What is Charles

A man-in-the-middle proxy that can be used to intercept network traffics between 2 devices.

By default it uses whatever the Java Swing default is, so… here we are:

Install FlatLAF for Arch Linux

Firstly, prepare our workspace directory and download FlatLAF 2.3:

sudo mkdir -p /opt/charles_flatlaf
sudo wget -O /opt/charles_flatlaf/flatlaf-2.3.jar \
	'https://search.maven.org/remotecontent?filepath=com/formdev/flatlaf/2.3/flatlaf-2.3.jar'

Write our loader to the workspace:

sudo tee /opt/charles_flatlaf/launch_charles <<'EOF'
#!/bin/sh

# Setup some variables...
JAVA="java"
CHARLES_LIB="/usr/share/java/charles"
THEME="com.formdev.flatlaf.FlatLightLaf"

exec "$JAVA" $OPTS \
  -Xmx1024M \
  -Dawt.useSystemAAFontSettings=on \
  -Dswing.aatext=true \
  -Dswing.defaultlaf="$THEME" \
  -Dswing.crossplatformlaf="$THEME" \
  -Dcharles.config="${XDG_CONFIG_HOME:-~/.config/charles}/.charles.config" \
  -Djava.library.path="$CHARLES_LIB" \
  -classpath "/opt/charles_flatlaf/flatlaf-2.3.jar:${CHARLES_LIB}/charles.jar" \
  com.xk72.charles.gui.MainWithClassLoader \
  "$@"

EOF

Finally, mark it as executable, and have it in the $PATH with higher priority:

sudo chmod a+x /opt/charles_flatlaf/launch_charles
sudo ln -s /opt/charles_flatlaf/launch_charles /usr/local/bin/charles

If we don’t want it anymore, just remove them:

sudo rm -rf "/opt/charles_flatlaf/"
sudo rm "/usr/local/bin/charles"

※ Flags were inspired from discussions in AUR ¹.

※ Does not work in Ubuntu. Please wait for update or adjust the script accordingly…

Install FlatLAF for Windows

Windows is a bit tricky - it uses an executable file to load the Java application, and ignores swing flags.

We’ll have to get our hands dirty in this case…

1. Install a full copy of JDK 11, for instance Adoptium JDK 11. Embedded JDK is missing some modules.
2. Remember the path you’ve installed to. The default should be:
   C:\Program Files\Eclipse Adoptium\jdk-11.0.15.10-hotspot\
3. Download the latest release of CharlesFlatLAF or compile your own, place it under <Charles>/lib;
4. Update Charles.ini:
   • Make a backup.
   • Insert the following line after classpath.1:
     classpath.2=lib/charles_flatlaf-1.0-SNAPSHOT-jar-with-dependencies.jar
   • Replace the line with main.class to:
     main.class=uk.jixun.charles.theme.Main
   • Insert the following line after vmarg.4:
     vmarg.5=-javaagent=lib/charles_flatlaf-1.0-SNAPSHOT-jar-with-dependencies.jar
   • Replace the line with vm.location to:
     vm.location=<JDK path>\bin\server\jvm.dll

… and your final Charles.ini should look some-what like this:

working.directory=.
classpath.1=lib/charles.jar
classpath.2=lib/CharlesFlatLAF-1.0-SNAPSHOT-jar-with-dependencies.jar
main.class=uk.jixun.charles.theme.Main
vm.version.min=11
vm.location=C:\Program Files\Eclipse Adoptium\jdk-11.0.15.10-hotspot\bin\server\jvm.dll
vmarg.1=-Dsun.java2d.d3d=false
vmarg.2=-Djava.net.preferIPv4Stack=false
vmarg.3=-Djava.net.preferIPv6Addresses=true
vmarg.4=-Djava.library.path=lib
vmarg.5=-javaagent:lib/CharlesFlatLAF-1.0-SNAPSHOT-jar-with-dependencies.jar
dde.enabled=true
dde.class=com.xk72.charles.win32.Win32DDEManager
dde.server.name=Charles
dde.topic=System
single.instance=dde
log.level=warning

[ErrorMessages]
java.not.found=The bundled Java installation was not found. Please uninstall and reinstall Charles.
java.failed=The bundled Java installation is broken. Please uninstall and reinstall Charles.

Start Charles via Desktop shortcut, just as expected:

Afterthoughts

You might have noticed that it looks exactly like zaproxy.

Indeed, I was researching for alternatives and I quite liked the zaproxy theming; however I’d like to make the layout closer to Charles…

I thought, they are both made of Java. There must’ve been a way to apply the same theme. So I went and looked around, got this Java Agent to monkey patch things.

Experimenting further under Linux, it works without the agent - what a surprise. Tried to back-port the steps to Windows, no joy. welp.