Module ngx_http_js_module

The ngx_http_js_module module is used to implement location and variable handlers in njs — a subset of the JavaScript language.

Download and install instructions are available here.

The example works since 0.4.0.

http {
    js_import http.js;

    js_set $foo     http.foo;
    js_set $summary http.summary;
    js_set $hash    http.hash;

    resolver 10.0.0.1;

    server {
        listen 8000;

        location / {
            add_header X-Foo $foo;
            js_content http.baz;
        }

        location = /summary {
            return 200 $summary;
        }

        location = /hello {
            js_content http.hello;
        }

        # since 0.7.0
        location = /fetch {
            js_content                   http.fetch;
            js_fetch_trusted_certificate /path/to/ISRG_Root_X1.pem;
        }

        # since 0.7.0
        location = /crypto {
            add_header Hash $hash;
            return     200;
        }
    }
}

The http.js file:

function foo(r) {
    r.log("hello from foo() handler");
    return "foo";
}

function summary(r) {
    var a, s, h;

    s = "JS summary\n\n";

    s += "Method: " + r.method + "\n";
    s += "HTTP version: " + r.httpVersion + "\n";
    s += "Host: " + r.headersIn.host + "\n";
    s += "Remote Address: " + r.remoteAddress + "\n";
    s += "URI: " + r.uri + "\n";

    s += "Headers:\n";
    for (h in r.headersIn) {
        s += "  header '" + h + "' is '" + r.headersIn[h] + "'\n";
    }

    s += "Args:\n";
    for (a in r.args) {
        s += "  arg '" + a + "' is '" + r.args[a] + "'\n";
    }

    return s;
}

function baz(r) {
    r.status = 200;
    r.headersOut.foo = 1234;
    r.headersOut['Content-Type'] = "text/plain; charset=utf-8";
    r.headersOut['Content-Length'] = 15;
    r.sendHeader();
    r.send("nginx");
    r.send("java");
    r.send("script");

    r.finish();
}

function hello(r) {
    r.return(200, "Hello world!");
}

// since 0.7.0
async function fetch(r) {
    let results = await Promise.all([ngx.fetch('https://nginx.org/'),
                                     ngx.fetch('https://nginx.org/en/')]);

    r.return(200, JSON.stringify(results, undefined, 4));
}

// since 0.7.0
async function hash(r) {
    let hash = await crypto.subtle.digest('SHA-512', r.headersIn.host);
    r.setReturnValue(Buffer.from(hash).toString('hex'));
}

export default {foo, summary, baz, hello, fetch, hash};

Sets an njs function as a response body filter. The filter function is called for each data chunk of a response body with the following arguments:

r

the HTTP request object

data

the incoming data chunk, may be a string or Buffer depending on the buffer_type value, by default is a string.

flags

an object with the following properties:

last

a boolean value, true if data is a last buffer.

The filter function can pass its own modified version of the input data chunk to the next body filter by calling r.sendBuffer(). For example, to transform all the lowercase letters in the response body:

function filter(r, data, flags) {
    r.sendBuffer(data.toLowerCase(), flags);
}

To stop filtering (following data chunks will be passed to client without calling js_body_filter), r.done() can be used.

If the filter function changes the length of the response body, then it is required to clear out the “Content-Length” response header (if any) in js_header_filter to enforce chunked transfer encoding.

As the js_body_filter handler returns its result immediately, it supports only synchronous operations. Thus, asynchronous operations such as r.subrequest() or setTimeout() are not supported.

The directive can be specified inside the if block since 0.7.7.

Sets an njs function as a location content handler. Since 0.4.0, a module function can be referenced.

The directive can be specified inside the if block since 0.7.7.

js_fetch_buffer_size 16k;

Sets the size of the buffer used for reading and writing with Fetch API.

js_fetch_ciphers HIGH:!aNULL:!MD5;

Specifies the enabled ciphers for HTTPS requests with Fetch API. The ciphers are specified in the format understood by the OpenSSL library.

The full list can be viewed using the “openssl ciphers” command.

js_fetch_max_response_buffer_size 1m;

Sets the maximum size of the response received with Fetch API.

js_fetch_protocols TLSv1 TLSv1.1 TLSv1.2;

Enables the specified protocols for HTTPS requests with Fetch API.

js_fetch_timeout 60s;

Defines a timeout for reading and writing for Fetch API. The timeout is set only between two successive read/write operations, not for the whole response. If no data is transmitted within this time, the connection is closed.

Specifies a file with trusted CA certificates in the PEM format used to verify the HTTPS certificate with Fetch API.

js_fetch_verify on;

Enables or disables verification of the HTTPS server certificate with Fetch API.

js_fetch_verify_depth 100;

Sets the verification depth in the HTTPS server certificates chain with Fetch API.

Sets an njs function as a response header filter. The directive allows changing arbitrary header fields of a response header.

As the js_header_filter handler returns its result immediately, it supports only synchronous operations. Thus, asynchronous operations such as r.subrequest() or setTimeout() are not supported.

The directive can be specified inside the if block since 0.7.7.

Imports a module that implements location and variable handlers in njs. The export_name is used as a namespace to access module functions. If the export_name is not specified, the module name will be used as a namespace.

js_import http.js;

Here, the module name http is used as a namespace while accessing exports. If the imported module exports foo(), http.foo is used to refer to it.

Several js_import directives can be specified.

The directive can be specified on the server and location level since 0.7.7.

Specifies a file that implements location and variable handlers in njs:

nginx.conf:
js_include http.js;
location   /version {
    js_content version;
}

http.js:
function version(r) {
    r.return(200, njs.version);
}

The directive was made obsolete in version 0.4.0 and was removed in version 0.7.1. The js_import directive should be used instead.

Sets an additional path for njs modules.

The directive can be specified on the server and location level since 0.7.7.

Preloads an immutable object at configure time. The name is used a name of the global variable though which the object is available in njs code. If the name is not specified, the file name will be used instead.

js_preload_object map.json;

Here, the map is used as a name while accessing the preloaded object.

Several js_preload_object directives can be specified.

Sets an njs function for the specified variable. Since 0.4.0, a module function can be referenced.

The function is called when the variable is referenced for the first time for a given request. The exact moment depends on a phase at which the variable is referenced. This can be used to perform some logic not related to variable evaluation. For example, if the variable is referenced only in the log_format directive, its handler will not be executed until the log phase. This handler can be used to do some cleanup right before the request is freed.

As the js_set handler returns its result immediately, it supports only synchronous operations. Thus, asynchronous operations such as r.subrequest() or setTimeout() are not supported.

The directive can be specified on the server and location level since 0.7.7.

Declares a writable variable. The value can contain text, variables, and their combination. The variable is not overwritten after a redirect unlike variables created with the set directive.

The directive can be specified on the server and location level since 0.7.7.

Each HTTP njs handler receives one argument, a request object.