[ExternalSources] Cache downloads.

Closes #820

lib/cocoapods.rb

@@ -16,6 +16,20 @@ module Pod
     end
   end
 
+  # @return [String] The directory where CocoaPods caches the downloads.
+  #
+  # @todo   The {Installer::PodSourceInstaller} and the #{ExternalSources}
+  #         classes build and configure the downloader from scratch.
+  #
+  CACHE_ROOT = "~/Library/Caches/CocoaPods"
+
+  # @return [Fixnum] The maximum size for the cache expressed in Mb.
+  #
+  # @todo   The {Installer::PodSourceInstaller} and the #{ExternalSources}
+  #         classes build and configure the downloader from scratch.
+  #
+  MAX_CACHE_SIZE = 500
+
   require 'cocoapods-core'
   require 'xcodeproj'
   require 'cocoapods/downloader'

lib/cocoapods/external_sources.rb

@@ -122,6 +122,9 @@ module Pod
       #         marked as pre-downloaded indicating to the installer that only
       #         clean operations are needed.
       #
+      # @todo  The downloader configuration is the same of the
+      #        #{PodSourceInstaller} and it needs to be kept in sync.
+      #
       # @return [void]
       #
       def pre_download(sandbox)
@@ -129,6 +132,9 @@ module Pod
           target = sandbox.root + name
           target.rmtree if target.exist?
           downloader = Downloader.for_target(target, params)
+          downloader.cache_root = CACHE_ROOT
+          downloader.max_cache_size = MAX_CACHE_SIZE
+          downloader.aggressive_cache = false
           downloader.download
           store_podspec(sandbox, target + "#{name}.podspec")
           sandbox.store_pre_downloaded_pod(name)

lib/cocoapods/installer/pod_source_installer.rb

@@ -152,14 +152,6 @@ module Pod
 
       # @!group Dependencies
 
-      # @return [String] The directory where CocoaPods caches the downloads.
-      #
-      CACHE_ROOT = "~/Library/Caches/CocoaPods"
-
-      # @return [Fixnum] The maximum size for the cache expressed in Mb.
-      #
-      MAX_CACHE_SIZE = 500
-
       # @return [Downloader] The downloader to use for the retrieving the
       #         source.
       #