dfrankland/how_to_use_wireshark_with_nodejs.md

## how_to_use_wireshark_with_nodejs.md

      
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              how_to_use_wireshark_with_nodejs.md
            
          
    How to use Wireshark with Node.js (especially with HTTPS / TLS / SSL)

It can be difficult to trace network traffic from a Node.js application.
Typically, folks will just instrument some logging to check that everything is
working as it is supposed to. Unfortunately, sometimes there are too many
abstractions or possible race conditions to accurately get a good trace. To get
the most objective possible trace of network traffic Wireshark can be used.
Wireshark is a network protocol analyzer that makes it extremely simple to
capture and trace network activity from any source on your computer. It also has
tools built in to decrypt traffic like that of HTTPS (TLS / SSL).
Setup

In the case of capturing HTTPS (TLS / SSL) traffic, there is some setup before
capturing traffic. If all you need is to capture unencrypted HTTP, then skip to
the Wireshark installation, since Wireshark can do so out-of-the-box.
SSL key logging for HTTPS (TLS / SSL) decryption

If you'd like to decrypt HTTPS (TLS / SSL) you will need to set a path via an
environmental variable to collect SSL keys for use in Wireshark. This same
environmental variable works for most browsers and some other applications as
well.
export SSLKEYLOGFILE=~/ssl_key_log_file.log

Set the path and file name to whatever you would like.

Node.js SSL key logging

Node.js v12.3.0 introduced a keylog API to store SSL keys, but it can be
unwieldy to setup and integrate with existing libraries. It also does not work
with the SSLKEYLOGFILE environmental variable. Luckily, there is a simple way
to set up using an npm module: sslkeylog. sslkeylog sets up global hooks
into the https module to capture any SSL keys used which makes it the
recommended way of capturing SSL keys. sslkeylog can be installed with npm
like below:
npm i -D sslkeylog
Once sslkeylog is installed, import it and active its hooks before making any
HTTP(S) calls. For example:
import sslkeylog from 'sslkeylog';

sslkeylog.hookAll();

// start the application after this
If you use TypeScript, you may need to include a declaration file like below:
// sslkeylog.d.ts

declare module 'sslkeylog';
Once capturing traffic is complete, you can remove all the code related to SSL
key logging.
Wireshark

First things first, you must install Wireshark program. On macOS you can use
brew to not only install the CLI, but the UI app as well:
brew cask install wireshark
For Wireshark to be able to decrypt HTTPS (TLS / SSL) traffic it needs to read
the SSL Key log generated by Node.js or other applications. To configure this
for Wireshark, open up the application and then open the preferences for
Wireshark. Once the preferences are open, open the "Protocols" dropdown in the
left sidebar menu listing and scroll down to "TLS", then click on it. On older
versions of Wireshark, look for "SSL" instead of "TLS". Once the settings for
"TLS" (or "SSL" for older versions) is open, look for the "(Pre)-Master-Secret
log filename" setting and set the path to the same one that was configured above
via the SSLKEYLOGFILE environmental variable. You might need to create an
empty file at the path given.
Capturing traffic

Now that you are all setup, you can begin capturing traffic. Open up Wireshark
and select the capture interface, which for macOS is usually en0 (Wi-Fi).
Once capturing has begun you should start to see logs of all sorts of traffic
to be listed, unless you are not connected to the internet.
This traffic can be overwhelming and mostly unrelated to Node.js or the
application you are trying to inspect. This where filters come in handy.
For example, to filter requests on a domain:
http.host matches "google.com"

Or to filter on a certain IP address:
ip.addr = 255.255.255.255

Filters can also be combined with conditional operators && and ||.
Once capturing has begun, you can start your app up as normal and try to cause
network activity that is in need of being traced.
Hopefully, with a combination with the filters you will be able to find the
exact requests and responses you are looking for. If you find either a request
or a response you can right click on a line item and select "Follow > HTTP
Stream" to see the both of the request and response.
Additionally, you can save any traffic captured for later use or to send to
peers for inspection.