Lesson 4. Complete the signing of transactions by API in CosmosSDK

Thursday, 28/05/2020

Tram Ho

In the previous article, I showed you how to write a rest-server so that users can trade at API, but there is still a problem that users still have to use the command-line to sign and broadcast the transaction. Today, in this final article, I will show you how users can sign and broadcast transactions by API, contributing to making the application flow below for users more transparent.

1. Learn about the `tx sign` command and how to get user information from the system

Back to the previous article, when a user creates a transaction, that transaction is only in proposal form, the user must sign and broadcast it for it to take effect.

The tx sign statement has the following structure:

nscli tx sign unsignedTx.json --from alice --offline --chain-id namechain --sequence 0 --account-number 4

1 2	nscli tx sign unsignedTx.json --from alice --offline --chain-id namechain --sequence 0 --account-number 4

See the source of the command here . Pay attention to the following important parameters:

The parameter immediately behind the sign must be a file, in this case usignedTx.json
The parameter after the --from flag is either the name or address of the user who created the transaction
The after flag --sequence increases from zero after each person’s transaction whether or not the transaction is successful, the meaning of this parameter is to help the system to arrange the transactions in the correct order, avoiding being double spending.
The parameter immediately after the --accountn-number flag is the --accountn-number of that user in the system

Thus, in order for the user to be able to sign a transaction using the API, the request that the user has to send must have: unsigned transaction, the name or address of that user, sequence, account-number.

The parameters of address, sequence, account-number are parameters that are calculated and given to the user by the system, users cannot know it in advance, so I will first write a route so that users can query get my address through the name, then use the default route http://localhost:1317/auth/accounts/$address to query the sequence parameters, account-number , as well as the token balance of the that user.

Open the file x/nameservice/client/rest/query.go and add the following:

Import the os/exec package at the beginning of the file to be able to execute the command.

<span class="token keyword">import</span> <span class="token punctuation">(</span>
    <span class="token operator">...</span>
    <span class="token string">"os/exec"</span>
    <span class="token operator">...</span>
<span class="token punctuation">)</span>

import (

...

"os/exec"

...

)

Add the request handler function below

<span class="token keyword">func</span> <span class="token function">accAddressHandler</span> <span class="token punctuation">(</span> cliCtx context <span class="token punctuation">.</span> CLIContext <span class="token punctuation">)</span> http <span class="token punctuation">.</span> HandlerFunc <span class="token punctuation">{</span>
	<span class="token keyword">return</span> <span class="token keyword">func</span> <span class="token punctuation">(</span> w http <span class="token punctuation">.</span> ResponseWriter <span class="token punctuation">,</span> r <span class="token operator">*</span> http <span class="token punctuation">.</span> Request <span class="token punctuation">)</span> <span class="token punctuation">{</span>
		vars <span class="token operator">:=</span> mux <span class="token punctuation">.</span> <span class="token function">Vars</span> <span class="token punctuation">(</span> r <span class="token punctuation">)</span>
		name <span class="token operator">:=</span> vars <span class="token punctuation">[</span> <span class="token string">"name"</span> <span class="token punctuation">]</span>

		cmd <span class="token operator">:=</span> exec <span class="token punctuation">.</span> <span class="token function">Command</span> <span class="token punctuation">(</span> <span class="token string">"nscli"</span> <span class="token punctuation">,</span> <span class="token string">"keys"</span> <span class="token punctuation">,</span> <span class="token string">"show"</span> <span class="token punctuation">,</span> name <span class="token punctuation">,</span> <span class="token string">"-a"</span> <span class="token punctuation">)</span> <span class="token comment">// chạy ngầm câu lệnh show key của một name</span>
		stdout <span class="token punctuation">,</span> err <span class="token operator">:=</span> cmd <span class="token punctuation">.</span> <span class="token function">Output</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token comment">// bắt giá trị trả về</span>
		<span class="token keyword">if</span> err <span class="token operator">!=</span> <span class="token boolean">nil</span> <span class="token punctuation">{</span>
			rest <span class="token punctuation">.</span> <span class="token function">WriteErrorResponse</span> <span class="token punctuation">(</span> w <span class="token punctuation">,</span> http <span class="token punctuation">.</span> StatusBadRequest <span class="token punctuation">,</span> err <span class="token punctuation">.</span> <span class="token function">Error</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">)</span>
			<span class="token keyword">return</span>
		<span class="token punctuation">}</span>

		address <span class="token operator">:=</span> <span class="token function">string</span> <span class="token punctuation">(</span> stdout <span class="token punctuation">)</span> <span class="token comment">// ép kiểu về string</span>
		result <span class="token operator">:=</span> strings <span class="token punctuation">.</span> <span class="token function">Trim</span> <span class="token punctuation">(</span> address <span class="token punctuation">,</span> <span class="token string">"n"</span> <span class="token punctuation">)</span> <span class="token comment">// cắt bỏ n</span>
		rest <span class="token punctuation">.</span> <span class="token function">PostProcessResponse</span> <span class="token punctuation">(</span> w <span class="token punctuation">,</span> cliCtx <span class="token punctuation">,</span> result <span class="token punctuation">)</span> <span class="token comment">// trả về kết quả cho ngươi dùng</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>

func accAddressHandler ( cliCtx context . CLIContext ) http . HandlerFunc {

return func ( w http . ResponseWriter , r * http . Request ) {

vars := mux . Vars ( r )

name := vars [ "name" ]

stdout , err := cmd . Output ( ) // bắt giá trị trả về

if err != nil {

rest . WriteErrorResponse ( w , http . StatusBadRequest , err . Error ( ) )

return

}

address := string ( stdout ) // ép kiểu về string

result := strings . Trim ( address , "n" ) // cắt bỏ n

rest . PostProcessResponse ( w , cliCtx , result ) // trả về kết quả cho ngươi dùng

}

Add a route to the file x/nameservice/client/rest/rest.go to call the above handler:

r <span class="token punctuation">.</span> <span class="token function">HandleFunc</span> <span class="token punctuation">(</span> fmt <span class="token punctuation">.</span> <span class="token function">Sprintf</span> <span class="token punctuation">(</span> <span class="token string">"/%s/names/{name}/address"</span> <span class="token punctuation">,</span> storeName <span class="token punctuation">)</span> <span class="token punctuation">,</span> <span class="token function">accAddressHandler</span> <span class="token punctuation">(</span> cliCtx <span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">.</span> <span class="token function">Methods</span> <span class="token punctuation">(</span> <span class="token string">"GET"</span> <span class="token punctuation">)</span>

r . HandleFunc ( fmt . Sprintf ( "/%s/names/{name}/address" , storeName ) , accAddressHandler ( cliCtx ) ) . Methods ( "GET" )

2. Learn the `tx broadcast` command

The tx broadcast statement has the following structure:

nscli tx broadcast signedTx.json

1 2	nscli tx broadcast signedTx.json

You can see the code of the statement here

The argument immediately following the broadcast must be a file in this case signedTx.json

Combining the two statements, we can visualize the flow of the route we are about to code as follows:

The user sends a request with the parameters: usignedTx , sequence , account number
The server writes unsignedTx to the file unsignedTx.json
The server implements the tx sign command implicitly and writes the result into the signedTx.json file
The server implements tx broadcast implicitly

3. Code

Open the file x/nameserivce/client/rest/tx.go and add the following code:

<span class="token keyword">type</span> signTxReq <span class="token keyword">struct</span> <span class="token punctuation">{</span>
	BaseReq       rest <span class="token punctuation">.</span> BaseReq <span class="token string">`json:"base_req"`</span>
	Tx            <span class="token builtin">string</span>       <span class="token string">`json:"tx"`</span>
	Sequence      <span class="token builtin">string</span>       <span class="token string">`json:"sequence"`</span>
	AccountNumber <span class="token builtin">string</span>       <span class="token string">`json:"accountNumber"`</span>
<span class="token punctuation">}</span>

<span class="token keyword">func</span> <span class="token function">signTxHandler</span> <span class="token punctuation">(</span> cliCtx context <span class="token punctuation">.</span> CLIContext <span class="token punctuation">)</span> http <span class="token punctuation">.</span> HandlerFunc <span class="token punctuation">{</span>
	<span class="token keyword">return</span> <span class="token keyword">func</span> <span class="token punctuation">(</span> w http <span class="token punctuation">.</span> ResponseWriter <span class="token punctuation">,</span> r <span class="token operator">*</span> http <span class="token punctuation">.</span> Request <span class="token punctuation">)</span> <span class="token punctuation">{</span>

		<span class="token keyword">var</span> req signTxReq
		<span class="token keyword">if</span> <span class="token operator">!</span> rest <span class="token punctuation">.</span> <span class="token function">ReadRESTReq</span> <span class="token punctuation">(</span> w <span class="token punctuation">,</span> r <span class="token punctuation">,</span> cliCtx <span class="token punctuation">.</span> Codec <span class="token punctuation">,</span> <span class="token operator">&amp;</span> req <span class="token punctuation">)</span> <span class="token punctuation">{</span>
			rest <span class="token punctuation">.</span> <span class="token function">WriteErrorResponse</span> <span class="token punctuation">(</span> w <span class="token punctuation">,</span> http <span class="token punctuation">.</span> StatusBadRequest <span class="token punctuation">,</span> <span class="token string">"failed to parse request"</span> <span class="token punctuation">)</span>
			<span class="token keyword">return</span>
		<span class="token punctuation">}</span>

		baseReq <span class="token operator">:=</span> req <span class="token punctuation">.</span> BaseReq <span class="token punctuation">.</span> <span class="token function">Sanitize</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
		<span class="token keyword">if</span> <span class="token operator">!</span> baseReq <span class="token punctuation">.</span> <span class="token function">ValidateBasic</span> <span class="token punctuation">(</span> w <span class="token punctuation">)</span> <span class="token punctuation">{</span>
			<span class="token keyword">return</span>
		<span class="token punctuation">}</span>

		filePath <span class="token operator">:=</span> <span class="token string">"unsignedTx.json"</span>
		data <span class="token operator">:=</span> <span class="token punctuation">[</span> <span class="token punctuation">]</span> <span class="token function">byte</span> <span class="token punctuation">(</span> req <span class="token punctuation">.</span> Tx <span class="token punctuation">)</span>

		err <span class="token operator">:=</span> ioutil <span class="token punctuation">.</span> <span class="token function">WriteFile</span> <span class="token punctuation">(</span> filePath <span class="token punctuation">,</span> data <span class="token punctuation">,</span> <span class="token number">0644</span> <span class="token punctuation">)</span> <span class="token comment">// ghi tx mà user gửi lên vào file unsignedTx.json</span>
		<span class="token keyword">if</span> err <span class="token operator">!=</span> <span class="token boolean">nil</span> <span class="token punctuation">{</span>
			<span class="token function">panic</span> <span class="token punctuation">(</span> err <span class="token punctuation">)</span>
		<span class="token punctuation">}</span>

		cmd <span class="token operator">:=</span> exec <span class="token punctuation">.</span> <span class="token function">Command</span> <span class="token punctuation">(</span> <span class="token string">"nscli"</span> <span class="token punctuation">,</span> <span class="token string">"tx"</span> <span class="token punctuation">,</span> <span class="token string">"sign"</span> <span class="token punctuation">,</span> filePath <span class="token punctuation">,</span> <span class="token string">"--from"</span> <span class="token punctuation">,</span> req <span class="token punctuation">.</span> BaseReq <span class="token punctuation">.</span> From <span class="token punctuation">,</span> <span class="token string">"--offline"</span> <span class="token punctuation">,</span> <span class="token string">"--chain-id"</span> <span class="token punctuation">,</span> req <span class="token punctuation">.</span> BaseReq <span class="token punctuation">.</span> ChainID <span class="token punctuation">,</span> <span class="token string">"--sequence"</span> <span class="token punctuation">,</span> req <span class="token punctuation">.</span> Sequence <span class="token punctuation">,</span> <span class="token string">"--account-number"</span> <span class="token punctuation">,</span> req <span class="token punctuation">.</span> AccountNumber <span class="token punctuation">)</span> <span class="token comment">// thực hiện ký</span>
		stdout <span class="token punctuation">,</span> err <span class="token operator">:=</span> cmd <span class="token punctuation">.</span> <span class="token function">Output</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
		<span class="token keyword">if</span> err <span class="token operator">!=</span> <span class="token boolean">nil</span> <span class="token punctuation">{</span>
			rest <span class="token punctuation">.</span> <span class="token function">WriteErrorResponse</span> <span class="token punctuation">(</span> w <span class="token punctuation">,</span> http <span class="token punctuation">.</span> StatusBadRequest <span class="token punctuation">,</span> err <span class="token punctuation">.</span> <span class="token function">Error</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">)</span>
			<span class="token keyword">return</span>
		<span class="token punctuation">}</span>

		filePath <span class="token operator">=</span> <span class="token string">"signedTx.json"</span>
		data <span class="token operator">=</span> <span class="token punctuation">[</span> <span class="token punctuation">]</span> <span class="token function">byte</span> <span class="token punctuation">(</span> <span class="token function">string</span> <span class="token punctuation">(</span> stdout <span class="token punctuation">)</span> <span class="token punctuation">)</span>
		err <span class="token operator">=</span> ioutil <span class="token punctuation">.</span> <span class="token function">WriteFile</span> <span class="token punctuation">(</span> filePath <span class="token punctuation">,</span> data <span class="token punctuation">,</span> <span class="token number">0644</span> <span class="token punctuation">)</span> <span class="token comment">// ghi giao dịch đã ký vào filed signedTx.json</span>
		<span class="token keyword">if</span> err <span class="token operator">!=</span> <span class="token boolean">nil</span> <span class="token punctuation">{</span>
			<span class="token function">panic</span> <span class="token punctuation">(</span> err <span class="token punctuation">)</span>
		<span class="token punctuation">}</span>

		cmd <span class="token operator">=</span> exec <span class="token punctuation">.</span> <span class="token function">Command</span> <span class="token punctuation">(</span> <span class="token string">"nscli"</span> <span class="token punctuation">,</span> <span class="token string">"tx"</span> <span class="token punctuation">,</span> <span class="token string">"broadcast"</span> <span class="token punctuation">,</span> filePath <span class="token punctuation">)</span> <span class="token comment">// broadcase giao dịch đã được ký</span>
		stdout <span class="token punctuation">,</span> err <span class="token operator">=</span> cmd <span class="token punctuation">.</span> <span class="token function">Output</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
		<span class="token keyword">if</span> err <span class="token operator">!=</span> <span class="token boolean">nil</span> <span class="token punctuation">{</span>
			rest <span class="token punctuation">.</span> <span class="token function">WriteErrorResponse</span> <span class="token punctuation">(</span> w <span class="token punctuation">,</span> http <span class="token punctuation">.</span> StatusBadRequest <span class="token punctuation">,</span> err <span class="token punctuation">.</span> <span class="token function">Error</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">)</span>
			<span class="token keyword">return</span>
		<span class="token punctuation">}</span>

		rest <span class="token punctuation">.</span> <span class="token function">PostProcessResponse</span> <span class="token punctuation">(</span> w <span class="token punctuation">,</span> cliCtx <span class="token punctuation">,</span> <span class="token function">string</span> <span class="token punctuation">(</span> stdout <span class="token punctuation">)</span> <span class="token punctuation">)</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>

type signTxReq struct {

BaseReq rest . BaseReq `json:"base_req"`

Tx string `json:"tx"`

Sequence string `json:"sequence"`

AccountNumber string `json:"accountNumber"`

}

func signTxHandler ( cliCtx context . CLIContext ) http . HandlerFunc {

var req signTxReq

if ! rest . ReadRESTReq ( w , r , cliCtx . Codec , & req ) {

rest . WriteErrorResponse ( w , http . StatusBadRequest , "failed to parse request" )

return

}

baseReq := req . BaseReq . Sanitize ( )

if ! baseReq . ValidateBasic ( w ) {

return

}

filePath := "unsignedTx.json"

data := [ ] byte ( req . Tx )

err := ioutil . WriteFile ( filePath , data , 0644 ) // ghi tx mà user gửi lên vào file unsignedTx.json

if err != nil {

panic ( err )

}

cmd := exec . Command ( "nscli" , "tx" , "sign" , filePath , "--from" , req . BaseReq . From , "--offline" , "--chain-id" , req . BaseReq . ChainID , "--sequence" , req . Sequence , "--account-number" , req . AccountNumber ) // thực hiện ký

if err != nil {

return

}

filePath = "signedTx.json"

data = [ ] byte ( string ( stdout ) )

err = ioutil . WriteFile ( filePath , data , 0644 ) // ghi giao dịch đã ký vào filed signedTx.json

if err != nil {

panic ( err )

}

cmd = exec . Command ( "nscli" , "tx" , "broadcast" , filePath ) // broadcase giao dịch đã được ký

stdout , err = cmd . Output ( )

if err != nil {

return

}

rest . PostProcessResponse ( w , cliCtx , string ( stdout ) )

}

Open the file x/nameservice/client/rest/rest.go and add the following line:

r <span class="token punctuation">.</span> <span class="token function">HandleFunc</span> <span class="token punctuation">(</span> fmt <span class="token punctuation">.</span> <span class="token function">Sprintf</span> <span class="token punctuation">(</span> <span class="token string">"/%s/tx/sign"</span> <span class="token punctuation">,</span> storeName <span class="token punctuation">)</span> <span class="token punctuation">,</span> <span class="token function">signTxHandler</span> <span class="token punctuation">(</span> cliCtx <span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">.</span> <span class="token function">Methods</span> <span class="token punctuation">(</span> <span class="token string">"POST"</span> <span class="token punctuation">)</span>

r . HandleFunc ( fmt . Sprintf ( "/%s/tx/sign" , storeName ) , signTxHandler ( cliCtx ) ) . Methods ( "POST" )

4. Test

Make tools again, then init and start chain:

<span class="token function">make</span> <span class="token function">install</span>
./init.sh
nsd start

make install

./init.sh

nsd start

Open another terminal and start the server:

nscli rest-server --chain-id namechain --trust-node

1 2	nscli rest-server --chain-id namechain --trust-node

Open Post Man and test

Query address according to jack’s:
Query all jack infors:
jack to create the product:
The transaction log creates the product, noting the return value of the last route into the tx of this request
Query to see the product has been created
Query address of alice
Query all infice of alice:
Alice creates a buy product transaction
Alice signs a buy product transaction
Query the product again to see it passed to the owner
Query the information of the jack and the alice to see that 10nametoken has been moved from the alice to the jack