Filters Downloader

Filters downloader package

This utility tool resolves preprocessor directives in filter content.

Directives syntax

!#if condition
Anything goes here
!#include URL_or_a_relative_path
!#endif

or with an else branch:

!#if condition
!#include URL_or_a_relative_path
!#else
!#include another_URL_or_a_relative_path
!#endif

• !#if, !#else, !#endif — filters maintainers can use these conditions to supply different rules depending on the ad blocker type.
• condition — just like in some popular programming languages, pre-processor conditions are based on constants declared by ad blockers. Ad blocker authors define on their own what exact constants do they declare.
• !#include — this directive allows to include contents of a specified file into the filter.

Logical conditions

When an adblocker encounters an !#if directive and no !#else directive, it will compile the code between !#if and !#endif only if the specified condition is true.

If there is an !#else directive, the code between !#if and !#else will be compiled if the condition is true, otherwise the code between !#else and !#endif will be compiled.

Condition supports all the basic logical operators, i.e. &&, ||, ! and parentheses.

Example:

!#if (adguard && !adguard_ext_safari)
||example.org^$third-party
!#endif

Include

The !#include directive supports only files from the same origin to make sure that the filter maintainer is in control of the specified file. The included file can also contain pre-processor directives (even other !#include directives).

Ad blockers should consider the case of recursive !#include and implement a protection mechanism.

Examples:

Filter URL: https://example.org/path/filter.txt

!
! Valid (same origin):
!#include https://example.org/path/includedfile.txt
!
! Valid (relative path):
!#include /includedfile.txt
!#include ../path2/includedfile.txt
!
! Invalid (another origin):
!#include https://example.com/path/includedfile.txt

Build

To build one file for browser environment:

yarn build

See ./dist directory for results.

Usage

Installation

yarn add @adguard/filters-downloader

const FilterCompilerConditionsConstants = {
    adguard: true,
    // ...
    adguard_ext_android_cb: false
};

// Option One
let promise = FiltersDownloader.download("resources/rules.txt", FilterCompilerConditionsConstants);
promise.then((compiled) => {
    // Success
}, (exception) => {
    // Error
});

// Option Two
let promise = FiltersDownloader.compile(['rule'], 'http://example.com', FilterCompilerConditionsConstants);
promise.then((compiled) => {
    // Success
}, (exception) => {
    // Error
});

// The downloadWithRaw() method downloads a filter, applies patches if possible and resolves conditionals;
// if patch applying fails, isPatchUpdateFailed will be true.
const { filter, rawFilter, isPatchUpdateFailed } = await FiltersDownloader.downloadWithRaw(
    url,
    {
        force: false,
        rawFilter: prevRawFilter,
    },
);

Tests

yarn test

Linter

yarn lint