Download files to a temporary location first

So we know when it finished successfully

Author: lukel97

README.md

@@ -17,7 +17,7 @@ This is the Visual Studio Code extension for the [Haskell programming language](
 ## Requirements
 
 - For standalone `.hs`/`.lhs` files, [ghc](https://www.haskell.org/ghc/) must be installed and on the PATH. The easiest way to install it is with [ghcup](https://www.haskell.org/ghcup/).
-- For Cabal based projects, [cabal-install](https://www.haskell.org/cabal/) must be installed and on the PATH. It can also be installed with [ghcup](https://www.haskell.org/ghcup/).
+- For Cabal based projects, both ghc and [cabal-install](https://www.haskell.org/cabal/) must be installed and on the PATH. It can also be installed with [ghcup](https://www.haskell.org/ghcup/).
 - For Stack based projects, [stack](http://haskellstack.org) must be installed and on the PATH.
 
 ## Supported GHC versions
@@ -79,13 +79,13 @@ There are a few placeholders which will be expanded:
 
 Haskell Language Server can display Haddock documentation on hover and in code completion for your code if you have built your project with haddock enabled.
 
-For stack projects, in your project directory run
+For Stack projects, in your project directory run
 
 ```bash
 $ stack haddock --keep-going
 ```
 
-For cabal projects, run
+For Cabal projects, run
 
 ```bash
 $ cabal build --haddock

src/hlsBinaries.ts

@@ -155,10 +155,6 @@ export async function downloadServer(
   const serverName = `haskell-language-server-${release.tag_name}-${process.platform}-${ghcVersion}${exeExtension}`;
   const binaryDest = path.join(context.globalStoragePath, serverName);
 
-  if (fs.existsSync(binaryDest)) {
-    return binaryDest;
-  }
-
   const title = `Downloading haskell-language-server ${release.tag_name} for GHC ${ghcVersion}`;
   try {
     await downloadFile(title, binaryURL, binaryDest);

src/utils.ts

@@ -15,10 +15,19 @@ import { createGunzip } from 'zlib';
 export const userAgentHeader = { 'User-Agent': 'vscode-hie-server' };
 
 export async function downloadFile(titleMsg: string, srcUrl: url.UrlWithStringQuery, dest: string): Promise<void> {
+  // If it already is downloaded just use that
   if (fs.existsSync(dest)) {
     return;
   }
 
+  // Download it to a .tmp location first, then rename it!
+  // This way if the download fails halfway through or something then we know
+  // to delete it and try again
+  const downloadDest = dest + '.download';
+  if (fs.existsSync(downloadDest)) {
+    fs.unlinkSync(downloadDest);
+  }
+
   const downloadHieTask = window.withProgress(
     {
       location: ProgressLocation.Notification,
@@ -34,7 +43,7 @@ export async function downloadFile(titleMsg: string, srcUrl: url.UrlWithStringQu
         };
         getWithRedirects(opts, (res) => {
           const totalSize = parseInt(res.headers['content-length'] || '1', 10);
-          const fileStream = fs.createWriteStream(dest, { mode: 0o744 });
+          const fileStream = fs.createWriteStream(downloadDest, { mode: 0o744 });
           let curSize = 0;
 
           // Decompress it if it's a gzip
@@ -58,14 +67,16 @@ export async function downloadFile(titleMsg: string, srcUrl: url.UrlWithStringQu
           fileStream.on('close', resolve);
         }).on('error', reject);
       });
-      return p;
+      await p;
+      // Finally rename it to the actual dest
+      fs.renameSync(downloadDest, dest);
     }
   );
 
   try {
     return downloadHieTask;
   } catch (e) {
-    fs.unlinkSync(dest);
+    fs.unlinkSync(downloadDest);
     throw new Error(`Failed to download ${url.format(srcUrl)}`);
   }
 }