Allow run::bind config to specify different destination

Until now, the directories mentioned in this config key have always been
mounted at the same absolute path in the container as they exist on the
host. Extend this to allow a different destination path in the container:

  ...
  [run]
  bind =
    ...
    /src-path:/dst-path
    ...

All of the usual options already recognized are valid for entries
specified using this expanded syntax.

Change-Id: Iaa0e70325f576d71ea672da082ce1a76c9c81c94

ci/test.py

@@ -582,6 +582,32 @@ def test_bad_bind_option(self):
         )
         self.assertIn("Error: bad option(s) 'bad-option' for bind", s)
 
+    def test_bind_dest(self):
+        temp_dir = tempfile.mkdtemp("-pyrex")
+        self.addCleanup(shutil.rmtree, temp_dir)
+
+        temp_file = os.path.join(temp_dir, "data")
+
+        conf = self.get_config()
+        conf["run"]["bind"] += " %s:/foo" % (temp_dir)
+        conf.write_conf()
+
+        self.assertPyrexContainerShellCommand("echo 123 > /foo/data")
+
+        with open(temp_file, "r") as f:
+            self.assertEqual(f.read(), "123\n")
+
+    def test_malformed_bind_dest(self):
+
+        b = "/src:/dst:illegal-token"
+
+        conf = self.get_config()
+        conf["run"]["bind"] += " %s" % b
+        conf.write_conf()
+
+        s = self.assertPyrexContainerShellCommand("true", capture=True, returncode=1)
+        self.assertIn("Error: too many colons in run.bind entry '%s'." % b, s)
+
     def test_bad_confversion(self):
         # Verify that a bad config is an error
         conf = self.get_config()

pyrex.py

@@ -59,6 +59,10 @@ def __init__(self, *args, **kwargs):
         self.optionxform = lambda option: option
 
 
+class ParsingError(Exception):
+    pass
+
+
 def read_default_config(keep_defaults):
     with open(os.path.join(PYREX_ROOT, "pyrex.ini"), "r") as f:
         line = f.read().replace("@CONFVERSION@", PYREX_CONFVERSION)
@@ -346,7 +350,23 @@ def parse_bind_options(bind):
             else:
                 bad_options.append(opt)
 
-    return bind, options, bad_options
+    if bad_options:
+        raise ParsingError(
+            "bad option(s) '%s' for bind %s" % (" ".join(bad_options), bind)
+        )
+
+    binds = bind.split(":")
+
+    if len(binds) > 2:
+        raise ParsingError("too many colons in run.bind entry '%s'." % bind)
+    elif len(binds) == 1:
+        src = bind
+        dst = bind
+    else:
+        src = binds[0]
+        dst = binds[1]
+
+    return src, dst, options
 
 
 def prep_container(
@@ -528,22 +548,23 @@ def prep_container(
         + extra_bind
     )
     for b in set(binds):
-        b, options, bad_options = parse_bind_options(b)
-        if bad_options:
-            print("Error: bad option(s) '%s' for bind %s" % (" ".join(bad_options), b))
+        try:
+            src, dst, options = parse_bind_options(b)
+        except ParsingError as e:
+            print("Error: %s" % e)
             return []
 
-        if not os.path.exists(b):
+        if not os.path.exists(src):
             if options.optional:
                 continue
-            print("Error: bind source path {b} does not exist".format(b=b))
+            print("Error: bind source path {src} does not exist".format(src=src))
             return []
 
         engine_args.extend(
             [
                 "--mount",
-                "type=bind,src={b},dst={b}{ro}".format(
-                    b=b, ro=",readonly" if options.readonly else ""
+                "type=bind,src={src},dst={dst}{ro}".format(
+                    src=src, dst=dst, ro=",readonly" if options.readonly else ""
                 ),
             ]
         )