This is a mini HPACK encoder to experiment with HTTP/2.

I hope it follows the standard. It did my best to ensure it was OK, so any error could have slipped through. The "never indexed" encoding was not implemented because I didn't know what header to apply it to.

Build with "make".

Run Mark's fake-hdrs.py to produce a file (so that all variations are tested on identical data) :

 ./fake-hdrs.py > test.hdrs

Then feed this output file to mini-enc and compare the statistics for various encodings. The following encoders are available :

• draft-09 : no option
• first proposal "option 3" : "-1"
• updated proposal for "option 3" : "-2"
• Greg's following proposal : "-3"

./mini-enc < test.hdrs ./mini-enc -1 < test.hdrs ./mini-enc -2 < test.hdrs ./mini-enc -3 < test.hdrs

WARNING: Never ever reuse this code for a real implementation, it's dirty and was written quickly for experimentation. It lacks any form of bounds checking and definitely is insecure.

Current results : here we only look at the overall compression ratio and the average number of bytes per integer since we only play with integer encoding. All measures are also reported as percent compared to draft-09.

Draft-09 : Total input bytes : 7455384 Total output bytes : 2318395 (100%) Overall compression ratio : 0.310969 (100%) Total encoded integers: 218865 Total encoded integers bytes: 295036 (100%) Avg bytes per integers: 1.348027 (100%)

-1 : Total input bytes : 7455384 Total output bytes : 2268350 (97.84%) Overall compression ratio : 0.304257 (97.84%) Total encoded integers: 218865 Total encoded integers bytes: 244991 (83.03%) Avg bytes per integers: 1.119370 (83.03%)

-2 : Total input bytes : 7455384 Total output bytes : 2264722 (97.68%) Overall compression ratio : 0.303770 (97.68%) Total encoded integers: 218865 Total encoded integers bytes: 241363 (81.81%) Avg bytes per integers: 1.102794 (81.81%)

-3 : Total input bytes : 7455384 Total output bytes : 2280713 (98.37%) Overall compression ratio : 0.305915 (98.37%) Total encoded integers: 218865 Total encoded integers bytes: 257354 (87.23%) Avg bytes per integers: 1.175857 (87.23%)

The integer encoding is 17-18% smaller on average with the new proposal and its revised version. This means the savings can definitely be good for headers with shorter values (eg: IP addresses). The current test set contains average headers. The overall savings compared to draft-09 on this test set is 2.1 to 2.3% depending on the proposal. Greg's proposal saves a bit less, probably because it leaves extra bits for already large data and a bit less for small data. But it definitely improves the situation compared to draft-09.