[monorepo] read empty content from its hash, in a shared blob store base (#36831)

The hash of empty content is a property of the content rather than of anything stored: every project's empty file has it, whether or not a blob was ever written under it, and a file may reference it before anything has. Eight blob stores were each paying a lookup -- a database query, an HTTP request, a read of a cache that offline mode may be the only thing standing in for -- to be told what the hash already says, and clsi had already reinvented the answer on its own. overleaf-editor-core gains BlobStoreBase, which answers getString for that hash and delegates the rest to the fetchString its subclasses provide. getObject comes with it: four stores spelled out the same JSON.parse of getString, and a fifth wrapped it in a log line. Adopted by history-v1's BlobStore, BackupBlobStore, HashCheckBlobStore and recover_zip's RecoveryBlobStore, by project-history's BlobStore, by clsi's BlobStore, and by web's HistoryBlobStore, SimpleBlobStore and FrontendBlobStore. history-v1 keeps its own answers in getStream, getBlob and getBlobs, which no other store implements. Writing and copying a blob are untouched, so a project that wrote empty content still has a blob for it and a read answers the same either way. Two paths could not handle a project holding a tracked change or a comment at all. Loading such a file needs the ranges blob its rangesHash points at, and hashing one again needs to write it back, so a store missing getObject or putObject fails outright: - recover_zip died on `blobStore.getObject is not a function`, making every such project unrecoverable. The test covering it asserts a tracked delete is absent from the zip, which the script already asked for and never reached. - GET /projects/:project_id/latest/hashed_content returned 500 from the same cause, then would have hit a missing putObject in snapshot.store. HashCheckBlobStore becomes a class over the base and gains putObject. Co-authored-by: Claude Opus 5 <noreply@anthropic.com> GitOrigin-RevId: c84f62465beff6cf77ffac26aa772984e1b554cb
2026-11-14 14:13:43 +01:00 · 2026-09-17 12:06:30 +00:00
parent 7608d738a6
commit 6caa5fc3a3
18 changed files with 646 additions and 71 deletions
@@ -0,0 +1,95 @@
+'use strict'
+
+const { expect } = require('chai')
+
+const { Blob, BlobStoreBase } = require('../..')
+
+class TestBlobStore extends BlobStoreBase {
+  constructor(contentByHash = {}) {
+    super()
+    this.contentByHash = contentByHash
+    this.fetched = []
+  }
+
+  async fetchString(hash) {
+    this.fetched.push(hash)
+    if (!(hash in this.contentByHash)) {
+      throw new Error(`nothing stored under ${hash}`)
+    }
+    return this.contentByHash[hash]
+  }
+}
+
+const HASH = 'a1b2c3d4e5f60718293a4b5c6d7e8f9012345678'
+
+describe('BlobStoreBase', function () {
+  describe('getString', function () {
+    it('fetches the content of a hash something stored', async function () {
+      const blobStore = new TestBlobStore({ [HASH]: 'hello world' })
+
+      expect(await blobStore.getString(HASH)).to.equal('hello world')
+      expect(blobStore.fetched).to.deep.equal([HASH])
+    })
+
+    it('answers the hash of empty content without fetching', async function () {
+      // The store below has nothing stored under it and throws when asked, which is
+      // the point: the hash says what the content is, so no store has to be asked.
+      const blobStore = new TestBlobStore()
+
+      expect(await blobStore.getString(Blob.EMPTY_HASH)).to.equal('')
+      expect(blobStore.fetched).to.have.length(0)
+    })
+
+    it('passes on what the implementation throws', async function () {
+      const blobStore = new TestBlobStore()
+
+      try {
+        await blobStore.getString(HASH)
+        expect.fail('should have thrown')
+      } catch (err) {
+        expect(err.message).to.equal(`nothing stored under ${HASH}`)
+      }
+    })
+  })
+
+  describe('getObject', function () {
+    it('deserializes the content of the hash', async function () {
+      const blobStore = new TestBlobStore({
+        [HASH]: '{"comments":[],"trackedChanges":[]}',
+      })
+
+      expect(await blobStore.getObject(HASH)).to.deep.equal({
+        comments: [],
+        trackedChanges: [],
+      })
+    })
+
+    it('fails on the hash of empty content, which is not JSON', async function () {
+      // Nothing writes an empty ranges blob -- JSON.stringify never yields empty
+      // content -- so a hash reaching here is one something stored.
+      const blobStore = new TestBlobStore()
+
+      try {
+        await blobStore.getObject(Blob.EMPTY_HASH)
+        expect.fail('should have thrown')
+      } catch (err) {
+        expect(err).to.be.an.instanceof(SyntaxError)
+      }
+    })
+  })
+
+  describe('fetchString', function () {
+    it('names the store that has not implemented it', async function () {
+      class IncompleteBlobStore extends BlobStoreBase {}
+
+      try {
+        await new IncompleteBlobStore().getString(HASH)
+        expect.fail('should have thrown')
+      } catch (err) {
+        expect(err.message).to.equal(
+          'IncompleteBlobStore does not implement fetchString(hash)'
+        )
+      }
+    })
+  })
+})