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# Howto HTTP
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Le procotole HTTP (HyperText Transfer Protocol) est un protocole client/serveur de niveau 7 s'appuyant par convention sur la couche de transport TCP et le port 80. Sa version sécurisée est HTTPS qui s'appuye en plus sur la couche [SSL/TLS ](HowtoSSL ).
## Comprendre les différentes versions de HTTP grâce à telnet
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### HTTP/1.0
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La version la plus simple, ll'entête `Host:` est facultatif :
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~~~
$ telnet www.debian.org 80
Trying 5.153.231.4...
Connected to www.debian.org.
Escape character is '^]'.
GET / HTTP/1.0
HTTP/1.1 200 OK
Date: Wed, 05 Oct 2016 02:09:37 GMT
Server: Apache
Last-Modified: Fri, 08 Jan 2016 22:27:31 GMT
ETag: "1d8-528da17d9b160"
Accept-Ranges: bytes
Content-Length: 472
Vary: Accept-Encoding
X-Clacks-Overhead: GNU Terry Pratchett
Connection: close
Content-Type: text/html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
< HTML >
[...]
Connection closed by foreign host.
~~~
### HTTP/1.1
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L'entête `Host:` est obligatoire :
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~~~
$ telnet www.debian.org 80
Trying 5.153.231.4...
Connected to www.debian.org.
Escape character is '^]'.
GET / HTTP/1.1
Host: www.debian.org
HTTP/1.1 200 OK
Date: Wed, 05 Oct 2016 02:11:37 GMT
Server: Apache
Content-Location: index.en.html
Vary: negotiate,accept-language,Accept-Encoding
TCN: choice
Last-Modified: Tue, 04 Oct 2016 15:27:56 GMT
ETag: "3baf-53e0bb4711c9f"
Accept-Ranges: bytes
Content-Length: 15279
Cache-Control: max-age=86400
Expires: Thu, 06 Oct 2016 02:11:37 GMT
X-Clacks-Overhead: GNU Terry Pratchett
Connection: close
Content-Type: text/html
Content-Language: en
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
< html lang = "en" >
[...]
Connection closed by foreign host.
~~~
### HTTPS
On gère le tunnel SSL avec `openssl` puis tout est en clair :
~~~
$ openssl s_client -host www.debian.org -port 443
CONNECTED(00000003)
depth=3 C = SE, O = AddTrust AB, OU = AddTrust External TTP Network, CN = AddTrust External CA Root
verify return:1
depth=2 C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority
verify return:1
depth=1 C = FR, ST = Paris, L = Paris, O = Gandi, CN = Gandi Standard SSL CA 2
verify return:1
depth=0 OU = Domain Control Validated, OU = Gandi Standard SSL, CN = debian.org
verify return:1
---
Certificate chain
0 s:/OU=Domain Control Validated/OU=Gandi Standard SSL/CN=debian.org
i:/C=FR/ST=Paris/L=Paris/O=Gandi/CN=Gandi Standard SSL CA 2
1 s:/C=FR/ST=Paris/L=Paris/O=Gandi/CN=Gandi Standard SSL CA 2
[...]
Start Time: 1475633567
Timeout : 300 (sec)
Verify return code: 0 (ok)
---
GET / HTTP/1.0
HTTP/1.1 200 OK
Date: Wed, 05 Oct 2016 02:12:56 GMT
Server: Apache
[...]
~~~
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### HTTP/2.0
< https: / / fr . wikipedia . org / wiki / Hypertext_Transfer_Protocol / 2 >
## Outils
### HEAD/GET/POST
~~~
# apt install libwww-perl
~~~~
Voir < http: / / gcolpart . evolix . net / blog21 / faire-du-postgethead-en-ligne-de-commande / >
### cURL
Voir [TipsCurl]()
### ab : apache bench
~~~
# apt install apache2-utils
~~~
Utilisation :
~~~{.bash}
$ ab -n 1000 -c 100 -l http://127.0.0.1/helloworld.txt
~~~
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* `-n` : nombre de requêtes
* `-c` : nombre de requêtes effectuées en simultané
* `-l` : option importante qui tolère la variation de la réponse du serveur (si non, les requêtes seront notées en *Failed requests* )
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* `-k` : active le HTTP KeepAlive
