optimize: now we pre-calculate the exact size of the resulting Lua table and preallocate the table space, which makes it 8%+ faster for a request with a dozen request headers and 40%+ faster for a hundred request headers.

Author: agentzh

src/ngx_http_lua_headers.c

@@ -322,7 +322,18 @@ ngx_http_lua_ngx_req_get_headers(lua_State *L)
 
     ngx_http_lua_check_fake_request(L, r);
 
-    lua_createtable(L, 0, 4);
+    part = &r->headers_in.headers.part;
+    count = part->nelts;
+    while (part->next) {
+        part = part->next;
+        count += part->nelts;
+    }
+
+    if (max > 0 && count > max) {
+        count = max;
+    }
+
+    lua_createtable(L, 0, count);
 
     if (!raw) {
         lua_pushlightuserdata(L, &ngx_http_lua_req_get_headers_metatable_key);
@@ -366,7 +377,7 @@ ngx_http_lua_ngx_req_get_headers(lua_State *L)
                        "lua request header: \"%V: %V\"",
                        &header[i].key, &header[i].value);
 
-        if (max > 0 && ++count == max) {
+        if (--count == 0) {
             ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                            "lua hit request header limit %d", max);