A story about taking an HTTP trace using Charles to find out what requests the Java library is making to Slack

Overview

Legacy Java applications used slack-api to notify me, but by early March 2020 the notification failed. To troubleshoot on my Mac, I wanted to see what the payload of a request that failed to notify was. I tried to take a trace using Fiddler, but it didn't come in, so [Charles](https://www.charlesproxy. To use com /). In curl, referring to here, if you specify the proxy to localhost: 8888 with -x, you can get the log with Chales. ..

.sh

curl -x localhost:8888 -X POST --data-urlencode "payload={\"channel\": \"#general\", \"username\": \"gpedro Bot\", \"text\": \"this is#Posted in general.\", \"icon_emoji\": \":ghost:\"}" https://hooks.slack.com/services/<YOUR>/<TOKEN>

For Java applications, I wasn't quite sure how to take Http traces with Charles, so I decided to look into it.

manner

My application used this library. It's been left untouched for a long time, and it seems to be minor, so I think that the people who are reading this article are definitely not using this library. However, by implementing Proxy class or equivalent settings, some form I suspect that there is a way to send an HTTP request via a Proxy in any library. [^ 1] When using this library, instead of creating an instance that calls the API by default, Proxy class I was able to create an instance by specifying (/reflect/Proxy.html). When I instantiated this way, I was able to use Charles to take an HTTP trace of requests for this library. If you want to troubleshoot the library, I hope it will be helpful in some way.

Charles installation

Install by referring to this article. Trust the certificate Charles Proxy .... in your keychain.

Export Charles Certificate

In the keychain, right-click on the Charles Proxy ... certificate and select Export-> [Export Charles Proxy CA] to export the certificate. The name of the certificate contains a lot of escape characters, so change the name to something simple if necessary.

Import certificate into JDK library

Import as per this article. In my case, I was using AWS Corretto 8, so I imported it below. The password was as in the article above.

.sh

sudo keytool -import -trustcacerts -file ~/Documents/charles_proxy.cer  -keystore /Library/Java/JavaVirtualMachines/amazon-corretto-8.jdk/Contents/Home/jre/lib/security/cacerts -alias ca

Request by specifying Proxy

Make a request by specifying port 8888 for Charles, as you did with curl. In this library

import net.gpedro.integrations.slack.SlackApi;
import net.gpedro.integrations.slack.SlackMessage;

import java.net.InetSocketAddress;
import java.net.Proxy;

public class SlackExecute {

    public static void main(String[] args) {

        SlackMessage slackMessage = new SlackMessage(
                "#genearal",
                "gpedro Bot",
                "Can I make a Slack request with gpedro?"
        );
        slackMessage.setIcon(":ghost:");
        SlackApi api = new SlackApi(
                "https://hooks.slack.com/services/<SOME>/<TOKEN>", 
                new Proxy(
                    Proxy.Type.HTTP,
                    new InetSocketAddress("localhost", 8888)
                )
         );
        api.call(slackMessage);
    }
}

Launch Charles and run the application

Now, in Charles' left pane, https://hooks.slack.com will appear and you can trace the content.

.json

{
    "channel": "#genearal",
    "username": "gpedro Bot",
    "icon_emoji": ":ghost:",
    "unfurl_media": false,
    "unfurl_links": false,
    "link_names": false,
    "text": "Can I request with gpedro"
}

[^ 1]: For example, make a request to Spring 5 [WebClient interface](https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/reactive/function/client/ WebClient.html) and specify the proxy in this article How to do it is described. For this class, [WebClient.Builder # clientConnector method](https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/reactive/function/client/WebClient.Builder. There is html # clientConnector-org.springframework.http.client.reactive.ClientHttpConnector-). The argument of this method can be ClientHttpConnector class .. [Constructor](https: /) of ReactorClientHttpConnector of this implementation class /docs.spring.io/spring/docs/current/javadoc-api/org/springframework/http/client/reactive/ReactorClientHttpConnector.html#ReactorClientHttpConnector-reactor.netty.http.client.HttpClient-) (https://projectreactor.io/docs/netty/release/api/reactor/netty/http/client/HttpClient.html) can be specified. TcpConfiguration method of HttpClient release / api / reactor / netty / http / client / HttpClient.html # tcpConfiguration-java.util.function.Function-) is the [TcpClient class](https://projectreactor.io/docs/netty/release/api/ TcpClient class with a function that takes reactor / netty / tcp / TcpClient.html) as an argument , Proxy method is ProxyProvider.TypeSpec takes a function as an argument. ProxyProvider.TypeSpec interface type method, Set the Proxy type to [ProxyProvider.TypeSpec interface type method](https://projectreactor.io/docs/netty/release/api/reactor/netty/tcp/ProxyProvider.TypeSpec.html#type-reactor. In the implementation of ProxyProvider.AddressSpec of the return value of netty.tcp.ProxyProvider.Proxy-) You can specify the host or the InetSocketAddress class (https://docs.oracle.com/javase/jp/8/docs/api/java/net/InetSocketAddress.html). It doesn't use the Proxy class (https://docs.oracle.com/javase/jp/8/docs/api/java/lang/reflect/Proxy.html), but it does the same thing.