How does the Rest API refresh the cache

[xiaoyv404]

Only the previous data can always be obtained, for example, the request at 12:52 will obtain the data at 12:49

I'm using a translator

[xiaoyv404]

My current version is version 5.4 build 1723

[AuroraLS3]

Plan uses the json cache to not lock the webserver.

The mechanism for this is same for older version, but what is returned by webserver is a bit different in newer version.

The update mechanism

1. Request arrives
2. A new task to update the data in the background is started
3. Data is read from the cache
4. Cached data is returned in Response (200 OK or 304 Not Changed) (Blue line in the image)
5. Task finishes in the background
6. Data is written to the cache (Orange line in image)

In 5.5 build 2195 or higher

Timestamp	Where?	What?	Description
Cached JSON timestamp	JSON timestamp	{"timestamp": 1677912750123, "timestamp_f": "Today, 06:52", ...}	Time when Plan updated the data
HTTP Cache timestamp	HTTP response header ETag, request header If-Match	Response: ETag: "1677912750123", Request: If-Match: "1677912750123"	Time when browser got new data

If Browser cache is empty (No ETag)

200 OK
Request-Headers
{None}

Response Headers
ETag: 1677912750123

Body
{"timestamp": 1677912750123, "timestamp_f": "Today, 06:52", ...}

If Browser cache has data

If-Match: >= Cached JSON timestamp (We don't have newer data)

304 Not Changed
Request-Headers
If-Match: 1677912750123

Response Headers
ETag: 1677912750123

Body
{empty}

ETag < Cached JSON timestamp (We have newer data)

200 OK
Request-Headers
If-Match: 1677912750123

Response Headers
ETAg: 1677913348120

Body
{"timestamp": 1677913348120, "timestamp_f": "Today, 07:02", ...}

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag

In 5.4 build 1723

200 OK

Body
{"timestamp": 1677912750123, "timestamp_f": "Today, 06:52", ...}

Later

200 OK

Body
{"timestamp": 1677913348120, "timestamp_f": "Today, 07:02", ...}

How to get newest data

• Store time when you start request var requestStartTime=new Date()
• Compare request start time to JSON timestamp
• If requestStartTime < json.timestamp, you have newest data
• Else Request again

[xiaoyv404]

Thank you very much for your answer