npm ci post review

1 files changed, 27 insertions, 22 deletions

diff --git a/site/posts/2018-08-01-testing-npm-ci-reproducible-dependencies.org b/site/posts/2018-08-01-testing-npm-ci-reproducible-dependencies.org
index 80d7049..73db53e 100644
--- a/site/posts/2018-08-01-testing-npm-ci-reproducible-dependencies.org
+++ b/site/posts/2018-08-01-testing-npm-ci-reproducible-dependencies.org
@@ -1,12 +1,12 @@
 ---
-title: Testing npm ci reproducible dependencies
+title: Verifying npm ci reproducibility
 date: 2018-08-01
 ---
-When [[https://blog.npmjs.org/post/161081169345/v500][npm@5]] came and along bringing [[https://docs.npmjs.com/files/package-locks][package-locks]] with it, I was confused on the benefits it provided, since running =npm install= more than once could resolve all the dependencies again and yield yet another =package-lock.json= fresh file. The message saying "you should add this file to version control" left me hesitant on what to do[fn:npm-install].
+When [[https://blog.npmjs.org/post/161081169345/v500][npm@5]] came bringing [[https://docs.npmjs.com/files/package-locks][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 =package-lock.json= fresh file. The message saying "you should add this file to version control" left me hesitant on what to do[fn:npm-install].
 
-However the [[https://blog.npmjs.org/post/171556855892/introducing-npm-ci-for-faster-more-reliable][addition of =npm ci= ]] filled this gapped: it's a more strict variation of =npm install= which guarantees that "[[https://docs.npmjs.com/files/package-lock.json][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.
+However the [[https://blog.npmjs.org/post/171556855892/introducing-npm-ci-for-faster-more-reliable][addition of =npm ci=]] filled this gapped: it's a stricter variation of =npm install= which guarantees that "[[https://docs.npmjs.com/files/package-lock.json][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
-I quickly searched for a way to check for the hash signature of a full combined directory tree, but I couldn't find one. I've made a poor man's [[https://en.wikipedia.org/wiki/Merkle_tree][Merkle tree]] implementation using =sha256sum= and a few piped comands at the terminal:
+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 [[https://en.wikipedia.org/wiki/Merkle_tree][Merkle tree]] implementation using =sha256sum= and a few piped comands at the terminal:
 #+BEGIN_SRC bash -n
   merkle-tree () {
     dirname="${1-.}"
@@ -20,25 +20,21 @@ I quickly searched for a way to check for the hash signature of a full combined
   }
 #+END_SRC
 Going through it line by line:
-- at #1 we create a Bash function called =merkle-tree=;
-- at #2 it accepts a single argument: the directory to compute the merkle tree from. If nothing is given, it runs on the current directory (=.=);
-- at #3 we go to the directory, so we don't get different prefixes in =find='s output (like =../a/b=);
-- at #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;
-- at #5 we need to sort the output, since different filesystems and =find= implementations may return files in different orders;
-- at #6 we use =xargs= to compute the hash of each file individually through =sha256sum=. Since a file may contain spaces we need to embed it within quotes;
-- at #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;
-- at #8 we get the final hash output, excluding the =<filename>= (which is =-= in this case, aka =stdin=).
-
-Positive points:
-
+- #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 filesystems 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 scape 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;
-
-Limitations:
-
+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:
+*** Testing locally with sample data
 #+BEGIN_SRC bash -n
   mkdir /tmp/merkle-tree-test/
   cd /tmp/merkle-tree-test/
@@ -56,6 +52,8 @@ Testing locally with sample data:
   merkle-tree . # output changed  471fae0d074947e4955e9ac53e95b56e4bc08d263d89d82003fb58a0ffba66f5
 #+END_SRC
 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./
 
@@ -70,9 +68,16 @@ In this test case I'll take the main repo of [[https://lernajs.io/][Lerna]][fn:j
   rm -rf node_modules/
   npm ci
   merkle-tree node_modules/
+  npm ci      # test if it also works with an existing node_modules/ folder
+  merkle-tree node_modules/
 #+END_SRC
 Good job =npm ci= :)
 
-#6 and #9 take some time to run (21s in my machine), but this specific use case isn't performance sensitive.
+#6 and #9 take some time to run (21s 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 [[mailto:eu@euandre.org][like to know]].
+
 [fn:npm-install] The [[https://docs.npmjs.com/cli/install#description][documentation]] claims =npm install= is driven by the existing =package-lock.json=, but that' actually [[https://github.com/npm/npm/issues/17979#issuecomment-332701215][a little bit tricky]].
-[fn:js-repos] It was harder than I expected when I tried to find a big known repo that actually committed the =package-lock.json= file.
+[fn:js-repos] Finding a big known repo that actually committed the =package-lock.json= file was harder than I expected.