问题
I'm trying to use etags in order to reduce both my bandwidth and my quota usage but /search returns an new etag even when nothing changed. It also still sends the content if I specify the previous etag in the header.
Is it supported for that api call or am I probably doing something wrong?
回答1:
Etags are supported by youtube but it depends on what kind of data you are asking
ETags, a standard part of the HTTP protocol, allow applications to refer to a specific version of a particular API resource. The resource could be an entire feed or an item in that feed. This functionality supports the following use cases:
Caching and conditional retrieval – Your application can cache API resources and their ETags. Then, when your application requests a stored resource again, it specifies the ETag associated with that resource. If the resource has changed, the API returns the modified resource and the ETag associated with that version of the resource. If the resource has not changed, the API returns an HTTP 304 response (Not Modified), which indicates that the resource has not changed. Your application can reduce latency and bandwidth usage by serving cached resources in this manner.
The client libraries for Google APIs differ in their support of ETags. For example, the JavaScript client library supports ETags via a whitelist for allowed request headers that includes If-Match and If-None-Match. The whitelist allows normal browser caching to occur so that if a resource's ETag has not changed, the resource can be served from the browser cache. The Obj-C client, on the other hand, does not support ETags. Protecting against inadvertent overwrites of changes – ETags help to ensure that multiple API clients don't inadvertently overwrite each other's changes. When updating or deleting a resource, your application can specify the resource's ETag. If the ETag doesn't match the most recent version of that resource, then the API request fails.
Using ETags in your application provides several benefits:
The API responds more quickly to requests for cached but unchanged resources, yielding lower latency and lower bandwidth usage. Your application will not inadvertently overwrite changes to a resource that were made from another API client.
https://developers.google.com/youtube/v3/getting-started#etags
I usually scrape Youtube for Videos searches and I just store the Etag that it return. To use the etag, create a header request and put "If-None-Match" equal to your etag value. Note this should be a request header and not appended to the endpoint call. You can also use "If-Match".
Depending on what kind of API you are using, the way of inserting a new value to the request header may differ slightly
来源：https://stackoverflow.com/questions/35354607/does-the-youtube-api-v3-search-support-etags