Add support for SSE comments - #478
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`ServerSentEvent` now carries a `comments` field, so that comment lines (those starting with `:`) can be both parsed and serialised. Per the WhatWG specification such lines are ignored by clients, which makes them the idiomatic keep-alive: they stop proxies from dropping an idle connection without dispatching an event to the application. Binary compatibility with 1.7.18 is preserved in the same way as for `ContentTypeRange`: the old-arity constructor, `copy` and `apply` are kept alongside the new ones. Closes #379 Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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August 28, 2026 14:44
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Fixes #379.
ServerSentEventgains acomments: List[String]field, so comment lines (those starting with:) round-trip through bothparseandtoString.ServerSentEvent.comment("ping")builds the keep-alive frame the WhatWG specification recommends sending every 15 seconds or so, to stop legacy proxies from dropping an idle connection.Design notes
List[String]rather thanOption[String], because a single event block may carry several comment lines.There is deliberately no assertion that a comment and data aren't both set (as considered in the issue discussion). The specification ignores comments per line, not per event, so a block such as
is valid and still dispatches
abc. A guard would reject valid streams.Binary compatibility
Preserved with the same approach already used for
ContentTypeRange: the old-arity constructor,copyandapplyare kept alongside the new ones.Note one source-level (not binary) change: downstream positional patterns like
case ServerSentEvent(d, e, i, r)now need a fifth_. This is inherent to adding a field and is not visible to MiMa.