Simplify readFirstAvailableStream() (#6022)

* The calling function already knows which paths we tried

* This generic function isn't specific to tarballs

* Return only non-null paths, and return them as an array

This makes the function more convenient to use

* Only use real paths in readFirstAvailableStream()

* Return stream directly

src/fetchers/git-fetcher.js

@@ -59,23 +59,24 @@ export default class GitFetcher extends BaseFetcher {
     return path.join(this.dest, constants.TARBALL_FILENAME);
   }
 
-  *getLocalPaths(override: ?string): Generator<?string, void, void> {
-    if (override) {
-      yield path.resolve(this.config.cwd, override);
-    }
-    yield this.getTarballMirrorPath();
-    yield this.getTarballMirrorPath({
-      withCommit: false,
-    });
-    yield this.getTarballCachePath();
+  getLocalPaths(override: ?string): Array<string> {
+    const paths: Array<?string> = [
+      override ? path.resolve(this.config.cwd, override) : null,
+      this.getTarballMirrorPath(),
+      this.getTarballMirrorPath({withCommit: false}),
+      this.getTarballCachePath(),
+    ];
+    // $FlowFixMe: https://github.com/facebook/flow/issues/1414
+    return paths.filter(path => path != null);
   }
 
   async fetchFromLocal(override: ?string): Promise<FetchedOverride> {
-    const {stream, triedPaths} = await fsUtil.readFirstAvailableStream(this.getLocalPaths(override));
+    const tarPaths = this.getLocalPaths(override);
+    const stream = await fsUtil.readFirstAvailableStream(tarPaths);
 
     return new Promise((resolve, reject) => {
       if (!stream) {
-        reject(new MessageError(this.reporter.lang('tarballNotInNetworkOrCache', this.reference, triedPaths)));
+        reject(new MessageError(this.reporter.lang('tarballNotInNetworkOrCache', this.reference, tarPaths)));
         return;
       }
       invariant(stream, 'cachedStream should be available at this point');

src/fetchers/tarball-fetcher.js

@@ -118,20 +118,23 @@ export default class TarballFetcher extends BaseFetcher {
     return {validateStream, extractorStream};
   }
 
-  *getLocalPaths(override: ?string): Generator<?string, void, void> {
-    if (override) {
-      yield path.resolve(this.config.cwd, override);
-    }
-    yield this.getTarballMirrorPath();
-    yield this.getTarballCachePath();
+  getLocalPaths(override: ?string): Array<string> {
+    const paths: Array<?string> = [
+      override ? path.resolve(this.config.cwd, override) : null,
+      this.getTarballMirrorPath(),
+      this.getTarballCachePath(),
+    ];
+    // $FlowFixMe: https://github.com/facebook/flow/issues/1414
+    return paths.filter(path => path != null);
   }
 
   async fetchFromLocal(override: ?string): Promise<FetchedOverride> {
-    const {stream, triedPaths} = await fsUtil.readFirstAvailableStream(this.getLocalPaths(override));
+    const tarPaths = this.getLocalPaths(override);
+    const stream = await fsUtil.readFirstAvailableStream(tarPaths);
 
     return new Promise((resolve, reject) => {
       if (!stream) {
-        reject(new MessageError(this.reporter.lang('tarballNotInNetworkOrCache', this.reference, triedPaths)));
+        reject(new MessageError(this.reporter.lang('tarballNotInNetworkOrCache', this.reference, tarPaths)));
         return;
       }
       invariant(stream, 'stream should be available at this point');

src/util/fs.js

@@ -814,24 +814,16 @@ export async function makeTempDir(prefix?: string): Promise<string> {
   return dir;
 }
 
-export async function readFirstAvailableStream(
-  paths: Iterable<?string>,
-): Promise<{stream: ?ReadStream, triedPaths: Array<string>}> {
-  let stream: ?ReadStream;
-  const triedPaths = [];
-  for (const tarballPath of paths) {
-    if (tarballPath) {
-      try {
-        const fd = await open(tarballPath, 'r');
-        stream = fs.createReadStream(tarballPath, {fd});
-        break;
-      } catch (err) {
-        // Try the next one
-        triedPaths.push(tarballPath);
-      }
+export async function readFirstAvailableStream(paths: Iterable<string>): Promise<?ReadStream> {
+  for (const path of paths) {
+    try {
+      const fd = await open(path, 'r');
+      return fs.createReadStream(path, {fd});
+    } catch (err) {
+      // Try the next one
     }
   }
-  return {stream, triedPaths};
+  return null;
 }
 
 export async function getFirstSuitableFolder(