first commit

services/history-v1/storage/lib/chunk_buffer/index.js

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+'use strict'
+
+/**
+ * @module storage/lib/chunk_buffer
+ */
+
+const chunkStore = require('../chunk_store')
+const redisBackend = require('../chunk_store/redis')
+const metrics = require('@overleaf/metrics')
+/**
+ * Load the latest Chunk stored for a project, including blob metadata.
+ *
+ * @param {string} projectId
+ * @return {Promise.<Chunk>}
+ */
+async function loadLatest(projectId) {
+  const cachedChunk = await redisBackend.getCurrentChunk(projectId)
+  const chunkRecord = await chunkStore.loadLatestRaw(projectId)
+  const cachedChunkIsValid = redisBackend.checkCacheValidityWithMetadata(
+    cachedChunk,
+    chunkRecord
+  )
+  if (cachedChunkIsValid) {
+    metrics.inc('chunk_buffer.loadLatest', 1, {
+      status: 'cache-hit',
+    })
+    return cachedChunk
+  } else {
+    metrics.inc('chunk_buffer.loadLatest', 1, {
+      status: 'cache-miss',
+    })
+    const chunk = await chunkStore.loadLatest(projectId)
+    await redisBackend.setCurrentChunk(projectId, chunk)
+    return chunk
+  }
+}
+
+module.exports = {
+  loadLatest,
+}