How to get a list of all trains at a station in a given time frame?

[plnms]

For a personal project I'd like to get a list of all trains at a station in a certain time frame such as provided by bahn.expert and DBF. I can't use one of /stops/:id/arrivals or /stops/:id/departures, at least not with only one query, since AFAIK /stops/:id/departures misses the data of trains that end at the station queried and /stops/:id/arrivals misses the trains that start at this station. I tried to use /trips with a station ID and a time frame, but every request that I have tried has returned a 400.

Is there any easy way to achieve my goal? And could you maybe extend the documentation for /trips, because I really don't understand how to use this?

[derhuerst]

I assume you're referring to the v6.db.transport.rest? I'm asking because this repo is an "umbrella" repo for multiple APIs.

For a personal project I'd like to get a list of all trains at a station in a certain time frame […]. I can't use one of /stops/:id/arrivals or /stops/:id/departures, at least not with only one query, since AFAIK /stops/:id/departures misses the data of trains that end at the station queried and /stops/:id/arrivals misses the trains that start at this station.

Indeed, you'd have fetch both sets of trains/trips and combine them. You can use the rel=next Link header exposed by the API to iterate over departures and/or arrivals:

curl 'https://v6.db.transport.rest/stops/8000263/departures?when=2023-02-14T10%3A43%2B01%3A00' -fsSL -I | grep link
# link: […] <?when=2023-02-14T10%3A53%2B01%3A00>; rel=next

I tried to use /trips with a station ID and a time frame, but every request that I have tried has returned a 400.

This is an unfortunate combination of two issues:

• hafas-rest-api@6, a library used by v6.db.transport.rest, used to require a query, so you'd have to send query=* to still get all trains/trips, which is very unobvious. I have changed this, now omitting query should work.
• HAFAS's JourneyMatch, the API beneath the /trips endpoint, is a very maverick thing: It only accepts very specific combinations of parameters, and I don't know anyone who has completely reverse-engineered it (my attempt). For many queries it either yields NO_MATCH or TOO_MANY. Unfortunately, this means that it is barely usable to fulfil use cases like yours.

Is there any easy way to achieve my goal? And could you maybe extend the documentation for /trips, because I really don't understand how to use this?

I would like to, but as I said: I don't know either what its limitations are.

[plnms]

Excuse me for not specifying it but yes, I am referring to v6.db.transport.rest. Also excuse me for the late reply. Your explanations are very helpful, thank you! The /trips endpoint / HAFAS's JourneyMatch really are behaving weirdly now that I know how to play with /trips. If I find out anything helpful I'll let you know.

One minor request: What do you think of adding an example request to both /trips and /locations/nearby in the documentation? They are the only endpoints not to have one, and I found these examples very helpful in the other documentation entries. When experimenting, it's easier to find mistakes in a request altered from one known to work than in an entirely made up one. A very simple example for /trips would be

https://v6.db.transport.rest/trips?query=ICE%20529&onlyCurrentlyRunning=false

– but feel free to use a better one. I haven't played around with the other endpoint.

[plnms]

Example using some more features, not using query:

https://v6.db.transport.rest/trips?fromWhen=2023-02-21T19:00:00Z&untilWhen=2023-02-21T20:00:00Z&currentlyStoppingAt=8000287&onlyCurrentlyRunning=false

This means "give me all trains meeting the following criteria":

• time frame of one hour, today 8pm to 9pm (German time): selected by fromWhen and untilWhen
• stopping at Oberkotzau station: selected by currentlyStoppingAt – the parameter is confusingly named in this context, as my query selects every train that will be "currently" stopping at the station in the given time frame
• show trains that are not currently running, because they might not have begun their journey for time frames ending in the future / they might already have reached their terminus: selected by onlyCurrentlyRunning=false

This is actually pretty close to what I originally wanted to achieve. If cautiously used with additionally filtering out everything that's not a train (bus=false etc.) I can use it even for stations as big as Cologne central (8000207) without running into the fearsome TOO_MANY phenomenon.

[derhuerst]

Yes, please submit a PR with example URLs! Just add multiple, with a comment on each explaining what it does.

You'll have to adapt examples in api-docs.js; Then, please test your changes using npm run docs.

[plnms]

The more I'm playing around with this, the weirder it gets. I don't want to give unhelpful information, so expect this to take some time.

Also, I've never really used Node, but I'm happy to execute this one command if it's just that.

[derhuerst]

Also, I've never really used Node, but I'm happy to execute this one command if it's just that.

If it's about not "polluting" your system with a toolchain that you usually don't need, you can do it in Docker: docker run --rm -it -v $PWD:/app node:18-alpine /bin/sh -c 'npm run docs'.

If it's about getting used to a new toolchain: Let me know if you encounter any issues! (Preferably, in the aforementioned PR.)

[plnms]

Well. Both. Excuse me if I'm stupid, but I can't execute this either way. The Docker command (with nom replaced by npm) returns that it can't find '//package.json', and a locally installed npm, when called with npm run docs, is apparently looking for a script called 'docs' which does not exist.

[derhuerst]

The Docker command (with nom replaced by npm) returns that it can't find //package.json.

True, the command specified can't work. docker run --rm -it -v $PWD:/app -w /app node:18-alpine /bin/sh -c 'npm i && npm run docs' does for me.

a locally installed npm, when called with npm run docs, is apparently looking for a script called 'docs' which does not exist.

Did you run it inside the db-rest repo? All those commands refer to db-rest.

[derhuerst]

Summing this up:

Unfortunately, AFAICT, the very network-centric use case "give me all trips in a certain time frame connecting A and B" is not well-served by the underlying HAFAS API, as it has always been mainly user-/routing-centric. HAFAS' JourneyMatch is weird and fussy about possible inputs.

If you do find out more helpful information about it, please don't hesitate to comment in https://github.com/derhuerst/BahnhofsAbfahrten/pull/1, so that others can benefit from this knowledge, too! It would also be great to add documentation about JourneyMatch to `hafts-client's API docs.

As a workaround, you can of course always use /stops/:id/departures & /stops/:id/arrivals, with the aforementioned limitations.

Please re-open this Issues if you have more related questions.