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Building a travel toolkit

2025-01-02T00:00:00Z

The container for my toolkit, a UGREEN “travel accessories” bag

For a while now, whenever I’ve traveled anywhere I’ve dumped a selection of tools into my backpack just in case I need them. Originally this was mostly focused around being able to open and fix my laptop if anything went wrong, but over time has slowly expanded to include other useful tools.

Repeatedly packing these tools and then returning them to where they belonged was tedious, though. I couldn’t just leave them in the backpack as I often needed them for non-travelling purposes, and I didn’t want to just buy duplicate tools that spent most of their life a few meters away from each other, so I ignored the problem and just dealt with the tedium.

Eventually I acquired enough tools that — while not quite duplicates — I wouldn’t miss often if they were kept in the backpack. Building on these I’ve created a little travel toolkit that contains everything I might want (and more) while away.

The base

The biggest challenge I had before was finding a screwdriver set. I have an iFixit Mako set that did the in-and-out-of-the-bag routine for several years. Nothing else covered the range of drivers I wanted for generic electronic tinkering and more chunky work. I finally found one in the form of a Wera Tool-Check PLUS TR-Edition. “TR” stands for “Tool Rebel” and is Wera’s “fan club” brand. Its signature features over the normal Tool-Check PLUS are a fancy fabric case and a 152mm bit extender; but it also comes with a much different set of bits, which is why I picked it up.

Here’s a comparison

Type	Standard version	Tool Rebel edition
Phillips	2x PH1 3x PH2 1x PH3	1x PH00 1x PH0 1x PH1 1x PH2 1x PH3
Pozidrive	None	1x PZ1 3x PZ2
Slotted	1x 5.5mm	1x 4mm 1x 4.5mm 2x 5.5mm 1x 6.5mm
Torx	1x T10 1x T15 1x T20 1x T25 1x T30 1x T40	1x T10 1x T15 1x T20 1x T25 1x T30 1x T40
Security Torx	1x T10 1x T15 1x T20 1x T25 1x T30	1x T25
Hex	1x H3 1x H4 1x H5 1x H6 1x H8	1x H1.5 1x H2 1x H2.5 1x H3 1x H4 1x H6 1x H8

There are only five bits present in the standard version that are missing in the TR edition: 5mm hex (pretty uncommon) and four sizes of security torx (rare). In exchange for those and the removal of a bunch of duplicates, you get two extra phillips sizes (0 and 00, both very useful for electronics and spectacles), some pozidrive bits (extremely common on random hardware/furniture/etc), smaller hex bits (for electronics, 3D printers, and so on), and a few other bits and pieces.

Overall it’s a vastly superior selection for my needs. And while it doesn’t have the full range of bits provided by the iFixit kit, it does cover almost everything I’m ever actually likely to need while travelling, and it’s probably around a third of the size.

The other core part of the toolkit is the bag. I had a UGREEN “travel accessory” bag hanging around unused, and noticed it was almost the exact right size for the Tool-Check. Now, how many other tools could I stuff in there?

All the tools

The array of tools that make up the travel toolkit

The kit can be broken down into a few sections:

Screwdriving

The aforementioned Wera Tool-Check
Its 152mm bit extender

I’ve talked enough about this already, I think, so I’ll spare you any additional commentary on screwdrivers and bits.

Splitting, gripping and cutting

Engineer tweezers
Engineer mini snips
Engineer mini screw removal pliers
Knipex mini waterpump pliers
Two iFixit spudgers (one metal, one plastic)
iFixit jimmy

I have bigger or slightly different versions of these that stay in my normal toolkit. The tweezers and snips are useful in a variety of situations, and the spudgers are handy for getting inside laptops and other devices. The pliers are less useful, but they’re one of those things where when you do need them there aren’t any good alternatives.

Sewing

Two needles
Some black thread
Set of mini clips

You never know when you’re going to rip a seam in something. I find the clips a lot less fiddly than using pins for keeping material in place when I’m trying to sew.

Computering

Retractable ethernet cable
RJ45 coupler
USB-C to RJ45 adapter
Dual USB-A and USB-C thumb drive, with an Arch ISO on it

Sometimes Wi-Fi just doesn’t cut it, or you need to fiddle with a router that doesn’t expose its admin UI over Wi-Fi. The USB-C adapter is for use with my phone, as it’s often easier to move that get the laptop where it needs to be.

I can boot from the thumb drive into an Arch environment, and from there reinstall my laptop from scratch if needed. There’s enough space left over so it can be used to transfer files as well.

Miscellaneousing

Fabric tape measure
Spirit level
Sharpie
Superglue
Spare batteries: 2 CR2032s, 2 AA, 2 AAA

I’m almost certain I won’t use the spirit level, but it’s tiny and I had a spare so it went in. Everything else is just in the “generally handy to have” category.

Putting it all together

The nicely-organised side of the toolkit

The Tool-Check PLUS fits almost perfectly into one side of the UGREEN bag, leaving a little wiggle room along the side for the longer parts like spudgers. The middle pockets can’t fit much in, but keep the batteries and sewing bits out of the way. Everything else is in a big zip-up compartment in the other side, which is slightly messy but still easy enough to dig through to find whatever I need.

The complete kit weighs in at around 1.2KG, so it’s not exactly lightweight, but it goes in a bag with a heavy laptop and all of its peripherals so it’s not as noticeable as it might otherwise be.

It remains to be seen how much use I’ll actually get out of any of this. Maybe I’ll put a bit of paper in so that I can track how often I use each tool…

Obfuscating Kotlin code with ProGuard

2019-10-21T00:00:00Z

Kotlin + Proguard = fun

Obfuscating code is the process of modifying source code or build output in order to make it harder for humans to understand. It’s often employed as a tactic to deter reverse engineering of commercial applications or libraries when you have no choice but to ship binaries or byte code. For Android apps, ProGuard is part of the default toolchain and obfuscation is usually only a config switch away.

I was recently working on an Android library written in Kotlin that my client wanted obfuscated to try and protect some of their trade secrets that were included. Not a problem, I thought: it’s just a few lines of ProGuard config and we’re away. Four hours and lots of hair pulling later I finally got it working…

If at first you don’t succeed…

At first it seemed like ProGuard was refusing to obfuscate any class with a keep rule. With a simple test class:

class Test {

    private val secret = 123
    var name = "Chris"

    fun greet() {
        println("Hi $name! Enter a number: ")
        readLine()?.let { guess(it.toInt()) }
    }

    private fun guess(attempt: Int) = println(
        if (attempt == secret) {
            "Correct!"
        } else {
            "Nope!"
        }
    )

}

And a ProGuard rule of:

-keep public class Test {
    public void greet();
}

I expected that the Test class and the greet method would remain, but both fields and the guess method would be obfuscated. When I built the project and opened the class from Android Studio’s APK inspector I was disappointed:

public final class Test public constructor() {
    public final var name: kotlin.String /* compiled code */

    private final val secret: kotlin.Int /* compiled code */

    public final fun greet(): kotlin.Unit { /* compiled code */ }

    private final fun guess(attempt: kotlin.Int): kotlin.Unit { /* compiled code */ }
}

Having your secret sauce in a field labelled “secret” isn’t exactly the level of obfuscation I was hoping for. ProGuard has lots of knobs that you can twist to affect what it keeps and what it renames, but all the incantations of -keep, -keepmembernames, -allowobfuscation, and so on, that I could come up with either resulted in the class completely vanishing (because it wasn’t kept) or showing up with all its symbols intact.

There are lots of useful Stack Overflow posts describing how to obfuscate a single method, or keep a single method and obfuscate the rest, but nothing I tried seemed to make a difference. I’m not the biggest fan of ProGuard, but I’ve used it enough before to know that it’s not usually that hard to make it submit to your demands. Obviously something else was going on.

… Maybe you’re solving the wrong problem

My next thought was that perhaps Android Studio was doing something clever like reading the ProGuard mapping file and automatically deobfuscating the output for me. Looking at the mapping file it seems that ProGuard has indeed decided to rename some things:

Test -> Test:
    int secret -> a
    java.lang.String name -> b
    void greet() -> greet
    void <init>() -> <init>

The obvious solution is to look at the class file in something less smart than Android Studio. A couple of unzips later and I could do a quick test to see if the original names were still present:

$ strings Test.class | grep secret
secret

The problem is evidently not with Android Studio, as secret shouldn’t end up in the class file at all: it should have been entirely replaced with a like the mapping file says. The output from javap -p doesn’t show any hint of the original names, however:

$ javap -p Test
public final class Test {
  private final int a;
  private java.lang.String b;
  public final void greet();
  public Test();
}

But, given the names show up in strings, they must be kicking around somewhere. None of the various outputs from javap helped until I hit -verbose. Right at the end of the class is:

RuntimeVisibleAnnotations:
  0: #58(#84=[I#2,I#2,I#4],#69=[I#2,I#1,I#3],#81=I#2,#70=[s#40],#71=[s#55,s#39,s#43,s#85,s#39,s#72,s#42,s#91,s#47,s#90,s#39,s#73,s#39,s#74,s#67,s#83])
    kotlin.Metadata(
      mv=[1,1,15]
      bv=[1,0,3]
      k=1
      d1=["\u0000\"\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u000e\n\u0002\b\u0005\n\u0002\u0010\b\n\u0000\n\u0002\u0010\u0002\n\u0002\b\u0003\u0018\u00002\u00020\u0001B\u0005¢\u0006\u0002\u0010\u0002J\u0006\u0010\u000b\u001a\u00020\fJ\u0010\u0010\r\u001a\u00020\f2\u0006\u0010\u000e\u001a\u00020\nH\u0002R\u001a\u0010\u0003\u001a\u00020\u0004X\u0086\u000e¢\u0006\u000e\n\u0000\u001a\u0004\b\u0005\u0010\u0006\"\u0004\b\u0007\u0010\bR\u000e\u0010\t\u001a\u00020\nX\u0082D¢\u0006\u0002\n\u0000¨\u0006\u000f"]
      d2=["LTest;","","()V","name","","getName","()Ljava/lang/String;","setName","(Ljava/lang/String;)V","secret","","greet","","guess","attempt","lib_release"]
    )

There’s a Kotlin annotation containing all of the symbols we were trying to obfuscate away! Kotlin apparently uses this annotation for reflection and for keeping track of various language features that don’t have a direct mapping in Java bytecode (such as members with internal access). Sure enough, switching back to Android Studio and making it “decompile” the Kotlin code into Java shows the annotation:

@Metadata(
   mv = {1, 1, 15},
   bv = {1, 0, 3},
   k = 1,
   d1 = {"\u0000\"\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u000e\n\u0002\b\u0005\n\u0002\u0010\b\n\u0000\n\u0002\u0010\u0002\n\u0002\b\u0003\u0018\u00002\u00020\u0001B\u0005¢\u0006\u0002\u0010\u0002J\u0006\u0010\u000b\u001a\u00020\fJ\u0010\u0010\r\u001a\u00020\f2\u0006\u0010\u000e\u001a\u00020\nH\u0002R\u001a\u0010\u0003\u001a\u00020\u0004X\u0086\u000e¢\u0006\u000e\n\u0000\u001a\u0004\b\u0005\u0010\u0006\"\u0004\b\u0007\u0010\bR\u000e\u0010\t\u001a\u00020\nX\u0082D¢\u0006\u0002\n\u0000¨\u0006\u000f"},
   d2 = {"LTest;", "", "()V", "name", "", "getName", "()Ljava/lang/String;", "setName", "(Ljava/lang/String;)V", "secret", "", "greet", "", "guess", "attempt", "lib_release"}
)
public final class Test {

Solving the right problem

Now I had an idea of what was happening I was able to find a couple of other reports of people having the same issue. There’s an open feature request for ProGuard to support Kotlin’s metadata annotation but it’s not yet supported.

As this was a library with a fairly straight forward interface I reasoned I could probably get ProGuard to strip out the metadata annotation. If I stopped Kotlin reflection working in the process then that would actually be a small bonus. Unfortunately other people with the same idea had reported back that they were unsuccessful: even when not using the default ProGuard config, somehow the annotations are kept.

Adding a -printconfiguration instruction to my configuration lets me see the full configuration being passed to ProGuard, and the reason for keeping quickly becomes obvious:

-keepattributes *Annotation*,*Annotation*

This appears to be added by the Android build plugin before it invokes ProGuard, and there’s no obvious way to disable it. ProGuard doesn’t offer a way to reverse this instruction, either, but fortunately the build plugin seems to concatenate all of the -keepattribute values together and puts our user-supplied ones first. Adding a negative filter:

-keepattributes !*Annotation*

Results in the following in the printed configuration:

-keepattributes !*Annotation*,*Annotation*,*Annotation*

The negative filter prevents any subsequent filters from matching. Recompiling and looking at the class file again looks a lot more sensible:

import kotlin.io.ConsoleKt;

public final class Test {
   private final int a = 123;
   private String b = "Chris";

   public final void greet() {
      String var1 = "Hi " + this.b + "! Enter a number: ";
      System.out.println(var1);
      String var10000 = ConsoleKt.readLine();
      if (var10000 != null) {
         var1 = var10000;
         int var3 = Integer.parseInt(var1);
         var1 = var3 == 123 ? "Correct!" : "Nope!";
         System.out.println(var1);
      }
   }
}

And that’s the story of how I spent half a day making a one line change.