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169 lines
11 KiB
Markdown
169 lines
11 KiB
Markdown
# Writing a profile
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**Per endpoint, `hafas-client` has an endpoint-specific customisation called *profile*** which may for example do the following:
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- handle the additional requirements of the endpoint (e.g. authentication),
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- extract additional information from the data provided by the endpoint,
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- guard against triggering bugs of certain endpoints (e.g. time limits).
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This guide is about writing such a profile. If you just want to use an already supported endpoint, refer to the [API documentation](readme.md) instead.
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*Note*: **If you get stuck, ask for help by [creating an issue](https://github.com/public-transport/hafas-client/issues/new)!** We want to help people expand the scope of this library.
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## 0. How do the profiles work?
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A profile may consist of three things:
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- **mandatory details about the HAFAS endpoint**
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- `endpoint`: The protocol, host and path of the endpoint.
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- `locale`: The [BCP 47](https://en.wikipedia.org/wiki/IETF_language_tag) [locale](https://en.wikipedia.org/wiki/Locale_(computer_software)) of your endpoint (or the area that your endpoint covers).
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- `timezone`: An [IANA-time-zone](https://www.iana.org/time-zones)-compatible [timezone](https://en.wikipedia.org/wiki/Time_zone) of your endpoint.
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- **flags indicating that features are supported by the endpoint** – e.g. `journeyRef`
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- **methods overriding the [default profile](../lib/default-profile.js)**
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As an example, let's say we have an [Austrian](https://en.wikipedia.org/wiki/Austria) endpoint:
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```js
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const myProfile = {
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endpoint: 'https://example.org/bin/mgate.exe',
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locale: 'de-AT',
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timezone: 'Europe/Vienna'
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}
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```
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Assuming the endpoint returns all lines names prefixed with `foo `, We can strip them like this:
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```js
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// get the default line parser
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const createParseLine = require('hafas-client/parse/line')
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const createParseLineWithoutFoo = (profile, opt, data) => {
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const parseLine = createParseLine(profile, opt, data)
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// wrapper function with additional logic
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const parseLineWithoutFoo = (l) => {
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const line = parseLine(l)
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line.name = line.name.replace(/foo /g, '')
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return line
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}
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return parseLineWithoutFoo
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}
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profile.parseLine = createParseLineWithoutFoo
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```
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If you pass this profile into `hafas-client`, the `parseLine` method will override [the default one](../parse/line.js).
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## 1. Setup
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*Note*: There are many ways to find the required values. This way is rather easy and has worked for most of the apps that we've looked at so far.
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1. **Get an iOS or Android device and download the "official" app** for the public transport provider that you want to build a profile for.
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2. **Configure a [man-in-the-middle HTTP proxy](https://docs.mitmproxy.org/stable/concepts-howmitmproxyworks/)** like [mitmproxy](https://mitmproxy.org).
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- Configure your device to trust the self-signed SSL certificate, [as outlined in the mitmproxy docs](https://docs.mitmproxy.org/stable/concepts-certificates/).
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- *Note*: This method does not work if the app uses [public key pinning](https://en.wikipedia.org/wiki/HTTP_Public_Key_Pinning). In this case (the app won't be able to query data), please [create an issue](https://github.com/public-transport/hafas-client/issues/new), so we can discuss other techniques.
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3. **Record requests of the app.**
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- [There's a video showing this step](https://stuff.jannisr.de/how-to-record-hafas-requests.mp4).
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- Make sure to cover all relevant sections of the app, e.g. "journeys", "departures", "live map". Better record more than less; You will regret not having enough information later on.
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- To help others in the future, post the requests (in their entirety!) on GitHub, e.g. in as format like [this](https://gist.github.com/derhuerst/5fa86ed5aec63645e5ae37e23e555886). This will also let us help you if you have any questions.
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## 2. Basic profile
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- **Identify the `endpoint`.** The protocol, host and path of the endpoint, *but not* the query string.
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- *Note*: **`hafas-client` for now only supports the interface providing JSON** (generated from XML), which is being used by the corresponding iOS/Android apps. It supports neither the JSONP, nor the XML, nor the HTML interface. If the endpoint does not end in `mgate.exe`, it mostly likely won't work.
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- **Identify the `locale`.** Basically guess work; Use the date & time formats as an indicator.
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- **Identify the `timezone`.** This may be tricky, a for example [Deutsche Bahn](https://en.wikipedia.org/wiki/Deutsche_Bahn) returns departures for Moscow as `+01:00` instead of `+03:00`.
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- **Copy the authentication** and other meta fields, namely `ver`, `ext`, `client` and `lang`.
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- You can find these fields in the root of each request JSON. Check [a VBB request](https://gist.github.com/derhuerst/5fa86ed5aec63645e5ae37e23e555886#file-1-http-L13-L22) and [the corresponding VBB profile](https://github.com/public-transport/hafas-client/blob/6e61097687a37b60d53e767f2711466b80c5142c/p/vbb/index.js#L22-L29) for an example.
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- Add a function `transformReqBody(body)` to your profile, which assigns them to `body`.
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- Some profiles have a `checksum` parameter (like [here](https://gist.github.com/derhuerst/2a735268bd82a0a6779633f15dceba33#file-journey-details-1-http-L1)) or two `mic` & `mac` parameters (like [here](https://gist.github.com/derhuerst/5fa86ed5aec63645e5ae37e23e555886#file-1-http-L1)). If you see one of them in your requests, jump to [*Appendix A: checksum, mic, mac*](#appendix-a-checksum-mic-mac). Unfortunately, this is necessary to get the profile working.
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You may want to use the [profile boilerplate code](profile-boilerplate.js).
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## 3. Products
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In `hafas-client`, there's a difference between the `mode` and the `product` field:
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- The `mode` field describes the mode of transport in general. [Standardised by the *Friendly Public Transport Format* `1.0.1`](https://github.com/public-transport/friendly-public-transport-format/blob/1.0.1/spec/readme.md#modes), it is on purpose limited to a very small number of possible values, e.g. `train` or `bus`.
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- The value for `product` relates to how a means of transport "works" *in local context*. Example: Even though [*S-Bahn*](https://en.wikipedia.org/wiki/Berlin_S-Bahn) and [*U-Bahn*](https://en.wikipedia.org/wiki/Berlin_U-Bahn) in Berlin are both `train`s, they have different operators, service patterns, stations and look different. Therefore, they are two distinct `product`s `subway` and `suburban`.
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**Specify `product`s that appear in the app** you recorded requests of. For a fictional transit network, this may look like this:
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```js
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const products = [
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{
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id: 'commuterTrain',
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mode: 'train',
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bitmasks: [16],
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name: 'ACME Commuter Rail',
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short: 'CR',
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default: true
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},
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{
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id: 'metro',
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mode: 'train',
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bitmasks: [8],
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name: 'Foo Bar Metro',
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short: 'M',
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default: true
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}
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]
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```
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Let's break this down:
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- `id`: A sensible, [camelCased](https://en.wikipedia.org/wiki/Camel_case#Variations_and_synonyms), alphanumeric identifier. Use it for the key in the `products` array as well.
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- `mode`: A [valid *Friendly Public Transport Format* `1.0.1` mode](https://github.com/public-transport/friendly-public-transport-format/blob/1.0.1/spec/readme.md#modes).
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- `bitmasks`: HAFAS endpoints work with a [bitmask](https://en.wikipedia.org/wiki/Mask_(computing)#Arguments_to_functions) that toggles the individual products. It should be an array of values that toggle the appropriate bit(s) in the bitmask (see below).
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- `name`: A short, but distinct name for the means of transport, *just precise enough in local context*, and in the local language. In Berlin, `S-Bahn-Schnellzug` would be too much, because everyone knows what `S-Bahn` means.
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- `short`: The shortest possible symbol that identifies the product.
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- `default`: Should the product be used for queries (e.g. journeys) by default?
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If you want, you can now **verify that the profile works**; We've prepared [a script](https://runkit.com/derhuerst/hafas-client-profile-example/0.2.0) for that. Alternatively, [submit a Pull Request](https://help.github.com/articles/creating-a-pull-request-from-a-fork/) and we will help you out with testing and improvements.
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### Finding the right values for the `bitmasks` field
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As shown in [the video](https://stuff.jannisr.de/how-to-record-hafas-requests.mp4), search for a journey and toggle off one product at a time, recording the requests. After extracting the products bitmask ([example](https://gist.github.com/derhuerst/193ef489f8aa50c2343f8bf1f2a22069#file-via-http-L34)) you will end up with values looking like these:
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```
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toggles value binary subtraction bit(s)
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all products 31 11111 31 - 0
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all but ACME Commuter Rail 15 01111 31 - 2^4 2^4
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all but Foo Bar Metro 23 10111 31 - 2^3 2^3
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all but product E 25 11001 31 - 2^2 - 2^1 2^2, 2^1
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all but product F 30 11110 31 - 2^0 2^0
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```
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## 4. Additional info
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We consider these improvements to be *optional*:
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- **Check if the endpoint supports the journey legs call.**
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- In the app, check if you can query details for the status of a single journey leg. It should load realtime delays and the current progress.
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- If this feature is supported, add `journeyLeg: true` to the profile.
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- **Check if the endpoint supports the live map call.** Does the app have a "live map" showing all vehicles within an area? If so, add `radar: true` to the profile.
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- **Consider transforming station & line names** into the formats that's most suitable for *local users*. Some examples:
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- `M13 (Tram)` -> `M13`. With Berlin context, it is obvious that `M13` is a tram.
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- `Berlin Jungfernheide Bhf` -> `Berlin Jungfernheide`. With local context, it's obvious that *Jungfernheide* is a train station.
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- **Check if the endpoint has non-obvious limitations** and let use know about these. Examples:
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- Some endpoints have a time limit, after which they won't return more departures, but silently discard them.
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---
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## Appendix A: `checksum`, `mic`, `mac`
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As far as we know, there are three different types of authentication used among HAFAS deployments.
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### unprotected endpoints
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You can just query these, as long as you send a formally correct request.
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### endpoints using the `checksum` query parameter
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`checksum` is a [message authentication code](https://en.wikipedia.org/wiki/Message_authentication_code): `hafas-client` will compute it by [hashing](https://en.wikipedia.org/wiki/Hash_function) the request body and a secret *salt*. **This secret can be read from the config file inside the app bundle.** There is no guide for this yet, so please [open an issue](https://github.com/public-transport/hafas-client/issues/new) instead.
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### endpoints using the `mic` & `mac` query parameters
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`mic` is a [message integrity code](https://en.wikipedia.org/wiki/Message_authentication_code), the [hash](https://en.wikipedia.org/wiki/Hash_function) of the request body.
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`mac` is a [message authentication code](https://en.wikipedia.org/wiki/Message_authentication_code), the hash of `mic` and a secret *salt*. **This secret can be read from the config file inside the app bundle.** There is no guide for this yet, so please [open an issue](https://github.com/public-transport/hafas-client/issues/new) instead.
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