[quicwg/base-drafts] NUM_PLACEHOLDERS MUST NOT be zero (#2753)

Kazuho Oku <notifications@github.com> Thu, 23 May 2019 03:52 UTC

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Subject: [quicwg/base-drafts] NUM_PLACEHOLDERS MUST NOT be zero (#2753)
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Currently, the text says:
```
The default value is 0. However, this value SHOULD be set to a non-zero value by servers.
```

I think we should change the default to unlimited or to some sensible number, and also introduce a minimum permitted number.

Prioritization is not something a client can enforce, therefore servers that prefer to ignore or mishandle placeholders can just ignore / mishandle them, as well as other information for prioritization (e.g. weights and dependencies).

To rephrase, communicating the capability of handling just one of the features of prioritization has marginal benefit compared to the complexity it introduces to the client side (e.g., the need to use different prioritization approach depending on if the server supports placeholders).

Or, if it is the case that we do not expect browsers to no longer use placeholders but are keeping it for proxies, we should remove "SHOULD", because that is a minor use case that has not seen actual use in HTTP/2.

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