# OpenCode Zen model_id strip proxy + SessionStart hook for Grok Build (mise shim)

> Source: <https://gist.github.com/km-tr/8cd435034fb848a5c1f374f0ec7b41c6>
> Published: 2026-08-06 18:26:15+00:00

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/** |
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* OpenCode Zen 向けローカルプロキシ |
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* |
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* Grok CLI が assistant 履歴に付ける非標準フィールド `model_id` を |
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* Chat Completions 送信前に削除してから upstream へ転送する |
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* |
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* 起動: bun ~/.grok/proxies/opencode-strip-model-id/proxy.ts |
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* 設定: base_url = "http://127.0.0.1:8787/v1" |
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*/ |
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const LISTEN_HOST = process.env.PROXY_HOST ?? "127.0.0.1" |
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const LISTEN_PORT = Number(process.env.PROXY_PORT ?? "8787") |
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const UPSTREAM_ORIGIN = ( |
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process.env.OPENCODE_UPSTREAM ?? "https://opencode.ai/zen" |
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).replace(/\/$/, "") |
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const LOG = process.env.PROXY_LOG === "1" |
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type JsonObject = Record<string, unknown> |
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function isObject(value: unknown): value is JsonObject { |
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return value != null && typeof value === "object" && !Array.isArray(value) |
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} |
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/** messages / input 配列内の model_id を削除する */ |
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function stripModelIdFromMessages(messages: unknown): { |
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stripped: number |
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value: unknown |
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} { |
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if (!Array.isArray(messages)) { |
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return { stripped: 0, value: messages } |
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} |
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let stripped = 0 |
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const next = messages.map((message) => { |
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if (!isObject(message) || !("model_id" in message)) { |
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return message |
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} |
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stripped += 1 |
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const { model_id: _modelId, ...rest } = message |
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return rest |
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}) |
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return { stripped, value: next } |
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} |
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/** Chat Completions / Responses など JSON body から model_id を除去 */ |
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function sanitizeRequestBody(bodyText: string): { |
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body: string |
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stripped: number |
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} { |
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if (bodyText.trim() === "") { |
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return { body: bodyText, stripped: 0 } |
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} |
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let parsed: unknown |
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try { |
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parsed = JSON.parse(bodyText) |
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} catch { |
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return { body: bodyText, stripped: 0 } |
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} |
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if (!isObject(parsed)) { |
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return { body: bodyText, stripped: 0 } |
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} |
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let stripped = 0 |
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if ("messages" in parsed) { |
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const result = stripModelIdFromMessages(parsed.messages) |
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parsed.messages = result.value |
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stripped += result.stripped |
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} |
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// Responses API 互換 (将来用) |
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if ("input" in parsed) { |
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const result = stripModelIdFromMessages(parsed.input) |
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parsed.input = result.value |
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stripped += result.stripped |
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} |
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if (stripped === 0) { |
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return { body: bodyText, stripped: 0 } |
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} |
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return { body: JSON.stringify(parsed), stripped } |
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} |
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function hopByHopHeaders(): Set<string> { |
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return new Set([ |
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"connection", |
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"keep-alive", |
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"proxy-authenticate", |
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"proxy-authorization", |
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"te", |
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"trailers", |
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"transfer-encoding", |
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"upgrade", |
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"host", |
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"content-length", |
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]) |
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} |
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function copyRequestHeaders(req: Request): Headers { |
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const headers = new Headers() |
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const skip = hopByHopHeaders() |
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req.headers.forEach((value, key) => { |
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if (skip.has(key.toLowerCase())) { |
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return |
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} |
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headers.set(key, value) |
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}) |
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return headers |
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} |
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function copyResponseHeaders(upstream: Response): Headers { |
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const headers = new Headers() |
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const skip = hopByHopHeaders() |
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upstream.headers.forEach((value, key) => { |
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if (skip.has(key.toLowerCase())) { |
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return |
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} |
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headers.set(key, value) |
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}) |
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return headers |
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} |
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function log(...args: unknown[]): void { |
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if (LOG) { |
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console.log(new Date().toISOString(), ...args) |
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} |
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} |
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const server = Bun.serve({ |
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hostname: LISTEN_HOST, |
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port: LISTEN_PORT, |
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idleTimeout: 255, |
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async fetch(req: Request): Promise<Response> { |
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const url = new URL(req.url) |
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const targetUrl = `${UPSTREAM_ORIGIN}${url.pathname}${url.search}` |
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const method = req.method.toUpperCase() |
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try { |
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const requestHeaders = copyRequestHeaders(req) |
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let body: string | Uint8Array | undefined |
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let stripped = 0 |
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if (method !== "GET" && method !== "HEAD") { |
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const raw = await req.text() |
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const shouldSanitize = |
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url.pathname.includes("/chat/completions") || |
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url.pathname.includes("/responses") || |
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url.pathname.endsWith("/messages") |
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if (shouldSanitize && raw !== "") { |
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const sanitized = sanitizeRequestBody(raw) |
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body = sanitized.body |
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stripped = sanitized.stripped |
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if (stripped > 0) { |
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requestHeaders.set( |
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"content-type", |
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requestHeaders.get("content-type") ?? "application/json" |
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) |
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} |
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} else { |
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body = raw |
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} |
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} |
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log( |
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method, |
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url.pathname, |
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stripped > 0 ? `stripped_model_id=${stripped}` : "passthrough" |
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) |
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const upstream = await fetch(targetUrl, { |
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method, |
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headers: requestHeaders, |
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body, |
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// @ts-expect-error Bun は duplex を受け付ける |
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duplex: "half", |
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}) |
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// ストリームはそのままパイプ (SSE / chat streaming) |
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return new Response(upstream.body, { |
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status: upstream.status, |
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statusText: upstream.statusText, |
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headers: copyResponseHeaders(upstream), |
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}) |
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} catch (error) { |
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const message = error instanceof Error ? error.message : String(error) |
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console.error("[proxy] upstream error:", message) |
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return new Response( |
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JSON.stringify({ |
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error: { |
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message: `proxy upstream failed: ${message}`, |
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type: "proxy_error", |
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}, |
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}), |
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{ |
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status: 502, |
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headers: { "content-type": "application/json" }, |
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} |
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) |
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} |
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}, |
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}) |
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console.log( |
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`[opencode-strip-model-id] listening on http://${server.hostname}:${server.port}` |
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) |
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console.log(`[opencode-strip-model-id] upstream ${UPSTREAM_ORIGIN}`) |
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console.log( |
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`[opencode-strip-model-id] set base_url = "http://${server.hostname}:${server.port}/v1"` |
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) |
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console.log(`[opencode-strip-model-id] debug log: PROXY_LOG=1`) |