HTTP/2 COMPRESSION_ERROR issue - http2

Question

I'm working on a server-side HTTP/2 implementation.
Sometimes clients disconnect with a GOAWAY.COMPRESSION_ERROR in response to the server headers.
According to the Via header, in all of those cases, the client is an intermediary, 'Websense Web Security Gateway v7.6' (looks like a transparent caching solution)
The RFC says that COMPRESSION_ERROR can be sent in 2 cases.
1) A decoding error in a header block MUST be treated as a connection error of type COMPRESSION_ERROR
2) An endpoint receiving HEADERS, PUSH_PROMISE, or CONTINUATION frames needs to reassemble header blocks and perform decompression even if
the frames are to be discarded. A receiver MUST terminate the connection with a connection error of type COMPRESSION_ERROR if it does not decompress a header block
So in my case it's either an error on my side (bad headers encoding) or it's not an error but the client just discarded the response and sent a COMPRESSION_ERROR as specified by RFC.
If it's the latter then I don't need to fix anything.
But if it's the former then it's a bug in our implementation.
I'd like to rule out the bug case.
Below is a sample of such a session terminated with a COMPRESSION_ERROR.
It's hex dumps of data with my interpretation in {}.
S>C stands for server->client direction, C>S - client->server direction.
Can someone review the dump and tell me if it has some obvious issues with S>C frames or my interpretation of the data?
{preface stripped}
========== S>C frame: ============
00000000: 000024040000000000 ..$......
{type=SETTINGS stream=0 flags=NO_FLAGS(0) len=36 data={...}}
00000000: 00020000000000010000100000030000006400047fffffff000600007f380005 .................d...........8..
00000020: 00007ff7 ....
==================================
========== C>S frame: ============
00000000: 000012040000000000 .........
{type=SETTINGS stream=0 flags=NO_FLAGS(0) len=18 data={...}}
00000000: 000200000000000300000064000600008000 ...........d......
==================================
========== S>C frame: ============
00000000: 000000040100000000 .........
{type=SETTINGS stream=0 flags=ACK(1) len=0 data={}}
==================================
========== C>S frame: ============
00000000: 000004080000000000 .........
{type=WINDOW_UPDATE stream=0 flags=NO_FLAGS(0) len=4 data={inc=10485760}}
00000000: 00a00000 ....
==================================
========== C>S frame: ============
00000000: 000000040100000000 .........
{type=SETTINGS stream=0 flags=ACK(1) len=0 data={}}
==================================
========== C>S frame: ============
00000000: 00015c01050000000d ..\......
{type=HEADERS stream=13 flags=END_STREAM|END_HEADERS(5) len=348 data={...}}
00000000: 418aa4b2186cae824952fdea82449360d4cccb02005f603109a637e36a7c475e A....l..IR...D.`....._`1..7.j|G^
00000020: baa687539e352398ac782c75fd1a91cc56075d537d1a91cc563e7ebe58f9fbed ...S.5#..x,u....V.]S}...V>~.X...
00000040: 00177b73dc9d29ad171863c78f0ba0b54875fbd4c7f96a698a92c86b698072ca ..{s..)...c.....Hu....ji...ki.r.
00000060: 6a0c3497e2d4d3120f6d842c03210a8426c1c85f81cb2c4834903cefede170ed j.4......m.,.!..&.._..,H4.<...p.
00000080: 665435fb875c9b1a7b2dfceda35f7a67967e7ea3a19fde8dd02fdbf97d5e2ee9 fT5..\..{-..._zg.~~....../..}^..
000000a0: c97ad5d07f66a281b0dae053fae46aa43f8429a77a8102e0fb5396ae4e35fda9 .z...f.....S..j.?.).z....S..N5..
000000c0: 0d75d05e458f3192c36cbabb2e29fd66c7bf467fa5283752a988a4ea7fed4bd3 .u.^E.1..l...).f..F..(7R......K.
000000e0: d87a4ac3acae05d971e65708195370e51d8661b65d5d973f508d9bd9abfa5242 .zJ.....q.W..Sp...a.]].?P.....RB
00000100: cb40d25fa523b351b82d4b70ddf45abefb4005dffaee6fbed00177bebdcff7da .#._.#.Q.-Kp..Z..#....o...w.....
00000120: 002eefd7b9d6bda7efb4005dcfaf73ad8f37df6800bb7f5ee75b7f2fbed00176 ...........]..s..7.h...^.[./...v
00000140: bf7c99e458d05a9055391635371496d864fa5310d25f03f4a7775773 .|..X.Z.U9.57...d.S.._...wWs
==================================
========== S>C frame: ============
00000000: 00007c01040000000d ..|......
{type=HEADERS stream=13 flags=END_HEADERS(4) len=124 data={...}}
00000000: 3fe11f887684aa6355e76196c361be940bea435d8a08017d4006e32edc684a62 ?...v..cU.a..a....C]...}#....hJb
00000020: d1bf5f87352398ac5754df0f0d83644f3f6c96df3dbf4a09a5328ea50400bea0 .._.5#..WT....dO?l..=.J..2......
00000040: 1ab826ee32da98b46f628cfe5b234fb2566558923ffcff0f1596dd6d5f4a09e5 ..&.2...ob..[#O.VeX.?......m_J..
00000060: 21aec50400bea05ab8cbf700253168df588aa47e561cc581c034f001 !......Z....%1h.X..~V....4..
==================================
========== S>C frame: ============
00000000: 000cd900010000000d .........
{type=DATA stream=13 flags=END_STREAM(1) len=3289 data={...}}
{data stripped}
==================================
========== C>S frame: ============
00000000: 000014070000000000 .........
{type=GOAWAY stream=0 flags=NO_FLAGS(0) len=20 data={...}}
00000000: 0000000000000009000000000000033200000333 ...............2...3
{last_stream_id=0, error=COMPRESSION_ERROR}
==================================
========== S>C frame: ============
00000000: 000008070000000000 .........
{type=GOAWAY stream=0 flags=NO_FLAGS(0) len=8 data={...}}
00000000: 0000000d00000000 ........
==================================
C>S headers decoded:
:path: /img3/2019/1_24/TH4hGo.png HTTP/2.0
:authority: media3.scdn.vn
Accept: image/webp,image/apng,image/*,*/*;q=0.8
Referer: https://www.sendo.vn/?utm_medium=affiliate&utm_source=accesstrade&aff_sid=...
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.103 Safari/537.36
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9,vi;q=0.8,zh;q=0.7,zh-CN;q=0.6,zh-HK;q=0.5,zh-TW;q=0.4
Via: Websense Web Security Gateway v7.6
S>C HEADERS frame decoded:
3fe11f
{set dyn table size 4096}
{dyn table size=0/4096}
88
{indexed header ix=8 :status: 200}
{dyn table not changed}
7684aa6355e7
{literal indexed header ix=54 Server: nginx }
{dyn table size=43/4096:
ix=62 off=0 size=43 Server: nginx
}
6196c361be940bea435d8a08017d4006e32edc684a62d1bf
{literal indexed header ix=33 Date: Fri, 19 Apr 2019 01:37:42 GMT }
{dyn table size=108/4096:
ix=62 off=0 size=65 Date: Fri, 19 Apr 2019 01:37:42 GMT
ix=63 off=65 size=43 Server: nginx
}
5f87352398ac5754df
{literal indexed header ix=31 Content-Type: image/png}
{dyn table size=161/4096:
ix=62 off=0 size=53 Content-Type: image/png
ix=63 off=53 size=65 Date: Fri, 19 Apr 2019 01:37:42 GMT
ix=64 off=118 size=43 Server: nginx
}
0f0d83644f3f
{literal not indexed header ix=28 Content-Length: 3289}
{dyn table not changed}
6c96df3dbf4a09a5328ea50400bea01ab826ee32da98b46f
{literal indexed header ix=44 Last-Modified: Thu, 24 Jan 2019 04:25:35 GMT }
{dyn table size=235/4096:
ix=62 off=0 size=74 Last-Modified: Thu, 24 Jan 2019 04:25:35 GMT
ix=63 off=74 size=53 Content-Type: image/png
ix=64 off=127 size=65 Date: Fri, 19 Apr 2019 01:37:42 GMT
ix=65 off=192 size=43 Server: nginx
}
628cfe5b234fb2566558923ffcff
{literal indexed header ix=34 ETag: "5c493e3f-cd9"}
{dyn table size=285/4096:
ix=62 off=0 size=50 ETag: "5c493e3f-cd9"
ix=63 off=50 size=74 Last-Modified: Thu, 24 Jan 2019 04:25:35 GMT
ix=64 off=124 size=53 Content-Type: image/png
ix=65 off=177 size=65 Date: Fri, 19 Apr 2019 01:37:42 GMT
ix=66 off=242 size=43 Server: nginx
}
0f1596dd6d5f4a09e521aec50400bea05ab8cbf700253168df
{literal not indexed header ix=36 Expires: Sun, 28 Apr 2019 14:39:02 GMT}
{dyn table not changed}
588aa47e561cc581c034f001
{literal indexed header ix=24 Cache-Control: max-age=604800}
{dyn table size=344/4096:
ix=62 off=0 size=59 Cache-Control: max-age=604800
ix=63 off=59 size=50 ETag: "5c493e3f-cd9"
ix=64 off=109 size=74 Last-Modified: Thu, 24 Jan 2019 04:25:35 GMT
ix=65 off=183 size=53 Content-Type: image/png
ix=66 off=236 size=65 Date: Fri, 19 Apr 2019 01:37:42 GMT
ix=67 off=301 size=43 Server: nginx
}
The decoded S>C headers:
:status: 200
Server: nginx
Date: Fri, 19 Apr 2019 01:37:42 GMT
Content-Type: image/png
Content-Length: 3289
Last-Modified: Thu, 24 Jan 2019 04:25:35 GMT
ETag: "5c493e3f-cd9"
Expires: Sun, 28 Apr 2019 14:39:02 GMT
Cache-Control: max-age=604800

Answer 1

I added an hpack decoder to h2get here: https://github.com/deweerdt/h2get/pull/18/files and i'm seeing the same results as you are:
$ ./hpack_decoder 3fe11f887684aa6355e76196c361be940bea435d8a08017d4006e32edc684a62d1bf5f87352398ac5754df0f0d83644f3f6c96df3dbf4a09a5328ea50400bea01ab826ee32da98b46f628cfe5b234fb2566558923ffcff0f1596dd6d5f4a09e521aec50400bea05ab8cbf700253168df588aa47e561cc581c034f001
dyn table resize to 4096
[:status] => [200]
[server] => [nginx]
[date] => [Fri, 19 Apr 2019 01:37:42 GMT]
[content-type] => [image/png]
[content-length] => [3289]
[last-modified] => [Thu, 24 Jan 2019 04:25:35 GMT]
[etag] => ["5c493e3f-cd9"]
[expires] => [Sun, 28 Apr 2019 14:39:02 GMT]
[cache-control] => [max-age=604800]