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版本：11.x

订阅

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简介​

订阅是客户端与服务器之间的实时事件流机制。当需要向客户端推送实时更新时，请使用订阅功能。

通过 tRPC 的订阅功能，客户端将与服务器建立并维护持久连接，并在连接中断时借助 tracked() 事件自动尝试优雅重连和恢复。

WebSockets 还是 Server-sent Events？​

在 tRPC 中设置实时订阅时，您可以选择使用 WebSockets 或 Server-sent Events（SSE）。

若不确定选择哪种方案，我们推荐使用 SSE 实现订阅，因为它更易于设置且无需搭建 WebSocket 服务器。

参考项目​

TypeExample TypeLink
WebSocketsBare-minimum Node.js WebSockets example/examples/standalone-server
SSEFull-stack SSE implementationgithub.com/trpc/examples-next-sse-chat
WebSocketsFull-stack WebSockets implementationgithub.com/trpc/examples-next-prisma-websockets-starter

基础示例​

技巧

完整示例请参考 我们的全栈 SSE 示例。

server.ts
ts
import { initTRPC } from '@trpc/server';
const t = initTRPC.create();
const ee = new EventEmitter();
export const appRouter = router({
  onPostAdd: publicProcedure.subscription(async function* (opts) {
    // listen for new events
    for await (const [data] of on(ee, 'add', {
      // Passing the AbortSignal from the request automatically cancels the event emitter when the request is aborted
      signal: opts.signal,
    })) {
      const post = data as Post;
      yield post;
    }
  }),
});
server.ts
ts
import { initTRPC } from '@trpc/server';
const t = initTRPC.create();
const ee = new EventEmitter();
export const appRouter = router({
  onPostAdd: publicProcedure.subscription(async function* (opts) {
    // listen for new events
    for await (const [data] of on(ee, 'add', {
      // Passing the AbortSignal from the request automatically cancels the event emitter when the request is aborted
      signal: opts.signal,
    })) {
      const post = data as Post;
      yield post;
    }
  }),
});

使用 tracked() 自动追踪 ID（推荐）​

当您使用 tracked() 辅助函数 yield 包含 id 的事件时，客户端在连接中断时会自动重连并发送最后已知的 ID。

初始化订阅时可发送初始 lastEventId，浏览器在接收数据时会自动更新该值。

  • 对于 SSE，此机制遵循 EventSource 规范，并通过 .input() 中的 lastEventId 传递

  • 对于 WebSockets，我们的 wsLink 会自动发送并更新最后已知 ID

技巧

若需基于 lastEventId 获取数据且事件完整性至关重要，请务必先设置事件监听器再获取数据库事件（如全栈 SSE 示例所示），避免在基于 lastEventId 生成原始批次时忽略新产生的事件。

ts
import EventEmitter, { on } from 'events';
import type { Post } from '@prisma/client';
import { tracked } from '@trpc/server';
import { z } from 'zod';
import { publicProcedure, router } from '../trpc';
const ee = new EventEmitter();
export const subRouter = router({
  onPostAdd: publicProcedure
    .input(
      z
        .object({
          // lastEventId is the last event id that the client has received
          // On the first call, it will be whatever was passed in the initial setup
          // If the client reconnects, it will be the last event id that the client received
          lastEventId: z.string().nullish(),
        })
        .optional(),
    )
    .subscription(async function* (opts) {
      // We start by subscribing to the ee so that we don't miss any new events while fetching
      const iterable = ee.toIterable('add', {
        // Passing the AbortSignal from the request automatically cancels the event emitter when the request is aborted
        signal: opts.signal,
      });
      if (opts.input.lastEventId) {
        // [...] get the posts since the last event id and yield them
        // const items = await db.post.findMany({ ... })
        // for (const item of items) {
        //   yield tracked(item.id, item);
        // }
      }
      // listen for new events
      for await (const [data] of on(ee, 'add', {
        signal: opts.signal,
      })) {
        const post = data as Post;
        // tracking the post id ensures the client can reconnect at any time and get the latest events this id
        yield tracked(post.id, post);
      }
    }),
});
ts
import EventEmitter, { on } from 'events';
import type { Post } from '@prisma/client';
import { tracked } from '@trpc/server';
import { z } from 'zod';
import { publicProcedure, router } from '../trpc';
const ee = new EventEmitter();
export const subRouter = router({
  onPostAdd: publicProcedure
    .input(
      z
        .object({
          // lastEventId is the last event id that the client has received
          // On the first call, it will be whatever was passed in the initial setup
          // If the client reconnects, it will be the last event id that the client received
          lastEventId: z.string().nullish(),
        })
        .optional(),
    )
    .subscription(async function* (opts) {
      // We start by subscribing to the ee so that we don't miss any new events while fetching
      const iterable = ee.toIterable('add', {
        // Passing the AbortSignal from the request automatically cancels the event emitter when the request is aborted
        signal: opts.signal,
      });
      if (opts.input.lastEventId) {
        // [...] get the posts since the last event id and yield them
        // const items = await db.post.findMany({ ... })
        // for (const item of items) {
        //   yield tracked(item.id, item);
        // }
      }
      // listen for new events
      for await (const [data] of on(ee, 'add', {
        signal: opts.signal,
      })) {
        const post = data as Post;
        // tracking the post id ensures the client can reconnect at any time and get the latest events this id
        yield tracked(post.id, post);
      }
    }),
});

循环拉取数据​

此方案适用于需要定期检查数据库等数据源，并将新数据推送给客户端的场景。

server.ts
ts
import type { Post } from '@prisma/client';
import { tracked } from '@trpc/server';
import { z } from 'zod';
import { publicProcedure, router } from '../trpc';
export const subRouter = router({
  onPostAdd: publicProcedure
    .input(
      z.object({
        // lastEventId is the last event id that the client has received
        // On the first call, it will be whatever was passed in the initial setup
        // If the client reconnects, it will be the last event id that the client received
        // The id is the createdAt of the post
        lastEventId: z.coerce.date().nullish(),
      }),
    )
    .subscription(async function* (opts) {
      // `opts.signal` is an AbortSignal that will be aborted when the client disconnects.
      let lastEventId = opts.input?.lastEventId ?? null;
      // We use a `while` loop that checks `!opts.signal.aborted`
      while (!opts.signal!.aborted) {
        const posts = await db.post.findMany({
          // If we have a `lastEventId`, we only fetch posts created after it.
          where: lastEventId
            ? {
                createdAt: {
                  gt: lastEventId,
                },
              }
            : undefined,
          orderBy: {
            createdAt: 'asc',
          },
        });
        for (const post of posts) {
          // `tracked` is a helper that sends an `id` with each event.
          // This allows the client to resume from the last received event upon reconnection.
          yield tracked(post.createdAt.toJSON(), post);
          lastEventId = post.createdAt;
        }
        // Wait for a bit before polling again to avoid hammering the database.
        await sleep(1_000);
      }
    }),
});
server.ts
ts
import type { Post } from '@prisma/client';
import { tracked } from '@trpc/server';
import { z } from 'zod';
import { publicProcedure, router } from '../trpc';
export const subRouter = router({
  onPostAdd: publicProcedure
    .input(
      z.object({
        // lastEventId is the last event id that the client has received
        // On the first call, it will be whatever was passed in the initial setup
        // If the client reconnects, it will be the last event id that the client received
        // The id is the createdAt of the post
        lastEventId: z.coerce.date().nullish(),
      }),
    )
    .subscription(async function* (opts) {
      // `opts.signal` is an AbortSignal that will be aborted when the client disconnects.
      let lastEventId = opts.input?.lastEventId ?? null;
      // We use a `while` loop that checks `!opts.signal.aborted`
      while (!opts.signal!.aborted) {
        const posts = await db.post.findMany({
          // If we have a `lastEventId`, we only fetch posts created after it.
          where: lastEventId
            ? {
                createdAt: {
                  gt: lastEventId,
                },
              }
            : undefined,
          orderBy: {
            createdAt: 'asc',
          },
        });
        for (const post of posts) {
          // `tracked` is a helper that sends an `id` with each event.
          // This allows the client to resume from the last received event upon reconnection.
          yield tracked(post.createdAt.toJSON(), post);
          lastEventId = post.createdAt;
        }
        // Wait for a bit before polling again to avoid hammering the database.
        await sleep(1_000);
      }
    }),
});

从服务器停止订阅​

若需从服务器端停止订阅，只需在生成器函数中执行 return。

ts
import { publicProcedure, router } from '../trpc';
export const subRouter = router({
  onPostAdd: publicProcedure
    .input(
      z.object({
        lastEventId: z.string().coerce.number().min(0).optional(),
      }),
    )
    .subscription(async function* (opts) {
      let index = opts.input.lastEventId ?? 0;
      while (!opts.signal!.aborted) {
        const idx = index++;
        if (idx > 100) {
          // With this, the subscription will stop and the client will disconnect
          return;
        }
        await new Promise((resolve) => setTimeout(resolve, 10));
      }
    }
  }),
});
ts
import { publicProcedure, router } from '../trpc';
export const subRouter = router({
  onPostAdd: publicProcedure
    .input(
      z.object({
        lastEventId: z.string().coerce.number().min(0).optional(),
      }),
    )
    .subscription(async function* (opts) {
      let index = opts.input.lastEventId ?? 0;
      while (!opts.signal!.aborted) {
        const idx = index++;
        if (idx > 100) {
          // With this, the subscription will stop and the client will disconnect
          return;
        }
        await new Promise((resolve) => setTimeout(resolve, 10));
      }
    }
  }),
});

在客户端，直接对订阅执行 .unsubscribe() 即可。

副作用清理​

如需清理订阅产生的副作用，可采用 try...finally 模式。当订阅因任何原因终止时，trpc 会调用生成器实例的 .return()。

ts
import EventEmitter, { on } from 'events';
import type { Post } from '@prisma/client';
import { z } from 'zod';
import { publicProcedure, router } from '../trpc';
const ee = new EventEmitter();
export const subRouter = router({
  onPostAdd: publicProcedure.subscription(async function* (opts) {
    let timeout;
    try {
      for await (const [data] of on(ee, 'add', {
        signal: opts.signal,
      })) {
        timeout = setTimeout(() => console.log('Pretend like this is useful'));
        const post = data as Post;
        yield post;
      }
    } finally {
      if (timeout) clearTimeout(timeout);
    }
  }),
});
ts
import EventEmitter, { on } from 'events';
import type { Post } from '@prisma/client';
import { z } from 'zod';
import { publicProcedure, router } from '../trpc';
const ee = new EventEmitter();
export const subRouter = router({
  onPostAdd: publicProcedure.subscription(async function* (opts) {
    let timeout;
    try {
      for await (const [data] of on(ee, 'add', {
        signal: opts.signal,
      })) {
        timeout = setTimeout(() => console.log('Pretend like this is useful'));
        const post = data as Post;
        yield post;
      }
    } finally {
      if (timeout) clearTimeout(timeout);
    }
  }),
});

错误处理​

在生成器函数中抛出错误会传递至后端 trpc 的 onError()。

若抛出 5xx 错误，客户端将基于通过 tracked() 追踪的最后事件 ID 自动重连。其他错误将导致订阅取消并触发 onError() 回调。

输出验证​

由于订阅是异步迭代器，必须通过迭代器遍历才能验证输出结果。

zod v4 示例​

zAsyncIterable.ts
ts
import type { TrackedEnvelope } from '@trpc/server';
import { isTrackedEnvelope, tracked } from '@trpc/server';
import { z } from 'zod';
function isAsyncIterable<TValue, TReturn = unknown>(
  value: unknown,
): value is AsyncIterable<TValue, TReturn> {
  return !!value && typeof value === 'object' && Symbol.asyncIterator in value;
}
const trackedEnvelopeSchema =
  z.custom<TrackedEnvelope<unknown>>(isTrackedEnvelope);
/**
 * A Zod schema helper designed specifically for validating async iterables. This schema ensures that:
 * 1. The value being validated is an async iterable.
 * 2. Each item yielded by the async iterable conforms to a specified type.
 * 3. The return value of the async iterable, if any, also conforms to a specified type.
 */
export function zAsyncIterable<
  TYieldIn,
  TYieldOut,
  TReturnIn = void,
  TReturnOut = void,
  Tracked extends boolean = false,
>(opts: {
  /**
   * Validate the value yielded by the async generator
   */
  yield: z.ZodType<TYieldIn, TYieldOut>;
  /**
   * Validate the return value of the async generator
   * @remark not applicable for subscriptions
   */
  return?: z.ZodType<TReturnIn, TReturnOut>;
  /**
   * Whether if the yielded values are tracked
   * @remark only applicable for subscriptions
   */
  tracked?: Tracked;
}) {
  return z
    .custom<
      AsyncIterable<
        Tracked extends true ? TrackedEnvelope<TYieldIn> : TYieldIn,
        TReturnIn
      >
    >((val) => isAsyncIterable(val))
    .transform(async function* (iter) {
      const iterator = iter[Symbol.asyncIterator]();
      try {
        let next;
        while ((next = await iterator.next()) && !next.done) {
          if (opts.tracked) {
            const [id, data] = trackedEnvelopeSchema.parse(next.value);
            yield tracked(id, await opts.yield.parseAsync(data));
            continue;
          }
          yield opts.yield.parseAsync(next.value);
        }
        if (opts.return) {
          return await opts.return.parseAsync(next.value);
        }
        return;
      } finally {
        await iterator.return?.();
      }
    }) as z.ZodType<
    AsyncIterable<
      Tracked extends true ? TrackedEnvelope<TYieldIn> : TYieldIn,
      TReturnIn,
      unknown
    >,
    AsyncIterable<
      Tracked extends true ? TrackedEnvelope<TYieldOut> : TYieldOut,
      TReturnOut,
      unknown
    >
  >;
}
zAsyncIterable.ts
ts
import type { TrackedEnvelope } from '@trpc/server';
import { isTrackedEnvelope, tracked } from '@trpc/server';
import { z } from 'zod';
function isAsyncIterable<TValue, TReturn = unknown>(
  value: unknown,
): value is AsyncIterable<TValue, TReturn> {
  return !!value && typeof value === 'object' && Symbol.asyncIterator in value;
}
const trackedEnvelopeSchema =
  z.custom<TrackedEnvelope<unknown>>(isTrackedEnvelope);
/**
 * A Zod schema helper designed specifically for validating async iterables. This schema ensures that:
 * 1. The value being validated is an async iterable.
 * 2. Each item yielded by the async iterable conforms to a specified type.
 * 3. The return value of the async iterable, if any, also conforms to a specified type.
 */
export function zAsyncIterable<
  TYieldIn,
  TYieldOut,
  TReturnIn = void,
  TReturnOut = void,
  Tracked extends boolean = false,
>(opts: {
  /**
   * Validate the value yielded by the async generator
   */
  yield: z.ZodType<TYieldIn, TYieldOut>;
  /**
   * Validate the return value of the async generator
   * @remark not applicable for subscriptions
   */
  return?: z.ZodType<TReturnIn, TReturnOut>;
  /**
   * Whether if the yielded values are tracked
   * @remark only applicable for subscriptions
   */
  tracked?: Tracked;
}) {
  return z
    .custom<
      AsyncIterable<
        Tracked extends true ? TrackedEnvelope<TYieldIn> : TYieldIn,
        TReturnIn
      >
    >((val) => isAsyncIterable(val))
    .transform(async function* (iter) {
      const iterator = iter[Symbol.asyncIterator]();
      try {
        let next;
        while ((next = await iterator.next()) && !next.done) {
          if (opts.tracked) {
            const [id, data] = trackedEnvelopeSchema.parse(next.value);
            yield tracked(id, await opts.yield.parseAsync(data));
            continue;
          }
          yield opts.yield.parseAsync(next.value);
        }
        if (opts.return) {
          return await opts.return.parseAsync(next.value);
        }
        return;
      } finally {
        await iterator.return?.();
      }
    }) as z.ZodType<
    AsyncIterable<
      Tracked extends true ? TrackedEnvelope<TYieldIn> : TYieldIn,
      TReturnIn,
      unknown
    >,
    AsyncIterable<
      Tracked extends true ? TrackedEnvelope<TYieldOut> : TYieldOut,
      TReturnOut,
      unknown
    >
  >;
}

zod v3 示例​

zAsyncIterable.ts
ts
import type { TrackedEnvelope } from '@trpc/server';
import { isTrackedEnvelope, tracked } from '@trpc/server';
import { z } from 'zod';
function isAsyncIterable<TValue, TReturn = unknown>(
  value: unknown,
): value is AsyncIterable<TValue, TReturn> {
  return !!value && typeof value === 'object' && Symbol.asyncIterator in value;
}
const trackedEnvelopeSchema =
  z.custom<TrackedEnvelope<unknown>>(isTrackedEnvelope);
/**
 * A Zod schema helper designed specifically for validating async iterables. This schema ensures that:
 * 1. The value being validated is an async iterable.
 * 2. Each item yielded by the async iterable conforms to a specified type.
 * 3. The return value of the async iterable, if any, also conforms to a specified type.
 */
export function zAsyncIterable<
  TYieldIn,
  TYieldOut,
  TReturnIn = void,
  TReturnOut = void,
  Tracked extends boolean = false,
>(opts: {
  /**
   * Validate the value yielded by the async generator
   */
  yield: z.ZodType<TYieldIn, any, TYieldOut>;
  /**
   * Validate the return value of the async generator
   * @remark not applicable for subscriptions
   */
  return?: z.ZodType<TReturnIn, any, TReturnOut>;
  /**
   * Whether if the yielded values are tracked
   * @remark only applicable for subscriptions
   */
  tracked?: Tracked;
}) {
  return z
    .custom<
      AsyncIterable<
        Tracked extends true ? TrackedEnvelope<TYieldIn> : TYieldIn,
        TReturnIn
      >
    >((val) => isAsyncIterable(val))
    .transform(async function* (iter) {
      const iterator = iter[Symbol.asyncIterator]();
      try {
        let next;
        while ((next = await iterator.next()) && !next.done) {
          if (opts.tracked) {
            const [id, data] = trackedEnvelopeSchema.parse(next.value);
            yield tracked(id, await opts.yield.parseAsync(data));
            continue;
          }
          yield opts.yield.parseAsync(next.value);
        }
        if (opts.return) {
          return await opts.return.parseAsync(next.value);
        }
        return;
      } finally {
        await iterator.return?.();
      }
    }) as z.ZodType<
    AsyncIterable<
      Tracked extends true ? TrackedEnvelope<TYieldIn> : TYieldIn,
      TReturnIn,
      unknown
    >,
    any,
    AsyncIterable<
      Tracked extends true ? TrackedEnvelope<TYieldOut> : TYieldOut,
      TReturnOut,
      unknown
    >
  >;
}
zAsyncIterable.ts
ts
import type { TrackedEnvelope } from '@trpc/server';
import { isTrackedEnvelope, tracked } from '@trpc/server';
import { z } from 'zod';
function isAsyncIterable<TValue, TReturn = unknown>(
  value: unknown,
): value is AsyncIterable<TValue, TReturn> {
  return !!value && typeof value === 'object' && Symbol.asyncIterator in value;
}
const trackedEnvelopeSchema =
  z.custom<TrackedEnvelope<unknown>>(isTrackedEnvelope);
/**
 * A Zod schema helper designed specifically for validating async iterables. This schema ensures that:
 * 1. The value being validated is an async iterable.
 * 2. Each item yielded by the async iterable conforms to a specified type.
 * 3. The return value of the async iterable, if any, also conforms to a specified type.
 */
export function zAsyncIterable<
  TYieldIn,
  TYieldOut,
  TReturnIn = void,
  TReturnOut = void,
  Tracked extends boolean = false,
>(opts: {
  /**
   * Validate the value yielded by the async generator
   */
  yield: z.ZodType<TYieldIn, any, TYieldOut>;
  /**
   * Validate the return value of the async generator
   * @remark not applicable for subscriptions
   */
  return?: z.ZodType<TReturnIn, any, TReturnOut>;
  /**
   * Whether if the yielded values are tracked
   * @remark only applicable for subscriptions
   */
  tracked?: Tracked;
}) {
  return z
    .custom<
      AsyncIterable<
        Tracked extends true ? TrackedEnvelope<TYieldIn> : TYieldIn,
        TReturnIn
      >
    >((val) => isAsyncIterable(val))
    .transform(async function* (iter) {
      const iterator = iter[Symbol.asyncIterator]();
      try {
        let next;
        while ((next = await iterator.next()) && !next.done) {
          if (opts.tracked) {
            const [id, data] = trackedEnvelopeSchema.parse(next.value);
            yield tracked(id, await opts.yield.parseAsync(data));
            continue;
          }
          yield opts.yield.parseAsync(next.value);
        }
        if (opts.return) {
          return await opts.return.parseAsync(next.value);
        }
        return;
      } finally {
        await iterator.return?.();
      }
    }) as z.ZodType<
    AsyncIterable<
      Tracked extends true ? TrackedEnvelope<TYieldIn> : TYieldIn,
      TReturnIn,
      unknown
    >,
    any,
    AsyncIterable<
      Tracked extends true ? TrackedEnvelope<TYieldOut> : TYieldOut,
      TReturnOut,
      unknown
    >
  >;
}

现在你可以使用这个辅助函数来验证订阅过程的输出：

_app.ts
ts
import { publicProcedure, router } from '../trpc';
import { zAsyncIterable } from './zAsyncIterable';
export const appRouter = router({
  mySubscription: publicProcedure
    .input(
      z.object({
        lastEventId: z.coerce.number().min(0).optional(),
      }),
    )
    .output(
      zAsyncIterable({
        yield: z.object({
          count: z.number(),
        }),
        tracked: true,
      }),
    )
    .subscription(async function* (opts) {
      let index = opts.input.lastEventId ?? 0;
      while (true) {
        index++;
        yield tracked(index, {
          count: index,
        });
        await new Promise((resolve) => setTimeout(resolve, 1000));
      }
    }),
});
_app.ts
ts
import { publicProcedure, router } from '../trpc';
import { zAsyncIterable } from './zAsyncIterable';
export const appRouter = router({
  mySubscription: publicProcedure
    .input(
      z.object({
        lastEventId: z.coerce.number().min(0).optional(),
      }),
    )
    .output(
      zAsyncIterable({
        yield: z.object({
          count: z.number(),
        }),
        tracked: true,
      }),
    )
    .subscription(async function* (opts) {
      let index = opts.input.lastEventId ?? 0;
      while (true) {
        index++;
        yield tracked(index, {
          count: index,
        });
        await new Promise((resolve) => setTimeout(resolve, 1000));
      }
    }),
});