[git commit] httpd: Don't add Last-Modified header to response

[Denys Vlasenko]

commit: https://git.busybox.net/busybox/commit/?id=b6efac31d864cffdf618744fd8a6fddbdee3eb4b
branch: https://git.busybox.net/busybox/commit/?id=refs/heads/master

The Last-Modified header is used for caching.
The client (browser) will send back the received date to server via If-Modified-Since request header.
But both headers MUST be an RFC 1123 formatted string.
And the formatting consumes resources on request parsing and response generation.
Instead we can use ETag header.
This simplifies logic and the only downside is that in JavaScript the document.lastModified will return null.

Signed-off-by: Sergey Ponomarev <stokito at gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 networking/httpd.c | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/networking/httpd.c b/networking/httpd.c
index a1f841aa8..94f7297ad 100644
--- a/networking/httpd.c
+++ b/networking/httpd.c
@@ -215,6 +215,16 @@
 //config:	Makes httpd send files using GZIP content encoding if the
 //config:	client supports it and a pre-compressed <file>.gz exists.
 //config:
+//config:config FEATURE_HTTPD_LAST_MODIFIED
+//config:	bool "Add Last-Modified header to response"
+//config:	default y
+//config:	depends on HTTPD
+//config:	help
+//config:	The Last-Modified header is used for cache validation.
+//config:	The client sends last seen mtime to server in If-Modified-Since.
+//config:	Both headers MUST be an RFC 1123 formatted, which is hard to parse.
+//config:	Use ETag header instead.
+//config:
 //config:config FEATURE_HTTPD_DATE
 //config:	bool "Add Date header to response"
 //config:	default y
@@ -1046,11 +1056,12 @@ static void log_and_exit(void)
  */
 static void send_headers(unsigned responseNum)
 {
+#if ENABLE_FEATURE_HTTPD_DATE || ENABLE_FEATURE_HTTPD_LAST_MODIFIED
 	static const char RFC1123FMT[] ALIGN1 = "%a, %d %b %Y %H:%M:%S GMT";
 	/* Fixed size 29-byte string. Example: Sun, 06 Nov 1994 08:49:37 GMT */
 	char date_str[40]; /* using a bit larger buffer to paranoia reasons */
-
 	struct tm tm;
+#endif
 	const char *responseString = "";
 	const char *infoString = NULL;
 #if ENABLE_FEATURE_HTTPD_ERROR_PAGES
@@ -1058,7 +1069,6 @@ static void send_headers(unsigned responseNum)
 #endif
 	unsigned len;
 	unsigned i;
-	time_t timer = time(NULL);
 
 	for (i = 0; i < ARRAY_SIZE(http_response_type); i++) {
 		if (http_response_type[i] == responseNum) {
@@ -1079,11 +1089,13 @@ static void send_headers(unsigned responseNum)
 	 * always fit into those kbytes.
 	 */
 
+	{
 #if ENABLE_FEATURE_HTTPD_DATE
-	strftime(date_str, sizeof(date_str), RFC1123FMT, gmtime_r(&timer, &tm));
-	/* ^^^ using gmtime_r() instead of gmtime() to not use static data */
+		time_t timer = time(NULL);
+		strftime(date_str, sizeof(date_str), RFC1123FMT, gmtime_r(&timer, &tm));
+		/* ^^^ using gmtime_r() instead of gmtime() to not use static data */
 #endif
-	len = sprintf(iobuf,
+		len = sprintf(iobuf,
 			"HTTP/1.1 %u %s\r\n"
 #if ENABLE_FEATURE_HTTPD_DATE
 			"Date: %s\r\n"
@@ -1093,7 +1105,8 @@ static void send_headers(unsigned responseNum)
 #if ENABLE_FEATURE_HTTPD_DATE
 			,date_str
 #endif
-	);
+		);
+	}
 
 	if (responseNum != HTTP_OK || found_mime_type) {
 		len += sprintf(iobuf + len,
@@ -1145,7 +1158,9 @@ static void send_headers(unsigned responseNum)
 #endif
 
 	if (file_size != -1) {    /* file */
+#if ENABLE_FEATURE_HTTPD_LAST_MODIFIED
 		strftime(date_str, sizeof(date_str), RFC1123FMT, gmtime_r(&last_mod, &tm));
+#endif
 #if ENABLE_FEATURE_HTTPD_RANGES
 		if (responseNum == HTTP_PARTIAL_CONTENT) {
 			len += sprintf(iobuf + len,
@@ -1190,7 +1205,9 @@ static void send_headers(unsigned responseNum)
 #if ENABLE_FEATURE_HTTPD_RANGES
 			"Accept-Ranges: bytes\r\n"
 #endif
+#if ENABLE_FEATURE_HTTPD_LAST_MODIFIED
 			"Last-Modified: %s\r\n"
+#endif
 	/* Because of 4.4 (5), we can forgo sending of "Content-Length"
 	 * since we close connection afterwards, but it helps clients
 	 * to e.g. estimate download times, show progress bars etc.
@@ -1198,7 +1215,9 @@ static void send_headers(unsigned responseNum)
 	 * but de-facto standard is to send it (see comment below).
 	 */
 			"Content-Length: %"OFF_FMT"u\r\n",
+#if ENABLE_FEATURE_HTTPD_LAST_MODIFIED
 				date_str,
+#endif
 				file_size
 		);
 	}