JS

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

In our repositories, the module is built dynamically and is available as a separate package named angie-module-njs or angie-pro-module-njs.

Configuration Example

http {
    js_import http.js;

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

    resolver 127.0.0.53;

    server {
        listen 8000;

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

        location = /summary {
            return 200 $summary;
        }

        location = /hello {
            js_content http.hello;
        }

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

        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!");
}

async function fetch(r) {
    let results = await Promise.all([ngx.fetch('https://google.com/'),
                                     ngx.fetch('https://google.ru/')]);

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

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

js_body_filter

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

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.

Note

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.

js_content

Syntax	js_content function | module.function;
Default	—
Context	location, if in location, limit_except

Sets an njs function as a location content handler. Module functions can be referenced.

js_fetch_buffer_size

Syntax	js_fetch_buffer_size size;
Default	js_fetch_buffer_size 16k;
Context	http, server, location

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

js_fetch_ciphers

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

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

The list of ciphers depends on the version of OpenSSL installed. The full list can be viewed using the openssl ciphers command.

js_fetch_max_response_buffer_size

Syntax	js_fetch_max_response_buffer_size size;
Default	js_fetch_max_response_buffer_size 1m;
Context	http, server, location

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

js_fetch_protocols

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

Enables the specified protocols for HTTPS connections with Fetch API.

js_fetch_timeout

Syntax	js_fetch_timeout time;
Default	js_fetch_timeout 60s;
Context	http, server, location

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.

js_fetch_trusted_certificate

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

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

js_fetch_verify

Syntax	js_fetch_verify on | off;
Default	js_fetch_verify on;
Context	http, server, location

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

js_fetch_verify_depth

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

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

js_header_filter

Syntax	js_header_filter function | module.function;
Default	—
Context	location, if in location, limit_except

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

Note

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.

js_import

Syntax	js_import module.js | export_name from module.js;
Default	—
Context	http, server, location

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.

js_path

Syntax	js_path path;
Default	—
Context	http, server, location

Sets an additional path for njs modules.

js_preload_object

Syntax	js_preload_object name.json | name from file.json;
Default	—
Context	http, server, location

Preloads an immutable object at configure time. The name is used as 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.

js_set

Syntax	js_set $variable function | module.function;
Default	—
Context	http, server, locatio

Sets an njs function for the specified variable. Module functions 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.

Note

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.

js_shared_dict_zone

Syntax	js_shared_dict_zone zone=name:size [timeout=time] [type=string | number] [evict];
Default	—
Context	http

Sets the name and size of the shared memory zone that keeps the key-value dictionary shared between worker processes.

type	the optional parameter, allows redefining the value type to number, by default the shared dictionary uses a string as a key and a value
timeout	the optional parameter, sets the time after which all shared dictionary entries are removed from the zone
evict	the optional parameter, removes the oldest key-value pair when the zone storage is exhausted

Examples:

example.conf:
    # Creates a 1Mb dictionary with string values,
    # removes key-value pairs after 60 seconds of inactivity:
    js_shared_dict_zone zone=foo:1M timeout=60s;

    # Creates a 512Kb dictionary with string values,
    # forcibly removes oldest key-value pairs when the zone is exhausted:
    js_shared_dict_zone zone=bar:512K timeout=30s evict;

    # Creates a 32Kb permanent dictionary with number values:
    js_shared_dict_zone zone=num:32k type=number;

example.js:
    function get(r) {
        r.return(200, ngx.shared.foo.get(r.args.key));
    }

    function set(r) {
        r.return(200, ngx.shared.foo.set(r.args.key, r.args.value));
    }

    function delete(r) {
        r.return(200, ngx.shared.bar.delete(r.args.key));
    }

    function increment(r) {
        r.return(200, ngx.shared.num.incr(r.args.key, 2));
    }

js_var

Syntax	js_var $variable [value];
Default	—
Context	stream, server

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.