Cache stream packages

packages/core/core/src/PackagerRunner.js

@@ -81,12 +81,15 @@ export default class PackagerRunner {
       map
     };
 
-    if (
-      cacheKey != null &&
-      // TODO This skips caching all packages that return Readable streams.
-      !(result.contents instanceof Readable)
-    ) {
+    if (cacheKey != null) {
       await this.writeToCache(cacheKey, result.contents, map);
+
+      if (result.contents instanceof Readable) {
+        return {
+          contents: this.options.cache.getStream(getContentKey(cacheKey)),
+          map: result.map
+        };
+      }
     }
 
     return result;
@@ -301,8 +304,8 @@ export default class PackagerRunner {
     contents: Readable,
     map: ?Readable
   |}> {
-    let contentKey = md5FromString(`${cacheKey}:content`);
-    let mapKey = md5FromString(`${cacheKey}:map`);
+    let contentKey = getContentKey(cacheKey);
+    let mapKey = getMapKey(cacheKey);
 
     let contentExists = await this.options.cache.blobExists(contentKey);
     if (!contentExists) {
@@ -318,12 +321,12 @@ export default class PackagerRunner {
   }
 
   async writeToCache(cacheKey: string, contents: Blob, map: ?Blob) {
-    let contentKey = md5FromString(`${cacheKey}:content`);
+    let contentKey = getContentKey(cacheKey);
 
     await this.options.cache.setStream(contentKey, blobToStream(contents));
 
     if (map != null) {
-      let mapKey = md5FromString(`${cacheKey}:map`);
+      let mapKey = getMapKey(cacheKey);
       await this.options.cache.setStream(mapKey, blobToStream(map));
     }
   }
@@ -410,3 +413,11 @@ function replaceReferences(
 
   return output;
 }
+
+function getContentKey(cacheKey: string) {
+  return md5FromString(`${cacheKey}:content`);
+}
+
+function getMapKey(cacheKey: string) {
+  return md5FromString(`${cacheKey}:map`);
+}