Can I add Access-Control-Allow-Origin: * to the default headers

Question

I'm currently running a G-WAN server that hosts static HTML files. Right now I'm using an iframe to show the contents of these files. I would like to be able to load them cross-domain with JavaScript. Which, by default, is not allowed by the browser.

A simple fix is to add the header: Access-Control-Allow-Origin: * to the HTTP response. The problem is, I would like to avoid making a G-WAN servlet for returning static HTML, just to add the header.

Is it possible to add the header by default?

score 0 · Accepted Answer · answered Jun 25 '13 at 11:33

0

Is it possible to add [HTTP] headers by default?

Sure, add the following code in a G-WAN connection handler:

  case HDL_BEFORE_WRITE:
  {
     char head[] = "Access-Control-Allow-Origin: *\r\n\r\n";
     http_header(HEAD_ADD, head, sizeof(head) - 1, argv);
     break;
  }

This will be available for all replies, static and dynamic.

If you want to be more selective, just add your filter in the code above.

answered Jun 25 '13 at 11:33

Gil

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Thanks a lot for your response. Do I have to create a main.c file in the /handlers/ dir for the hostname that I want this for? – Fu-Raz Jun 25 '13 at 14:36
Yes. Look at the examples for how to choose in **init()** which notification you wish to receive (here HDL_BEFORE_WRITE). The code above goes into the handler **main()**. – Gil Jun 26 '13 at 15:51
Be careful: using "\r\n\r\n" make current browsers complain about invalid encode. As RFC states, headers must be concluded with single "\r\n". I wasted hours because of this :-) (please see my ready-to-use main.c below, if interested) – lucaferrario Jun 05 '20 at 16:26

score 0 · Answer 2 · answered Jun 05 '20 at 16:35

I had to fight for hours to get to these few lines of code that solve the problem perfectly, so I share them here below. First, you have to create a main.c file into handlers folder (please create/rename the folder if it's not existing or it's disabled) of your G-WAN virtualhost and copy/paste what follows:

// Add simple CORS header (Access-Control-Allow-Origin: *) to all resources

#include "gwan.h"   // G-WAN exported functions

int init(int argc, char *argv[])
{
    u32 *states = (u32*)get_env(argv, US_HANDLER_STATES);
    *states = (1 << HDL_BEFORE_WRITE);
    return 0;
}

void clean(int argc, char *argv[])
{
}

int main(int argc, char *argv[])
{
    char head[] = "Access-Control-Allow-Origin: *\r\n";
    http_header(HEAD_ADD, head, sizeof(head) - 1, argv);  
    return(255);
}

Then, kill g-wan, run it as root to compile the script, re-kill and run it as your web user (please change /var/www path with your g-wan root and www-data-user with the web user you're using...also, use sudo if you're not logged in as root):

/var/www/gwan -k
/var/www/gwan

(now CTRL-C to exit)

/var/www/gwan -k
/var/www/gwan -d:www-data:www-data-user

Now all your resources will have a beautiful Access-Control-Allow-Origin: * header :-)

Can I add Access-Control-Allow-Origin: * to the default headers

2 Answers2