extmod/moduhashlib: Put hash obj in final state after digest is called.

If digest is called then the hash object is put in a "final" state and
calling update() or digest() again will raise a ValueError (instead of
silently producing the wrong result).

See issue #4119.

Signed-off-by: Damien George <damien@micropython.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/tests/extmod/uhashlib_final.py b/tests/extmod/uhashlib_final.py
new file mode 100644
index 000000000..f562cc178
--- /dev/null
+++ b/tests/extmod/uhashlib_final.py
@@ -0,0 +1,35 @@
+try:
+    import uhashlib
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+
+for algo_name in ("md5", "sha1", "sha256"):
+    algo = getattr(uhashlib, algo_name, None)
+    if not algo:
+        continue
+
+    # Running .digest() several times in row is not supported.
+    h = algo(b"123")
+    h.digest()
+    try:
+        h.digest()
+        print("fail")
+    except ValueError:
+        # Expected path, don't print anything so test output is the
+        # same even if the algorithm is not implemented on the port.
+        pass
+
+    # Partial digests are not supported.
+    h = algo(b"123")
+    h.digest()
+    try:
+        h.update(b"456")
+        print("fail")
+    except ValueError:
+        # Expected path, don't print anything so test output is the
+        # same even if the algorithm is not implemented on the port.
+        pass
+
+print("done")