OPTIM: lua: don't use expensive functions to parse headers in the HTTP applet

In the HTTP applet, we have to parse the response headers provided by
the application and to produce a response. strcasecmp() is expensive,
and chunk_append() even more as it uses a format string.

Here we check the string length before calling strcasecmp(), which
results in strcasecmp() being called only on the relevant header in
practise due to very few collisions on the name lengths, effectively
dividing the number of calls by 3, and we replace chunk_appendf()
with memcpy() as we already know the string lengths.

Doing just this makes the "hello-world" applet 5% faster, reaching
41400 requests/s on a core i5-3320M.

diff --git a/src/hlua.c b/src/hlua.c
index 349d3724f5a2557216b8d08895506095f64dc7ae..503675bad84a098e359b95ca94f86581a1912f2e 100644 (file)
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -4196,7 +4196,9 @@ __LJMP static int hlua_applet_http_start_response(lua_State *L)
        struct chunk *tmp = get_trash_chunk();
        struct hlua_appctx *appctx = MAY_LJMP(hlua_checkapplet_http(L, 1));
        const char *name;
+       size_t name_len;
        const char *value;
+       size_t value_len;
        int id;
        int hdr_connection = 0;
        long long hdr_contentlength = -1;
@@ -4231,7 +4233,7 @@ __LJMP static int hlua_applet_http_start_response(lua_State *L)
                                       lua_typename(L, lua_type(L, -2)));
                        WILL_LJMP(lua_error(L));
                }
-               name = lua_tostring(L, -2);
+               name = lua_tolstring(L, -2, &name_len);
 
                /* We expect an array as -1. */
                if (lua_type(L, -1) != LUA_TTABLE) {
@@ -4264,15 +4266,25 @@ __LJMP static int hlua_applet_http_start_response(lua_State *L)
                                               lua_typename(L, lua_type(L, -1)));
                                WILL_LJMP(lua_error(L));
                        }
-                       value = lua_tostring(L, -1);
+                       value = lua_tolstring(L, -1, &value_len);
 
                        /* Catenate a new header. */
-                       chunk_appendf(tmp, "%s: %s\r\n", name, value);
+                       if (tmp->len + name_len + 2 + value_len + 2 < tmp->size) {
+                               memcpy(tmp->str + tmp->len, name, name_len);
+                               tmp->len += name_len;
+                               tmp->str[tmp->len++] = ':';
+                               tmp->str[tmp->len++] = ' ';
+
+                               memcpy(tmp->str + tmp->len, value, value_len);
+                               tmp->len += value_len;
+                               tmp->str[tmp->len++] = '\r';
+                               tmp->str[tmp->len++] = '\n';
+                       }
 
                        /* Protocol checks. */
 
                        /* Check if the header conneciton is present. */
-                       if (strcasecmp("connection", name) == 0)
+                       if (name_len == 10 && strcasecmp("connection", name) == 0)
                                hdr_connection = 1;
 
                        /* Copy the header content length. The length conversion
@@ -4280,11 +4292,12 @@ __LJMP static int hlua_applet_http_start_response(lua_State *L)
                         * the content-length remains negative so that we can
                         * switch to either chunked encoding or close.
                         */
-                       if (strcasecmp("content-length", name) == 0)
+                       if (name_len == 14 && strcasecmp("content-length", name) == 0)
                                strl2llrc(value, strlen(value), &hdr_contentlength);
 
                        /* Check if the client annouces a transfer-encoding chunked it self. */
-                       if (strcasecmp("transfer-encoding", name) == 0 &&
+                       if (name_len == 17 && value_len == 7 &&
+                           strcasecmp("transfer-encoding", name) == 0 &&
                            strcasecmp("chunked", value) == 0)
                                hdr_chunked = 1;