python: Add python script to generate hpack-test-case json files

See https://github.com/Jxck/hpack-test-case for the json file
format.

python/hpackmake.py

@@ -0,0 +1,54 @@
+#!/usr/bin/env python
+#
+# This script reads input headers from json file given in the
+# command-line (each file must be written in the format described in
+# https://github.com/Jxck/hpack-test-case but we require only
+# 'headers' data). Then it encodes input header set and write the
+# encoded header block in the same format. The output files are
+# created under 'out' directory in the current directory. It must
+# exist, otherwise the script will fail. The output filename is the
+# same as the input filename.
+#
+import sys, base64, json, os.path
+from binascii import b2a_hex
+import nghttp2
+
+def testsuite(testdata, filename):
+    if testdata['context'] == 'request':
+        side = nghttp2.HD_SIDE_REQUEST
+    else:
+        side = nghttp2.HD_SIDE_RESPONSE
+
+    res = {
+        'draft':5, 'context': testdata['context'],
+        'description': '''\
+Encoded by nghttp2. The basic encoding strategy is described in \
+http://lists.w3.org/Archives/Public/ietf-http-wg/2013JulSep/1135.html \
+We use huffman encoding only if it produces strictly shorter byte string than \
+original. We make some headers not indexing at all, but this does not always \
+result in less bits on the wire.'''
+    }
+    cases = []
+    deflater = nghttp2.HDDeflater(side)
+    for casenum, item  in enumerate(testdata['cases']):
+        outitem = {
+            'header_table_size': 4096,
+            'headers': item['headers']
+        }
+        casenum += 1
+        hdrs = [(list(x.keys())[0].encode('utf-8'),
+                 list(x.values())[0].encode('utf-8')) \
+                for x in item['headers']]
+        outitem['wire'] = b2a_hex(deflater.deflate(hdrs)).decode('utf-8')
+        cases.append(outitem)
+    res['cases'] = cases
+    jsonstr = json.dumps(res, indent=2)
+    with open(os.path.join('out', filename), 'w') as f:
+        f.write(jsonstr)
+
+if __name__ == '__main__':
+    for filename in sys.argv[1:]:
+        sys.stderr.write('{}\n'.format(filename))
+        with open(filename) as f:
+            input = f.read()
+        testsuite(json.loads(input), os.path.basename(filename))