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CS144-lab0

2023/02/01 Blog CS144 计算机网络 共 16767 字，约 48 分钟

环境准备

  1. 实验资料，包括实验手册以及PPT

  2. 环境配置

    2.1申请EC2

    ​ 在lab0的实验手册中有不同的实验环境配置方案，这里我选择使用更方便的AWS的EC2。AWS为新用户提供为期一年的免费使用，需要使用Visa等信用卡注册，在国内也可以使用银联信用卡注册。注册以后申请EC2实例，选择Ubuntu version 18.04 LTS系统，登陆方式可以选择秘钥登陆或者密码登陆，如果未创建过秘钥对，选择创建秘钥对后会将私钥下载到本地。在安全组配置处开放SSH、SMTP、POP3、HTTP、HTTPS、ICMP等服务端口，当然也可以在实例启动以后再修改安全组规则。如果未开放SSH端口，则无法通过SHELL远程连接服务器，所以最好在申请实例时候一次性将所有需要端口配置好。

    2.2连接EC2

    ​ 使用SHELL连接服务器，WindTerm)是一款颜值高，且支持类似tmux和cmder分屏的工具。选择会话，新建会话，主机处输入IP地址，其余可根据个人喜好选择是否填写，然后弹出输入用户，用户名为ubuntu，EC2默认不允许远程使用root登陆，确认后选择秘钥路径然后登陆。

    image-20230124115551210

    在连接处AWS默认用户名为ubuntu，出于方便可配置用root用户登陆，也可以使用su -i或su root切换到root。

    2.3配置EC2

    ​ 2.3.1开启root用户登陆 ​ sudo passwd root可直接设置root用户的密码。 ​ su root输入设置的密码切换至root. ​ 2.3.2编辑 sshd 服务配置文件： ​ vi /etc/ssh/sshd_config ​ 将PermitRootLogin 设置为yes, ​ 确保passwordAuthentication 为yes. ​ 保存后重启sshd服务service sshd restart或者/bin/systemctl restart sshd.service即可。

    ​ 2.3.3配置实验依赖工具

    ​ 首先执行apt-get update更新apt-get版本和软件源。

    ​ 实验手册中给出了没有使用prepared image的安装说明，使用EC2服务器只需安装依赖的工具，官方已经给出了安装脚本

    wget https://web.stanford.edu/class/cs144/vm_howto/setup_dev_env.sh

    bash ./setup_dev_env.sh

    2.4构建Sponge项目Sponge quickstart

    git clone https://github.com/cs144/sponge
cd sponge
mkdir build
cd build
   
cmake ..
make -j$(nproc)

构建项目中可能会出现以下报错

/home/ubuntu/cs144/sponge/libsponge/util/parser.cc:36:13: error: shift count >= width of type [-Werror,-Wshift-count-overflow]
        ret <<= 8;
            ^   ~
将 ret <<=8; 换成 ret = ret << 8 即可正常运行

任务一：获取一个网页

我在EC2上安装了nginx，其默认自带静态首页，使用http协议通过浏览器访问我的EC2站点，结果如下，如果没有域名也可以直接使用http://ip来访问站点

image-20230124152502482

通过telnet获取网页

root@ip-172-31-12-241:~# telnet 127.0.0.1 http
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
GET /index.html HTTP/1.1
Host: localhost
Connection: close

HTTP/1.1 200 OK
Server: nginx/1.14.0 (Ubuntu)
Date: Tue, 24 Jan 2023 07:34:02 GMT
Content-Type: text/html
Content-Length: 612
Last-Modified: Tue, 17 Apr 2018 15:22:36 GMT
Connection: close
ETag: "5ad6113c-264"
Accept-Ranges: bytes

<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>
Connection closed by foreign host.

Assignment: Now that you know how to fetch a Web page by hand, show us you can! Use the above technique to fetch the URL http://cs144.keithw.org/lab0/sunetid, replacing sunetid with your own primary SUNet ID. You will receive a secret code in the X-Your-Code-Is: header. Save your SUNet ID and the code for inclusion in your writeup.

root@ip-172-31-12-241:~# telnet cs144.keithw.org http
Trying 104.196.238.229...
Connected to cs144.keithw.org.
Escape character is '^]'.
GET /lab0/gaozhiyuan HTTP/1.1
Host: cs144.keithw.org
Connection: close

HTTP/1.1 200 OK
Date: Tue, 24 Jan 2023 07:44:34 GMT
Server: Apache
X-You-Said-Your-SunetID-Was: gaozhiyuan
X-Your-Code-Is: 375453
Content-length: 114
Vary: Accept-Encoding
Connection: close
Content-Type: text/plain

Hello! You told us that your SUNet ID was "gaozhiyuan". Please see the HTTP headers (above) for your secret code.
Connection closed by foreign host.

任务二：发送邮件

邮件由三部分组成，用户代理、邮件传输代理、邮件分发代理

1.环境准备，选择使用postfix作为邮件传输代理，安全规则放行SMTP 25端口，POP3 110端口，IMAP 143端口

2.域名解析，在域名解析服务商处添加A记录，MX记录，CNAME记录

3.使用nslookup -type=MX mydomain.com或者dig mx mydomain.com查看解析是否生效

4.安装postfix

apt-get install postfix

在安装过程中会提示postfix配置

  • No configuration：表示不要做任何配置；

  • Internet Site：表示直接使用本地SMTP服务器发送和接收邮件；

  • Internet with smarthos： 表示使用本地SMTP服务器接收邮件，但发送邮件时不直接使用本地SMTP服务器，而是使用第三方smart host来转发邮件；

  • Satellite system：表示邮件的发送和接收都是由第三方smarthost来完成。

  • Local only：表示邮件只能在本机用户之间发送和接收。

然后会提示域名配置，输入mydomain.com

安装完成后查看端口监听情况：

root@ip-172-31-12-241:~# netstat -anptl | grep 25
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      2267/master         
tcp6       0      0 :::25                   :::*                    LISTEN      2267/master

可以看到SMTP 25端口正常监听

5.使用telnet测试收发邮件

#新建用户并设置密码
useradd -m -s /bin/bash gaozhiyuan
passwd gaozhiyuan
#输入密码

#测试SMTP25端口是否打开
telnet localhost 25
#输出如下说明正常
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 ip-172-31-12-241.ap-northeast-1.compute.internal ESMTP Postfix (Ubuntu)

#测试收发邮件
telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 ip-172-31-12-241.ap-northeast-1.compute.internal ESMTP Postfix (Ubuntu)

ehlo localhost
250-ip-172-31-12-241.ap-northeast-1.compute.internal
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250 SMTPUTF8

mail from: root@csmasterpath.top
250 2.1.0 Ok

rcpt to: gaozhiyuan@csmasterpath.top
250 2.1.5 Ok

data
354 End data with <CR><LF>.<CR><LF>
Subject: Test Mail
Hi, gaozhiyuan! This is a test e-mail. I'm your e-mail server manager!
.
250 2.0.0 Ok: queued as DDDB1824FD

quit
221 2.0.0 Bye
Connection closed by foreign host
#到此邮件已经发送到gaozhiyuan@csmasterpath.top,切换到gaozhiyuan查看
su gaozhiyuan
#查看收件箱
mail
"/var/mail/gaozhiyuan": 1 message 1 new
>N   1 root@csmasterway.t Tue Jan 24 08:26  12/585   Test Mail
? 

#输入数字查看收到的邮件
? 1
Return-Path: <root@csmasterpath.top>
X-Original-To: gaozhiyuan@csmasterpath.top
Delivered-To: gaozhiyuan@csmasterpath.top
Received: from localhost (localhost [127.0.0.1])
        by ip-172-31-12-241.ap-northeast-1.compute.internal (Postfix) with ESMTP id DDDB1824FD
        for <gaozhiyuan@csmasterpath.top>; Tue, 24 Jan 2023 08:24:21 +0000 (UTC)
Subject: Test Mail
Message-Id: <20230124082442.DDDB1824FD@ip-172-31-12-241.ap-northeast-1.compute.internal>
Date: Tue, 24 Jan 2023 08:24:21 +0000 (UTC)
From: root@csmasterpath.top

Hi, gaozhiyuan! This is a test e-mail. I'm your e-mail server manager!

#退出
?quit
Saved 1 message in /home/gaozhiyuan/mbox
Held 0 messages in /var/mail/gaozhiyuan

062785  3  307

测试用qq邮箱发送邮件到gaozhiyuan@csmasterpath.top

image-20230124180347554

查看结果

#当前在gaozhiyuan用户
mail
gaozhiyuan@ip-172-31-12-241:~$ mail
"/var/mail/gaozhiyuan": 1 message 1 new
>N   1 1428272985@qq.com  Tue Jan 24 08:35  69/3426  Test Mail
? 

#查看邮件
?1
Return-Path: <1428272985@qq.com>
X-Original-To: gaozhiyuan@csmasterpath.top
Delivered-To: gaozhiyuan@csmasterpath.top
Received: from out162-62-57-49.mail.qq.com (out162-62-57-49.mail.qq.com [162.62.57.49])
        by ip-172-31-12-241.ap-northeast-1.compute.internal (Postfix) with ESMTPS id 0A0D9824FD;
        Tue, 24 Jan 2023 08:35:56 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=qq.com; s=s201512;
        t=1674549353; bh=/fqKGf5ndjblJ8iuoR8ElmrgZ0YeFP5GJs10BbhET0o=;
        h=Date:From:To:Cc:Subject;
        b=tDPxc3JALzwyKAHCIgaENZR9Yy4i8sy/gShsnoDvVxv/vOtPxMU2L62BS0A301pux
         cZ/+jCl0yvmLz+JgaQ1a+lAtlyVDD2fQ2jdTD6mHmIQJPSQr2tZFVoV3387+d0eGGi
         h/j5Jt9zQHzQDhKDdP5/10tuoKnu0ngkt6qxSfTM=
Received: from DESKTOP-656JFJI ([111.52.51.180])
        by newxmesmtplogicsvrszc2-0.qq.com (NewEsmtp) with SMTP
        id 8F4140A3; Tue, 24 Jan 2023 16:35:52 +0800
X-QQ-mid: xmsmtpt1674549352t5k9frlac
Message-ID: <tencent_C3384D71D826E1EF6BE9C6857F9E08BDE205@qq.com>
X-QQ-XMAILINFO: MTmSu602bpi083hmynJjDf/cBFEEZKBOJXknSaJBHM2KlL3s7quN1B80By2/11
         7oWeO2T4A/qTl2l3s6bFJWof/dPMFFm3T4+fdl3r5qaaMVy35QnCfPL3aUUzp6gGmwWzVz1wfjzb
         iGKrJuZUeJBldmUZmiHE/bR1HFT/q8mtGt6q8c7p6/wk8Iv0FoPsRm2wJSTEvRZ7DVWgMTT1i47j
         QTOe2VB2PYoA5akbhnEeg8+5zLgI/IJNRCUShxaTZ9xKps0GNjVCHuhUfH+VNSv2wvhEAIMys0Ny
         EvSoi1irr4GmaCjdJDd5E7CP6dV0VP7mIrs0nodieneW4mzdZ9P1sUxSWTfEgFrAPfP2SCVWGE8L
         Jyczlp7YCHRXHB/03MQeziuDT6JStIdFpfUqFfo0vpyUKn5Mcc6FZkYbg2bOdUbaccJWQlNOgCSg
         uCt+VyMNt9/qWHcfuzv8zrMvKBOwNGKBA974mWiX2X9sDwYzlao8TIpYbhjyJS6kG4MotmwK2kyY
         DNpSziqhEY84ulLELSlKGUdwwG5/8kf/F8qg+q1bhZ7grPyKfCfaIEr1mXei0HUirV6LnCs2CI9L
         u1ffA5FI4IoTTdgA5/c2UIOOiWVPe7tJ5w7WTV+XkppbZ9t+1WivevUGsSt2EpBiQaNYtVv24aOS
         eHOIrD2a2jKg057T6nfXqXVP933yj16/lQQd7rQBnyoNyPtjYkhF7Pfl5mX8sSTOC8JZlyEvYKcT
         Od4PW7EEmgJwAyJDUdC5uHFLx+R7ZLuW6LxBYfC6r06grwL+SK6YEgYmC5yNLVFcsVgIX2wP6Vam
         IXB2cOub5FrSKEF1aknFtq5YZ3R88oZ+SobJDPn0qAJDHDcblWuacq+scx6uSXZxWCf6uev9x36E
         O+vBLYNQhDJHHe3PgZXeBB5QIPi3uMvpmUXiAUkWGNgnf0ufiVWuOqqZYYDkJ02hLmk+GTCya9
Date: Tue, 24 Jan 2023 16:35:54 +0800
From: "1428272985@qq.com" <1428272985@qq.com>
To: gaozhiyuan <gaozhiyuan@csmasterpath.top>
Cc: root <root@csmasterpath.top>
Subject: Test Mail
X-Priority: 3
X-GUID: EDA9983B-B8AF-4C07-B414-4545E99D0F80
X-Has-Attach: no
X-Mailer: Foxmail 7.2.25.178[cn]
Mime-Version: 1.0
X-OQ-MSGID: <202301241635540061581@qq.com>
Content-Type: multipart/alternative;
        boundary="----=_001_NextPart522038763015_=----"

This is a multi-part message in MIME format.

------=_001_NextPart522038763015_=----
Content-Type: text/plain;
        charset="us-ascii"
Content-Transfer-Encoding: base64

DQpTZW5kIGEgdGVzdCBlLW1haWwgZnJvbSBxcS5jb20gdG8gY3NtYXN0ZXJ3YXkudGVjaA0KDQoN
CjE0MjgyNzI5ODVAcXEuY29tDQo=

------=_001_NextPart522038763015_=----
Content-Type: text/html;
        charset="us-ascii"
Content-Transfer-Encoding: quoted-printable

<html><head><meta http-equiv=3D"content-type" content=3D"text/html; charse=
t=3Dus-ascii"><style>body { line-height: 1.5; }body { font-size: 14px; fon=
t-family: "Microsoft YaHei UI"; color: rgb(0, 0, 0); line-height: 1.5; }</=
style></head><body>=0A<div><span></span><br></div>=0A<div>Send a test e-ma=
il from qq.com to csmasterpath.top</div><hr style=3D"WIDTH: 210px; HEIGHT:=
 1px" color=3D"#b5c4df" size=3D"1" align=3D"left">=0A<div><span><div style=
=3D"MARGIN: 10px; FONT-FAMILY: verdana; FONT-SIZE: 10pt"><div>1428272985@q=
q.com</div></div></span></div>=0A</body></html>
------=_001_NextPart522038763015_=------

#查看抄送到root的邮件
root@ip-172-31-12-241:~# mail
"/var/mail/root": 1 message 1 new
>N   1 1428272985@qq.com  Tue Jan 24 08:35  69/3414  Test Mail
? 1
Return-Path: <1428272985@qq.com>
X-Original-To: root@csmasterpath.top
Delivered-To: root@csmasterpath.top
Received: from out162-62-57-49.mail.qq.com (out162-62-57-49.mail.qq.com [162.62.57.49])
        by ip-172-31-12-241.ap-northeast-1.compute.internal (Postfix) with ESMTPS id 0A0D9824FD;
        Tue, 24 Jan 2023 08:35:56 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=qq.com; s=s201512;
        t=1674549353; bh=/fqKGf5ndjblJ8iuoR8ElmrgZ0YeFP5GJs10BbhET0o=;
        h=Date:From:To:Cc:Subject;
        b=tDPxc3JALzwyKAHCIgaENZR9Yy4i8sy/gShsnoDvVxv/vOtPxMU2L62BS0A301pux
         cZ/+jCl0yvmLz+JgaQ1a+lAtlyVDD2fQ2jdTD6mHmIQJPSQr2tZFVoV3387+d0eGGi
         h/j5Jt9zQHzQDhKDdP5/10tuoKnu0ngkt6qxSfTM=
Received: from DESKTOP-656JFJI ([111.52.51.180])
        by newxmesmtplogicsvrszc2-0.qq.com (NewEsmtp) with SMTP
        id 8F4140A3; Tue, 24 Jan 2023 16:35:52 +0800
X-QQ-mid: xmsmtpt1674549352t5k9frlac
Message-ID: <tencent_C3384D71D826E1EF6BE9C6857F9E08BDE205@qq.com>
X-QQ-XMAILINFO: MTmSu602bpi083hmynJjDf/cBFEEZKBOJXknSaJBHM2KlL3s7quN1B80By2/11
         7oWeO2T4A/qTl2l3s6bFJWof/dPMFFm3T4+fdl3r5qaaMVy35QnCfPL3aUUzp6gGmwWzVz1wfjzb
         iGKrJuZUeJBldmUZmiHE/bR1HFT/q8mtGt6q8c7p6/wk8Iv0FoPsRm2wJSTEvRZ7DVWgMTT1i47j
         QTOe2VB2PYoA5akbhnEeg8+5zLgI/IJNRCUShxaTZ9xKps0GNjVCHuhUfH+VNSv2wvhEAIMys0Ny
         EvSoi1irr4GmaCjdJDd5E7CP6dV0VP7mIrs0nodieneW4mzdZ9P1sUxSWTfEgFrAPfP2SCVWGE8L
         Jyczlp7YCHRXHB/03MQeziuDT6JStIdFpfUqFfo0vpyUKn5Mcc6FZkYbg2bOdUbaccJWQlNOgCSg
         uCt+VyMNt9/qWHcfuzv8zrMvKBOwNGKBA974mWiX2X9sDwYzlao8TIpYbhjyJS6kG4MotmwK2kyY
         DNpSziqhEY84ulLELSlKGUdwwG5/8kf/F8qg+q1bhZ7grPyKfCfaIEr1mXei0HUirV6LnCs2CI9L
         u1ffA5FI4IoTTdgA5/c2UIOOiWVPe7tJ5w7WTV+XkppbZ9t+1WivevUGsSt2EpBiQaNYtVv24aOS
         eHOIrD2a2jKg057T6nfXqXVP933yj16/lQQd7rQBnyoNyPtjYkhF7Pfl5mX8sSTOC8JZlyEvYKcT
         Od4PW7EEmgJwAyJDUdC5uHFLx+R7ZLuW6LxBYfC6r06grwL+SK6YEgYmC5yNLVFcsVgIX2wP6Vam
         IXB2cOub5FrSKEF1aknFtq5YZ3R88oZ+SobJDPn0qAJDHDcblWuacq+scx6uSXZxWCf6uev9x36E
         O+vBLYNQhDJHHe3PgZXeBB5QIPi3uMvpmUXiAUkWGNgnf0ufiVWuOqqZYYDkJ02hLmk+GTCya9
Date: Tue, 24 Jan 2023 16:35:54 +0800
From: "1428272985@qq.com" <1428272985@qq.com>
To: gaozhiyuan <gaozhiyuan@csmasterpath.top>
Cc: root <root@csmasterpath.top>
Subject: Test Mail
X-Priority: 3
X-GUID: EDA9983B-B8AF-4C07-B414-4545E99D0F80
X-Has-Attach: no
X-Mailer: Foxmail 7.2.25.178[cn]
Mime-Version: 1.0
X-OQ-MSGID: <202301241635540061581@qq.com>
Content-Type: multipart/alternative;
        boundary="----=_001_NextPart522038763015_=----"

This is a multi-part message in MIME format.

------=_001_NextPart522038763015_=----
Content-Type: text/plain;
        charset="us-ascii"
Content-Transfer-Encoding: base64

DQpTZW5kIGEgdGVzdCBlLW1haWwgZnJvbSBxcS5jb20gdG8gY3NtYXN0ZXJ3YXkudGVjaA0KDQoN
CjE0MjgyNzI5ODVAcXEuY29tDQo=

------=_001_NextPart522038763015_=----
Content-Type: text/html;
        charset="us-ascii"
Content-Transfer-Encoding: quoted-printable

<html><head><meta http-equiv=3D"content-type" content=3D"text/html; charse=
t=3Dus-ascii"><style>body { line-height: 1.5; }body { font-size: 14px; fon=
t-family: "Microsoft YaHei UI"; color: rgb(0, 0, 0); line-height: 1.5; }</=
style></head><body>=0A<div><span></span><br></div>=0A<div>Send a test e-ma=
il from qq.com to csmasterpath.top</div><hr style=3D"WIDTH: 210px; HEIGHT:=
 1px" color=3D"#b5c4df" size=3D"1" align=3D"left">=0A<div><span><div style=
=3D"MARGIN: 10px; FONT-FAMILY: verdana; FONT-SIZE: 10pt"><div>1428272985@q=
q.com</div></div></span></div>=0A</body></html>
------=_001_NextPart522038763015_=------

测试使用gaozhiyuan@csmasterpath.top发送邮件给1428272985@qq.com

gaozhiyuan@ip-172-31-12-241:/root$ telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 ip-172-31-12-241.ap-northeast-1.compute.internal ESMTP Postfix (Ubuntu)
ehlo localhost
250-ip-172-31-12-241.ap-northeast-1.compute.internal
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250 SMTPUTF8
mail from: gaozhiyuan@csmasterpath.top
250 2.1.0 Ok
rcpt to:1428272985@qq.com
250 2.1.5 Ok
data
354 End data with <CR><LF>.<CR><LF>
Subject:Test Mail
This is a test e-mail from gaozhiyuan@csmasterpath.top
.
250 2.0.0 Ok: queued as 611C4824FD
quit
221 2.0.0 Bye
Connection closed by foreign host.

此时已经显示发送成功但是在QQ邮箱中并未收到邮件，原因EC2默认封禁了SMTP 25端口出方向流量，需要根据AWS官方的说明申请解封25端口。

2.2：使用telnet建立通信

image-20230124202239693

任务三：使用OS stream socket实现一个网络程序

这里和上述通过telnet客户端获取网页是一样的流程。

TCPSocket socket{};
socket.connect(Address(host,"http"));
socket.write("GET " + path + " HTTP/1.1\r\nHost: " + host + "\r\n\r\n");
socket.shutdown(SHUT_WR);
while(!socket.eof())
{
    cout << socket.read();
}
socket.close();

任务四:实现内存中的支持读写的可靠字节流

​ 根据实验手册，此测试只有单台主机。字节流可以从输入方写入，从输出方读出，当读取到“EOF”（end of file）时候，表示当前已经没有可以被读取的字节流。首先想到的就是先入先出的队列，如果将数组封装成循环队列，这样不仅能够提高效率，内存也能够充分利用。但是实验手册要求使用“Modern C++”，尽量避免使用普通指针，同时为使用对象的方法从而方便输入和读取操作，选用deque。

byte_stream.hh

class ByteStream {
  private:
    // Your code here -- add private members as necessary.
    // Init reading and writing memory that will be used to communicate.
    std::deque<char> _buffer{};
    // The memory capacity.
    size_t _capacity{0};
    // The bytes num that writer has written into the memory.
    size_t _written_bytes{0};
    // The bytes num that reader has read from the memory.
    size_t _read_bytes{0};
    //!< Flag indicating that the input byte stream is finished.
    bool _input_ended{false};
    bool _error{false};  //!< Flag indicating that the stream suffered an error.
}

byte_stram.cc

//Init he memory capacity
ByteStream::ByteStream(const size_t capacity) :_capacity{capacity}{}

size_t ByteStream::write(const string &data) {
    if(_input_ended){
        return 0;
    }
    // Only the minimum between remaining capacity and the data size can be written into the buffer.
    size_t written_len = 0;
    data.size() >= remaining_capacity() ? written_len = remaining_capacity() : written_len = data.size();
    _buffer.insert(_buffer.end(),data.begin(),data.begin() + written_len);
    _written_bytes += written_len;
    return written_len;
}

//! \param[in] len bytes will be copied from the output side of the buffer
string ByteStream::peek_output(const size_t len) const {
   // Only the maximum between the parameter len and the maximum amount that can currently be peeked/read can be peeked.
   size_t peeked_len = 0;
   len >= _buffer.size() ? peeked_len = _buffer.size() : peeked_len = len;
   return string(_buffer.begin(),_buffer.begin() + peeked_len);
}

//! \param[in] len bytes will be removed from the output side of the buffer
void ByteStream::pop_output(const size_t len) {
     //Only the maximum between the parameter len and the maximum amount that can currently be peeked/read can be popped.
    size_t popped_len = 0;
    len >= buffer_size() ? popped_len = buffer_size() : popped_len = len;
    _buffer.erase(_buffer.begin(),_buffer.begin() + popped_len);
    _read_bytes += popped_len;
}

//! Read (i.e., copy and then pop) the next "len" bytes of the stream
//! \param[in] len bytes will be popped and returned
//! \returns a string
std::string ByteStream::read(const size_t len) {
    string res = peek_output(len);
    pop_output(res.size());
    return res;
}
// Signal that the byte stream has reached its ending
void ByteStream::end_input() {_input_ended = true;}
// `true` if the stream input has ended
bool ByteStream::input_ended() const { return _input_ended; }
// the maximum amount that can currently be peeked/read
size_t ByteStream::buffer_size() const { return _buffer.size(); }
// `true` if the buffer is empty
bool ByteStream::buffer_empty() const { return _buffer.empty(); }
// `true` if the output has reached the ending
bool ByteStream::eof() const { return input_ended() && buffer_empty();}
// Total number of bytes written
size_t ByteStream::bytes_written() const { return _written_bytes; }
// Total number of bytes popped
size_t ByteStream::bytes_read() const { return _read_bytes; }
// Returns the number of additional bytes that the stream has space for
size_t ByteStream::remaining_capacity() const { return _capacity - _buffer.size();}

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