mapbox / mapbox-gl-js

Interactive, thoroughly customizable maps in the browser, powered by vector tiles and WebGL
https://docs.mapbox.com/mapbox-gl-js/
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Handle 204 No content responses correctly as an empty tile and avoid trying to decode the response #9304

Open candux opened 4 years ago

candux commented 4 years ago

Tileserver-GL started sending empty 204 responses if a tile is not available. https://github.com/maptiler/tileserver-gl/blob/master/src/serve_data.js#L45 https://github.com/maptiler/tileserver-gl/pull/339

Mapbox-gl-js doesn't handle this very good. It creates an error message every time a tile is fetched and doesn't cache the server response (but the browser maybe does).

mapbox-gl-js version: Since 1.7.0. 1.6.0 is not affected browser: Chrome, Firefox

Steps to Trigger Behavior

  1. Open the Demonstration
  2. See Errors in Console
  3. Scroll in and out. The 204 requests are repeated every time

Link to Demonstration

https://jsbin.com/loyajulodu/edit?html,output

Expected Behavior

andrewharvey commented 4 years ago

It seems we are trying to read the content of a 204 in the same way as a 200. It seems reasonable to me that we treat 204 responses as they should be, as empty content and avoid throwing the error.

Some background in #1800 which backs up this request.

ryanhamley commented 4 years ago

We'll need to be careful that any changes in handling 204 errors don't exacerbate the problem of overdrawing in sparse tile sets as in https://github.com/mapbox/mapbox-gl-js/issues/6768. This issue was partially fixed with https://github.com/mapbox/mapbox-gl-js/pull/6803.

GL Native treats 204 and 404 responses as No Content

https://github.com/mapbox/mapbox-gl-native/blob/6ddff19ceedb8f6cb095792b90121330afcc38cf/platform/android/src/http_file_source.cpp#L141-L142

jingsam commented 4 years ago

204 means No Content, 404 means Not Found. They are two different things. Suppose we have a mbtile storing a tileset. If users request a z/x/y tile, server side query the tile table of the mbtile to get tile data. When the tile table do have the z/x/y record and tile_data is null or zero length blob, then server side should response 204, client side should treat as "OK, I get the tile, but the tile is empty, means this area have nothing to render, so I just need to render the background". On the other side, When tile table do not have the z/x/y record, then server side should response 404, client side should treat as "Ops, I can not get the tile, means the tile is missing and this area may have features to render, I should overzoom the upper level tile to fill this area". In conclusion, empty tile and missing tile are two different things.

ahk commented 4 years ago

I think I read two bugs here:

  1. No Content (empty content?) shouldn't throw errors.
  2. HTTP 204 and 404 should be differentiated as No Content and Missing Content respectively (and result in different rendering). This is something the native side would also need to change.

cc @mapbox/gl-js @mapbox/gl-native

owl1n commented 4 years ago

Any updates?

robinsummerhill commented 4 years ago

This is hitting me too using hillshading mbtiles datasets from https://openmaptiles.com/. We're using a custom tile server that responds with 204 No Content if the tile url is valid but no hillshading data is present for that tile.

ghost commented 9 months ago

Looked around a bit:

JS / web:

Native:

Looking at the code I don't think 204 is specifically handled and mostly seems to depend on the data being zero length? Most changes seem to be about avoiding errors on empty data, assuming it was a 204.

I was under the impression 204 worked fine (force tile to be empty), but this issue implies there isn't explicit support for this in many clients. I even expected that 404 worked fine (using tiles from other zoom levels to pad the data), but that probably doesn't work correctly - although I did not check?

After briefly looking at the different renderers, I'm not so sure anymore whether it's a good idea to depend on these status code to convey meaning in tile-servers right now..

sylvio-ruiz commented 9 months ago

I have an Nginx server with static tile files in PBF format. Therefore, the assets are vectors, not images. Libraries like MapLibre GL and Mapbox GL can handle missing files (204 or any other response status) and use the vectors below to render them at a higher zoom level. The main difference between a 204 status and others like 4xx or 50xx is that browsers do not throw errors. For instance, if the server sends a 404 response, the browser will throw an error in the console, even though the libraries know what to do to render the missing tile. My server sends a 204 status for all 404 requests and asks the browser to cache it. This makes sense as there are no errors in the console and the 204 status is cached.