[GH-ISSUE #53] same weblink on multiple displays - update problems #571

New Issue

sascha_hemi · 2026-03-20T18:10:35+01:00

sascha_hemi commented

2026-03-20 18:10:35 +01:00

Originally created by @eokgnah on GitHub (May 31, 2023).
Original GitHub issue: https://github.com/OpenEPaperLink/OpenEPaperLink/issues/53

Originally assigned to: @nlimper on GitHub.

If i have the same url on several displays the update procedure is buggy.

for example:

display 1 = http://myserver.com/image.jpg (versionA)
display 2 = http://myserver.com/image.jpg (versionA)
i start both displays initially and they both get the (versionA) picture.
i update my image.jpg on my server to (versionB).
for example display1 checks in and sees "there is a new image" (versionB), downloads it and displays it.
then after some time display2, who has still (versionA) on it checks in.
The server looks at my server and compares it to the locally stored.
(Server and ESP have versionB)
so it decides (wrongly) to do nothing!
the display who is 2nd (or more) in line is stuck with the old image and never gehts a update.

Can the esp keep track which picture version on which display is?
Then it can decide if the picture needs an update, because the local picture is newer then the picture on the display, even if the local cached picture is the same then the one on the webserver.

Originally created by @eokgnah on GitHub (May 31, 2023). Original GitHub issue: https://github.com/OpenEPaperLink/OpenEPaperLink/issues/53 Originally assigned to: @nlimper on GitHub. If i have the same url on several displays the update procedure is buggy. for example: 1. display 1 = http://myserver.com/image.jpg (versionA) display 2 = http://myserver.com/image.jpg (versionA) 2. i start both displays initially and they both get the (versionA) picture. 3. i update my image.jpg on my server to (versionB). 4. for example display1 checks in and sees "there is a new image" (versionB), downloads it and displays it. 5. then after some time display2, who has still (versionA) on it checks in. The server looks at my server and compares it to the locally stored. (Server and ESP have versionB) so it decides (wrongly) to do nothing! 6. the display who is 2nd (or more) in line is stuck with the old image and never gehts a update. Can the esp keep track which picture version on which display is? Then it can decide if the picture needs an update, because the local picture is newer then the picture on the display, even if the local cached picture is the same then the one on the webserver.

sascha_hemi added the bug label 2026-03-20 18:10:35 +01:00

sascha_hemi closed this issue

2026-03-20 18:10:35 +01:00

sascha_hemi commented

2026-03-20 18:10:36 +01:00

@nlimper commented on GitHub (May 31, 2023):

Nothing gets cached. The last fetched date of an image is kept with the data of a specific tag, and send along with a 'if-modified-since' header, to let your server determine if a new image is needed. But I will look into it.
I'm assuming you're running the latest version of the esp32 firmware.

@nlimper commented on GitHub (May 31, 2023): Nothing gets cached. The last fetched date of an image is kept with the data of a specific tag, and send along with a 'if-modified-since' header, to let your server determine if a new image is needed. But I will look into it. I'm assuming you're running the latest version of the esp32 firmware.

sascha_hemi commented

2026-03-20 18:10:36 +01:00

@nlimper commented on GitHub (Jun 1, 2023):

fixed. There was a bug in the If-Modified-Since-header.
db88de1f75

@nlimper commented on GitHub (Jun 1, 2023): fixed. There was a bug in the If-Modified-Since-header. https://github.com/jjwbruijn/OpenEPaperLink/commit/db88de1f7549a2be64733ff80ff1fcf94813ff54

Sign in to join this conversation.

1 Participants

Notifications

Due Date

No due date set.

Dependencies

No dependencies set.

Reference: starred/OpenEPaperLink#571