1 files changed, 54 insertions, 3 deletions

diff --git a/networking/httpd.c b/networking/httpd.c
index 94f7297ad..0297cf9ec 100644
--- a/networking/httpd.c
+++ b/networking/httpd.c
@@ -215,6 +215,19 @@
 //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_ETAG
+//config:       bool "Support caching via ETag header"
+//config:       default y
+//config:       depends on HTTPD
+//config:       help
+//config:       If server responds with ETag then next time client (browser)
+//config:       resend it via If-None-Match header.
+//config:       Then httpd will check if file wasn't modified and if not,
+//config:       return 304 Not Modified status code.
+//config:       The ETag value is constructed from last modification date
+//config:       in unix epoch, and size: "hex(last_mod)-hex(file_size)".
+//config:       It's not completely reliable as hash functions but fair enough.
+//config:
 //config:config FEATURE_HTTPD_LAST_MODIFIED
 //config:       bool "Add Last-Modified header to response"
 //config:       default y
@@ -328,6 +341,7 @@ enum {
         HTTP_OK = 200,
         HTTP_PARTIAL_CONTENT = 206,
         HTTP_MOVED_TEMPORARILY = 302,
+        HTTP_NOT_MODIFIED = 304,
         HTTP_BAD_REQUEST = 400,       /* malformed syntax */
         HTTP_UNAUTHORIZED = 401, /* authentication needed, respond with auth hdr */
         HTTP_NOT_FOUND = 404,
@@ -345,7 +359,6 @@ enum {
         HTTP_NO_CONTENT = 204,
         HTTP_MULTIPLE_CHOICES = 300,
         HTTP_MOVED_PERMANENTLY = 301,
-        HTTP_NOT_MODIFIED = 304,
         HTTP_PAYMENT_REQUIRED = 402,
         HTTP_BAD_GATEWAY = 502,
         HTTP_SERVICE_UNAVAILABLE = 503, /* overload, maintenance */
@@ -358,6 +371,9 @@ static const uint16_t http_response_type[] ALIGN2 = {
         HTTP_PARTIAL_CONTENT,
 #endif
         HTTP_MOVED_TEMPORARILY,
+#if ENABLE_FEATURE_HTTPD_ETAG
+        HTTP_NOT_MODIFIED,
+#endif
         HTTP_REQUEST_TIMEOUT,
         HTTP_NOT_IMPLEMENTED,
 #if ENABLE_FEATURE_HTTPD_BASIC_AUTH
@@ -374,7 +390,6 @@ static const uint16_t http_response_type[] ALIGN2 = {
         HTTP_NO_CONTENT,
         HTTP_MULTIPLE_CHOICES,
         HTTP_MOVED_PERMANENTLY,
-        HTTP_NOT_MODIFIED,
         HTTP_BAD_GATEWAY,
         HTTP_SERVICE_UNAVAILABLE,
 #endif
@@ -389,6 +404,9 @@ static const struct {
         { "Partial Content", NULL },
 #endif
         { "Found", NULL },
+#if ENABLE_FEATURE_HTTPD_ETAG
+        { "Not Modified" },
+#endif
         { "Request Timeout", "No request appeared within 60 seconds" },
         { "Not Implemented", "The requested method is not recognized" },
 #if ENABLE_FEATURE_HTTPD_BASIC_AUTH
@@ -405,7 +423,6 @@ static const struct {
         { "No Content" },
         { "Multiple Choices" },
         { "Moved Permanently" },
-        { "Not Modified" },
         { "Bad Gateway", "" },
         { "Service Unavailable", "" },
 #endif
@@ -419,6 +436,9 @@ struct globals {
         smallint content_gzip;
 #endif
         time_t last_mod;
+#if ENABLE_FEATURE_HTTPD_ETAG
+        char *if_none_match;
+#endif
         char *rmt_ip_str;       /* for $REMOTE_ADDR and $REMOTE_PORT */
         const char *bind_addr_or_port;
 
@@ -453,6 +473,9 @@ struct globals {
 #define sizeof_hdr_buf COMMON_BUFSIZE
         char *hdr_ptr;
         int hdr_cnt;
+#if ENABLE_FEATURE_HTTPD_ETAG
+        char etag[sizeof("'%llx-%llx'") + 2 * sizeof(long long)*3];
+#endif
 #if ENABLE_FEATURE_HTTPD_ERROR_PAGES
         const char *http_error_page[ARRAY_SIZE(http_response_type)];
 #endif
@@ -1208,6 +1231,10 @@ static void send_headers(unsigned responseNum)
 #if ENABLE_FEATURE_HTTPD_LAST_MODIFIED
                         "Last-Modified: %s\r\n"
 #endif
+#if ENABLE_FEATURE_HTTPD_ETAG
+                        "ETag: %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.
@@ -1218,6 +1245,9 @@ static void send_headers(unsigned responseNum)
 #if ENABLE_FEATURE_HTTPD_LAST_MODIFIED
                                 date_str,
 #endif
+#if ENABLE_FEATURE_HTTPD_ETAG
+                                G.etag,
+#endif
                                 file_size
                 );
         }
@@ -1730,6 +1760,7 @@ static NOINLINE void send_file_and_exit(const char *url, int what)
                 }
         } else {
                 fd = open(url, O_RDONLY);
+                /* file_size and last_mod are already populated */
         }
         if (fd < 0) {
                 if (DEBUG)
@@ -1741,6 +1772,19 @@ static NOINLINE void send_file_and_exit(const char *url, int what)
                         send_headers_and_exit(HTTP_NOT_FOUND);
                 log_and_exit();
         }
+#if ENABLE_FEATURE_HTTPD_ETAG
+        /* ETag is "hex(last_mod)-hex(file_size)" e.g. "5e132e20-417" */
+        sprintf(G.etag, "\"%llx-%llx\"", (unsigned long long)last_mod, (unsigned long long)file_size);
+
+        if (G.if_none_match) {
+                if (DEBUG)
+                        bb_perror_msg("If-None-Match and file's ETag are: '%s' '%s'\n", G.if_none_match, G.etag);
+                /* Weak ETag comparision.
+                 * If-None-Match may have many ETags but they are quoted so we can use simple substring search */
+                if (strstr(G.if_none_match, G.etag))
+                        send_headers_and_exit(HTTP_NOT_MODIFIED);
+        }
+#endif
         /* If you want to know about EPIPE below
          * (happens if you abort downloads from local httpd): */
         signal(SIGPIPE, SIG_IGN);
@@ -2480,6 +2524,13 @@ static void handle_incoming_and_exit(const len_and_sockaddr *fromAddr)
                         continue;
                 }
 #endif
+#if ENABLE_FEATURE_HTTPD_ETAG
+                if (STRNCASECMP(iobuf, "If-None-Match:") == 0) {
+                        free(G.if_none_match);
+                        G.if_none_match = xstrdup(skip_whitespace(iobuf + sizeof("If-None-Match:") - 1));
+                        continue;
+                }
+#endif
 #if ENABLE_FEATURE_HTTPD_CGI
                 if (cgi_type != CGI_NONE) {
                         bool ct = (STRNCASECMP(iobuf, "Content-Type:") == 0);