= Verifying "npm ci" reproducibility :updatedat: 2019-05-22 :empty: :npm-5: https://blog.npmjs.org/post/161081169345/v500 :package-locks-old: https://docs.npmjs.com/files/package-locks :package-lock: https://docs.npmjs.com/files/package-lock.json :add-npm-ci: https://blog.npmjs.org/post/171556855892/introducing-npm-ci-for-faster-more-reliable :cli-docs: https://docs.npmjs.com/cli/install#description :tricky-issue: https://github.com/npm/npm/issues/17979#issuecomment-332701215 When {npm-5}[npm@5] came bringing {package-locks-old}[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{empty}footnote:package-lock-message[ {cli-docs}[documentation] claims `npm install` is driven by the existing `package-lock.json`, but that's actually {tricky-issue}[a little bit tricky]. ]. However the {add-npm-ci}[addition of `npm ci`] filled this gap: it's a stricter variation of `npm install` which guarantees that "{package-lock}[subsequent installs are able to generate identical trees]". 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 :merkle-tree: https://en.wikipedia.org/wiki/Merkle_tree 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}[Merkle tree] implementation using `sha256sum` and a few piped commands at the terminal: [source,sh] ---- 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 ` `, 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 `` (which is `-` in this case, aka `stdin`). === Positive points: . ignore timestamp: running more than once on different installation yields the same hash; . the name of the file is included in the final hash computation. === Limitations: . it ignores empty folders from the hash computation; . 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 [source,sh] ---- 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 https://lernajs.io/[Lerna]footnote:lerna-package-lock[ Finding a big known repo that actually committed the `package-lock.json` file was harder than I expected. ]: ```bash 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, shoot me an email, as I'd like to know it. == *Edit* 2019-05-22: Fix spelling.