.NET Maui, Android Emulator, Fiddler – watch only emulator traffic

1. 1. Install Fiddler Classic:
   2. Download and install Fiddler Classic from the official website.
2. Configure Fiddler Classic:
   • Open Fiddler and go to Tools > Options > Connections.
   • Check the box for Allow remote computers to connect.
   • Note the port number (default is 8888).
   • Restart Fiddler to apply the changes.
3. Find Your IP Address:
   • Hover over the Online indicator in the top right corner of Fiddler to see your IP address.
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4. Configure the Android Emulator:
   • Start your Android emulator from Visual Studio.
   • In the emulator, go to Settings > Wi-Fi.
   • Long press on the connected network (usually “Wired eth1”) and select Modify Network.
   • Enable Show advanced options.
   • Set Proxy to Manual.
   • Enter your IP address and the port number (8888).
   • Note: if you move around to different work locations your ip address will likely change and need to be updated here.
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5. Install Fiddler Root Certificate:
   • Open the emulator’s browser and navigate to http://ipv4.fiddler:8888/.
   • Download and install the Fiddler root certificate.
   • Follow the prompts to install the certificate in the system account.
6. Turn Off Cellular Data
   • Open emulator settings, navigate to network & internet / internet / the click on the gear icon for the mobile provider.
   • Click the slider to turn off use this sim
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   • I have had a time or two when for some odd reason I can’t turn the sim off.  In that case I turn mobile data off and then that forces traffic through wifi and the proxy.
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7. Turn off laptop LAN Settings automatically detect
   • navigate to control panel/ network and internet / click on Internet Options/ click on the connections tab / click the LAN settings button 
   • uncheck automatic detection.
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8. Set Filters in Fiddler
   • In fiddler click on the filters icon, I set the filters to remove some noise entries.  Note that you don’t have to actually turn on Catpure Traffic under the File menu to monitor traffic from your emulator at this point.   The proxy on the emulator forwards the information directly to fiddler and capturing traffic is not needed in that capture traffic would be looking at the network traffic on your laptop.  
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   • You can also filter traffic to a particular process and you might find this helpful under certain circumstances.
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   • For example: the web site openlibrary.org is where I am currently working.  Figuring out their API’s.  I usually have 25 or more tabs open in edge, fortunately when the tab is asleep the title of the tab does not show up in the drop down list.  And it’s easy to find the tab that I want to monitor traffic from.   I can then filter on that process and select File Capture traffic and now I have monitored traffic from the emulator and from the one website that I am interested in.
9. Capture Traffic:
   • Now that I have the emulator setup to forward to fiddler and the filters set to watch traffic from the one browser tab I am interested.  I can start File/Capture Traffic and see what all is going on with my app and the website it’s interacting with.
   • Launch the app you want to test in the emulator.
10. A couple of examples of using fiddler.
    1. OpenLibrary.org does not have a documented API to update the reading status of a book that is a person’s bookshelf.   You can set a book to want to read, reading, already read.   The mobile I am building I want to be able to do the same thing.   In order to figure out how to make API call’s into openlibrary.org to do this I executed the steps in the web browser on openlibrary.org and updated a book.
    2. Looking at the traffic you can pick out the multi part form post that sets the status on book.
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    3. Then when writing your code to execute the same post you can look at what your app is actually sending and compare it to what works and make adjustments.  Here I ran my app found the post that is attempting to set the date a book was read.  click on that post in the right hand window there are several ways to look at the post.   I like the raw view.   
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       • For example here is one of my first attempts at setting the data a book was read.  I was able to see that the code was using \u0002 for a double quote.  When ultimately I needed the json to look like:
         

          

         {“event_type”:2,”year”:2018,”month”:5,”day”:18,”event_id”:null}

       • POST https://openlibrary.org/works/OL20643179W/check-ins HTTP/1.1

         Content-Type: application/json; charset=utf-8

         Cookie: pd=; session=/people/mynextbook%2C2024-09-06T14%3A56%3A52%2C04338%248a8ba7b97c5c121f24604a0332e40cc1

         User-Agent: Dalvik/2.1.0 (Linux; U; Android 15; sdk_gphone64_x86_64 Build/AP31.240517.022)

         Host: openlibrary.org

         Connection: Keep-Alive

         Accept-Encoding: gzip

         Content-Length: 124

          

         “{\u0022event_type\u0022: 2, \u0022year\u0022: 2018, \u0022month\u0022: 5, \u0022day\u0022: 18, \u0022event_id\u0022: null}”

Hope this provides some insight on how to utilize fiddler to help fill in the gaps on web apps you are integrating with and how you can troubleshoot your own apps by tracking exactly what api’s are being called and what they look like.