A list could leave the instance as a TREK file, which only another TREK
reads. Export now asks for a format, and GPX is the second one: the
places as waypoints, for OsmAnd, Organic Maps, a Garmin or gpx.studio.
Import takes a GPX in the same dialog as a list file. Asked for in
discussion #2301.
The GPX is written from the very list file the JSON export returns, so
what may leave the instance is still decided in one place. Name,
description and address, notes, website and category go into GPX's own
elements, where every app shows them. Labels, status, phone and the
rest travel in a TREK extension namespace, so a GPX made by TREK comes
back as the same list. A place without coordinates cannot be a
waypoint; it is left out and the export says how many were.
A GPX is read on the server, sent as text, with the XML library the
trip importer already uses. A document with a DOCTYPE is refused before
parsing, which closes both external entities and entity expansion. Size
is capped like the list file, and the element count is capped before a
tree is built. The reader only turns the GPX into a list file: the
browser previews it and imports it through the existing route, so one
contract, one transaction and one skipped counter cover both formats.
Waypoints and named route points become places; tracks and unnamed
route points are counted in the preview and not imported.
The two list-file routes get a body ceiling of twice the file limit.
The global 100 kB cap refused most real favourites files, and it
already refused list files well under the megabyte the contract allows.
Sharing a list works between people on the same TREK. This is the other
case: giving one to somebody who runs their own, or keeping a copy. Export
sits beside Edit and Share in the list header and downloads the open list;
Import sits beside New list in the rail, reads a file, shows what is in it
and makes a new list of it. Desktop only, which the route already decides.
What travels is what somebody wrote down: the list's name, colour and
description, its labels, and each place with its address, coordinates,
notes, status, contact details, category name and labels. A file is dull
JSON on purpose, so it can be read and edited by a person.
What does not travel is everything that only means something on the instance
it came from. Ids of every kind, since the receiver issues its own and a
category crosses over by name. Star ratings and members, because a rating is
an opinion somebody gave the people on that list. Provenance into trips,
which points at rows the receiver cannot see. And an image path under
/uploads, which resolves on the sender's server: only an absolute https URL
survives.
A file is a stranger's JSON and is read as one. It is parsed in the browser
that chose it and never uploaded; the parsed list goes through the same
contract on both sides; and a link that is not http(s) arrives as nothing
rather than as an anchor. Strict where it must refuse, forgiving where it
can drop: a file that does not say what it is never reaches the importer,
while one unreadable place inside it is skipped and counted, and one bad
field on a good place costs that field alone.
An import is always a new list. Importing into an existing one would mean
deciding what happens to a place that is already there, and every answer to
that is a merge nobody asked for.
Maurice