9. 用Rust手把手编写一个wmproxy(代理，内网穿透等), HTTP2改造篇之HPACK示例, 了解http2头信息如何处理
项目 ++wmproxy++
gite: https://gitee.com/tickbh/wmproxy
github: https://github.com/tickbh/wmproxy
关于HPACK相关数据的示例
长度编码的示例，用5位的前缀示例
- 将10进行编码，10小于2^5-1，故
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| X | X | X | 0 | 1 | 0 | 1 | 0 | 10 stored on 5 bits
+---+---+---+---+---+---+---+---+
- 将1337进行编码
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| X | X | X | 1 | 1 | 1 | 1 | 1 | 31
+---+---+---+---+---+---+---+---+
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 1 | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 26
+---+---+---+---+---+---+---+---+
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 10
+---+---+---+---+---+---+---+---+
最终的填充值：
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| X | X | X | 1 | 1 | 1 | 1 | 1 | Prefix = 31, I = 1306
| 1 | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 1306>=128, encode(154), I=1306/128
| 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 10 custom-key:
| custom-header
动态表 (解码之后):
[ 1] (占用 55) custom-key: custom-header
占用长度: 10+13+32=55
名字在列表中，但不索引，未使用HUFFMAN
以下示例
:path: /sample/path
十六进制表示
040c 2f73 616d 706c 652f 7061 7468 | ../sample/path
解码过程
04 | == 0000开头，请求不索引 ==
| name从索引取 (idx = 4)
| 值为:path
0c | value (长度12)
2f73 616d 706c 652f 7061 7468 | /sample/path
| -> :path: /sample/path
永不索引，未使用HUFFMAN
以下示例
password: secret
十六进制表示
1008 7061 7373 776f 7264 0673 6563 7265 | ..password.secre
74 | t
解码过程
10 | == 0001开头不索引 ==
08 | name (长度8)
7061 7373 776f 7264 | password
06 | value (长度6)
7365 6372 6574 | secret
| -> password: secret
完整的请求示例，不使用HUFFMAN
以下几个示例将连接请求，后续的会用到前面的动态列表
第一次请求. 示例如下
:method: GET
:scheme: http
:path: /
:authority: www.example.com
十六进制表示
8286 8441 0f77 7777 2e65 7861 6d70 6c65 | ...A.www.example
2e63 6f6d | .com
解码过程
82 | == Indexed - 静态表 ==
| idx = 2
| -> :method: GET
86 | == Indexed - 静态表 ==
| idx = 6
| -> :scheme: http
84 | == Indexed - 静态表 ==
| idx = 4
| -> :path: /
41 | == 01开头请求索引 indexed ==
| Indexed name (idx = 1)
| :authority
0f | Literal value (长度15)
7777 772e 6578 616d 706c 652e 636f 6d | www.example.com
| -> :authority:
| www.example.com
动态列表 (解码后):
[ 1->62] (s = 57) :authority: www.example.com
列表长度: 57
第二次请求. 示例如下，新加了cache-control字段，其它和第一次一样
:method: GET
:scheme: http
:path: /
:authority: www.example.com
cache-control: no-cache
十六进制表示
8286 84be 5808 6e6f 2d63 6163 6865 | ....X.no-cache
解码过程
82 | == Indexed - 静态表 ==
| idx = 2
| -> :method: GET
86 | == Indexed - 静态表 ==
| idx = 6
| -> :scheme: http
84 | == Indexed - 静态表 ==
| idx = 4
| -> :path: /
be | == Indexed - 动态表，索引值62及以上的为动态表 ==
| idx = 62
| -> :authority:
| www.example.com
58 | == Literal indexed ==
| Indexed name (idx = 24)
| cache-control
08 | Literal value (8)
6e6f 2d63 6163 6865 | no-cache
| -> cache-control: no-cache
动态列表 (解码后):
[ 1->62] (s = 53) cache-control: no-cache
[ 2->63] (s = 57) :authority: www.example.com
总长度: 110
第三次请求. 示例如下
:method: GET
:scheme: https
:path: /index.html
:authority: www.example.com
custom-key: custom-value
十六进制表示
8287 85bf 400a 6375 7374 6f6d 2d6b 6579 | ....@.custom-key
0c63 7573 746f 6d2d 7661 6c75 65 | .custom-value
解码过程
82 | == Indexed - 静态表 ==
| idx = 2
| -> :method: GET
87 | == Indexed - 静态表 ==
| idx = 7
| -> :scheme: https
85 | == Indexed - 静态表 ==
| idx = 5
| -> :path: /index.html
bf | == Indexed - 动态表 ==
| idx = 63
| -> :authority:
| www.example.com
40 | == Literal indexed ==
0a | Literal name (长度10)
6375 7374 6f6d 2d6b 6579 | custom-key
0c | Literal value (长度12)
6375 7374 6f6d 2d76 616c 7565 | custom-value
| -> custom-key:
| custom-value
动态列表 (解码后):
[ 1->62] (s = 54) custom-key: custom-value
[ 2->63] (s = 53) cache-control: no-cache
[ 3->64] (s = 57) :authority: www.example.com
总长度: 164
完整的请求示例（和上述例子一模一样，但是使用HUFFMAN)
以下几个示例将连接请求，后续的会用到前面的动态列表
第一次请求. 示例如下
:method: GET
:scheme: http
:path: /
:authority: www.example.com
十六进制表示
8286 8441 8cf1 e3c2 e5f2 3a6b a0ab 90f4 | ...A......:k....
ff | .
比之前少了3字节
解码过程
82 | == Indexed - 静态表 ==
| idx = 2
| -> :method: GET
86 | == Indexed - 静态表 ==
| idx = 6
| -> :scheme: http
84 | == Indexed - 静态表 ==
| idx = 4
| -> :path: /
41 | == Literal indexed ==
| Indexed name (idx = 1)
| :authority
8c | Literal value (长度12)
| Huffman encoded:
f1e3 c2e5 f23a 6ba0 ab90 f4ff | .....:k.....
| Decoded:
| www.example.com
| -> :authority:
| www.example.com
动态列表 (解码后):
[ 1->62] (s = 57) :authority: www.example.com
列表长度: 57
第二次请求. 示例如下，新加了cache-control字段，其它和第一次一样
:method: GET
:scheme: http
:path: /
:authority: www.example.com
cache-control: no-cache
十六进制表示
8286 84be 5886 a8eb 1064 9cbf | ....X....d..
比之前少了2字节
解码过程
82 | == Indexed - 静态表 ==
| idx = 2
| -> :method: GET
86 | == Indexed - 静态表 ==
| idx = 6
| -> :scheme: http
84 | == Indexed - 静态表 ==
| idx = 4
| -> :path: /
be | == Indexed - 动态表 ==
| idx = 62
| -> :authority:
| www.example.com
58 | == Literal indexed ==
| Indexed name (idx = 24)
| cache-control
86 | Literal value (长度6)
| Huffman encoded:
a8eb 1064 9cbf | ...d..
| Decoded:
| no-cache
| -> cache-control: no-cache
动态列表 (解码后):
[ 1->62] (s = 53) cache-control: no-cache
[ 2->63] (s = 57) :authority: www.example.com
列表长度: 110
第三次请求. 示例如下
:method: GET
:scheme: https
:path: /index.html
:authority: www.example.com
custom-key: custom-value
十六进制表示
8287 85bf 4088 25a8 49e9 5ba9 7d7f 8925 | ....@.%.I.[.}..%
a849 e95b b8e8 b4bf | .I.[....
比之前少了5字节
解码过程
82 | == Indexed - 静态表 ==
| idx = 2
| -> :method: GET
87 | == Indexed - 静态表 ==
| idx = 7
| -> :scheme: https
85 | == Indexed - 静态表 ==
| idx = 5
| -> :path: /index.html
bf | == Indexed - 动态表 ==
| idx = 63
| -> :authority:
| www.example.com
40 | == Literal indexed ==
88 | Literal name (长度8)
| Huffman encoded:
25a8 49e9 5ba9 7d7f | %.I.[.}.
| Decoded:
| custom-key
89 | Literal value (长度9)
| Huffman encoded:
25a8 49e9 5bb8 e8b4 bf | %.I.[....
| Decoded:
| custom-value
| -> custom-key:
| custom-value
动态列表 (解码后):
[ 1->62] (s = 54) custom-key: custom-value
[ 2->63] (s = 53) cache-control: no-cache
[ 3->64] (s = 57) :authority: www.example.com
总长度: 164
HUFFMAN编码在于首次如果数据较大的时候优势会更加明显，如果数据较小，或者在后续的时候与普通编码命中索引时基本一致。
完整的返回示例(HUFFMAN)
HUFFMAN与普通的差别在于字符串编解码时的差别，这里只介绍一种，并且设置
SETTINGS_HEADER_TABLE_SIZE为256
以下几个示例将连接请求，后续的会用到前面的动态列表
第一次返回. 示例如下
:status: 302
cache-control: private
date: Mon, 21 Oct 2013 20:13:21 GMT
location: https://www.example.com
十六进制表示
4882 6402 5885 aec3 771a 4b61 96d0 7abe | H.d.X...w.Ka..z.
9410 54d4 44a8 2005 9504 0b81 66e0 82a6 | ..T.D. .....f...
2d1b ff6e 919d 29ad 1718 63c7 8f0b 97c8 | -..n..)...c.....
e9ae 82ae 43d3 | ....C.
解码过程
48 | == Literal indexed ==
| Indexed name (idx = 8)
| :status
82 | Literal value (长度2)
| Huffman encoded:
6402 | d.
| Decoded:
| 302
| -> :status: 302
58 | == Literal indexed ==
| Indexed name (idx = 24)
| cache-control
85 | Literal value (长度5)
| Huffman encoded:
aec3 771a 4b | ..w.K
| Decoded:
| private
| -> cache-control: private
61 | == Literal indexed ==
| Indexed name (idx = 33)
| date
96 | Literal value (长度22)
| Huffman encoded:
d07a be94 1054 d444 a820 0595 040b 8166 | .z...T.D. .....f
e082 a62d 1bff | ...-..
| Decoded:
| Mon, 21 Oct 2013 20:13:21
| GMT
| -> date: Mon, 21 Oct 2013
| 20:13:21 GMT
6e | == Literal indexed ==
| Indexed name (idx = 46)
| location
91 | Literal value (长度17)
| Huffman encoded:
9d29 ad17 1863 c78f 0b97 c8e9 ae82 ae43 | .)...c.........C
d3 | .
| Decoded:
| https://www.example.com
| -> location:
| https://www.example.com
动态列表 (解码后):
[ 1->62] (s = 63) location: https://www.example.com
[ 2->63] (s = 65) date: Mon, 21 Oct 2013 20:13:21 GMT
[ 3->64] (s = 52) cache-control: private
[ 4->65] (s = 42) :status: 302
Table size: 222
第二次请求. 示例如下，只是状态码发生了变更
:status: 307
cache-control: private
date: Mon, 21 Oct 2013 20:13:21 GMT
location: https://www.example.com
十六进制表示
4883 640e ffc1 c0bf | H.d.....
解码过程
48 | == Literal indexed ==
| Indexed name (idx = 8)
| :status
83 | Literal value (长度3)
| Huffman encoded:
640e ff | d..
| Decoded:
| 307
| - evict: :status: 302
| -> :status: 307
c1 | == Indexed - Add ==
| idx = 65
| -> cache-control: private
c0 | == Indexed - Add ==
| idx = 64
| -> date: Mon, 21 Oct 2013
| 20:13:21 GMT
bf | == Indexed - Add ==
| idx = 63
| -> location:
| https://www.example.com
动态列表 (解码后):
[ 1->62] (s = 42) :status: 307
[ 2->63] (s = 63) location: https://www.example.com
[ 3->64] (s = 65) date: Mon, 21 Oct 2013 20:13:21 GMT
[ 4->65] (s = 52) cache-control: private
Table size: 222
由于(:status, 302)的长度为42，且42+222=264>256，所以舍弃最大值
第三次请求. 示例如下
:status: 200
cache-control: private
date: Mon, 21 Oct 2013 20:13:22 GMT
location: https://www.example.com
content-encoding: gzip
set-cookie: foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; max-age=3600; version=1
十六进制表示
88c1 6196 d07a be94 1054 d444 a820 0595 | ..a..z...T.D. ..
040b 8166 e084 a62d 1bff c05a 839b d9ab | ...f...-...Z....
77ad 94e7 821d d7f2 e6c7 b335 dfdf cd5b | w..........5...[
3960 d5af 2708 7f36 72c1 ab27 0fb5 291f | 9`..'..6r..'..).
9587 3160 65c0 03ed 4ee5 b106 3d50 07 | ..1`e...N...=P.
比之前少了5字节
解码过程
88 | == Indexed - 静态表 ==
| idx = 8
| -> :status: 200
c1 | == Indexed - 动态表 ==
| idx = 65
| -> cache-control: private
61 | == Literal indexed ==
| Indexed name (idx = 33)
| date
96 | Literal value (长度22)
| Huffman encoded:
d07a be94 1054 d444 a820 0595 040b 8166 | .z...T.D. .....f
e084 a62d 1bff | ...-..
| Decoded:
| Mon, 21 Oct 2013 20:13:22
| GMT
| - evict: cache-control:
| private
| -> date: Mon, 21 Oct 2013
| 20:13:22 GMT
c0 | == Indexed - Add ==
| idx = 64
| -> location:
| https://www.example.com
5a | == Literal indexed ==
| Indexed name (idx = 26)
| content-encoding
83 | Literal value (长度3)
| Huffman encoded:
9bd9 ab | ...
| Decoded:
| gzip
| - evict: date: Mon, 21 Oct
| 2013 20:13:21 GMT
| -> content-encoding: gzip
77 | == Literal indexed ==
| Indexed name (idx = 55)
| set-cookie
ad | Literal value (长度45)
| Huffman encoded:
94e7 821d d7f2 e6c7 b335 dfdf cd5b 3960 | .........5...[9`
d5af 2708 7f36 72c1 ab27 0fb5 291f 9587 | ..'..6r..'..)...
3160 65c0 03ed 4ee5 b106 3d50 07 | 1`e...N...=P.
| Decoded:
| foo=ASDJKHQKBZXOQWEOPIUAXQ
| WEOIU; max-age=3600; versi
| on=1
| - evict: location:
| https://www.example.com
| - evict: :status: 307
| -> set-cookie: foo=ASDJKHQ
| KBZXOQWEOPIUAXQWEOIU; ma
| x-age=3600; version=1
动态列表 (解码后):
[ 1->62] (s = 98) set-cookie: foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU;
max-age=3600; version=1
[ 2->63] (s = 52) content-encoding: gzip
[ 3->64] (s = 65) date: Mon, 21 Oct 2013 20:13:22 GMT
总长度: 215
动态列表保留着一个最大的缓存大小值，每一个键值对的计算为name的字节数+value的字节数+32为确定的大小值。超出大小部分则丢弃不缓存，默认大小为4096。
总结
HPACK管理着HTTP2的头部的协议部分，有着高压缩比和重复请求的高复用性，双方编码解码需要各自维持一份动态表，动态根据处理数据来动态拓展，保证双方维持的表一模一样。从而保证ID索引不会乱。Huffman编码把头里面需要用到字符串的数据进行进一步的压缩，相对来说整个过程复杂度比HTTP1高很多，但相对的对使用者完全透明，在不影响其使用的情况下提高传输效率，并减少带宽的使用量。
