[PATCH] If-Modified-Since support in httpd

[jmp]

If-Modified-Since is already sent by most web browsers to httpd. This
patch adds a check to server_file_access before we send the file back.

This does not do any checks for autoindex directories as the size and
last modification dates of files would not get updated properly.

I separated the logic for checking the header values as it can be
reused for different side effects of other headers like Range.


Index: usr.sbin/httpd/server_file.c
===================================================================
RCS file: /cvs/src/usr.sbin/httpd/server_file.c,v
retrieving revision 1.51
diff -u -p -r1.51 server_file.c
--- usr.sbin/httpd/server_file.c        12 Feb 2015 10:05:29 -0000      1.51
+++ usr.sbin/httpd/server_file.c        18 Apr 2015 16:41:55 -0000
@@ -42,6 +42,7 @@ int    server_file_request(struct httpd *,
            struct stat *);
 int     server_file_index(struct httpd *, struct client *, struct stat *);
 int     server_file_method(struct client *);
+int     server_file_modified_since(struct http_descriptor *, struct stat *);
 
 int
 server_file_access(struct httpd *env, struct client *clt,
@@ -123,6 +124,10 @@ server_file_access(struct httpd *env, st
                goto fail;
        }
 
+       if ((ret = server_file_modified_since(desc, &st)) != -1) {
+               return ret;
+       }
+
        return (server_file_request(env, clt, path, &st));
 
  fail:
@@ -466,4 +471,24 @@ server_file_error(struct bufferevent *be
        }
        server_close(clt, "unknown event error");
        return;
+}
+
+int
+server_file_modified_since(struct http_descriptor * desc, struct stat * st)
+{
+       struct kv                key, *since;
+       struct tm                tm;
+
+       memset(&tm, 0, sizeof(struct tm));
+
+       key.kv_key = "If-Modified-Since";
+       if ((since = kv_find(&desc->http_headers, &key)) != NULL &&
+           since->kv_value != NULL) {
+               if (strptime(since->kv_value, "%a, %d %h %Y %T %Z", &tm) != 
NULL &&
+                   timeoff(&tm, 0L) >= st->st_mtim.tv_sec) {
+                       return 304;
+               }
+       }
+
+       return (-1);
 }