Improve CER/DER encoding of GeneralizedTimefix-generalized-time-encoding

- Added support for subseconds CER/DER encoding edge cases in
  `GeneralizedTime` codec
- Fixed 3-digit fractional seconds value CER/DER encoding of
  `GeneralizedTime`

3 files changed, 76 insertions, 23 deletions

diff --git a/CHANGES.rst b/CHANGES.rst
index e979039..448e372 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -29,6 +29,10 @@ Revision 0.4.6, released XX-06-2019
 - Added `PyAsn1UnicodeDecodeError`/`PyAsn1UnicodeDecodeError` exceptions
   to help the caller treating unicode errors happening internally
   to pyasn1 at the upper layers.
+- Added support for subseconds CER/DER encoding edge cases in
+  `GeneralizedTime` codec.
+- Fixed 3-digit fractional seconds value CER/DER encoding of
+  `GeneralizedTime`.
 - Fixed `AnyDecoder` to accept possible `TagMap` as `asn1Spec`
   to make dumping raw value operational
 
diff --git a/pyasn1/codec/cer/encoder.py b/pyasn1/codec/cer/encoder.py
index 788567f..3fdcc1d 100644
--- a/pyasn1/codec/cer/encoder.py
+++ b/pyasn1/codec/cer/encoder.py
@@ -31,17 +31,20 @@ class RealEncoder(encoder.RealEncoder):
 # specialized GeneralStringEncoder here
 
 class TimeEncoderMixIn(object):
-    zchar, = str2octs('Z')
-    pluschar, = str2octs('+')
-    minuschar, = str2octs('-')
-    commachar, = str2octs(',')
-    minLength = 12
-    maxLength = 19
+    Z_CHAR = ord('Z')
+    PLUS_CHAR = ord('+')
+    MINUS_CHAR = ord('-')
+    COMMA_CHAR = ord(',')
+    DOT_CHAR = ord('.')
+    ZERO_CHAR = ord('0')
+
+    MIN_LENGTH = 12
+    MAX_LENGTH = 19
 
     def encodeValue(self, value, asn1Spec, encodeFun, **options):
-        # Encoding constraints:
+        # CER encoding constraints:
         # - minutes are mandatory, seconds are optional
-        # - sub-seconds must NOT be zero
+        # - sub-seconds must NOT be zero / no meaningless zeros
         # - no hanging fraction dot
         # - time in UTC (Z)
         # - only dot is allowed for fractions
@@ -49,20 +52,46 @@ class TimeEncoderMixIn(object):
         if asn1Spec is not None:
             value = asn1Spec.clone(value)
 
-        octets = value.asOctets()
-
-        if not self.minLength < len(octets) < self.maxLength:
-            raise error.PyAsn1Error('Length constraint violated: %r' % value)
+        numbers = value.asNumbers()
 
-        if self.pluschar in octets or self.minuschar in octets:
-            raise error.PyAsn1Error('Must be UTC time: %r' % octets)
+        if self.PLUS_CHAR in numbers or self.MINUS_CHAR in numbers:
+            raise error.PyAsn1Error('Must be UTC time: %r' % value)
 
-        if octets[-1] != self.zchar:
-            raise error.PyAsn1Error('Missing "Z" time zone specifier: %r' % octets)
+        if numbers[-1] != self.Z_CHAR:
+            raise error.PyAsn1Error('Missing "Z" time zone specifier: %r' % value)
 
-        if self.commachar in octets:
+        if self.COMMA_CHAR in numbers:
             raise error.PyAsn1Error('Comma in fractions disallowed: %r' % value)
 
+        if self.DOT_CHAR in numbers:
+
+            isModified = False
+
+            numbers = list(numbers)
+
+            searchIndex = min(numbers.index(self.DOT_CHAR) + 4, len(numbers) - 1)
+
+            while numbers[searchIndex] != self.DOT_CHAR:
+                if numbers[searchIndex] == self.ZERO_CHAR:
+                    del numbers[searchIndex]
+                    isModified = True
+
+                searchIndex -= 1
+
+            searchIndex += 1
+
+            if searchIndex < len(numbers):
+                if numbers[searchIndex] == self.Z_CHAR:
+                    # drop hanging comma
+                    del numbers[searchIndex - 1]
+                    isModified = True
+
+            if isModified:
+                value = value.clone(numbers)
+
+        if not self.MIN_LENGTH < len(numbers) < self.MAX_LENGTH:
+            raise error.PyAsn1Error('Length constraint violated: %r' % value)
+
         options.update(maxChunkSize=1000)
 
         return encoder.OctetStringEncoder.encodeValue(
@@ -71,13 +100,13 @@ class TimeEncoderMixIn(object):
 
 
 class GeneralizedTimeEncoder(TimeEncoderMixIn, encoder.OctetStringEncoder):
-    minLength = 12
-    maxLength = 19
+    MIN_LENGTH = 12
+    MAX_LENGTH = 20
 
 
 class UTCTimeEncoder(TimeEncoderMixIn, encoder.OctetStringEncoder):
-    minLength = 10
-    maxLength = 14
+    MIN_LENGTH = 10
+    MAX_LENGTH = 14
 
 
 class SetEncoder(encoder.SequenceEncoder):
diff --git a/tests/codec/cer/test_encoder.py b/tests/codec/cer/test_encoder.py
index ea8f813..130fe17 100644
--- a/tests/codec/cer/test_encoder.py
+++ b/tests/codec/cer/test_encoder.py
@@ -87,7 +87,7 @@ class GeneralizedTimeEncoderTestCase(BaseTestCase):
     def testDecimalCommaPoint(self):
         try:
             assert encoder.encode(
-                    useful.GeneralizedTime('20150501120112,1Z')
+                useful.GeneralizedTime('20150501120112,1Z')
              )
         except PyAsn1Error:
             pass
@@ -96,9 +96,29 @@ class GeneralizedTimeEncoderTestCase(BaseTestCase):
 
     def testWithSubseconds(self):
         assert encoder.encode(
-                    useful.GeneralizedTime('20170801120112.59Z')
+                useful.GeneralizedTime('20170801120112.59Z')
              ) == ints2octs((24, 18, 50, 48, 49, 55, 48, 56, 48, 49, 49, 50, 48, 49, 49, 50, 46, 53, 57, 90))
 
+    def testWithSubsecondsWithZeros(self):
+        assert encoder.encode(
+                useful.GeneralizedTime('20170801120112.099Z')
+             ) == ints2octs((24, 18, 50, 48, 49, 55, 48, 56, 48, 49, 49, 50, 48, 49, 49, 50, 46, 57, 57, 90))
+
+    def testWithSubsecondsMax(self):
+        assert encoder.encode(
+                useful.GeneralizedTime('20170801120112.999Z')
+             ) == ints2octs((24, 19, 50, 48, 49, 55, 48, 56, 48, 49, 49, 50, 48, 49, 49, 50, 46, 57, 57, 57, 90))
+
+    def testWithSubsecondsMin(self):
+        assert encoder.encode(
+                useful.GeneralizedTime('20170801120112.000Z')
+             ) == ints2octs((24, 15, 50, 48, 49, 55, 48, 56, 48, 49, 49, 50, 48, 49, 49, 50, 90))
+
+    def testWithSubsecondsDanglingDot(self):
+        assert encoder.encode(
+                useful.GeneralizedTime('20170801120112.Z')
+             ) == ints2octs((24, 15, 50, 48, 49, 55, 48, 56, 48, 49, 49, 50, 48, 49, 49, 50, 90))
+
     def testWithSeconds(self):
         assert encoder.encode(
                     useful.GeneralizedTime('20170801120112Z')