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關於 import web3 ，我們在網路上蒐集到這些相關的討論、資訊與評價

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在import web3這個產品中，有3篇Facebook貼文，粉絲數超過3,460的網紅Taipei Ethereum Meetup，也在其Facebook貼文中提到， 📜 [專欄新文章] Solidity Weekly #20 ✍️ mingderwang 📥 歡迎投稿： https://medium.com/taipei-ethereum-meetup #徵技術分享文 #使用心得 #教學文 #medium Metamask “Privacy Mode”...

import web3 在 Taipei Ethereum Meetup Facebook 的精選貼文

Taipei Ethereum Meetup By Taipei Ethereum Meetup

2018-12-01 12:51:17 有 5 人按讚
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📜 [專欄新文章] Solidity Weekly #20
✍️ mingderwang
📥 歡迎投稿： https://medium.com/taipei-ethereum-meetup #徵技術分享文 #使用心得 #教學文 #medium

Metamask “Privacy Mode”

前一陣子，Metamask 與其他幾家 Ether 數位錢包公司，為了安全起見，決定改變叫用帳號的流程。舊的 Ðapp 網站需要改寫，才能搭配使用，這裏來做個介紹。

Breaking Change: No Accounts Exposed by Default，這篇文章有做完整的說明，從 2018 年 11 月 ６日起，Metamask plugin 錢包與 Status，Mist，以及 ImToken 計畫一起提供一個新而且更安全的方法 (EIP-1102)，來讀取錢包帳號的資料，例如它的 balance，交易歷史，以及一些敏感資料，未來錢包的 “Privacy Mode” 將預設為開啟。也就是在使用舊有的 Ðapp 網頁, Metamask “Privacy Mode” 必須是關閉，才能跟以前一樣使用，直接可讀取 Metamask 裡的帳號資料，進行交易。

對程式設計師而言，簡單講就是要叫用一個新的 ethereum.enable() function，它會 return 一個 Promise。如果 user 同意讓 Ðapp 使用他的帳號, 就會回傳 provider 結果，否則回傳 Error。這個 ethereum 物件，是 Metamask 在啟動時，會加到瀏覽器的 window 裡的，所以程式範例如下(僅供參考, 它還可以寫得更好)；

import Web3 from ‘web3’

let web3;

if (typeof web3 !== ‘undefined’ && window.ethereum) {

const ethereum = window.ethereum;

ethereum.enable().then((account) => {

const defaultAccount = account[0]

console.log(defaultAccount);}).error(console.log);

web3 = new Web3(web3.currentProvider);// orweb3 = new Web3(ethereum);

} else {console.log('maybe user does not install metamask');

// set the provider you want from Web3.providers

web3 = new Web3(new Web3.providers.HttpProvider(“http://localhost:8545"));

}

v4.14.0 版以後的 Metamask，provider 的 window.ethereum 就開始支援 enable() function，只是預設值是關閉的。

如上圖，新版 MetaMask v5.0.x 設定裡也已經可以看到 Privacy Mode 的開關。目前版本的預設是關著的。以後新版將會預設成開。有些舊 ÐApp 網站沒搭配著修改，就無法使用。但為了相容起見，user 關掉 Privacy Mode，還是能正常使用，但這樣對使用者來講就不安全了。

這個標準定義在 EIP-1102，想深入了解底層的開發者可以參考。

相關 Links：

EIP-1102: How to prepare your dapp

Tutorial — How To Connect A JavaScript Front-End To A Smart Contract On Ethereum

Solidity Weekly #20 was originally published in Taipei Ethereum Meetup on Medium, where people are continuing the conversation by highlighting and responding to this story.

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import web3 在 Taipei Ethereum Meetup Facebook 的最佳貼文

Taipei Ethereum Meetup By Taipei Ethereum Meetup

2018-09-17 16:46:25 有 2 人按讚
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📜 [專欄新文章] Solidity Weekly #12
✍️ mingderwang
📥 歡迎投稿： https://medium.com/taipei-ethereum-meetup #徵技術分享文 #使用心得 #教學文 #medium

functions 什麼時候用 external、private、或 internal

function 跟 (storage) state 全區域合約變數預設不同，變數宣告只有在 public 才會對外開放，讓別人看得到值；而 function 剛好相反，預設是 public。也就是說你沒刻意去宣告，它是可以被外面的程式或合約呼叫。

但如果你刻意用 external、private、或 internal 來宣告 function 的被 call 的屬性，能對最佳化得到一些好處。而 public 與 external 都會讓 function 公開；相反的 internal 與 private 的 functions 只能被合約內部叫用。

限制多寡的順序是︰ public < external < internal < private。

公開 use cases︰

比如說，如果你確定不對內公開，最好宣告為 external。external 有個好處是 call 的參數是從 CALLDATA 獲得，不需要 copy 到 memory 才能執行該 function call。所以比較省 gas，尤其是處理參數是 array 時更凸顯其效果。

但用 external，自己合約如果要調用，反而要寫 this.f() 編譯器才能接受，通常是多此一舉。而且會呼叫 CALL 指令，跟 JUMP 指令比，花更多 gas。

不公開 use cases︰

當合約自己內部的 functions 不想被外部合約或程式調用，最好是用 internal 或甚至用 private 來做限制。internal 還可以被繼承的合約來調用，而 private 就只能自己合約內使用。

它們會被用 JUMP 指令來呼叫，比較省 gas。

我們用 StackOverflow 的範例來做測試，改寫成 Test.sol 如下;

// Test.sol pragma solidity^0.4.12;

contract Test {

// spend 662 gasfunction test(uint[20] a) public pure returns (uint) { return a[10] * 2; }

// spend 317 gasfunction test2(uint[20] a) external pure returns (uint) { return a[10] * 2; }

function test3(uint[20] a) internal pure returns (uint) { return a[10] * 2; } function test4(uint[20] a) private pure returns (uint) { return a[10] * 2; }}

測試程式 (DoTest.sol) 如下︰

// DoTest.solpragma solidity ^0.4.18;

import "./Test.sol";

contract DoTest is Test {uint[20] a;uint public xx;

constructor() public { a[10]=3; } function test_1() external returns(uint) { xx = test(a); return xx; } function test_2() external returns(uint) { xx = this.test2(a); // <-- use this. return xx; } function test_3() external returns(uint) { xx = test3(a); return xx; } function test_4() external returns(uint) { xx = test4(a); // <-- compile error return xx; }}

如果你用 remix 測試，會發現 DoTest 測試繼承 Test 來的不同宣告方式的 functions，會有不同的效果。且 test3() 跟 test4() 對外是看不到的。

links 分享;

Learn X in Y minutes, where X = Solidity Ming> 雖然所用的 solidity 版本 ^0.4.19 還有點舊，但註解做得很好，值得初學者參考。

Ethernaut Lvl 12 Privacy Walkthrough: How Ethereum optimizes storage to save space and be less gassy — (Nicole Zhu) Ming > Coinmonks 的 Medium 裡還有其他很多非常精彩的文章，請自己來尋寶。

The Ethernaut by Zeppelin Ming> 一個 web3/solidity 闖關遊戲平台。

Solidity Weekly #12 was originally published in Taipei Ethereum Meetup on Medium, where people are continuing the conversation by highlighting and responding to this story.

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We have regular meeting twice per month on discussing blockchain technology, smart contracts and DApps development! We would love to have you join us!
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import web3 在 Taipei Ethereum Meetup Facebook 的最佳解答

Taipei Ethereum Meetup By Taipei Ethereum Meetup

2017-04-18 13:37:49 有 7 人按讚
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By Frank Wang

[使用 go-ethereum 1.6 Clique PoA consensus 建立 Private chain (1)] -- by Frank Wang
Ethereum Proof of Authority

在 Ethereum 官方的共識機制是使用 PoW，Miner 必須靠使用算力去解決密碼學問題來取得寫帳(打包 Block)權。但 PoW 機制在私有鏈或聯盟鏈上並不是一個那麼有效率的共識機制，私有鏈的維運者必須花費多餘的算力來維持私有鏈的運作。

而 Proof of Authority 思維是直接指定哪些節點有寫帳權，其他節點透過演算法如果是被授權的節點打包 Block 則判定 Block 有效。

Ethereum Client 中有不同語言的實作，之前 Parity 版本的實作就有提供 PoA 的共識機制(介紹)。而在前段時間發佈的 geth 1.6 也支援了 PoA 的共識機制。不過 geth 的 PoA 使用方法跟機制和 Parity 的版本不同，geth 實作了 ethereum/EIPs#225 一個稱作 Clique 的共識機制。所以這篇主要筆記如何建立一個 geth Clique Private chain。

情境中會使用 4 個節點，分別代表兩個普通的節點發起交易，一個創世塊指定的授權節點，一個後期加入的授權節點來玩玩 Clique 。

安裝 geth

由於 go-ethereum 使用 golang 開發的，所有的程式都被編譯成單一的可執行檔了，執接下載下來就可以直接執行。

geth & tools 1.6 — https://ethereum.github.io/go-ethereum/downloads/

找到相對應 OS 後下載，記得下載 geth & tools 的版本，接下來會使用 geth 1.6 版本的一個創 Private chain 的工具 puppeth 來建立 Clique Private chain。

最後記得將這些執行檔加入 PATH 方便呼叫。

環境準備

待會要建置的環境將會使用 4 個 ethereum 節點，並且全部節點跑在同一台機器上，這樣比較省事。先創好 4 個資料夾，分別叫 node1 node2 signer1 signer2 ，node 是一般的 ethereum client，signer 在接下來的情境中當成打包 block 的角色。

-> % lsnode1 node2 signer1 signer2

建立 Ethereum 帳號

接著我們要替這四個角色各建立一個 Ethereum 帳號。

frank@frank-linux [10:51:22 AM] [~/src/eth-poa] -> % cd node1

frank@frank-linux [10:55:08 AM] [~/src/eth-poa/node1] -> % geth --datadir ./data account newWARN [04–18|10:55:30] No etherbase set and no accounts found as default Your new account is locked with a password. Please give a password. Do not forget this password.Passphrase: Repeat passphrase: Address: {c7873030c2532aafe540d9dfd02a08330ee06465}

在這步驟切換到每個目錄底下，指令 geth --datadir ./data account new 這段指令是指要使用當下目錄底下的 data 目錄當作 geth 存放資料的地方，並且創一個新的 Account。在剛剛建立的 node1, node2, signer1, signer2 都下相同指令創一個帳號。

一下是我創好的每個角色的 Account address:

node1: c7873030c2532aafe540d9dfd02a08330ee06465

node2: 6d650780d493056f679a30b2c65cfa5e07835ad6

signer1: 5cc640ae524f70c39081d65bc699b3b61a67bd3f

signer2: 0fe2d8747d24156b342c9fa5c5e7138cf4047a8d

創好帳號後就可以開始建立 Private chain 了

建立創世塊設定

由於 Clique 並不像 Parity 版本的 PoA 靠設定檔設定授權的節點。Clique 是將授權節點的相關資訊放在 Block Header 中，所以我們必須對創世塊做一些設定才可以讓授權機制生效。(但這並不意味著新增或刪除授權節點需要更換創世塊，晚點介紹怎麼新增授權節點)

Clique 是將授權的資訊放在 extraData 中，但資料結夠的格式並沒有那麼直覺，所以在此使用 geth 1.6 提供的建立 Private Chain 的工具 puppeth 來建立創世塊，puppeth 是各互動式的程式，直接啟動照著指示輸入相關資訊。

frank@frank-linux [11:19:16 AM] [~/src/eth-poa] -> % puppeth+ — — — — — — — — — — — — — — — — — — — — — — — — — — — — — -+| Welcome to puppeth, your Ethereum private network manager || || This tool lets you create a new Ethereum network down to || the genesis block, bootnodes, miners and ethstats servers || without the hassle that it would normally entail. || || Puppeth uses SSH to dial in to remote servers, and builds || its network components out of Docker containers using the || docker-compose toolset. |+ — — — — — — — — — — — — — — — — — — — — — — — — — — — — — -+

Please specify a network name to administer (no spaces, please)> poa_for_fun

這裡會希望你給你的 Private chain 一個名字

Sweet, you can set this via — network=poa_for_fun next time!

INFO [04–18|11:19:21] Administering Ethereum network name=poa_for_funWARN [04–18|11:19:21] No previous configurations found path=/home/frank/.puppeth/poa_for_fun

What would you like to do? (default = stats) 1. Show network stats 2. Configure new genesis 3. Track new remote server 4. Deploy network components> 2

這裡選 2 ，要建立一個新的創世塊設定

Which consensus engine to use? (default = clique) 1. Ethash — proof-of-work 2. Clique — proof-of-authority> 2

共識機制，選 2，Clique PoA

How many seconds should blocks take? (default = 15)> 10

多少秒數會產出一個 Block，在這裡設 10 秒。當然你可以自己設定你想要的

Which accounts are allowed to seal? (mandatory at least one)> 0x5cc640ae524f70c39081d65bc699b3b61a67bd3f> 0x

指定一個 Account address 作為授權打包的角色。這裡使用上面產出的 Signer1 的 address。

Which accounts should be pre-funded? (advisable at least one)> 0xc7873030c2532aafe540d9dfd02a08330ee06465> 0x5cc640ae524f70c39081d65bc699b3b61a67bd3f> 0x

指定要不要事先給一些 ether。這裡選 node1 和 signer1 的 address，當然這隨你指定

Specify your chain/network ID if you want an explicit one (default = random)>

Network Id，直接用 random

Anything fun to embed into the genesis block? (max 32 bytes)>

沒什麼需要特別加入 genesis 的，留空

What would you like to do? (default = stats) 1. Show network stats 2. Save existing genesis 3. Track new remote server 4. Deploy network components> 2

選 2 存檔

Which file to save the genesis into? (default = poa_for_fun.json)> INFO [04–18|11:19:50] Exported existing genesis block

What would you like to do? (default = stats) 1. Show network stats 2. Save existing genesis 3. Track new remote server 4. Deploy network components> ^C

ctrl+c 離開，會在當下目錄看到一個 poa_for_fun.json 檔案。

替 4 個節點初始化 Private chain

使用 geth init 指令，分別替換 4 個 node 的 datadir

frank@frank-linux [11:38:07 AM] [~/src/eth-poa] -> % lsnode1 node2 poa_for_fun.json signer1 signer2frank@frank-linux [11:38:07 AM] [~/src/eth-poa] -> % geth --datadir node1/data init poa_for_fun.json INFO [04–18|11:39:10] Allocated cache and file handles database=/home/frank/src/eth-poa/node1/data/geth/chaindata cache=128 handles=1024INFO [04–18|11:39:10] Writing custom genesis block INFO [04–18|11:39:10] Successfully wrote genesis state hash=5722d7…47e737frank@frank-linux [11:39:10 AM] [~/src/eth-poa] -> % geth --datadir node2/data init poa_for_fun.jsonINFO [04–18|11:39:14] Allocated cache and file handles database=/home/frank/src/eth-poa/node2/data/geth/chaindata cache=128 handles=1024INFO [04–18|11:39:14] Writing custom genesis block INFO [04–18|11:39:14] Successfully wrote genesis state hash=5722d7…47e737frank@frank-linux [11:39:14 AM] [~/src/eth-poa] -> % geth --datadir signer1/data init poa_for_fun.jsonINFO [04–18|11:39:21] Allocated cache and file handles database=/home/frank/src/eth-poa/signer1/data/geth/chaindata cache=128 handles=1024INFO [04–18|11:39:21] Writing custom genesis block INFO [04–18|11:39:21] Successfully wrote genesis state hash=5722d7…47e737frank@frank-linux [11:39:21 AM] [~/src/eth-poa] -> % geth --datadir signer2/data init poa_for_fun.jsonINFO [04–18|11:39:24] Allocated cache and file handles database=/home/frank/src/eth-poa/signer2/data/geth/chaindata cache=128 handles=1024INFO [04–18|11:39:24] Writing custom genesis block INFO [04–18|11:39:24] Successfully wrote genesis state hash=5722d7…47e737

到目前我們已經準備好讓節點可以啟動和互相連線了。

啟動 geth client 並設定 peers 間的連線

分別在 node1, node2 目錄使用指令啟動 geth

geth --datadir ./data --networkid 55661 --port 2000 console

這裡需要注意的是 datadir 參數沒問題，先前的步驟已經在每個節點各自的目錄都建立了 data 目錄。networkid 大家一定都要用同一個值才可以互相連線。port 用來讓 geth 跟其他 geth 連線所 listen 的一個 port，由於四個節點都在本機，所以這裡必須都指定不同的值。以下使用 node1 2000, node2 2001, signer1 2002, signer 2003 當範例。

如果節點是授權打包 block 的節點，那你啟動時要先 unlock 你的 account，這樣才可以進行交易的打包。多帶一個 unlock 參數，以及你要解鎖的 account address。啟動後會要求輸入當時創 account 時的 passphrase。所以在這裡啟動 signer1 和 signer2 時都要用 unlock 參數帶入他們各自的 address 解鎖。

geth --datadir ./data --networkid 55661 --port 2002 --unlock 5cc640ae524f70c39081d65bc699b3b61a67bd3f console

啟動後會看到這樣的結果，如果沒噴任何錯誤就是啟動成功了，同時會啟動一個 console 的互動介面，可以打像是 admin.nodeInfo 這類的指令來操作 geth。

在啟動訊息中有一段

INFO [04–18|12:01:31] RLPx listener up self=enode://87692411dd1af113ccc04d3f6d3d7d47366c81e595525c861c7a3c902ca0a86f46e8d7a837f431536822dbb012f68d942ed96910385805864e990efdf3839a1e@[::]:2000

由於目前是在 private chain 上，沒有設定啟動節點也沒設定 static node，各節點啟動後是沒辦法找到對方的。所以在此我們把 node2, singer1, signer2 都加入 node1 為自己的節點連上。geth 要連上對方的節點就必須好 enode://@:這格式，複製剛剛啟動 node1 時出現的 enode 資訊將 [::] 換為 127.0.0.1 讓其他節點加入就可以連上了。

在 node2, signer1, signer2 的 geth console 頁面分別打入指令

>admin.addPeer(“enode://87692411dd1af113ccc04d3f6d3d7d47366c81e595525c861c7a3c902ca0a86f46e8d7a837f431536822dbb012f68d942ed96910385805864e990efdf3839a1e@127.0.0.1:2000”)

完成後回到 node1 的 geth console 打入 admin.peers 應該要看到三個節點資訊。

到這步 geth 節點已經連上可以開始進行 PoA 挖礦和交易了。

啟動 Miner

到 signer1 的 console 打入 miner.start() 這時候如果你本機之前沒有啟動過 miner，geth 會先產生 DAG 等 DAG 產生完後就會開始挖礦了。

在 signer1 的 console 會出現正在 mining 的訊息。

其他節點則會收到 import block 的訊息。

Make a transaction

到這裡 Clique 的 Private chain 已經設定完成了，我們可以開始在這條鏈上做一些交易。接下來為了方便會使用 geth 的 console 來做 send ether 交易，如果你不習慣的話也可以使用 mist 這類的 UI 錢包來做。

node1 console

還記得在建立創世塊的時候有先給了 node1 和 signer1 的 address 一些 ether 吧？先用這令看看這些 ether 有沒有真的在鏈上。使用指令 ")" target="_blank">eth.getBalance("

") 來查詢。

> eth.getBalance(“c7873030c2532aafe540d9dfd02a08330ee06465”)9.04625697166532776746648320380374280103671755200316906558262375061821325312e+74> eth.getBalance(“6d650780d493056f679a30b2c65cfa5e07835ad6”)0>

確定 node1 有 ether 但 node2 沒有，接著用 eth.sendTransaction 指令來把一些 ether 從 node1 轉到 node2 吧。

現在 node1 的 console 把自己的 Account unlock

> personal.unlockAccount("c7873030c2532aafe540d9dfd02a08330ee06465")

Unlock account c7873030c2532aafe540d9dfd02a08330ee06465Passphrase:true>

轉出 0.05 ether 到 6d650780d493056f679a30b2c65cfa5e07835ad6

>eth.sendTransaction({from:"c7873030c2532aafe540d9dfd02a08330ee06465", to:"6d650780d493056f679a30b2c65cfa5e07835ad6", value: web3.toWei(0.05, "ether")})INFO [04-18|12:39:53] Submitted transaction fullhash=0xa7a9da239b8f96b9f6fe4007ee88773915f034be2365b2dab234fd8c0545aa37 recipient=0xc7873030c2532aafe540d9dfd02a08330ee06465"0xa7a9da239b8f96b9f6fe4007ee88773915f034be2365b2dab234fd8c0545aa37">

如果你 singer1 的 miner 沒關掉的話，在幾秒後就會看到一個含有一筆交易的 block 產出

再來看看 node1 和 node2 的 ether

> " target="_blank">eth.getBalance("c7873030c2532aafe540d9dfd02a08330ee06465")9.04625697166532776746648320380374280103671755200316906558211535061821325312e+74> " target="_blank">eth.getBalance("6d650780d493056f679a30b2c65cfa5e07835ad6")50000000000000000>

交易完成！

加入一個新的信任節點

在 Clique 共識機制中是使用 Clique 提供的 API 來做節點管理，現在只 demo 加入節點進入信任名單。

signer2

signer2 是一開始沒設定在創世塊中信任列表的節點，如果這時候讓它啟動 miner 會怎麼樣呢？會噴一個未授權的錯誤

> miner.start()INFO [04-18|12:49:51] Starting mining operationnull> INFO [04-18|12:49:51] Commit new mining work number=46 txs=0 uncles=0 elapsed=284.189µsWARN [04-18|12:49:51] Block sealing failed err=unauthorized

必須回到已經在授權名單內的節點將新的節點加入。

signer1

回到 signer1 的 console 輸入加入的指令

> clique.propose("0x0fe2d8747d24156b342c9fa5c5e7138cf4047a8d", true)

singer2

接著回到 signer2 的 cosole

開始打包交易了

結語

由於 geth 1.6 才發佈不久，關於 Clique 的相關文章還蠻少的。提供如何使用 geth 1.6 建立一個 Clique private chain 的簡單教學，其實大部分都是我自己在建置時的筆記，內容省略了很多關於 Clique 的一些特性和原理，有興趣的建議直接看 ethereum/EIPs#225。希望這篇可以幫助到使用 geth 但又想用用 PoA 共識機制的同伴們XD

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