[quicwg/base-drafts] QPACK sample encoder bug (#1455)

afrind <notifications@github.com> Fri, 15 June 2018 22:04 UTC

Date: Fri, 15 Jun 2018 15:04:43 -0700
From: afrind <notifications@github.com>
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Subject: [quicwg/base-drafts] QPACK sample encoder bug (#1455)
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```
delta = largestReference - baseIndex
sign = delta > 0 ? 0x80 : 0
encodeInteger(prefixBuffer, sign, delta, 7)
```

encodeInteger is meant to be an HPACK integer encoder, which cannot encode negative numbers.  It should be 

`encodeInteger(prefixBuffer, sign, abs(delta), 7)`

Another option is to use a more explicit conditional: 

```
if baseIndex >= largestReference:
  encodeInteger(prefixBuffer, 0, baseIndex - largestReference, 7)
else:
  encodeInteger(prefixBuffer, 0x80, largestReference  - baseIndex, 7)
```

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