func parse(rawURL string, viaRequest bool) (*URL, error) {
 		if i := strings.Index(authority, "/"); i >= 0 {
 			authority, rest = authority[:i], authority[i:]
 		}
-		url.User, url.Host, err = parseAuthority(authority)
+		url.User, url.Host, err = parseAuthority(url.Scheme, authority)
 		if err != nil {
 			return nil, err
 		}
@@ -509,12 +509,12 @@ func parse(rawURL string, viaRequest bool) (*URL, error) {
 	return url, nil
 }
 
-func parseAuthority(authority string) (user *Userinfo, host string, err error) {
+func parseAuthority(scheme, authority string) (user *Userinfo, host string, err error) {
 	i := strings.LastIndex(authority, "@")
 	if i < 0 {
-		host, err = parseHost(authority)
+		host, err = parseHost(scheme, authority)
 	} else {
-		host, err = parseHost(authority[i+1:])
+		host, err = parseHost(scheme, authority[i+1:])
 	}
 	if err != nil {
 		return nil, "", err
@@ -546,7 +546,7 @@ func parseAuthority(authority string) (user *Userinfo, host string, err error) {
 
 // parseHost parses host as an authority without user
 // information. That is, as host[:port].
-func parseHost(host string) (string, error) {
+func parseHost(scheme, host string) (string, error) {
 	if openBracketIdx := strings.LastIndex(host, "["); openBracketIdx != -1 {
 		// Parse an IP-Literal in RFC 3986 and RFC 6874.
 		// E.g., "[fe80::1]", "[fe80::1%25en0]", "[fe80::1]:80".
@@ -603,9 +603,22 @@ func parseHost(host string) (string, error) {
 		}
 		return "[" + unescapedHostname + "]" + unescapedColonPort, nil
 	} else if i := strings.Index(host, ":"); i != -1 {
-		if j := strings.LastIndex(host, ":"); urlstrictcolons.Value() == "0" && j != i {
+		lastColon := strings.LastIndex(host, ":")
-			urlstrictcolons.IncNonDefault()
+		if lastColon != i {
-			i = j
+			if scheme == "postgresql" || scheme == "postgres" {
+				// PostgreSQL relies on non-RFC-3986 parsing to accept
+				// a comma-separated list of hosts (with optional ports)
+				// in the host subcomponent:
+				// https://www.postgresql.org/docs/11/libpq-connect.html#LIBPQ-MULTIPLE-HOSTS
+				//
+				// Since we historically permitted colons to appear in the host,
+				// continue to permit it for postgres:// URLs only.
+				// https://go.dev/issue/75223
+				i = lastColon
+			} else if urlstrictcolons.Value() == "0" {
+				urlstrictcolons.IncNonDefault()
+				i = lastColon
+			}
 		}
 		colonPort := host[i:]
 		if !validOptionalPort(colonPort) {

src/net/url/url_test.go

@@ -606,6 +606,26 @@ var urltests = []URLTest{
 		},
 		"mailto:?subject=hi",
 	},
+	// PostgreSQL URLs can include a comma-separated list of host:post hosts.
+	// https://go.dev/issue/75859
+	{
+		"postgres://host1:1,host2:2,host3:3",
+		&URL{
+			Scheme: "postgres",
+			Host:   "host1:1,host2:2,host3:3",
+			Path:   "",
+		},
+		"postgres://host1:1,host2:2,host3:3",
+	},
+	{
+		"postgresql://host1:1,host2:2,host3:3",
+		&URL{
+			Scheme: "postgresql",
+			Host:   "host1:1,host2:2,host3:3",
+			Path:   "",
+		},
+		"postgresql://host1:1,host2:2,host3:3",
+	},
 }
 
 // more useful string for debugging than fmt's struct printer