Added a class that implements read only of a file.

The file is expected to contain a set of information pieces. One per line.
The class acts like a list, except that it's non-mutable..

example/flask_op/static/jwks.json

@@ -1 +1 @@
-{"keys": [{"kty": "RSA", "use": "sig", "kid": "bXNmZXROQ3N2dDI2SWY5VlNWTG5yOXZqYlpLenVsalhwUWR5RW9BMHNCaw", "n": "uGVI-b6qr-OTc2knp7bpmDtiCQoWFXZ8mUV-SX0rCMtcc_IRmc_J7AfNEfnYk3dv0cKQK_Dgv3vicoeuf4KQ9ZZY-xI3bnRl9_HnhRpz_cJScDirkNKlsv8aQuYBO_gIiHp8B32YC0nx3BUQV5I6QGEiyG-lZT9PmXsUO1uKPPhny_vtQ6cUpvtuLySBu2ZYpaTDQqCv5Y6EKC49NYWhBB4B6f6TNKCoQTaxA8ZoM3lh7kFbu5DPEXKFAtuNiOtUNP7Ei9KfBtyBYSaZQBY8VkwAm1yKCA2sfv1mBwx0dT53MPJlNkoltf89mv1NM2OJPQAgGE6ygwGS2fyBLAn_bQ", "e": "AQAB"}, {"kty": "EC", "use": "sig", "kid": "U0pLNmFBRE4waDYyZG9ZdjNPb2pTZXAwZzdrbmpZdG0ya3lpaFJwZU9ncw", "crv": "P-256", "x": "DYUyBfiD53SEtUuKLjFCFpIkqyhbmBppAMjOat9qiY0", "y": "-SUSvVeOv7EA84qHLLEkDP24iZree-fomICuA4baeeA"}]}
+{"keys": [{"kty": "RSA", "use": "sig", "kid": "bXNmZXROQ3N2dDI2SWY5VlNWTG5yOXZqYlpLenVsalhwUWR5RW9BMHNCaw", "e": "AQAB", "n": "uGVI-b6qr-OTc2knp7bpmDtiCQoWFXZ8mUV-SX0rCMtcc_IRmc_J7AfNEfnYk3dv0cKQK_Dgv3vicoeuf4KQ9ZZY-xI3bnRl9_HnhRpz_cJScDirkNKlsv8aQuYBO_gIiHp8B32YC0nx3BUQV5I6QGEiyG-lZT9PmXsUO1uKPPhny_vtQ6cUpvtuLySBu2ZYpaTDQqCv5Y6EKC49NYWhBB4B6f6TNKCoQTaxA8ZoM3lh7kFbu5DPEXKFAtuNiOtUNP7Ei9KfBtyBYSaZQBY8VkwAm1yKCA2sfv1mBwx0dT53MPJlNkoltf89mv1NM2OJPQAgGE6ygwGS2fyBLAn_bQ"}, {"kty": "EC", "use": "sig", "kid": "U0pLNmFBRE4waDYyZG9ZdjNPb2pTZXAwZzdrbmpZdG0ya3lpaFJwZU9ncw", "crv": "P-256", "x": "DYUyBfiD53SEtUuKLjFCFpIkqyhbmBppAMjOat9qiY0", "y": "-SUSvVeOv7EA84qHLLEkDP24iZree-fomICuA4baeeA"}]}

src/idpyoidc/storage/listfile.py

@@ -0,0 +1,94 @@
+import logging
+import os
+import time
+
+from filelock import FileLock
+
+logger = logging.getLogger(__name__)
+
+
+class ReadOnlyListFile(object):
+
+    def __init__(self, file_name):
+        self.file_name = file_name
+        self.fmtime = 0
+        self.lst = None
+
+        if not os.path.exists(file_name):
+            fp = open(file_name, "x")
+            fp.close()
+
+
+    def __getitem__(self, item):
+        if self.is_changed(self.file_name):
+            self.lst = self._read_info(self.file_name)
+        return self.lst[item]
+
+    def __len__(self):
+        if self.is_changed(self.file_name):
+            self.lst = self._read_info(self.file_name)
+        if self.lst is None or self.lst == []:
+            return 0
+
+        return len(self.lst)
+
+    @staticmethod
+    def get_mtime(fname):
+        """
+        Find the time this file was last modified.
+
+        :param fname: File name
+        :return: The last time the file was modified.
+        """
+        try:
+            mtime = os.stat(fname).st_mtime_ns
+        except OSError:
+            # The file might be right in the middle of being written
+            # so sleep
+            time.sleep(1)
+            mtime = os.stat(fname).st_mtime_ns
+
+        return mtime
+
+    def is_changed(self, fname):
+        """
+        Find out if this file has been modified since last
+
+        :param fname: A file name
+        :return: True/False
+        """
+        if os.path.isfile(fname):
+            mtime = self.get_mtime(fname)
+
+            if self.fmtime == 0:
+                self.fmtime = mtime
+                return True
+
+            if mtime > self.fmtime:  # has changed
+                self.fmtime = mtime
+                return True
+            else:
+                return False
+        else:
+            logger.error("Could not access {}".format(fname))
+            raise FileNotFoundError()
+
+    def _read_info(self, fname):
+        if os.path.isfile(fname):
+            try:
+                lock = FileLock(f"{fname}.lock")
+                with lock:
+                    fp = open(fname, "r")
+                    info = [x.strip() for x in fp.readlines()]
+                lock.release()
+                if info == "":
+                    return None
+                else:
+                    return info
+            except Exception as err:
+                logger.error(err)
+                raise
+        else:
+            _msg = f"No such file: '{fname}'"
+            logger.error(_msg)
+        return None

tests/test_14_read_only_list_file.py

@@ -0,0 +1,27 @@
+import os
+
+from idpyoidc.storage.listfile import ReadOnlyListFile
+
+BASEDIR = os.path.abspath(os.path.dirname(__file__))
+
+
+def full_path(local_file):
+    return os.path.join(BASEDIR, local_file)
+
+FILE_NAME = full_path("read_only")
+def test_read_only_list_file():
+    if os.path.exists(FILE_NAME):
+        os.unlink(FILE_NAME)
+        os.unlink(f"{FILE_NAME}.lock")
+
+    _read_only = ReadOnlyListFile(FILE_NAME)
+    assert len(_read_only) == 0
+
+    with open(FILE_NAME, "w") as fp:
+        for item in ["one", "two", "three"]:
+            fp.write(item)
+            fp.write("\n")
+
+    assert len(_read_only) == 3
+    assert set(_read_only) == {"one", "two", "three"}
+    assert _read_only[-1] == "three"