In sse.go function trimHeader calls data = bytes.TrimSpace(data), which removes all whitespace left and right of the data value.
But the spec says:
If value starts with a U+0020 SPACE character, remove it from value.
My service sends data:  lines where the data can start with whitespace, which should be preserved. E.g.
data:  word (two spaces, one from the SSE format and one as part of the value).