Re-use registry HTTP agent for package info requests

server/utils/getNpmPackageInfo.js

@@ -0,0 +1,55 @@
+const createCache = require("./createCache");
+const createMutex = require("./createMutex");
+const fetchNpmPackageInfo = require("./fetchNpmPackageInfo");
+
+const cache = createCache("packageInfo");
+const notFound = "PackageNotFound";
+
+const mutex = createMutex((packageName, callback) => {
+  cache.get(packageName, (error, value) => {
+    if (error) {
+      callback(error);
+    } else if (value != null) {
+      callback(null, value === notFound ? null : value);
+    } else {
+      fetchNpmPackageInfo(packageName).then(
+        value => {
+          if (value == null) {
+            // Cache 404s for 5 minutes. This prevents us from making
+            // unnecessary requests to the registry for bad package names.
+            // In the worst case, a brand new package's info will be
+            // available within 5 minutes.
+            cache.set(packageName, notFound, 300, () => {
+              callback(null, value);
+            });
+          } else {
+            // Cache valid package info for 1 minute.
+            cache.set(packageName, value, 60, () => {
+              callback(null, value);
+            });
+          }
+        },
+        error => {
+          // Do not cache errors.
+          cache.del(packageName, () => {
+            callback(error);
+          });
+        }
+      );
+    }
+  });
+});
+
+function getNpmPackageInfo(packageName) {
+  return new Promise((resolve, reject) => {
+    mutex(packageName, (error, value) => {
+      if (error) {
+        reject(error);
+      } else {
+        resolve(value);
+      }
+    });
+  });
+}
+
+module.exports = getNpmPackageInfo;