Module ngx_http_js_module

Example Configuration
Directives
     js_body_filter
     js_content
     js_fetch_ciphers
     js_fetch_protocols
     js_fetch_trusted_certificate
     js_fetch_verify_depth
     js_header_filter
     js_import
     js_include
     js_path
     js_set
     js_var
Request Argument

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.

Example Configuration

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;

    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('http://nginx.org/'),
                                     ngx.fetch('http://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};

Directives

Syntax: js_body_filter function | module.function [buffer_type=string | buffer];
Default:
Context: location, limit_except

This directive appeared in version 0.5.2.

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.

Syntax: js_content function | module.function;
Default:
Context: location, limit_except

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

Syntax: js_fetch_ciphers ciphers;
Default:
js_fetch_ciphers HIGH:!aNULL:!MD5;
Context: http, server, location

This directive appeared in version 0.7.0.

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.

Syntax: js_fetch_protocols [TLSv1] [TLSv1.1] [TLSv1.2] [TLSv1.3];
Default:
js_fetch_protocols TLSv1 TLSv1.1 TLSv1.2;
Context: http, server, location

This directive appeared in version 0.7.0.

Enables the specified protocols for HTTPS requests with Fetch API.

Syntax: js_fetch_trusted_certificate file;
Default:
Context: http, server, location

This directive appeared in version 0.7.0.

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

Syntax: js_fetch_verify_depth number;
Default:
js_fetch_verify_depth 100;
Context: http, server, location

This directive appeared in version 0.7.0.

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

Syntax: js_header_filter function | module.function;
Default:
Context: location, limit_except

This directive appeared in version 0.5.1.

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

Syntax: js_import module.js | export_name from module.js;
Default:
Context: http

This directive appeared in version 0.4.0.

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.

Syntax: js_include file;
Default:
Context: http

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 is deprecated since 0.4.0, the js_import directive should be used instead.

Syntax: js_path path;
Default:
Context: http

This directive appeared in version 0.3.0.

Sets an additional path for njs modules.

Syntax: js_set $variable function | module.function;
Default:
Context: http

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 callbacks. Thus, asynchronous callbacks such as r.subrequest() or setTimeout() are not supported.

Syntax: js_var $variable [value];
Default:
Context: http

This directive appeared in version 0.5.3.

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.

Request Argument

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