日本欧洲视频一区_国模极品一区二区三区_国产熟女一区二区三区五月婷_亚洲AV成人精品日韩一区18p

COMP26020代做、代寫Lab 5 - Solidity

時間:2024-05-03  來源:  作者: 我要糾錯



COMP26020: Programming Languages and Paradigms
Lab 5 - Solidity
Joseph Razavi and Richard Banach
1 Introduction
This lab exercise is about learning a programming language with unusual aspects from its documentation.
We focus on the Solidity programming language, in particular Solidity version 6, which you can read about
here:
https://docs.soliditylang.org/en/v0.6.0/
Solidity is a language designed to write so-called “smart contracts”. These are pieces of code which are
supposed to run on a public “blockchain” – a system which keeps a log of every event which happens, and
where no user can single-handedly affect what happens. That means that once your code is deployed, you
can no longer influence it, unless you have programmed mechanisms to do so. And if you find a bug, the
bug is there forever!
In addition, the blockchain is designed to support payments of various kinds – for instance a smart
contract has a balance of currency (called ‘wei’ for the Etherium blockchain on which Solidity contracts run)
which it must use to pay for its own computing resources. Contracts can charge each other and pay each
other for services.
Whether or not any of this is a sensible technical or social project is perhaps debatable, but it certainly
creates interesting design challenges for a programming language – and where weird programming languages
lead, let us follow!
Read about Solidity’s notion of a contract, and its execution model (the ‘Ethereum Virtual Machine’) here:
https://docs.soliditylang.org/en/v0.6.0/introduction-to-smart-contracts.html
Refer to the Solidity documentation to complete the exercises below. Aside from the above these sections
are particularly useful:
• https://docs.soliditylang.org/en/v0.6.0/solidity-by-example.html
• https://docs.soliditylang.org/en/v0.6.0/solidity-in-depth.html
If you prefer videos, I have made available on Blackboard some videos designed to help you get started.
Note these videos belong to the lab and are not part of the content of any week. Solidity will be used only
for the lab, and is not examinable.
In this lab exercise, rather than deploying our code on the real public blockchain (and having to pay
to run it!) we will use a simulated version of the Etherium Virtual Machine which is used for developing
code and testing it before deploying it for real. You must use the version provided on Blackboard; see next
section.
1
2 Setup
Make sure you have downloaded Remix from Blackboard:
https://online.manchester.ac.uk/bbcswebdav/courses/I3132-COMP-26020-1231-1YR-040494/remix-d624303.zip
(If the link above does not work, check the Lab 5 folder on Blackboard for information.)
and that you can compile and run programs. To do this, you might need to click on the ‘plug’ icon on the
left hand menu, and made sure ‘Solidity compiler’ and ‘deploy and run transactions’ are enabled. This will
let you compile and run Solidity programs in Remix as seen in the videos. Remix is a browser based editor,
and has been tested for this course on Google Chrome on Linux and Windows. With other browsers you
may get strange behaviour. It is better to edit in a separate text editor and paste into Remix for testing, as
it can have problems with saving files and allowing text to be copied out of it in some browsers. Make sure
you always have a copy of your code in another editor so that you don’t lose your work. Clone the gitlab
repository
26020-lab5-S-Solidity_
where is replaced by your username. This contains the files you will need for the exercise.
3 Background
The exercises concern three contracts which should interact with each other, alongside other contracts which
we assume exist (but do not implement or worry about the implementation of). The first contract we consider is a ‘paylock’. The idea is that a supplier does some work, which can then be collected by a customer.
If the customer collects early, they get a discount, and how much discount they get depends on how early:
there are two deadlines. If they miss the second deadline they forfeit their discount altogether.
Done_2 Forfeit
Done_1 Delay
 Working Completed
Start
Signal
Collect_1_Y Collect_1_N
Collect_2_Y Collect_2_N
The blobs indicate possible states of the paylock, and the arrows represent function calls. The ‘Start’
arrow represents the constructor. The idea is that the functions should only succeed if the paylock is in
the state at the beginning of the arrow, and then the resulting state should be the one at the end. Of
course, there are other conditions: collect_1_Y should only succeed if called before the first deadline,
and collect_1_N should only succeed if called once the first deadline has passed; similar considerations
apply to the other two collect functions. Look in the file paylock.sol to see a partially finished implementation of the paylock. The first two exercises (see next section) concern only the logic of the paylock.
They are about adding features to the implementation, though we never complete a realistic implementation.
The subsequent exercises are about implementing a supplier which has to interact with both the paylock
contract and a rental contract which it needs to use to complete its work. As above, we will only model
2
certain aspects of these contracts. On the one hand this makes the exercises manageable, but on the other
hand it can be confusing if not pointed out: you would naturally wonder when we would add the rest of the
necessary features!
4 Exercises
The implementation of the paylock which you are given does not model the passage of time. To do this, we
will add a tick function, representing the passage of one unit of time. We shall assume for the moment that
the tick function is going to be called by a neutral third party, who we trust to call it at a regular interval.
For now we also trust all other contracts in the universe not to call this function. (And assume that the
blockchain updates quickly enough that this is a reasonable model of time! This is not how one would deal
with time in a real smart contract system.)
EXERCISE 1: (2 marks)
Add an int variable clock and a tick function which models the passage of time. Modify the various
collect functions to adhere to the deadlines, where we consider the first deadline to happen if the clock
has reached 4 units of time or more, and the second deadline to be when the clock has increased by
4 units of time or more from when collect_1_N was called.
We now need to make sure this tick function can only be called by the agreed third party.
EXERCISE 2: (2 marks)
Add an address variable timeAdd to the contract. Add an argument to the constructor and set the
value of timeAdd to that argument. Now modify tick so that it can only be called by someone from
the address timeAdd .
Tip: when testing your code, copy one of the addresses from the ‘Account’ dropdown menu and paste
it into the constructor argument. That should make it easier to experiment.
Look in the file supplier.txt and paste its contents at the end of paylock.sol . Note how the Supplier
contract interacts with the paylock, indicating to the paylock when it has finished its task. In the next
exercise, we will make it interact with the Rental contract too. The idea is that in order to finish its job,
the Supplier must rent a resource, then return it, before calling finish will succeed.
EXERCISE 3: (2 marks)
Add functions aquire_resource and return_resource which must be called in that order to the
Supplier contract. To do this you will need to add new local variables. Add a local variable
representing an instance of the Rental contract, and allow the address of an instance of Rental to
be passed as an argument to the constructor. Modify the aquire_resource and return_resource
functions so that they call the appropriate functions of the Rental contract.
Tip: Since the constructor of Supplier requires the addresses of a Paylock and a Rental, make sure
you deploy instances of those first when testing.
We will now make our model of the Rental contract somewhat more realistic, by requiring the payment
of a deposit which is returned once the rented resource is re- turned. For the purposes of the lab we assume
that the deposit is 1 wei.
Since the Rental contract is not supposed to assume that it is being called be a Supplier, it should
assume that the contract it is connected to implements a receive function; you can read about this in the
Solidity language documentation:
https://docs.soliditylang.org/en/v0.6.0/contracts.html#receive-ether-function.
3
Since we are not allowed to assume the calling contract is a Supplier, it is also useful to look at the
functions which can be applied to any address:
https://docs.soliditylang.org/en/v0.6.0/types.html#members-of-addresses .
In fact, our intention is to make as few assumptions about the other contract as possible, so we will use
the low-level .call() function. Find out how to make this work and attach a value to it.
EXERCISE 4: (2 marks)
Modify the Rental contract in the following way. First find the commented line
//CHECK FOR PAYMENT HERE
and replace it with something which prevents the function from succeeding unless proper payment is
made. You will also have to make the functions payable. Then find the commented line
//RETURN DEPOSIT HERE
and replace it with a single use of the .call function which returns the deposit. Modify the Supplier
contract so that it has a receive function, and make sure that Rental does not assume that the
contract which calls its functions is an instance of Supplier. Modify the external function calls made
by Supplier to Rental so that they transfer the deposit as appropriate.
At this point you should copy the file paylock.sol to supplier2.sol and work in supplier2.sol .
The rental contract as implemented has a security flaw (which is described in the ‘Reentrancy’ section of
chapter 9 of Antonopoulos’s book Mastering Etherium (available online from the library, and also at
https://github.com/ethereumbook/ethereumbook/blob/develop/09smart-contracts-security.asciidoc
EXERCISE 5: (1 mark)
Modify the Supplier contract to take advantage of this security flaw to take more Ether belonging
to the Rental contract than it has sent to the contract, if more ehter is available. Make sure this
work is saved in the file supplier2.sol
At this point you should copy the file supplier2.sol to suppler3.sol and work in supplier3.sol .
EXERCISE 6: (1 mark)
Re-order the lines of the retrieve_resource function of the Rental contract so that the vulnerability
above is fixed. Make sure this work is saved in the file supplier2.sol
Note: You need only prevent the attack described here while preserving correct functionality; you do
not need to solve any other security flaws.
5 Submission
Submission is by gitlab, following the same procedure as the other labs for this unit. Ensure that you have
pushed a commit containing your submission (i.e. make sure you have added all files to the repository),
tagged with the tag lab5-submission , by 6pm on 03/05.
Check SPOT to make sure your submission has been received correctly, and contact me (Joe) if you
notice any strange behaviour from SPOT.
請加QQ:99515681  郵箱:99515681@qq.com   WX:codinghelp





 

標簽:

掃一掃在手機打開當前頁
  • 上一篇:代寫program、代做c/c++,Python語言編程
  • 下一篇:EBU4201代做、代寫Java設計編程
  • 無相關信息
    昆明生活資訊

    昆明圖文信息
    蝴蝶泉(4A)-大理旅游
    蝴蝶泉(4A)-大理旅游
    油炸竹蟲
    油炸竹蟲
    酸筍煮魚(雞)
    酸筍煮魚(雞)
    竹筒飯
    竹筒飯
    香茅草烤魚
    香茅草烤魚
    檸檬烤魚
    檸檬烤魚
    昆明西山國家級風景名勝區
    昆明西山國家級風景名勝區
    昆明旅游索道攻略
    昆明旅游索道攻略
  • NBA直播 短信驗證碼平臺 幣安官網下載 歐冠直播 WPS下載

    關于我們 | 打賞支持 | 廣告服務 | 聯系我們 | 網站地圖 | 免責聲明 | 幫助中心 | 友情鏈接 |

    Copyright © 2025 kmw.cc Inc. All Rights Reserved. 昆明網 版權所有
    ICP備06013414號-3 公安備 42010502001045

    日本欧洲视频一区_国模极品一区二区三区_国产熟女一区二区三区五月婷_亚洲AV成人精品日韩一区18p

              午夜精品福利电影| 国产人成一区二区三区影院| 亚洲欧美日本精品| 国产精品亚洲综合一区在线观看| 久久激情婷婷| 一区二区三欧美| 亚洲高清在线观看| 国产精品黄视频| 欧美国产日韩a欧美在线观看| 亚洲欧美日韩国产| 亚洲三级免费电影| 一区二区三区在线免费观看| 国产精品美女久久| 欧美精品久久久久久久免费观看| 欧美激情精品久久久久久大尺度| 国产精品久久久久久久久久ktv | 国产精品成人一区二区三区吃奶| 久久国产精品亚洲77777| 一区二区三区www| 亚洲精品乱码久久久久久蜜桃91| 狠狠色丁香婷婷综合影院 | 一本高清dvd不卡在线观看| 精品不卡在线| 国产综合精品| 欧美日韩精品一区二区三区四区 | 欧美精品在线观看播放| 久久久久.com| 欧美人妖在线观看| 久久精品视频在线观看| 亚洲在线1234| 欧美一级网站| 久久人人爽人人爽爽久久| 欧美与黑人午夜性猛交久久久| 亚洲欧美日韩天堂| 久久黄色网页| 久久欧美肥婆一二区| 久久久久久九九九九| 久久久久一本一区二区青青蜜月| 久久另类ts人妖一区二区| 久久久久久午夜| 欧美成人国产| 国产精品swag| 国产视频精品va久久久久久| 国产亚洲欧美日韩美女| 在线欧美一区| 亚洲精品午夜| 亚洲午夜久久久久久久久电影网| 亚洲一级在线| 久久久久国产精品人| 久久久久久久97| 欧美日韩国产欧| 国产精品网站在线| 娇妻被交换粗又大又硬视频欧美| 精品1区2区| 一本色道**综合亚洲精品蜜桃冫| 一区二区三区四区五区视频| 亚洲欧美激情四射在线日| 久久精品一区二区国产| 欧美日韩国产首页| 国产日韩综合| 亚洲精品女人| 午夜久久99| 欧美精品999| 国产亚洲一区在线| 亚洲精品在线观看免费| 欧美在线视频免费| 欧美日韩中文| 亚洲黄色免费网站| 久久岛国电影| 国产精品家教| 亚洲欧洲日本一区二区三区| 欧美亚洲免费电影| 欧美另类女人| 亚洲国产精品激情在线观看| 亚洲自拍电影| 欧美日本免费一区二区三区| 韩日在线一区| 欧美一区二区精品久久911| 欧美精品亚洲精品| 悠悠资源网亚洲青| 亚洲性图久久| 欧美日本韩国| 亚洲国产精品999| 久久精品国产欧美亚洲人人爽| 国产精品福利网| 一本久久知道综合久久| 另类成人小视频在线| 国产一区美女| 欧美在线播放一区| 国产热re99久久6国产精品| 一区二区三区精品视频在线观看| 免播放器亚洲一区| 狠狠色狠狠色综合系列| 欧美在线免费观看亚洲| 国产伦精品一区二区三区视频孕妇 | 国产精品自拍在线| 国模私拍一区二区三区| 亚洲桃色在线一区| 亚洲精品影院在线观看| 久久久久久久久久久成人| 久久久五月天| 国产欧美亚洲精品| 午夜精品久久久| 国产精品成人一区二区网站软件| 午夜在线观看免费一区| 亚洲日本激情| 亚洲女爱视频在线| 一本久久青青| 欧美伊人影院| 欧美日韩亚洲成人| 国产精品99一区二区| 久久精品道一区二区三区| 亚洲一区欧美激情| 免费av成人在线| 欧美日韩色一区| 国产精品久久久久久福利一牛影视| 国产午夜亚洲精品不卡| 国产精品久久久久久户外露出| 国产伦精品一区二区三区四区免费 | 亚洲大胆av| 欧美国产一区视频在线观看| 一本大道久久a久久综合婷婷| 欧美网站在线观看| 久久精品国产久精国产思思| 影音先锋国产精品| 欧美日韩精品一本二本三本| 性欧美暴力猛交69hd| 亚洲国产欧美在线| 欧美视频在线观看| 久久综合久久久久88| 一区二区三区欧美| 在线看欧美日韩| 国产精品免费一区二区三区观看| 麻豆精品网站| 香蕉久久夜色| 日韩亚洲欧美中文三级| 国内外成人免费激情在线视频网站| 欧美高清一区| 久久久一区二区| 亚洲男人的天堂在线aⅴ视频| 亚洲第一页在线| 国产欧美日韩免费| 欧美日韩人人澡狠狠躁视频| 美女免费视频一区| 久久疯狂做爰流白浆xx| 亚洲午夜精品视频| 91久久综合亚洲鲁鲁五月天| 国内精品久久久久影院优| 国产精品久久久久aaaa| 欧美精品在线一区| 久热国产精品| 久久精品噜噜噜成人av农村| 亚洲欧美韩国| 亚洲欧美一区二区三区久久| 一区二区三区精品视频在线观看| 极品少妇一区二区三区精品视频| 国产精品免费区二区三区观看| 欧美激情一区二区| 蜜臀av一级做a爰片久久 | 国内不卡一区二区三区| 欧美日韩妖精视频| 欧美日韩一本到| 欧美精品一区二区精品网| 久久综合国产精品| 久久精品女人| 久久婷婷国产麻豆91天堂| 久久久久久久激情视频| 久久精品日产第一区二区| 欧美一区日韩一区| 久久精品国产一区二区三区| 欧美亚洲综合久久| 久久不射中文字幕| 久久久美女艺术照精彩视频福利播放 | 久久久综合香蕉尹人综合网| 久久久久国产成人精品亚洲午夜| 久久精品中文字幕一区| 久久亚洲综合| 欧美精品一二三| 欧美少妇一区二区| 国产日韩欧美亚洲| 国产一区二区视频在线观看 | 亚洲国产高清aⅴ视频| 亚洲精品一区在线| 一区二区三区你懂的| 亚洲性图久久| 久久国产天堂福利天堂| 麻豆精品网站| 欧美日韩亚洲高清一区二区| 国产精品伦一区| 国语精品一区| 99re66热这里只有精品4| 亚洲永久精品国产| 久久一区二区三区四区五区| 欧美成人午夜激情视频| 欧美视频日韩| 黑人巨大精品欧美黑白配亚洲 | 日韩一级精品视频在线观看| 午夜精品久久久久久久99热浪潮 | 欧美日韩美女在线| 国产亚洲欧美日韩在线一区|