net: http_server: Add support for generic HTTP1 500 response

In case of internal server errors during HTTP1 request processing,
send 500 Internal Server Error response before shutting down the
connection.

Make sure http1_headers_sent is set whenever sever starts replying, to
avoid duplicate response in case of errors, as that would be protocol
violation.

Signed-off-by: Robert Lubos <[email protected]>

Author: rlubos

subsys/net/lib/http/Kconfig

@@ -188,6 +188,13 @@ config HTTP_SERVER_TLS_USE_ALPN
 	  protocol for TLS connections. Web browsers use this mechanism to determine
 	  whether HTTP2 is supported.
 
+config HTTP_SERVER_REPORT_FAILURE_REASON
+	bool "Report failure reason in HTTP 500 Internal Server Error reply"
+	help
+	  If enabled, the server will include the failure reason within
+	  HTTP 500 Internal Server Error response. Otherwise, no information
+	  is provided within the message.
+
 config WEBSOCKET_CONSOLE
 	bool
 	default y if HTTP_SERVER_WEBSOCKET && SHELL_BACKEND_WEBSOCKET

subsys/net/lib/http/http_server_http1.c

@@ -71,6 +71,51 @@ static int send_http1_409(struct http_client_ctx *client)
 				       sizeof(conflict_response) - 1);
 }
 
+static void send_http1_500(struct http_client_ctx *client, int error_code)
+{
+#define HTTP_500_RESPONSE_TEMPLATE			\
+	"HTTP/1.1 500 Internal Server Error\r\n"	\
+	"Content-Type: text/plain\r\n"			\
+	"Content-Length: %d\r\n\r\n"			\
+	"Internal Server Error%s%s\r\n"
+#define MAX_ERROR_DESC_LEN 32
+
+	/* Placeholder for the error description. */
+	char error_str[] = "xxx";
+	char http_response[sizeof(HTTP_500_RESPONSE_TEMPLATE) +
+			   sizeof("xx") + /* Content-Length */
+			   MAX_ERROR_DESC_LEN + 1]; /* For the error description */
+	const char *error_desc;
+	const char *desc_separator;
+	int desc_len;
+
+	if (IS_ENABLED(CONFIG_HTTP_SERVER_REPORT_FAILURE_REASON)) {
+		/* Try to fetch error description, fallback to error number if
+		 * not available
+		 */
+		error_desc = strerror(error_code);
+		if (strlen(error_desc) == 0) {
+			/* Cast error value to uint8_t to avoid truncation warnings. */
+			(void)snprintk(error_str, sizeof(error_str), "%u",
+				       (uint8_t)error_code);
+			error_desc = error_str;
+		}
+		desc_separator = ": ";
+		desc_len = MIN(MAX_ERROR_DESC_LEN, strlen(error_desc));
+		desc_len += 2; /* For ": " */
+	} else {
+		error_desc = "";
+		desc_separator = "";
+		desc_len = 0;
+	}
+
+	(void)snprintk(http_response, sizeof(http_response),
+		       HTTP_500_RESPONSE_TEMPLATE,
+		       sizeof("Internal Server Error\r\n") - 1 + desc_len,
+		       desc_separator, error_desc);
+	(void)http_server_sendall(client, http_response, strlen(http_response));
+}
+
 static int handle_http1_static_resource(
 	struct http_resource_detail_static *static_detail,
 	struct http_client_ctx *client)
@@ -119,6 +164,8 @@ static int handle_http1_static_resource(
 		return ret;
 	}
 
+	client->http1_headers_sent = true;
+
 	ret = http_server_sendall(client, data, len);
 	if (ret < 0) {
 		return ret;
@@ -483,6 +530,8 @@ int handle_http1_static_fs_resource(struct http_resource_detail_static_fs *stati
 		goto close;
 	}
 
+	client->http1_headers_sent = true;
+
 	/* read and send file */
 	remaining = file_size;
 	while (remaining > 0) {
@@ -545,6 +594,7 @@ static int handle_http1_dynamic_resource(
 				return ret;
 			}
 
+			client->http1_headers_sent = true;
 			dynamic_detail->holder = NULL;
 
 			return 0;
@@ -839,12 +889,14 @@ int handle_http1_request(struct http_client_ctx *client)
 
 	if (parsed > client->data_len) {
 		LOG_ERR("HTTP/1 parser error, too much data consumed");
-		return -EBADMSG;
+		ret = -EBADMSG;
+		goto error;
 	}
 
 	if (client->parser.http_errno != HPE_OK) {
 		LOG_ERR("HTTP/1 parsing error, %d", client->parser.http_errno);
-		return -EBADMSG;
+		ret = -EBADMSG;
+		goto error;
 	}
 
 	if (client->parser_state < HTTP1_RECEIVED_HEADER_STATE) {
@@ -863,7 +915,8 @@ int handle_http1_request(struct http_client_ctx *client)
 		size_t frag_headers_len;
 
 		if (parsed < client->http1_frag_data_len) {
-			return -EBADMSG;
+			ret = -EBADMSG;
+			goto error;
 		}
 
 		frag_headers_len = parsed - client->http1_frag_data_len;
@@ -892,36 +945,49 @@ int handle_http1_request(struct http_client_ctx *client)
 
 				detail->path_len = path_len;
 				client->current_detail = detail;
-				return handle_http1_to_websocket_upgrade(client);
+
+				ret = handle_http1_to_websocket_upgrade(client);
+				if (ret < 0) {
+					goto error;
+				}
+
+				return 0;
 			}
 
 			goto upgrade_not_found;
 		}
 
 		if (client->http2_upgrade) {
-			return handle_http1_to_http2_upgrade(client);
+			ret = handle_http1_to_http2_upgrade(client);
+			if (ret < 0) {
+				goto error;
+			}
+
+			return 0;
 		}
 
 upgrade_not_found:
 		ret = http_server_sendall(client, upgrade_required,
 					  sizeof(upgrade_required) - 1);
 		if (ret < 0) {
 			LOG_DBG("Cannot write to socket (%d)", ret);
-			return ret;
+			goto error;
 		}
 
+		client->http1_headers_sent = true;
+
 		ret = http_server_sendall(client, needed_upgrade,
 					  strlen(needed_upgrade));
 		if (ret < 0) {
 			LOG_DBG("Cannot write to socket (%d)", ret);
-			return ret;
+			goto error;
 		}
 
 		ret = http_server_sendall(client, upgrade_msg,
 					  sizeof(upgrade_msg) - 1);
 		if (ret < 0) {
 			LOG_DBG("Cannot write to socket (%d)", ret);
-			return ret;
+			goto error;
 		}
 	}
 
@@ -934,30 +1000,32 @@ int handle_http1_request(struct http_client_ctx *client)
 				(struct http_resource_detail_static *)detail,
 				client);
 			if (ret < 0) {
-				return ret;
+				goto error;
 			}
 #if defined(CONFIG_FILE_SYSTEM)
 		} else if (detail->type == HTTP_RESOURCE_TYPE_STATIC_FS) {
 			ret = handle_http1_static_fs_resource(
 				(struct http_resource_detail_static_fs *)detail, client);
 			if (ret < 0) {
-				return ret;
+				goto error;
 			}
 #endif
 		} else if (detail->type == HTTP_RESOURCE_TYPE_DYNAMIC) {
 			ret = handle_http1_dynamic_resource(
 				(struct http_resource_detail_dynamic *)detail,
 				client);
 			if (ret < 0) {
-				return ret;
+				goto error;
 			}
 		}
 	} else {
 not_found: ; /* Add extra semicolon to make clang to compile when using label */
 		ret = send_http1_404(client);
 		if (ret < 0) {
-			return ret;
+			goto error;
 		}
+
+		client->http1_headers_sent = true;
 	}
 
 	client->cursor += parsed;
@@ -974,4 +1042,16 @@ not_found: ; /* Add extra semicolon to make clang to compile when using label */
 	}
 
 	return 0;
+
+error:
+	/* Best effort try to send HTTP 500 Internal Server Error response in
+	 * case of errors. This can only be done however if we haven't sent
+	 * response header elsewhere (i. e. can't send another reply if the
+	 * error ocurred amid resource processing).
+	 */
+	if (ret != -EAGAIN && !client->http1_headers_sent) {
+		send_http1_500(client, -ret);
+	}
+
+	return ret;
 }

subsys/net/lib/http/http_server_http2.c

@@ -1018,6 +1018,8 @@ int handle_http1_to_http2_upgrade(struct http_client_ctx *client)
 			goto error;
 		}
 
+		client->http1_headers_sent = true;
+
 		/* The first HTTP/2 frame sent by the server MUST be a server connection
 		 * preface.
 		 */

subsys/net/lib/http/http_server_ws.c

@@ -70,6 +70,8 @@ int handle_http1_to_websocket_upgrade(struct http_client_ctx *client)
 		goto error;
 	}
 
+	client->http1_headers_sent = true;
+
 	ret = http_server_sendall(client, tmp, strlen(tmp));
 	if (ret < 0) {
 		NET_DBG("Cannot write to socket (%d)", ret);