Improve performance: Push for the usage of ETag/If-None-Match

[tdelmas]

What is the issue and why is it an issue?

In order to reduce the load both on producers and consumers, caching mechanisms could be improved.

Please describe some potential solutions you have considered (even if they aren’t related to GBFS).

Following the discussion during the International Mobility Data Summit (#703), I would like to suggest this addition to the specification in the "File Distribution" section:

• HTTP responses SHOULD include the ETag HTTP header.
• Clients receiving Etags SHOULD use the If-None-Match HTTP header for subsequent requests.
• HTTP responses to requests including the If-None-Match HTTP header SHOULD respect it by returning a 304 Not Modified when appropriate.

Is your potential solution a breaking change?

• Yes
• No
• Unsure