builder: use the same tar extract logic for all artifacts

Before only the staging area had symbolic links handled, now
strata and systems will have the same logic.

1 files changed, 81 insertions, 10 deletions

diff --git a/morphlib/bins.py b/morphlib/bins.py
index 8fd01182..3947e28d 100644
--- a/morphlib/bins.py
+++ b/morphlib/bins.py
@@ -24,6 +24,7 @@ Binaries are chunks, strata, and system images.
 import logging
 import os
 import re
+import stat
 import tarfile
 
 
@@ -109,17 +110,87 @@ def unpack_binary_from_file(f, dirname): # pragma: no cover
     '''
 
     tf = tarfile.open(fileobj=f)
-    tf.extractall(path=dirname)
-    tf.close()
-
-
-def unpack_binary(filename, dirname, ex):
-    '''Unpack a binary into a directory.
+        
+    # This is evil, but necessary. For some reason Python's system
+    # call wrappers (os.mknod and such) do not (always?) set the
+    # filename attribute of the OSError exception they raise. We
+    # fix that by monkey patching the tf instance with wrappers
+    # for the relevant methods to add things. The wrapper further
+    # ignores EEXIST errors, since we do not (currently!) care about
+    # overwriting files.
     
-    The directory must exist already.
+    def follow_symlink(path): # pragma: no cover
+        try:
+            return os.stat(path)
+        except OSError:
+            return None
     
-    '''
+    def prepare_extract(tarinfo, targetpath): # pragma: no cover
+        '''Prepare to extract a tar file member onto targetpath?
+        
+        If the target already exist, and we can live with it or
+        remove it, we do so. Otherwise, raise an error.
+        
+        It's OK to extract if:
+
+        * the target does not exist
+        * the member is a directory a directory and the 
+          target is a directory or a symlink to a directory
+          (just extract, no need to remove)
+        * the member is not a directory, and the target is not a directory
+          or a symlink to a directory (remove target, then extract)
+        
+        '''
+
+        try:
+            existing = os.lstat(targetpath)
+        except OSError:
+            return True # target does not exist
+
+        if tarinfo.isdir():
+            if stat.S_ISDIR(existing.st_mode):
+                return True
+            elif stat.S_ISLNK(existing.st_mode):
+                st = follow_symlink(targetpath)
+                return st and stat.S_ISDIR(st.st_mode)
+        else:
+            if stat.S_ISDIR(existing.st_mode):
+                return False
+            elif stat.S_ISLNK(existing.st_mode):
+                st = follow_symlink(targetpath)
+                if st and not stat.S_ISDIR(st.st_mode):
+                    os.remove(targetpath)
+                    return True
+            else:
+                os.remove(targetpath)
+                return True
+        return False
+
+    def monkey_patcher(real):
+        def make_something(tarinfo, targetpath): # pragma: no cover
+            prepare_extract(tarinfo, targetpath)
+            try:
+                return real(tarinfo, targetpath)
+            except OSError, e:
+                if e.errno != errno.EEXIST:
+                    if e.filename is None:
+                        e.filename = targetpath
+                        raise e
+                    else:
+                        raise
+        return make_something
+
+    tf.makedir = monkey_patcher(tf.makedir)
+    tf.makefile = monkey_patcher(tf.makefile)
+    tf.makeunknown = monkey_patcher(tf.makeunknown)
+    tf.makefifo = monkey_patcher(tf.makefifo)
+    tf.makedev = monkey_patcher(tf.makedev)
+    tf.makelink = monkey_patcher(tf.makelink)
 
-    logging.debug('Unpacking %s into %s' % (filename, dirname))
-    ex.runv(['tar', '-C', dirname, '-xvhf', filename])
+    tf.extractall(path=dirname)
+    tf.close
 
+def unpack_binary(filename, dirname):
+    f = open(filename, "rb")
+    unpack_binary_from_file(f, dirname)
+    f.close()