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diff --git a/_posts/2018-08-01-verifying-npm-ci-reproducibility.md b/_posts/2018-08-01-verifying-npm-ci-reproducibility.md deleted file mode 100644 index efb5fea..0000000 --- a/_posts/2018-08-01-verifying-npm-ci-reproducibility.md +++ /dev/null @@ -1,153 +0,0 @@ ---- -title: Verifying "npm ci" reproducibility -date: 2018-08-01 -layout: post ---- -When -[npm\@5](https://blog.npmjs.org/post/161081169345/v500) came bringing -[package-locks](https://docs.npmjs.com/files/package-locks) with it, I -was confused about the benefits it provided, since running `npm install` -more than once could resolve all the dependencies again and yield yet -another fresh `package-lock.json` file. The message saying \"you should -add this file to version control\" left me hesitant on what to do[^1]. - -However the [addition of -`npm ci`](https://blog.npmjs.org/post/171556855892/introducing-npm-ci-for-faster-more-reliable) -filled this gap: it\'s a stricter variation of `npm install` which -guarantees that \"[subsequent installs are able to generate identical -trees](https://docs.npmjs.com/files/package-lock.json)\". But are they -really identical? I could see that I didn\'t have the same problems of -different installation outputs, but I didn\'t know for **sure** if it -was really identical. - -Computing the hash of a directory\'s content --------------------------------------------- - -I quickly searched for a way to check for the hash signature of an -entire directory tree, but I couldn\'t find one. I\'ve made a poor -man\'s [Merkle tree](https://en.wikipedia.org/wiki/Merkle_tree) -implementation using `sha256sum` and a few piped commands at the -terminal: - -``` {.bash .numberLines startFrom=""} -merkle-tree () { - dirname="${1-.}" - pushd "$dirname" - find . -type f | \ - sort | \ - xargs -I{} sha256sum "{}" | \ - sha256sum | \ - awk '{print $1}' - popd -} -``` - -Going through it line by line: - -- \#1 we define a Bash function called `merkle-tree`; -- \#2 it accepts a single argument: the directory to compute the - merkle tree from. If nothing is given, it runs on the current - directory (`.`); -- \#3 we go to the directory, so we don\'t get different prefixes in - `find`\'s output (like `../a/b`); -- \#4 we get all files from the directory tree. Since we\'re using - `sha256sum` to compute the hash of the file contents, we need to - filter out folders from it; -- \#5 we need to sort the output, since different file systems and - `find` implementations may return files in different orders; -- \#6 we use `xargs` to compute the hash of each file individually - through `sha256sum`. Since a file may contain spaces we need to - escape it with quotes; -- \#7 we compute the hash of the combined hashes. Since `sha256sum` - output is formatted like `<hash> <filename>`, it produces a - different final hash if a file ever changes name without changing - it\'s content; -- \#8 we get the final hash output, excluding the `<filename>` (which - is `-` in this case, aka `stdin`). - -### Positive points: - -1. ignore timestamp: running more than once on different installation - yields the same hash; -2. the name of the file is included in the final hash computation. - -### Limitations: - -1. it ignores empty folders from the hash computation; -2. the implementation\'s only goal is to represent using a digest - whether the content of a given directory is the same or not. Leaf - presence checking is obviously missing from it. - -### Testing locally with sample data - -``` {.bash .numberLines startFrom=""} -mkdir /tmp/merkle-tree-test/ -cd /tmp/merkle-tree-test/ -mkdir -p a/b/ a/c/ d/ -echo "one" > a/b/one.txt -echo "two" > a/c/two.txt -echo "three" > d/three.txt -merkle-tree . # output is be343bb01fe00aeb8fef14a3e16b1c3d1dccbf86d7e41b4753e6ccb7dc3a57c3 -merkle-tree . # output still is be343bb01fe00aeb8fef14a3e16b1c3d1dccbf86d7e41b4753e6ccb7dc3a57c3 -echo "four" > d/four.txt -merkle-tree . # output is now b5464b958969ed81815641ace96b33f7fd52c20db71a7fccc45a36b3a2ae4d4c -rm d/four.txt -merkle-tree . # output back to be343bb01fe00aeb8fef14a3e16b1c3d1dccbf86d7e41b4753e6ccb7dc3a57c3 -echo "hidden-five" > a/b/one.txt -merkle-tree . # output changed 471fae0d074947e4955e9ac53e95b56e4bc08d263d89d82003fb58a0ffba66f5 -``` - -It seems to work for this simple test case. - -You can try copying and pasting it to verify the hash signatures. - -Using `merkle-tree` to check the output of `npm ci` ---------------------------------------------------- - -*I\'ve done all of the following using Node.js v8.11.3 and npm\@6.1.0.* - -In this test case I\'ll take the main repo of -[Lerna](https://lernajs.io/)[^2]: - -``` {.bash .numberLines startFrom=""} -cd /tmp/ -git clone https://github.com/lerna/lerna.git -cd lerna/ -git checkout 57ff865c0839df75dbe1974971d7310f235e1109 -npm ci -merkle-tree node_modules/ # outputs 11e218c4ac32fac8a9607a8da644fe870a25c99821167d21b607af45699afafa -rm -rf node_modules/ -npm ci -merkle-tree node_modules/ # outputs 11e218c4ac32fac8a9607a8da644fe870a25c99821167d21b607af45699afafa -npm ci # test if it also works with an existing node_modules/ folder -merkle-tree node_modules/ # outputs 11e218c4ac32fac8a9607a8da644fe870a25c99821167d21b607af45699afafa -``` - -Good job `npm ci` :) - -\#6 and \#9 take some time to run (21 seconds in my machine), but this -specific use case isn\'t performance sensitive. The slowest step is -computing the hash of each individual file. - -Conclusion ----------- - -`npm ci` really \"generates identical trees\". - -I\'m not aware of any other existing solution for verifying the hash -signature of a directory. If you know any I\'d [like to -know](mailto:eu@euandre.org). - -*Edit* ------- - -2019/05/22: Fix spelling. - -[^1]: The - [documentation](https://docs.npmjs.com/cli/install#description) - claims `npm install` is driven by the existing `package-lock.json`, - but that\' actually [a little bit - tricky](https://github.com/npm/npm/issues/17979#issuecomment-332701215). - -[^2]: Finding a big known repo that actually committed the - `package-lock.json` file was harder than I expected. |