inline http cookie header

[wbpcode]

The current cookie is not be implemented as O(1) inline header which make the cookie-related operation very expensive.

Perhaps we can set a special delimiter ; for the cookie to make the cookie an inline header.

[mattklein123]

cc @asraa @alyssawilk

[alyssawilk]

I think Dan actually fixed the delimiter issue (https://github.com/envoyproxy/envoy/blob/main/source/common/http/header_map_impl.cc#L437) but where I agree O(n) isn't good I suspect inlining cookies would break things for some users. it'd be nice to have a configurable bootstrap option for which headers to inline so folks could optimize on their own.

[mattklein123]

it'd be nice to have a configurable bootstrap option for which headers to inline so folks could optimize on their own.

FWIW when I wrote the custom inline header code I intended to eventually make it bootstrap configurable. It should be quite easy:

envoy/source/server/server.cc

Lines 350 to 362 in d3a9012

	// Immediate after the bootstrap has been loaded, override the header prefix, if configured to
	// do so. This must be set before any other code block references the HeaderValues ConstSingleton.
	if (!bootstrap_.header_prefix().empty()) {
	// setPrefix has a release assert verifying that setPrefix() is not called after prefix()
	ThreadSafeSingleton<Http::PrefixValue>::get().setPrefix(bootstrap_.header_prefix().c_str());
	}
	// TODO(mattklein123): Custom O(1) headers can be registered at this point for creating/finalizing
	// any header maps.
	ENVOY_LOG(info, "HTTP header map info:");
	for (const auto& info : Http::HeaderMapImplUtility::getAllHeaderMapImplInfo()) {
	ENVOY_LOG(info, " {}: {} bytes: {}", info.name_, info.size_,
	absl::StrJoin(info.registered_headers_, ","));
	}

[wbpcode]

Then, after that, we will have three ways to define the inline header.
The first is the macro definition in HeaderMap. This type of inline header provides related methods with the same name(getXXX, setXXX).
The second is to implement the inline header through RegisterCustomInlineHeader.
The third is to specify the header name to be set as the inline header in the bootstrap.

[github-actions]

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