Issue #10955: zipimport uses ASCII at bootstrap

zipimport uses ASCII encoding instead of cp497 to decode filenames, at
bootstrap, if the codec registry is not ready yet. It is still possible to have
non-ASCII filenames using the Unicode flag (UTF-8 encoding) for file entries in
the ZIP file.

Misc/NEWS

@@ -16,6 +16,11 @@ Core and Builtins
 Library
 -------
 
+- Issue #10955: zipimport uses ASCII encoding instead of cp497 to decode
+  filenames, at bootstrap, if the codec registry is not ready yet. It is still
+  possible to have non-ASCII filenames using the Unicode flag (UTF-8 encoding)
+  for file entries in the ZIP file.
+
 - Issue #10949: Improved robustness of rotating file handlers.
 
 - Issue #10955: Fix a potential crash when trying to mmap() a file past its

Modules/zipimport.c

@@ -725,6 +725,7 @@ read_directory(PyObject *archive_obj)
     long arc_offset; /* offset from beginning of file to start of zip-archive */
     PyObject *pathobj;
     const char *charset;
+    int bootstrap;
 
     if (PyUnicode_GET_SIZE(archive_obj) > MAXPATHLEN) {
         PyErr_SetString(PyExc_OverflowError,
@@ -801,13 +802,30 @@ read_directory(PyObject *archive_obj)
         *p = 0;         /* Add terminating null byte */
         header_offset += header_size;
 
+        bootstrap = 0;
         if (flags & 0x0800)
             charset = "utf-8";
+        else if (!PyThreadState_GET()->interp->codecs_initialized) {
+            /* During bootstrap, we may need to load the encodings
+               package from a ZIP file. But the cp437 encoding is implemented
+               in Python in the encodings package.
+
+               Break out of this dependency by assuming that the path to
+               the encodings module is ASCII-only. */
+            charset = "ascii";
+            bootstrap = 1;
+        }
         else
             charset = "cp437";
         nameobj = PyUnicode_Decode(name, name_size, charset, NULL);
-        if (nameobj == NULL)
+        if (nameobj == NULL) {
+            if (bootstrap)
+                PyErr_Format(PyExc_NotImplementedError,
+                    "bootstrap issue: python%i%i.zip contains non-ASCII "
+                    "filenames without the unicode flag",
+                    PY_MAJOR_VERSION, PY_MINOR_VERSION);
             goto error;
+        }
         Py_UNICODE_strncpy(path + length + 1, PyUnicode_AS_UNICODE(nameobj), MAXPATHLEN - length - 1);
 
         pathobj = PyUnicode_FromUnicode(path, Py_UNICODE_strlen(path));