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add contrib/unber.py utility

This tool is a replacement for asn1c 'unber' program with a much more
useful/readable output:
* contains hexadecimal raw tag values
* contains hexdump of value, rather than HTML entities in pseudo-XML

Change-Id: I22c1a461ccba04c2c8caaab7ca29ea6ae76e2ea3
---
A contrib/unber.py
1 file changed, 53 insertions(+), 0 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/pysim refs/changes/93/35493/1

diff --git a/contrib/unber.py b/contrib/unber.py
new file mode 100755
index 0000000..65262e1
--- /dev/null
+++ b/contrib/unber.py
@@ -0,0 +1,39 @@
+#!/usr/bin/env python3
+
+# A more useful verion of the 'unber' tool provided with asn1c:
+# Give a hierarchical decode of BER/DER-encoded ASN.1 TLVs
+
+import sys
+import argparse
+
+from pySim.utils import bertlv_parse_one, bertlv_encode_tag, b2h, h2b
+
+def process_one_level(content: bytes, indent: int):
+    remainder = content
+    while len(remainder):
+        tdict, l, v, remainder = bertlv_parse_one(remainder)
+        #print(tdict)
+        rawtag = bertlv_encode_tag(tdict)
+        if tdict['constructed']:
+            print("%s%s l=%d" % (indent*"  ", b2h(rawtag), l))
+            process_one_level(v, indent + 1)
+        else:
+            print("%s%s l=%d %s" % (indent*"  ", b2h(rawtag), l, b2h(v)))
+
+
+option_parser = argparse.ArgumentParser(description='BER/DER data dumper')
+group = option_parser.add_mutually_exclusive_group(required=True)
+group.add_argument('--file', help='Input file')
+group.add_argument('--hex', help='Input hexstring')
+
+
+if __name__ == '__main__':
+    opts = option_parser.parse_args()
+
+    if opts.file:
+        with open(opts.file, 'rb') as f:
+            content = f.read()
+    elif opts.hex:
+        content = h2b(opts.hex)
+
+    process_one_level(content, 0)

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