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71 lines
3.3 KiB
Markdown
71 lines
3.3 KiB
Markdown
# json-response
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`streamable_http_app(json_response=True)` — one `application/json` body per
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request instead of an SSE stream. Useful for serverless / edge runtimes that
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can't hold a stream open. The 2026-07-28 path is stateless and JSON-only today
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regardless of the flag; setting it makes the legacy (2025-era) branch on the
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same endpoint behave the same way.
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## Run it
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```bash
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# HTTP — the client self-hosts the app on a free port, runs the high-level
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# Client + raw-envelope probe, then tears it down
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uv run python -m stories.json_response.client --http
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# same, against the lowlevel-API server variant
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uv run python -m stories.json_response.client --http --server server_lowlevel
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# against a server you run yourself (real uvicorn on :8000)
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uv run python -m stories.json_response.server --port 8000 &
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SERVER_PID=$!
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uv run python -m stories.json_response.client --http http://127.0.0.1:8000/mcp
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# or POST the raw envelope yourself
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curl -s http://127.0.0.1:8000/mcp \
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-H 'content-type: application/json' \
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-H 'accept: application/json, text/event-stream' \
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-H 'mcp-protocol-version: 2026-07-28' \
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-H 'mcp-method: tools/list' \
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-d '{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{"_meta":{"io.modelcontextprotocol/protocolVersion":"2026-07-28","io.modelcontextprotocol/clientInfo":{"name":"curl","version":"0"},"io.modelcontextprotocol/clientCapabilities":{}}}}'
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kill "$SERVER_PID"
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```
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## What to look at
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- `client.py` `main` — `async with Client(target, mode=mode) as client:` is an
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ordinary high-level client; nothing about JSON mode is visible from this side.
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The same `main` also takes the raw `httpx.AsyncClient` so it can prove what
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the wire looks like underneath.
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- `client.py` `RAW_ENVELOPE_BODY` / `MODERN_HEADERS` — the exact 2026 wire
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shape: three `io.modelcontextprotocol/*` `_meta` keys replace the initialize
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handshake; `MCP-Protocol-Version` + `Mcp-Method` headers mirror the body so
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gateways can route without parsing JSON. `main` posts it by hand and asserts
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a single `application/json` response with no `Mcp-Session-Id`.
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- `server.py` `greet` calls `ctx.report_progress(0.5)` — and `main` proves the
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client's `progress_callback` is **never invoked**: JSON mode has no
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back-channel for mid-call notifications (the `progress_seen == []` assertion
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flips to `== [0.5]` once SSE buffering lands for the modern path).
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- `server_lowlevel.py` — same ASGI app built from `lowlevel.Server`; the
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`json_response=` / `transport_security=` knobs live on `streamable_http_app`,
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not the server class.
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## Caveats
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- DNS-rebinding protection is on by default; the harness disables it via
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`NO_DNS_REBIND` because the in-process httpx client sends no `Origin` header.
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- The `streamable_http_app()` call shape here will move when the free-function
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entry lands (see `_hosting.py`).
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- `Mcp-Name` is omitted for `tools/list` because the SDK only emits it on
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`tools/call` today.
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## Spec
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[Streamable HTTP — 2026-07-28](https://modelcontextprotocol.io/specification/draft/basic/transports/streamable-http)
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· [SEP-2243 standard headers](https://modelcontextprotocol.io/specification/draft/basic/transports/streamable-http#standard-request-headers)
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## See also
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`stateless_legacy/` (the one-liner `stateless_http=True` deploy),
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`legacy_routing/` (route by era at the entry), `streaming/` (progress that *is*
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delivered — over stdio/SSE).
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