util.error_text_str_to_safe_str: truncate long errors

The messages are sometimes logged and sometimes shown to the user,
- for logging we might not want to truncate or have higher limits,
- but when shown to the user, we definitely want to truncate the error text.
It is simplest to just do the truncation here, at the lowest level.

Note that we usually prepend the error text with a header e.g. "[DO NOT TRUST THIS MESSAGE]"
and if the error text is too long, this header at the beginning might get "lost" in some way.
Hence we should truncate the error text.

tests/test_util.py

@@ -362,7 +362,11 @@ class TestUtil(ElectrumTestCase):
                          util.error_text_bytes_to_safe_str(b'here is some unicode: \xe2\x82\xbf \xf0\x9f\x98\x80 \xf0\x9f\x98\x88'))
         # not even unicode
         self.assertEqual("""\'\\x00\\x01\\x02\\x03\\x04\\x05\\x06\\x07\\x08\\t\\n\\x0b\\x0c\\r\\x0e\\x0f\\x10\\x11\\x12\\x13\\x14\\x15\\x16\\x17\\x18\\x19\\x1a\\x1b\\x1c\\x1d\\x1e\\x1f !"#$%&\\\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\\x7f\\\\x80\\\\x81\\\\x82\\\\x83\\\\x84\\\\x85\\\\x86\\\\x87\\\\x88\\\\x89\\\\x8a\\\\x8b\\\\x8c\\\\x8d\\\\x8e\\\\x8f\\\\x90\\\\x91\\\\x92\\\\x93\\\\x94\\\\x95\\\\x96\\\\x97\\\\x98\\\\x99\\\\x9a\\\\x9b\\\\x9c\\\\x9d\\\\x9e\\\\x9f\\\\xa0\\\\xa1\\\\xa2\\\\xa3\\\\xa4\\\\xa5\\\\xa6\\\\xa7\\\\xa8\\\\xa9\\\\xaa\\\\xab\\\\xac\\\\xad\\\\xae\\\\xaf\\\\xb0\\\\xb1\\\\xb2\\\\xb3\\\\xb4\\\\xb5\\\\xb6\\\\xb7\\\\xb8\\\\xb9\\\\xba\\\\xbb\\\\xbc\\\\xbd\\\\xbe\\\\xbf\\\\xc0\\\\xc1\\\\xc2\\\\xc3\\\\xc4\\\\xc5\\\\xc6\\\\xc7\\\\xc8\\\\xc9\\\\xca\\\\xcb\\\\xcc\\\\xcd\\\\xce\\\\xcf\\\\xd0\\\\xd1\\\\xd2\\\\xd3\\\\xd4\\\\xd5\\\\xd6\\\\xd7\\\\xd8\\\\xd9\\\\xda\\\\xdb\\\\xdc\\\\xdd\\\\xde\\\\xdf\\\\xe0\\\\xe1\\\\xe2\\\\xe3\\\\xe4\\\\xe5\\\\xe6\\\\xe7\\\\xe8\\\\xe9\\\\xea\\\\xeb\\\\xec\\\\xed\\\\xee\\\\xef\\\\xf0\\\\xf1\\\\xf2\\\\xf3\\\\xf4\\\\xf5\\\\xf6\\\\xf7\\\\xf8\\\\xf9\\\\xfa\\\\xfb\\\\xfc\\\\xfd\\\\xfe\\\\xff\'""",
-                         util.error_text_bytes_to_safe_str(bytes(range(256))))
+                         util.error_text_bytes_to_safe_str(bytes(range(256)), max_len=1000))
+        # long text
+        t1 = util.error_text_bytes_to_safe_str(b"test" * 10000)
+        self.assertTrue(t1.endswith("... (truncated. orig_len=40002)"))
+        self.assertTrue(len(t1) < 550)
 
     def test_error_text_str_to_safe_str(self):
         # ascii
@@ -373,6 +377,10 @@ class TestUtil(ElectrumTestCase):
         # unicode
         self.assertEqual("'here is some unicode: \\\\u20bf \\\\U0001f600 \\\\U0001f608'",
                          util.error_text_str_to_safe_str("here is some unicode: ₿ 😀 😈"))
+        # long text
+        t1 = util.error_text_str_to_safe_str("test"*10000)
+        self.assertTrue(t1.endswith("... (truncated. orig_len=40002)"))
+        self.assertTrue(len(t1) < 550)
 
     def test_age(self):
         now = datetime(2023, 4, 16, 22, 30, 00)