├── README.md
└── encode.go


/README.md:
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 1 | # HPACK-Encode
 2 | Encode strings with HPACK to produce a valid Server header for Nginx.
 3 | 
 4 | <br/>
 5 | The Nginx source contains the Server header "nginx" when using HTTP/2:
 6 | 
 7 |     static const u_char nginx[5] = "\x84\xaa\x63\x55\xe7";
 8 | 
 9 | It can be seen here: https://trac.nginx.org/nginx/browser/nginx/src/http/v2/ngx_http_v2_filter_module.c#L148
10 | 
11 | <br/>
12 | To replace this we need to HPACK encode the replacement string.
13 | 
14 | Run the script with your desired Server header as the argument, and it will output the required line of code.
15 | If you get dependency errors, it may be necessary to run 'go get golang.org/x/net/http2/hpack' first.
16 | 
17 | For example, running the script with `go run encode.go 'Encrypt All The Things!!!'` will output the following:
18 | 
19 | 
20 |     static const u_char nginx[22] = "\x95\xc1\x51\x2c\xf5\x5a\x54\x86\x8a\x14\xdf\x39\x54\xdf\x39\xaa\x99\x1f\xc7\xf1\xfc\x7f";
21 |     
22 | Replace this in the Nginx source and build.
23 | 
24 | <br/>
25 | This script is based off the StackOverflow answer provided <a href="https://stackoverflow.com/questions/35655448/how-does-this-code-result-in-the-string-nginx/36890013#36890013">here</a>.
26 | 


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/encode.go:
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 1 | package main
 2 | 
 3 | import (
 4 |     "fmt"
 5 |     "golang.org/x/net/http2/hpack"
 6 |     "os"
 7 |     "strconv"
 8 | )
 9 | 
10 | func main() {
11 |     fmt.Println(Encode(os.Args[1]))
12 | }
13 | 
14 | func Encode(s string) string {
15 |     var result string
16 |     var count int
17 | 
18 |     hd := hpack.AppendHuffmanString(nil, s)
19 |     hl := hpack.HuffmanEncodeLength(s) | 0x80
20 | 
21 |     result += RenderByte(byte(hl))
22 | 
23 |     for _, b := range hd {
24 |         result += RenderByte(b)
25 |         count += 1
26 |     }
27 | 
28 |     return "static const u_char nginx[" + strconv.Itoa(count + 1) + "] = \"" + string(result) + "\";"
29 | }
30 | 
31 | func RenderByte(b byte) string {
32 |     return fmt.Sprintf("\\x%x", b)
33 | }
34 | 


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