Add API functions to libpq to interrogate SSL related stuff.

This makes it possible to query for things like the SSL version and cipher
used, without depending on OpenSSL functions or macros. That is a good
thing if we ever get another SSL implementation.

PQgetssl() still works, but it should be considered as deprecated as it
only works with OpenSSL. In particular, PQgetSslInUse() should be used to
check if a connection uses SSL, because as soon as we have another
implementation, PQgetssl() will return NULL even if SSL is in use.

src/interfaces/libpq/fe-secure-openssl.c

@@ -1488,6 +1488,18 @@ SSLerrfree(char *buf)
 		free(buf);
 }
 
+/* ------------------------------------------------------------ */
+/*					SSL information functions					*/
+/* ------------------------------------------------------------ */
+
+int
+PQsslInUse(PGconn *conn)
+{
+	if (!conn)
+		return 0;
+	return conn->ssl_in_use;
+}
+
 /*
  *	Return pointer to OpenSSL object.
  */
@@ -1499,6 +1511,62 @@ PQgetssl(PGconn *conn)
 	return conn->ssl;
 }
 
+void *
+PQsslStruct(PGconn *conn, const char *struct_name)
+{
+	if (!conn)
+		return NULL;
+	if (strcmp(struct_name, "OpenSSL") == 0)
+		return conn->ssl;
+	return NULL;
+}
+
+const char **
+PQsslAttributes(PGconn *conn)
+{
+	static const char *result[] = {
+		"library",
+		"key_bits",
+		"cipher",
+		"compression",
+		"protocol",
+		NULL
+	};
+	return result;
+}
+
+const char *
+PQsslAttribute(PGconn *conn, const char *attribute_name)
+{
+	if (!conn)
+		return NULL;
+	if (conn->ssl == NULL)
+		return NULL;
+
+	if (strcmp(attribute_name, "library") == 0)
+		return "OpenSSL";
+
+	if (strcmp(attribute_name, "key_bits") == 0)
+	{
+		static char sslbits_str[10];
+		int		sslbits;
+
+		SSL_get_cipher_bits(conn->ssl, &sslbits);
+		snprintf(sslbits_str, sizeof(sslbits_str), "%d", sslbits);
+		return sslbits_str;
+	}
+
+	if (strcmp(attribute_name, "cipher") == 0)
+		return SSL_get_cipher(conn->ssl);
+
+	if (strcmp(attribute_name, "compression") == 0)
+		return SSL_get_current_compression(conn->ssl) ? "on" : "off";
+
+	if (strcmp(attribute_name, "protocol") == 0)
+		return SSL_get_version(conn->ssl);
+
+	return NULL;		/* unknown attribute */
+}
 
 /*
  * Private substitute BIO: this does the sending and receiving using send() and