Njs: Content-type header lost when making a subrequest

[igabesz]

I have the following workflow in an nginx.conf file and NJS files:

• [conf] Receive a request (server, location)
• [conf] Pass execution to the NJS code (js_content)
• [JS] Make a subrequest to an internal route
• [conf] The internal route is a proxy_pass to an external server
• [JS] Get the response from the internal route
• [JS] Send back the status code, headers and body to the original request

I found that the returning Content-type header is lost. The external server returns application/json while the nginx returns text/plain. I don't see the Content-type field in the NJS code when processing the response of the subrequest (reply.headersOut). But if I call the proxy_pass directly (without NJS subrequest) then the response contains the proper Content-type header.

Edit: I do see the X-Powered-By header in reply.headersOut and others as well. So it's not that all of the headers are lost. But Content-Type and Content-Length are missing indeed.

Maybe I missed something or something avoided my attention in the docs, dunno... but it might as well be a bug.

=== CONFIGS ===

nginx.conf entry:

location /endpoint {
    js_content execRequest;
}

In the execRequest implementation. (I tried with and without the commented part.)

    r.subrequest('/proxy/endpoint', { 
        method: method,
        body: r.requestBody,
    }).then(reply => {
        r.status = reply.status;
        // No Content-type in the reply.headersOut
        // for (var header in reply.headersOut) { // This might or might not required
            // r.headersOut[header] = reply.headersOut[header];
        // }
        r.sendHeader();
        r.send(reply.responseBody);
        r.finish();
    });

And the proxy:

  location /proxy {
            # internal; // Turned off to check it manually
            proxy_pass_request_headers on;

            location /proxy/endpoint {
                proxy_pass http://$external_service/endpoint;
            }
    }

[xeioex]

Hi, @igabesz

what version of njs are you using?

See this commit https://github.com/nginx/njs/commit/2bd9dc97d3a733f3e81db3296ef3a7361d80b752, it was released as a part of 0.4.0.

The issue is that the Content-Type was available as r.headersOut["Content-type"], but was invisible during iterations over r.headersOut (because nginx stores content_type field in a special way).

The workaround for 0.3.9 and before is to copy Content-Type manually:

r.headersOut['Content-Type'] = reply.headersOut['Content-Type'];
r.headersOut['Content-Length'] = reply.headersOut['Content-Length'];

Also, this change https://github.com/nginx/njs/commit/f9a00172aa17c322f1d930786af00b84821c0c1e solves "Set-Cookie" issue, when only one Set-Cookie headers was available (#298). For "Set-Cookie" issue there is no simple workaround for 0.3.9 and before.

[igabesz]

Thanks, it works with 0.4.0! Now it copies all of the headers from the reply of the subrequest to the main response.

I was using nginx:latest (1.17.10 with NJS 3.9), now I moved to nginx:stable (1.18.0 with NJS 0.4.0) and it works smoothly.