allow usage of multiple nodejs versions

bin/compile

 #!/usr/bin/env bash
 # bin/compile <build-dir> <cache-dir>
 
-mktmpdir() {
+# fail fast
+set -e
+
+function error() {
+  echo " !     $*"
+  exit 1
+}
+
+function mktmpdir() {
   dir=$(mktemp -t node-$1-XXXX)
   rm -rf $dir
   mkdir -p $dir
@@ -30,12 +38,19 @@ run_npm() {
 unset GIT_DIR
 
 function manifest_versions() {
-  curl "http://${S3_BUCKET}.s3.amazonaws.com/manifest.${1}" -s -o -
+  curl "http://${S3_BUCKET}.s3.amazonaws.com/manifest.${1}" -s -o - | tr -s '\n' ' '
+}
+
+function resolve_versions() {
+  args=""
+  for version in $1; do args="${args} -v \"${version}\""; done
+  for version in $2; do args="${args} -r \"${version}\""; done
+  eval vendor/node-semver/bin/semver ${args} | tail -r | head -n1
 }
 
 # config
-NODE_VERSION="0.4.7"
-NPM_VERSION="1.0.94"
+DEFAULT_NODE_VERSION="0.4.7"
+DEFAULT_NPM_VERSION="1.0.94"
 SCONS_VERSION="1.2.0"
 S3_BUCKET="heroku-buildpack-nodejs"
 
@@ -46,6 +61,49 @@ LP_DIR=`cd $(dirname $0); cd ..; pwd`
 CACHE_STORE_DIR="$CACHE_DIR/node_modules/$NPM_VERSION"
 CACHE_TARGET_DIR="$BUILD_DIR/node_modules"
 
+# determine available versions
+NODEJS_VERSIONS=$(manifest_versions "nodejs")
+NPM_VERSIONS=$(manifest_versions "npm")
+
+# determine requested versions
+engines=$(cat $BUILD_DIR/package.json | $LP_DIR/vendor/json/json engines 2>&1)
+
+if [ $? == 0 ] && [ "$engines" != "" ]; then
+  REQUESTED_NODE_VERSION=$(cat $BUILD_DIR/package.json | $LP_DIR/vendor/json/json engines.node)
+  REQUESTED_NPM_VERSION=$(cat $BUILD_DIR/package.json | $LP_DIR/vendor/json/json engines.npm 2>&1)
+else
+  REQUESTED_NODE_VERSION=""
+  REQUESTED_NPM_VERSION=""
+fi
+
+# resolve node version
+if [ "${REQUESTED_NODE_VERSION}" == "" ]; then
+  NODE_VERSION=${DEFAULT_NODE_VERSION}
+else
+  RESOLVED_NODE=$(resolve_versions "${NODEJS_VERSIONS}" "${REQUESTED_NODE_VERSION}")
+
+  if [ "${RESOLVED_NODE}" == "" ]; then
+    error "Requested Node.js version: ${REQUESTED_NODE_VERSION} does not match available versions: ${NODEJS_VERSIONS}"
+  else
+    NODE_VERSION=${RESOLVED_NODE}
+  fi
+fi
+echo "-----> Using Node.js version: ${NODE_VERSION}"
+
+# resolve npm version
+if [ "${REQUESTED_NPM_VERSION}" == "" ]; then
+  NPM_VERSION=${DEFAULT_NPM_VERSION}
+else
+  RESOLVED_NPM=$(resolve_versions "${NPM_VERSIONS}" "${REQUESTED_NPM_VERSION}")
+
+  if [ "${RESOLVED_NPM}" == "" ]; then
+    error "Requested Node.js version: ${REQUESTED_NPM_VERSION} does not match available versions: ${NPMJS_VERSIONS}"
+  else
+    NPM_VERSION=${RESOLVED_NPM}
+  fi
+fi
+echo "-----> Using npm version: ${NPM_VERSION}"
+
 # s3 packages
 NODE_PACKAGE="http://${S3_BUCKET}.s3.amazonaws.com/nodejs-${NODE_VERSION}.tgz"
 NPM_PACKAGE="http://${S3_BUCKET}.s3.amazonaws.com/npm-${NPM_VERSION}.tgz"
@@ -56,9 +114,6 @@ VENDORED_NODE="$(mktmpdir node)"
 VENDORED_NPM="$(mktmpdir npm)"
 VENDORED_SCONS="$(mktmpdir scons)"
 
-# determine node version
-echo "available versions of node: $(manifest_versions "nodejs")"
-
 # download and unpack packages
 echo "-----> Fetching Node.js binaries"
 mkdir -p $VENDORED_NODE  && curl $NODE_PACKAGE -s -o -  | tar xzf - -C $VENDORED_NODE
@@ -67,7 +122,7 @@ mkdir -p $VENDORED_SCONS && curl $SCONS_PACKAGE -s -o - | tar xzf - -C $VENDORED
 
 # vendor node into the slug
 PATH="$BUILD_DIR/bin:$PATH"
-echo "-----> Vendoring node $NODE_VERSION"
+echo "-----> Vendoring node into slug"
 mkdir -p "$BUILD_DIR/bin"
 cp "$VENDORED_NODE/bin/node" "$BUILD_DIR/bin/node"
 
@@ -100,11 +155,15 @@ if [ -d $CACHE_STORE_DIR ]; then
 fi
 
 # install dependencies with npm
-echo "-----> Installing dependencies with npm $NPM_VERSION"
-
+echo "-----> Installing dependencies with npm"
 cd $BUILD_DIR
-run_npm install
-run_npm rebuild
+HOME="$BUILD_DIR" $VENDORED_NODE/bin/node $VENDORED_NPM/cli.js prune 2>&1 | indent
+HOME="$BUILD_DIR" $VENDORED_NODE/bin/node $VENDORED_NPM/cli.js install 2>&1 | indent
+if [ "${PIPESTATUS[*]}" != "0 0" ]; then
+  error "Failed to install dependencies with npm"
+else
+  echo "       Dependencies installed"
+fi
 
 echo "Dependencies installed" | indent