I understand that, if you send duplicate header values in subsequent requests, the dynamic table makes it so that you do not send the value again but a reference to it in the table is sent instead.
My question is whether this applies to the URL as well?
Say you have repeated requests to the same URL (possibly containing long IDs and/or tokens), would bandwidth be saved in this instance?
There are various options that a client can use to send headers under HTTP/2 as defined in the HPACK specification. These basically say whether to use a previously referred to header, whether to store a header for later reference, whether to never store a header for reuse...etc. The client decides which of these to use for headers it sends.
In HTTP/2 the URL is sent in the :path pseudo-header so unlike in HTTP/1.1 it is a just like any other HTTP Header so could be compressed. Typically a URL is not repeated often, however, so it would be sent as a Literal Header Field without Indexing, which means this is a once off header so don’t store it for reuse. Of course, as it’s an HTTP header much like any other, there’s nothing to stop an HTTP/2 client sending this as an indexed type, but web browsers are unlikely to do this, so this is probably only really an option for custom clients.
Incidentally if wishing to know more about this, and finding the spec a little difficult to follow, then my book HTTP/2 in Action, goes into this in a lot more detail in Chapter 8.
