modern-spf

Appearance

Multipart responses ​

Streaming is the modern equivalent of SPF's multipart responses: instead of a single JSON object, a server may answer an SPF request with an NDJSON stream of parts (Content-Type: application/x-spf+ndjson). Each line is one part, parsed and fired as an event as it arrives — the response is never held whole in memory before processing starts, which is useful for slow servers and big pages.

Note: the DOM is updated once the stream completes — streaming is incremental for parsing and events, not for fragment application. The aggregated response is applied (and cached) like a single JSON response; per-part events let you observe progress as the stream arrives.

Stream format ​

Parts follow the same order as the single response (title → url → head → attr → body → foot) and are terminated by a done part:

text
{"part":"title","value":"Page Title"}
{"part":"head","html":"<style>…</style>"}
{"part":"body","id":"content","html":"<p>New content</p>"}
{"part":"attr","id":"content","attrs":{"class":"wide"}}
{"part":"foot","html":"<script>…</script>"}
{"part":"done"}
PartFieldsEffect
titlevalueDocument title
urlvalueHistory URL replacement
headhtmlEarly CSS/JS into <head>
attrid, attrsSet attributes on element id
bodyid, htmlReplace content of element id
foothtmlLate JS/CSS
done—Terminates the stream; response is complete

The client decides which format to use from the response Content-Type; the single JSON format is always accepted as a fallback. See the wire protocol for the exact byte-level contract.

Part events ​

Each part fires two events as it arrives:

  • spfpartprocess — { part, response }; returning false skips the part;
  • spfpartdone — { part, response } — fired after the part was aggregated.

Because parts arrive incrementally, the response detail object is the partial aggregate so far — later parts will not be present yet.

Aggregation ​

All parts are aggregated into one SingleResponse object, which is what gets applied and cached. This means a streamed response behaves identically to a single JSON response after it arrives — the cache, apply pipeline and spfdone all see the same shape.