fix(sse): handle multi-line messages#2643
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kettanaito merged 3 commits intomswjs:mainfrom Dec 26, 2025
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Hi, @BSteffaniak. Thank you for fixing this! And an extra thanks for those test cases.
I've pushed a change related to how the message data is processed, making that processing conditional (no need to fallback to '' to then split via RegExp into an empty array).
Could you please share a link to the paragraph section that outlines how line terminators have to be handled in the SSE spec? We could leave it in the implementation for future references. Thanks.
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Here are some references in the spec: here's also some MDN docs around it too (a bit easier to read): |
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Thanks! This is great. |
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Released: v2.12.5 🎉This has been released in v2.12.5. Get these changes by running the following command: Predictable release automation by Release. |
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Fixes an issue where SSE messages containing newlines in the
datafield would be incorrectly parsed by the client.Per the SSE spec, multi-line data must be sent as multiple
data:lines that the EventSource parser concatenates. Previously, MSW sent the data as a singledata:field, which caused messages containing\n\nto be truncated (since\n\nterminates an SSE message).Before:
data:line1\n\nline2
Client receives:
"line1"(truncated)After:
data:line1
data:
data:line2
Client receives:
"line1\n\nline2"(correct)The fix handles all SSE line terminators per spec: LF (
\n), CR (\r), and CRLF (\r\n).Let me know your thoughts. Thanks!