I accidentally deployed a dodgy bit of code to one of my function apps. Then, even when I tried to revert to a “known good” version of my code via the GUI, it still didn’t work. No matter what I did, I kept getting the dreaded “Compilation Failed” error – but there was no more information. No useful compilation errors…
2016-10-23T20:35:46.853 Function started (Id=5ededb27-6144-40d1-8d14-8db77d70b771)
2016-10-23T20:35:47.901 Function compilation error
2016-10-23T20:35:47.901 Function completed (Failure, Id=5ededb27-6144-40d1-8d14-8db77d70b771)
2016-10-23T20:35:48.369 Exception while executing function: Functions.fetchDepartureBoardOrchestrator. Microsoft.Azure.WebJobs.Script: Script compilation failed.
It was so frustrating. Until I worked out that you can actually restart the power app host – just go to the Function App Settings then click “Go To App Service Settings” at the bottom. You’ll see the traditional “full” properties and settings blade, and at the top is a “Restart” button. Then I was able to save my updated code.
I’ve been playing around with my Nextion and a Particle Photon for a while. The idea is to pull data from a variety of services and have it available on a display by the front door – things like the weather, the outside temperature (from my Netatmo), and the next 3 trains to Seven Sisters from our station. Living, as we do, at the end of the Enfield Town branch line, it can be a bit hit and miss as to whether or not you make the train, or if it’s even running.
Anyway, I got the first part of this working. I regularly poll the National Rail SOAP API, parsing the content in to a simple minified JSON format using a Power App. Took me a while.
While trying to install the C# scripting package Microsoft.CodeAnalysis.CSharp.Scripting from nuget, but was getting odd messages about missing dependencies. I spent ages trying to figure it out as all the dependency versions appeared to match (e.g.
Unable to find a version of ‘Microsoft.CodeAnalysis.Common’ that is compatible with ‘Microsoft.CodeAnalysis.CSharp 2.0.0 constraint: Microsoft.CodeAnalysis.Common (= 2.0.0)’, ‘Microsoft.CodeAnalysis.Scripting.Common 2.0.0 constraint: Microsoft.CodeAnalysis.Common (= 2.0.0)’
however, eventually I discovered that you neeed .NET 4.6. Doh!
I started writing EnfieldTownBot using Azure Logic Apps. It’s pretty easy, but i soon hit a challenge – it’s so expensive! My app was pretty simple – a trigger, a “for…each”, a condition and a http callout to my Twitter Poster Function App:
So – if there are no delays, that’s (recurrence + httprequest + foreach + 3 x (condition)) = 6 actions. There could be up to 9 if the postToTwitter action also triggers. I want to run this function 2x (once for trains FROM Enfield Town, once for trains TO Enfield Town), so that’s 12-18 actions per request. And I want to run it every 15-30 seconds to get the latest information published ASAP. So that’s 48-72 actions per minute. Over a day, that’s 69,120 to 103,680 actions. Over a (31 day) month, that’s 2,142,720 to 3,214,080 actions. Taking a mean of these (2,678,400), and looking at the current pricing, it would cost me £450 a month to run this app. Wow. I don’t care about late trains THAT much…
So – I rewrote the whole lot as a function app (actually 2 or 3 function apps, as some of the items, such as parsing the XML from National Rail to JSON are reusable elsewhere). Each execution takes about 300ms, and it executes (24 hours x 60 minutes per hour x 4 times per minute) = 5,760 per day. Over a month that’s 178,560 executions. That’s well within the “permanent free grant” provided for Functions. In fact, I’d have to run it something like 30,000,000 times per month, or about 600 times per second to even hit a cost of £1.
The Function App will return a JSON with the data returned by the Twitter API, or an error. Note that as long as it gets SOME response from the Twitter API it’ll return a 200 code. In future I’ll work on making this more granular (e.g. pass through 50x errors).
Earlier this year, we got a new car, a BMW 3 series. It came subscribed to the BMW ConnectedDrive service, and that comes with an iPhone or Android app. So, of course, I immediately set about deconstructing the traffic to figure out what was going on, inspired by the work of Terence Eden. Unfortunately, BMW appears to have implemented certificate pinning in the time since Terrence wrote his paper, so my favourite tool, Charles Proxy, was useless – the BMW app simply dropped the connection.
So – I decided to reverse engineer the iphone app itself. I finally managed to get an OAuth appID and app secret from the code base – only to discover that the /webapi/v1/user/vehicles/:VIN/status method now requires location:
"description": "(SmartPhoneUtil-A-101) Mandatory
parameter(s) missed or blank: dlat and dlon are required for BMW
if i add the lat + long of my home as querystring paramaters (/?dlat=x&dlon=y) it works but i don’t get a lot of other data (e.g. door status) although i guess that’s to do with the options available on my car:
I have to say that the twitter API documentation is absolutely abysmal. It’s impossible to navigate – calls make reference to other calls but the major problem is that there are almost no examples – they almost all recommend that you use a library. So how on earth are you supposed to learn how the API works? How do you write a bot which tweets as itself (such as my https://twitter.com/EnfieldTownBot)?
Once I got a good grip on the API itself – which isn’t too bad – I now have to figure out how to create an Azure Function App to create and send the tweets – as OAuth 1.0 requires all messages to be signed (hashed). Twitter has a pretty good set of instructions on how to create the hash: https://dev.twitter.com/oauth/overview/creating-signatures
But – oh my gosh. This is a very complicated process. Here are some samples of libraries or code which i’m looking through to try to implement…
When we bought our house a few years ago, we totally gutted it and one of the things we installed was an evohome heating system. Honeywell has an iphone app for the evohome, so recently, I decided to explore the API. Unfortunately, Honeywell doesn’t seem to offer a public API, so I spent a bit of time deconstructing the app with the help of the excellent Charles Proxy.