EW-10817 Add WebSocketDataMessage helper for text-or-binary payloads

[harrishancock]

Owned text-or-binary message wrapper (and a non-owning Ptr counterpart) for the WebSocket auto-response and outgoing-message paths. Wraps kj::OneOf<kj::String, kj::Array<byte>> (and the pointer-shaped equivalent) with a domain-named, read-only inspection surface — isText / isBinary / tryGetText / tryGetBinary — plus size(), sendVia(kj::WebSocket&), asPtr() / toOwned(), asOneOf() for KJ_SWITCH_ONEOF dispatch, and operator==(kj::StringPtr) / operator==(kj::ArrayPtr<const byte>) for content-equality checks at matching sites.

Inspection on WebSocketDataMessage delegates through a temporary WebSocketDataMessagePtr, so KJ_SWITCH_ONEOF(msg.asOneOf()) cases bind to kj::StringPtr / kj::ArrayPtr<const byte> (not the owned types), and tryGetText/Binary return Maybe<StringPtr/ArrayPtr<const byte>>. This makes inspection implicitly read-only (no path to obtain a mutable reference into the owned storage) and hides the storage type from callers — owned-vs-borrowed is now purely a lifetime distinction.

This pattern — text-or-binary WebSocket payloads, never control frames — recurs across the codebase, and dealing with the equivalent kj::OneOf at every consuming site is awkward. The helper consolidates it into a single typed wrapper.

Assisted-by: OpenCode:claude-opus-4.7

[ask-bonk]

Clean wrapper — nice owned/borrowed split and thorough tests.

One medium-severity item: several methods on WebSocketDataMessage return non-owning views into *this's storage and should carry KJ_LIFETIMEBOUND so the compiler can warn on dangling use. The codebase already uses this annotation for the same pattern (e.g., blob.h getData() / getType()).

[ask-bonk]

I'm Bonk, and I've done a quick review of your PR.

Summary: Adds WebSocketDataMessage (owned) and WebSocketDataMessagePtr (borrowed) wrappers for text-or-binary WebSocket payloads with a read-only inspection surface, sendVia(), and equality operators.

Issues found (1):

1. Medium — Missing KJ_LIFETIMEBOUND on borrowed-view methods. asPtr(), asOneOf(), tryGetText(), and tryGetBinary() on WebSocketDataMessage all return non-owning views into *this's storage. Adding KJ_LIFETIMEBOUND enables the compiler to warn when the returned view outlives the object it borrows from. This annotation is already used for the same pattern elsewhere in src/workerd/api/ (e.g., blob.h getData() / getType()). Posted as 4 suggestion comments on the declarations.

github run

[codecov-commenter]

Codecov Report

❌ Patch coverage is 62.24189% with 128 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.75%. Comparing base (fd5b913) to head (09a0cce).

Files with missing lines	Patch %	Lines
src/workerd/api/web-socket-data-message-test.c++	56.22%	26 Missing and 90 partials ⚠️
src/workerd/api/web-socket-data-message.h	83.78%	0 Missing and 12 partials ⚠️

Additional details and impacted files

@@                              Coverage Diff                              @@
##           harris/EW-10817-hibernation-manager-tests    #6739      +/-   ##
=============================================================================
- Coverage                                      66.76%   66.75%   -0.02%     
=============================================================================
  Files                                            403      405       +2     
  Lines                                         116449   116788     +339     
  Branches                                       19496    19615     +119     
=============================================================================
+ Hits                                           77750    77961     +211     
- Misses                                         27026    27052      +26     
- Partials                                       11673    11775     +102     

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