92 lines
2.7 KiB
Go
92 lines
2.7 KiB
Go
package platform
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import (
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"context"
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"encoding/json"
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"net/http"
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)
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const modelStreamType = "application/vnd.foundry.canvas-model+ndjson;version=1"
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// The caller captures a coherent model while holding the workspace lock, then
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// releases its transaction before writing. A slow reader must not hold a writer.
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// This streams transfer/encoding; it does not stream database row acquisition.
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func writeCanvasModelStream(ctx context.Context, w http.ResponseWriter, model canvasModel) {
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token := newModelID()
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if token == "" {
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reject(w, 500, "model_stream_unavailable")
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return
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}
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view := model.view(nil)
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header := response{"streamVersion": 1, "kind": "header", "sequence": 0, "snapshotToken": token,
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"documentFormatVersion": canvasModelFormat, "projectId": model.Root, "canvases": view.Canvases,
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"versions": view.Versions, "tombstones": view.Tombstones, "removedCanvasIds": view.Removed, "elementCount": len(view.Elements)}
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const maxLine = 8 * 1024 * 1024
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const maxBytes = 64 * 1024 * 1024
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sequence, total := 0, 0
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started := false
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write := func(value response) bool {
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if ctx.Err() != nil {
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return false
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}
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raw, err := json.Marshal(value)
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if err != nil || len(raw) > maxLine || total+len(raw)+1 > maxBytes || sequence >= 4096 {
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if !started {
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reject(w, 413, "model_stream_budget")
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}
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return false
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}
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if !started {
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w.Header().Set("Content-Type", modelStreamType)
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w.Header().Set("Cache-Control", "no-store")
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w.Header().Add("Vary", "Accept")
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w.Header().Set("X-Content-Type-Options", "nosniff")
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w.WriteHeader(http.StatusOK)
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started = true
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}
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total += len(raw) + 1
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if n, writeErr := w.Write(append(raw, '\n')); writeErr != nil || n != len(raw)+1 {
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return false
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}
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sequence++
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// A missing terminal record is an explicit incomplete stream at the client.
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// Never append an unrelated JSON error after streaming has begun.
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return http.NewResponseController(w).Flush() == nil
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}
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if !write(header) {
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return
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}
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batch := []map[string]any{}
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batchBytes := 0
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flush := func() bool {
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if len(batch) == 0 {
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return true
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}
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if !write(response{"streamVersion": 1, "kind": "elements", "sequence": sequence, "snapshotToken": token, "elements": batch}) {
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return false
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}
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batch, batchBytes = []map[string]any{}, 0
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return true
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}
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for _, element := range view.Elements {
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if ctx.Err() != nil {
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return
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}
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raw, err := json.Marshal(element)
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if err != nil {
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return
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}
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if len(batch) > 0 && (len(batch) == 64 || batchBytes+len(raw) > 512*1024) {
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if !flush() {
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return
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}
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}
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batch = append(batch, element)
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batchBytes += len(raw)
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}
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if !flush() {
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return
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}
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write(response{"streamVersion": 1, "kind": "complete", "sequence": sequence, "snapshotToken": token, "elementCount": len(view.Elements)})
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}
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