Failed connection attempts include all errors

A single Connect("connstring") may actually make multiple connection
requests due to TLS or HA configuration. Previously, when all attempts
failed only the last error was returned. This could be confusing.
Now details of all failed attempts are included.

For example, the following connection string:

host=localhost,127.0.0.1,foo.invalid port=1,2,3

Will now return an error like the following:

failed to connect to `user=postgres database=pgx_test`:
	lookup foo.invalid: no such host
	[::1]:1 (localhost): dial error: dial tcp [::1]:1: connect: connection refused
	127.0.0.1:1 (localhost): dial error: dial tcp 127.0.0.1:1: connect: connection refused
	127.0.0.1:2 (127.0.0.1): dial error: dial tcp 127.0.0.1:2: connect: connection refused

#1929

Author: jackc

pgconn/config.go

@@ -118,6 +118,14 @@ type FallbackConfig struct {
 	TLSConfig *tls.Config // nil disables TLS
 }
 
+// connectOneConfig is the configuration for a single attempt to connect to a single host.
+type connectOneConfig struct {
+	network          string
+	address          string
+	originalHostname string      // original hostname before resolving
+	tlsConfig        *tls.Config // nil disables TLS
+}
+
 // isAbsolutePath checks if the provided value is an absolute path either
 // beginning with a forward slash (as on Linux-based systems) or with a capital
 // letter A-Z followed by a colon and a backslash, e.g., "C:\", (as on Windows).

pgconn/errors.go

@@ -62,23 +62,37 @@ func (pe *PgError) SQLState() string {
 // ConnectError is the error returned when a connection attempt fails.
 type ConnectError struct {
 	Config *Config // The configuration that was used in the connection attempt.
-	msg    string
 	err    error
 }
 
 func (e *ConnectError) Error() string {
-	sb := &strings.Builder{}
-	fmt.Fprintf(sb, "failed to connect to `host=%s user=%s database=%s`: %s", e.Config.Host, e.Config.User, e.Config.Database, e.msg)
-	if e.err != nil {
-		fmt.Fprintf(sb, " (%s)", e.err.Error())
+	prefix := fmt.Sprintf("failed to connect to `user=%s database=%s`:", e.Config.User, e.Config.Database)
+	details := e.err.Error()
+	if strings.Contains(details, "\n") {
+		return prefix + "\n\t" + strings.ReplaceAll(details, "\n", "\n\t")
+	} else {
+		return prefix + " " + details
 	}
-	return sb.String()
 }
 
 func (e *ConnectError) Unwrap() error {
 	return e.err
 }
 
+type perDialConnectError struct {
+	address          string
+	originalHostname string
+	err              error
+}
+
+func (e *perDialConnectError) Error() string {
+	return fmt.Sprintf("%s (%s): %s", e.address, e.originalHostname, e.err.Error())
+}
+
+func (e *perDialConnectError) Unwrap() error {
+	return e.err
+}
+
 type connLockError struct {
 	status string
 }