daniel has uploaded this change for review.

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tlv: Allow control over comprehension bit in COMPR_TLV_IE

This allows construction of a comprehension TLV with the bit set or
cleared. The default is comprehension=True to not break existing code.

```
>>> foo = Foo(decoded=b"2342", comprehension=True)
>>> bar = Foo(decoded=b"2342", comprehension=False)
```

Related: OS#6989
Change-Id: I9ca689b9b51152f3907ea470c7b42a0b12208459
---
M src/osmocom/tlv.py
1 file changed, 6 insertions(+), 5 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/python/pyosmocom refs/changes/56/42556/1

diff --git a/src/osmocom/tlv.py b/src/osmocom/tlv.py
index ada7380..07adfb9 100644
--- a/src/osmocom/tlv.py
+++ b/src/osmocom/tlv.py
@@ -58,11 +58,12 @@
         compr = bool(binary[0] & 0x80)
         return ({'comprehension': compr, 'tag': tag}, binary[1:])
 
-def comprehensiontlv_encode_tag(tag) -> bytes:
+def comprehensiontlv_encode_tag(tag, comprehension: bool = True) -> bytes:
     """Encode a single Tag according to ETSI TS 101 220 Section 7.1.1"""
     # permit caller to specify tag also as integer value
+    # This happens if the class is created in code. In that case the 
     if isinstance(tag, int):
-        compr = bool(tag < 0xff and tag & 0x80)
+        compr = comprehension
         tag = {'tag': tag, 'comprehension': compr}
     compr = tag.get('comprehension', False)
     if tag['tag'] in [0x00, 0x80, 0xff] or tag['tag'] > 0xff:
@@ -74,7 +75,7 @@
         return b'\x7f' + byte2.to_bytes(1, 'big') + byte3.to_bytes(1, 'big')
     else:
         # 1-byte format
-        ret = tag['tag']
+        ret = tag['tag'] & 0x7f
         if compr:
             ret |= 0x80
         return ret.to_bytes(1, 'big')
@@ -648,7 +649,7 @@
 
     def __init__(self, **kwargs):
         super().__init__(**kwargs)
-        self.comprehension = False
+        self.comprehension = kwargs.get("comprehension", True)
 
     @classmethod
     def _decode_tag(cls, do: bytes) -> Tuple[dict, bytes]:
@@ -672,7 +673,7 @@
             return ctag & 0x7f == rawtag & 0x7f
 
     def _encode_tag(self) -> bytes:
-        return comprehensiontlv_encode_tag(self._compute_tag())
+        return comprehensiontlv_encode_tag(self._compute_tag(), self.comprehension)
 
     def _encode_len(self, val: bytes) -> bytes:
         return bertlv_encode_len(len(val))

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