Most Regex engines will work very similarly (with minor differences). The dramatic difference is due to the way regular expressions get evaluated. But when given an invalid string, it takes nearly two seconds to complete the test, over ten times as long as it took to test a valid string. The entire process of testing it against a 30 characters long string takes around ~52ms. $ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCX")'ġ.79s user 0.02s system 99% cpu 1.812 total It most cases, it doesn't take very long for a regex engine to find a match: $ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCD")'Ġ.04s user 0.01s system 95% cpu 0.052 total The expression would match inputs such as ABBD, ABCCCCD, ABCBCCCD and ACCCCCD D Finally, we ensure this section of the string ends with a 'D'.The + at the end of this section states that we can look for one or more matches of this section. (B|C+)+ The string must then follow the letter A with either the letter 'B' or some number of occurrences of the letter 'C' (the + matches one or more times).A The string must start with the letter 'A'.This regular expression accomplishes the following: Let’s take the following regular expression as an example: regex = /A(B|C+)+D/ Regular expressions are incredibly powerful, but they aren't very intuitive and can ultimately end up making it easy for attackers to take your site down. The Regular expression Denial of Service (ReDoS) is a type of Denial of Service attack. There are many types of DoS attacks, ranging from trying to clog the network pipes to the system by generating a large volume of traffic from many machines (a Distributed Denial of Service - DDoS - attack) to sending crafted requests that cause a system to crash or take a disproportional amount of time to process. Var attack_str = "\u001B["+ " ".repeat(i* 10000) Ĭonsole.log( "attack_str.length: " + attack_str.length + ": " + time_cost+ " ms")ĭenial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its original and legitimate users. You can also use Imagemin by itself as a Node script.Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) due to the sub-patterns ()# ?]* and PoC import ansiRegex from 'ansi-regex' If you use one of these build tools, checkout the codelabs for Imagemin with webpack, gulp, or grunt. To compress the images in the "images/" directory and save them to the same directory, run the following command (overwrites the original files): $ imagemin images/* -out-dir =images Imagemin npm module # Imagemin uses the appropriate plugin based on the image format of the input. The Imagemin CLI works with 5 different plugins: imagemin-gifsicle, imagemin-jpegtran, imagemin-optipng, imagemin-pngquant, and imagemin-svgo. Image Format Lossy Plugin(s) Lossless Plugin(s) JPEG imagemin-mozjpeg imagemin-jpegtran PNG imagemin-pngquant imagemin-optipng GIF imagemin-giflossy imagemin-gifsicle SVG Imagemin-svgo WebP imagemin-webp Imagemin CLI # These aren't the only plugins available, but they'd all be good choices for your project. The table below lists popular Imagemin plugins. They offer significantly greater filesize savings, and you can customize the compression levels to meet your needs. If a plugin doesn't mention whether it is "lossy" or "lossless," you can tell by its API: if you can specify the image quality of the output, then it is "lossy."įor most people, lossy plugins are the best choice. Lossy compression reduces file size, but at the expense of possibly reducing image quality. The most important thing to consider when choosing a plugin is whether it is "lossy" or "lossless." In lossless compression, no data is lost. Popular image formats may have multiple plugins to pick from. Imagemin is built around "plugins." A plugin is an npm package that compresses a particular image format (e.g. Generally, the npm module is the best choice because it offers more configuration options, but the CLI can be a decent alternative if you want to try Imagemin without touching any code. Imagemin is available as both a CLI and an npm module. Imagemin is an excellent choice for image compression because it supports a wide variety of image formats and is easily integrated with build scripts and build tools. Lighthouse currently reports on opportunities to compress images in JPEG format only.
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