download to temporary file first. then move to it's place

lib/cloud.js

@@ -1,5 +1,9 @@
-import { createRelease, downloadAsset, getRelease, uploadAsset } from './github.js';
+import { createRelease, downloadAsset,
+  getRelease, uploadAsset } from './github.js';
+import { mkdirp, remove } from 'fs-promise';
 import assert from 'assert';
+import { moveFile } from './copy-file.js';
+import path from 'path';
 import { version } from '../package.json';
 
 function uniqueName (remote, names) {
@@ -36,6 +40,10 @@ export async function download (remote, local) {
   if (!assets.length) return false;
   assert(assets.length === 1);
   const asset = assets[0];
-  await downloadAsset(asset, local);
+  const tempFile = local + '.downloading';
+  await mkdirp(path.dirname(tempFile));
+  await downloadAsset(asset, tempFile);
+  await moveFile(tempFile, local);
+  await remove(tempFile);
   return true;
 }

lib/copy-file.js

@@ -3,3 +3,7 @@ import fs from 'fs-promise';
 export function copyFile (src, dest) {
   return fs.copy(src, dest);
 }
+
+export function moveFile (src, dest) {
+  return fs.move(src, dest);
+}

lib/github.js

@@ -51,16 +51,16 @@ export function createRelease (tag) {
   });
 }
 
-export function uploadAsset (local, release, name) {
+export function uploadAsset (file, release, name) {
   assert(!(/[\\/]/.test(name)));
   return new Promise((resolve, reject) => {
-    fs.stat(local, (error, stat) => {
+    fs.stat(file, (error, stat) => {
       if (error) return reject(error);
       const headers = {
         'Content-Length': stat.size,
         'Content-Type': 'application/octet-stream'
       };
-      const rs = fs.createReadStream(local);
+      const rs = fs.createReadStream(file);
       const subst = `?name=${name}`;
       const url = release.upload_url.replace(/\{\?name,label\}/, subst);
       const req = request2.post(url, { headers }, (error2, response, body) => {
@@ -72,10 +72,10 @@ export function uploadAsset (local, release, name) {
   });
 }
 
-export function downloadAsset (asset, local) {
+export function downloadAsset (asset, file) {
   return new Promise((resolve, reject) => {
     const headers = { Accept: 'application/octet-stream' };
-    const ws = fs.createWriteStream(local);
+    const ws = fs.createWriteStream(file);
     const url = asset.url;
     const req = request2.get(url, { headers }, (error, response) => {
       if (error) return reject(error);

lib/index.js

@@ -1,11 +1,10 @@
 import * as system from './system.js';
-import { exists, mkdirp } from 'fs-promise';
 import { hostArch, hostPlatform } from './system.js'; // eslint-disable-line no-duplicate-imports
 import { localPlace, remotePlace } from './places.js';
 import assert from 'assert';
 import { download } from './cloud.js';
+import { exists } from 'fs-promise';
 import patchesJson from '../patches/patches.json';
-import path from 'path';
 import semver from 'semver';
 import { version } from '../package.json';
 
@@ -39,7 +38,6 @@ export async function need ({
   }
   if (!dontDownload) {
     const remote = remotePlace({ arch, nodeVersion, platform, version });
-    await mkdirp(path.dirname(local));
     if (await download(remote, local)) return local;
   }
   if (!dontBuild) {