NGINX Module while Handling subrequest callback expected behvior when rc is NGX_AGAIN

Question

Writing an NGINX module that is depending on subrequest call.

on the callback, I am getting rc=NGX_AGAIN with request->out=NULL, of course that mean I cannot get the content of the subrequest response.

In that case what is the expected behavior of the callback ?

Here is the subrequest setup code

/// Setup callback
    ngx_http_request_t *sub_request;
    ngx_http_post_subrequest_t *callback = ngx_pcalloc(request->pool, sizeof(ngx_http_post_subrequest_t));
    callback->handler = callback_proc;
    callback->data = data;
    ngx_int_t result = ngx_http_subrequest(request, uri, NULL, &sub_request, callback, NGX_HTTP_SUBREQUEST_IN_MEMORY);

The following callback handler would

static ngx_int_t
callback_proc(ngx_http_request_t *request, void *data, ngx_int_t rc) {
    // unbox and sanity check    
    data->value->len = r->out->buf->last - r->out->buf->pos; // <<-- SIGSEV because r->out is NULL
    data->value->data = r->out->buf->pos;
    return rc;
}

score 0 · Answer 1 · answered Jul 23 '23 at 12:53

My issue was that my module handler were intercepting the response and were waiting for the subrequest to complete, and while waiting for the subrequest issued the NGX_AGAIN.

In your handler be sure to redirect to proper care for redirect your subrequest if they happen to handle the same type of content.

Meaning would have to test for request->parent which Should be NULL if main request.

NGINX Module while Handling subrequest callback expected behvior when rc is NGX_AGAIN

1 Answers1