226 IM Used

GET /large-dataset.json HTTP/1.1
Host: example.com
If-None-Match: "v1-baseline"
A-IM: vcdiff

app.get('/dataset', (req, res) => {
  const aim = req.headers['a-im'];
  const etag = req.headers['if-none-match'];
  
  // Hypothetical scenario checking for delta support
  if (aim === 'vcdiff' && etag === '"v1-baseline"') {
    // In reality, you'd calculate the binary diff here
    const deltaPayload = generateVcdiff(baselineData, currentData);
    
    res.set({
      'IM': 'vcdiff',
      'ETag': '"v2-current"',
      'Delta-Base': '"v1-baseline"',
      'Content-Type': 'application/vcdiff'
    });
    
    return res.status(226).send(deltaPayload);
  }
  
  // Fallback to sending the full resource (200 OK)
  res.json(currentData);
});

from fastapi import Request, Response

@app.get("/dataset")
def get_dataset(request: Request):
    aim = request.headers.get("A-IM")
    etag = request.headers.get("If-None-Match")
    
    if aim == "vcdiff" and etag == '"v1-baseline"':
        delta_payload = b'...' # Simulated binary diff
        headers = {
            "IM": "vcdiff",
            "ETag": '"v2-current"',
            "Delta-Base": '"v1-baseline"'
        }
        return Response(content=delta_payload, status_code=226, media_type="application/vcdiff", headers=headers)
        
    return {"data": "full_dataset"}

func handleDataset(w http.ResponseWriter, r *http.Request) {
    aim := r.Header.Get("A-IM")
    etag := r.Header.Get("If-None-Match")
    
    if aim == "vcdiff" && etag == `"v1-baseline"` {
        w.Header().Set("IM", "vcdiff")
        w.Header().Set("ETag", `"v2-current"`)
        w.Header().Set("Delta-Base", `"v1-baseline"`)
        w.Header().Set("Content-Type", "application/vcdiff")
        w.WriteHeader(226)
        w.Write([]byte("...delta payload..."))
        return
    }
    
    w.WriteHeader(200)
    w.Write([]byte("full dataset"))
}

curl -i -H "A-IM: vcdiff" -H "If-None-Match: \"v1-baseline\"" https://example.com/data