Implement requirements layer caching

Author: Maciej Wilczyński

lib/layer.js

@@ -3,6 +3,7 @@ const fse = require('fs-extra');
 const path = require('path');
 const JSZip = require('jszip');
 const { writeZip, addTree } = require('./zipTree');
+const {sha256Path, getRequirementsLayerPath} = require("./shared");
 
 BbPromise.promisifyAll(fse);
 
@@ -11,13 +12,33 @@ BbPromise.promisifyAll(fse);
  * @return {Promise} the JSZip object constructed.
  */
 function zipRequirements() {
-  const rootZip = new JSZip();
   const src = path.join('.serverless', 'requirements');
-  const runtimepath = 'python';
-
-  return addTree(rootZip.folder(runtimepath), src).then(() =>
-    writeZip(rootZip, path.join('.serverless', 'pythonRequirements.zip'))
+  const reqChecksum = sha256Path(path.join('.serverless', 'requirements.txt'));
+  const targetZipPath = path.join('.serverless', 'pythonRequirements.zip');
+  const zipCachePath = getRequirementsLayerPath(
+    reqChecksum,
+    targetZipPath,
+    this.options
   );
+
+  const promises = [];
+  if (fse.existsSync(zipCachePath)) {
+    this.serverless.cli.log("Found cached Python Requirements Lambda Layer file");
+  } else {
+    const rootZip = new JSZip();
+    const runtimepath = 'python';
+
+    promises.push(
+      addTree(rootZip.folder(runtimepath), src).then(() =>
+          writeZip(rootZip, zipCachePath)
+      )
+    );
+  }
+  return BbPromise.all(promises).then(() => {
+    if (zipCachePath !== targetZipPath) {
+      fse.symlink(zipCachePath, targetZipPath, 'file')
+    }
+  });
 }
 
 /**

lib/shared.js

@@ -76,6 +76,28 @@ function getRequirementsWorkingPath(
   return path.join(requirementsTxtDirectory, 'requirements');
 }
 
+/**
+ * Path of a cached requirements layer archive file
+ * @param  {string} subfolder
+ * @param  {string} fallback
+ * @param  {Object} options
+ * @return {string}
+ */
+function getRequirementsLayerPath(
+  hash,
+  fallback,
+  options
+) {
+  // If we want to use the static cache
+  if (hash && options && options.useStaticCache) {
+    hash = hash + '_slspyc.zip';
+    return path.join(getUserCachePath(options), hash);
+  }
+
+  // If we don't want to use the static cache, then fallback to requirements file in .serverless directory
+  return fallback;
+}
+
 /**
  * The static cache path that will be used for this system + options, used if static cache is enabled
  * @param  {Object} options
@@ -107,6 +129,7 @@ function sha256Path(fullpath) {
 module.exports = {
   checkForAndDeleteMaxCacheVersions,
   getRequirementsWorkingPath,
+  getRequirementsLayerPath,
   getUserCachePath,
   sha256Path,
 };