Setting a custom header on a proxied request

[Andrew Hutchings]

Hi Maxime,

I could be wrong here (I'm not an expert at this section of code), but I
believe what you need to set is:

r->upstream->headers_in

If this doesn't work please let me know and I'll build a test to try it
out here.

Kind Regards
Andrew

On 12/10/15 15:12, Maxime Henrion wrote:
> Hi all,
> 
> 
> I'm currently writing an nginx module that sends a number of subrequests to upstream servers based on application logic, and then aggregates the results and send them back. That part currently works just fine, thanks to the help I was given here in the past.
> 
> However, I am now trying to add a custom header to the request that is being proxied and currently failing at it. For various technical reasons, I need to add a header that contains the IP address and port (from the point of view of nginx) of the upstream server currently being contacted. In order to get at that address, I have hooked my module into the peer selection mechanism, much like the keepalive, ip_hash modules and others do. So far so good, I get at that address and can log it just fine. However, I can't seem to be able to add it as a header to my request.
> 
> Here's my init_peer callback :
> 
> static ngx_int_t
> ngx_http_dispatcher_upstream_init_peer(ngx_http_request_t *r,
>     ngx_http_upstream_srv_conf_t *us)
> {
>         ngx_http_dispatcher_upstream_peer_data_t *dp;
>         ngx_http_dispatcher_srv_conf_t *dscf;
>         ngx_int_t rc;
> 
>         dscf = ngx_http_conf_upstream_srv_conf(us, ngx_http_dispatcher_module);
> 
>         dp = ngx_palloc(r->pool, sizeof(ngx_http_dispatcher_upstream_peer_data_t));
>         if (dp == NULL) {
>                 return NGX_ERROR;
>         }
> 
>         rc = dscf->original_init_peer(r, us);
>         if (rc != NGX_OK) {
>                 return rc;
>         }
> 
>         dp->request = r;
>         dp->data = r->upstream->peer.data;
>         dp->original_get_peer = r->upstream->peer.get;
>         dp->original_free_peer = r->upstream->peer.free;
> 
>         r->upstream->peer.data = dp;
>         r->upstream->peer.get = ngx_http_dispatcher_upstream_get_peer;
>         r->upstream->peer.free = ngx_http_dispatcher_upstream_free_peer;
> 
> #if (NGX_HTTP_SSL)
>         dp->original_set_session = r->upstream->peer.set_session;
>         dp->original_save_session = r->upstream->peer.save_session;
>         r->upstream->peer.set_session = ngx_http_dispatcher_upstream_set_session;
>         r->upstream->peer.save_session = ngx_http_dispatcher_upstream_save_session;
> #endif
> 
>         return NGX_OK;
> }
> 
> Note that I save the pointer to the ngx_http_request_t object in my peer data structure to access it later. Now here's my peer selection hook :
> 
> static ngx_int_t
> ngx_http_dispatcher_upstream_get_peer(ngx_peer_connection_t *pc, void *data)
> {
>         ngx_http_dispatcher_upstream_peer_data_t *dp = data;
>         u_char addrbuf[NGX_SOCKADDR_STRLEN];
>         ngx_http_request_t *r;
>         ngx_table_elt_t *h;
>         ngx_str_t peeraddr;
>         ngx_int_t rc;
> 
>         rc = dp->original_get_peer(pc, dp->data);
>         if (rc != NGX_OK) {
>                 return rc;
>         }
> 
>         peeraddr.data = addrbuf;
>         peeraddr.len = ngx_sock_ntop(pc->sockaddr, pc->socklen, addrbuf,
>             sizeof(addrbuf), 1);
> 
>         ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,
>             "Selected peer address is: %V", &peeraddr);
> 
>         r = dp->request;
> 
>         h = ngx_list_push(&r->headers_in.headers);
>         if (h == NULL) {
>                 return NGX_ERROR;
>         }
>         h->hash = 1;
>         ngx_str_set(&h->key, "X-Shard-Addr");
>         h->value.data = ngx_pstrdup(r->pool, &peeraddr);
>         if (h->value.data == NULL) {
>                 return NGX_ERROR;
>         }
> 
>         h->value.len = peeraddr.len;
> 
>         return NGX_OK;
> }
> 
> So after getting at the actual address we're forwarding our request to, I try to add a custom header to r->headers_in, on the request object that I saved in my peer data.
> 
> I suspect I'm not actually dealing with the correct request here, because no matter what I try, I can't get this code to actually alter the headers of the forwarded request in any way.
> 
> Any help would be greatly appreciated!
> Thanks,
> Maxime
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> 

-- 
Andrew Hutchings (LinuxJedi)
Senior Developer Advocate, Nginx Inc.