(1) add a var/cache directory under spack. (2) downloads from URLFetchStrategy check the cache and skip the download if the source is available there.

lib/spack/spack/__init__.py

@@ -46,6 +46,8 @@
 stage_path     = join_path(var_path, "stage")
 repos_path     = join_path(var_path, "repos")
 share_path     = join_path(spack_root, "share", "spack")
+cache_path     = join_path(spack_root, "var", "cache")
+mkdirp(cache_path)
 
 prefix = spack_root
 opt_path       = join_path(prefix, "opt")

lib/spack/spack/fetch_strategy.py

@@ -156,6 +156,11 @@ def fetch(self):
         if self.archive_file:
             tty.msg("Already downloaded %s" % self.archive_file)
             return
+        cached = self.check_cache()
+        if cached:
+            tty.msg("Cached %s." % cached)
+            shutil.copy(cached, "./")
+            return
 
         tty.msg("Trying to fetch from %s" % self.url)
 
@@ -211,6 +216,9 @@ def fetch(self):
 
         if not self.archive_file:
             raise FailedDownloadError(self.url)
+        else:
+            shutil.copy(self.archive_file, spack.cache_path)
+
 
     @property
     def archive_file(self):
@@ -283,6 +291,17 @@ def check(self):
                     "%s checksum failed for %s" % (checker.hash_name, self.archive_file),
                     "Expected %s but got %s" % (self.digest, checker.sum))
 
+
+    def check_cache(self):
+        if not self.digest:
+            return
+        checker = crypto.Checker(self.digest)
+        paths = (join_path(spack.cache_path, f) for f in os.listdir(spack.cache_path))
+        for p in paths:
+            if checker.check(p):
+                return p
+
+
     @_needs_stage
     def reset(self):
         """Removes the source path if it exists, then re-expands the archive."""