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Using E-Tags

An Entity Tag (or E-Tag) is an identifier for a version of data. It is a mechanism that uses caching to reduce the load on the server.

The E-Tag header provides a means for consuming systems to check if any cache they are keeping is up to date. You can query requests for data that return an E-Tag response header again, using the same E-Tag header value in the request.

If the server detects no changes since the E-Tag, it will return a 304 response code with an empty body. This means the data has not changed.

A 304 response code with an empty body, indicates no changes to the data was made since the E-Tag was issued. If the data changes, the system will return only the differences between the requested E-Tag and the current state. It will include a new E-Tag in the response header.

Example​

In our implementation, if you request the field boundary information, the server sends it to you.

If the API gets the same request again, it will reply with a 304 response code. It will not provide any data if it has not updated since the last request.

Below is a table of how key-value pairs would look like in this scenario:

KeyValue
Ocp-Apim-Subscription-Key{{Ocp-Apim-Subscription-Key}}
ETagfb16c641-1b17-43e5-af95-4d0edab94...
AuthorizationBearer {{AccessToken}}