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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…

HTTP/2 and TLS Server Name Indication

2024-05-25T00:00:00Z

I was recently alerted to a bug in Centauri, a simple reverse proxy I wrote. The initial report was that it was serving completely the wrong website, but only sometimes, and it behaved differently in different browsers, and no-one else could reproduce it.

I use Centauri for all of my web-facing services (including this site!) so it’s a little surprising such a major bug would have escaped my notice. Shane, who first noticed the bug, was persistent though and eventually managed to figure out some exact reproduction steps.

A brief overview of Centauri and SNI

Centauri originally only proxied HTTPS requests¹. When it receives a HTTPS request, it first looks at the Server Name Indication (or SNI) field in the TLS ClientHello message. It uses this field to determine which TLS certificate to respond with (as one Centauri instance will typically serve many websites across many domain names, each with their own certificate). That’s what the field exists for: before SNI, if you wanted to host two HTTPS sites on the same machine you’d need separate IP addresses for them!

Once the TLS session was established Centauri would read in the HTTP request, select which backend it was going to be sent to based on the SNI field, and then proxy it on. The HTTP request itself contains a Host header which identifies which host the request is for, but that will always be the same as the SNI field… or so I thought.

HTTP connection reuse

When accessing a website, your browser will request dozens of resources in a short space of time: the webpage itself, some stylesheets, maybe some scripts, plus any images, fonts, videos, etc. It would be extremely inefficient to open a new connection for each individual request, as setting up the connection requires several round trips between the client and the server.

To address this issue, HTTP/1.1 formalised the idea of “persistent connections”, which allow the client to keep a connection open and send another request once the first has completed. HTTP/2 takes this a step much further and allows full multiplexing — sending multiple requests at once and allowing the server to respond out-of-order.

Obviously, you can only reuse the connection if you’re requesting further resources from the same host: if your browser makes a request to example.com and that includes a script from example.net, it has to open a new connection for the other domain. However, HTTP/2 expands this slightly:

For “https” resources, connection reuse additionally depends on
having a certificate that is valid for the host in the URI. The
certificate presented by the server MUST satisfy any checks that the
client would perform when forming a new TLS connection for the host
in the URI.

Putting it all together

The reproduction steps that Shane figured out involved visiting sites hosted on two subdomains. The first site to be visited got “stuck” and subsequent requests to the other site were routed there instead. This only worked for one specific domain, though, and it turns out because that domain was configured in Centauri to use a wildcard TLS certificate (i.e., the certificate served for the request to the first site was also valid for the second site).

The certificate being valid for both sites allowed the browser to use the same connection. This breaks my assumption that the SNI field would always match the HTTP host, as all requests are sent over the same TLS connection that had the SNI field set to the first site’s subdomain. While perfectly in spec, the behaviour is quite surprising.

The fix for this was trivial: Centauri now checks the HTTP Host header instead of routing based on the SNI field. I found the bug itself interesting though, as it has such an awkward set of conditions for it to occur:

There must be multiple sites that share a certificate (the default behaviour in Centauri is to obtain one certificate per site)
A user must visit two of those sites
The browser must still have a connection open to the first site when visiting the second

It’s also one of those rare bugs where everything is working as intended, it’s just that the intention was slightly wrong for some reason. In this case it was because I wasn’t aware of the fairly significant shift in behaviour introduced in HTTP/2 for that one tiny part of the spec².

Thanks again to Shane for the debugging he did to figure this all out!

It now also proxies HTTP requests but only if they come over a Tailscale connection. Otherwise, plain HTTP requests are redirected to HTTPS. ↩︎
I think it’s this kind of thing that drives software devs to become carpenters or farmers. You don’t suddenly get a Door 2.0 specification that invalidates all your assumptions about how hinges work when certain people try to open it. ↩︎