test and implementation to detect un-downloadable binaries

CHANGELOG.md

 ## Upcoming
 
 - Fix runtime signature cache invalidation
+- Provide error messaging for un-downloadable binaries
 
 ## v77
 

lib/binaries.sh

@@ -18,7 +18,8 @@ install_nodejs() {
 
   echo "Downloading and installing node $version..."
   local download_url="http://s3pository.heroku.com/node/v$version/node-v$version-$os-$cpu.tar.gz"
-  curl "$download_url" -s -o - | tar xzf - -C /tmp
+  curl "$download_url" --silent --fail -o /tmp/node.tar.gz || (echo "Unable to download node $version; does it exist?" && false)
+  tar xzf /tmp/node.tar.gz -C /tmp
   mv /tmp/node-v$version-$os-$cpu/* $dir
   chmod +x $dir/bin/*
 }
@@ -34,7 +35,8 @@ install_iojs() {
 
   echo "Downloading and installing iojs $version..."
   local download_url="https://iojs.org/dist/v$version/iojs-v$version-$os-$cpu.tar.gz"
-  curl $download_url -s -o - | tar xzf - -C /tmp
+  curl "$download_url" --silent --fail -o /tmp/node.tar.gz || (echo "Unable to download iojs $version; does it exist?" && false)
+  tar xzf /tmp/node.tar.gz -C /tmp
   mv /tmp/iojs-v$version-$os-$cpu/* $dir
   chmod +x $dir/bin/*
 }

test/fixtures/invalid-node-version/package.json → test/fixtures/invalid-io/package.json

@@ -6,7 +6,9 @@
     "type" : "git",
     "url" : "http://github.com/example/example.git"
   },
+  "dependencies": {
+  },
   "engines": {
-    "node": ">2.0"
+    "iojs": "2.0.99"
   }
 }

test/fixtures/invalid-node/README.md

+A fake README, to keep npm from polluting stderr.
\ No newline at end of file

test/fixtures/invalid-node/package.json

+{
+  "name": "node-buildpack-test-app",
+  "version": "0.0.1",
+  "description": "node buildpack integration test app",
+  "repository" : {
+    "type" : "git",
+    "url" : "http://github.com/example/example.git"
+  },
+  "dependencies": {
+  },
+  "engines": {
+    "node": "0.11.33"
+  }
+}

test/run

 #!/usr/bin/env bash
 # See README.md for info on running these tests.
 
+testInvalidNode() {
+  compile "invalid-node"
+  assertCaptured "Downloading and installing node 0.11.33"
+  assertCaptured "Unable to download node 0.11.33"
+  assertCapturedError
+}
+
+testInvalidIo() {
+  compile "invalid-io"
+  assertCaptured "Downloading and installing iojs 2.0.99"
+  assertCaptured "Unable to download iojs 2.0.99"
+  assertCapturedError
+}
+
 testBuildWithCache() {
   cache=$(mktmpdir)