Merge pull request #42 from MatrixAI/feature-middlware-composition

feat: incorporate timeoutMiddleware to allow for server to utilise client's caller timeout

Author: amydevs

README.md

@@ -899,6 +899,45 @@ main();
 
 ```
 ![img.png](images/unaryTest.png)
+
+## Specifications
+
+### Throwing Timeouts
+
+By default, a timeout will not cause an RPC call to automatically throw, this must be manually done by the handler when it receives the abort signal from `ctx.signal`. An example of this is like so:
+
+```ts
+class TestMethod extends UnaryHandler {
+  public handle = async (
+    input: JSONValue,
+    cancel: (reason?: any) => void,
+    meta: Record<string, JSONValue> | undefined,
+    ctx: ContextTimed,
+  ): Promise<JSONValue> => {
+    const abortProm = utils.promise<never>();
+    ctx.signal.addEventListener('abort', () => {
+      resolveCtxP(ctx);
+      abortProm.resolveP(ctx.signal.reason);
+    });
+    throw await abortProm.p;
+  };
+}
+```
+
+### Timeout Middleware
+
+The `timeoutMiddleware` sets an RPCServer's timeout based on the lowest timeout between the Client and the Server. This is so that handlers can eagerly time out and stop processing as soon as it is known that the client has timed out.
+
+This case can be seen in the first diagram, where the server is able to stop the processing of the handler, and close the associated stream of the RPC call based on the shorter timeout sent by the client:
+
+![RPCServer sets timeout based on RPCClient](images/timeoutMiddlewareClientTimeout.svg)
+
+Where the `RPCClient` sends a timeout that is longer than that set on the `RPCServer`, it will be rejected. This is as the timeout of the client should never be expected to exceed that of the server, so that the server's timeout is an absolute limit.
+
+![RPCServer rejects longer timeout sent by RPCClient](images/timeoutMiddlewareServerTimeout.svg)
+
+The `timeoutMiddleware` is enabled by default, and uses the `.metadata.timeout` property on a JSON-RPC request object for the client to send it's timeout.
+
 ## Development
 
 Run `nix-shell`, and once you're inside, you can use:

images/timeoutMiddlewareClientTimeout.svg

@@ -287,7 +287,9 @@ class RPCServer {
         // Input generator derived from the forward stream
         const inputGen = async function* (): AsyncIterable<I> {
           for await (const data of forwardStream) {
-            ctx.timer.refresh();
+            if (ctx.timer.status !== 'settled') {
+              ctx.timer.refresh();
+            }
             yield data.params as I;
           }
         };
@@ -296,7 +298,9 @@ class RPCServer {
           timer: ctx.timer,
         });
         for await (const response of handlerG) {
-          ctx.timer.refresh();
+          if (ctx.timer.status !== 'settled') {
+            ctx.timer.refresh();
+          }
           const responseMessage: JSONRPCResponseResult = {
             jsonrpc: '2.0',
             result: response,
@@ -570,13 +574,16 @@ class RPCServer {
       }
       // Setting up Timeout logic
       const timeout = this.defaultTimeoutMap.get(method);
-      if (timeout != null && timeout < this.handlerTimeoutTime) {
-        // Reset timeout with new delay if it is less than the default
-        timer.reset(timeout);
-      } else {
-        // Otherwise refresh
-        timer.refresh();
+      if (timer.status !== 'settled') {
+        if (timeout != null && timeout < this.handlerTimeoutTime) {
+          // Reset timeout with new delay if it is less than the default
+          timer.reset(timeout);
+        } else {
+          // Otherwise refresh
+          timer.refresh();
+        }
       }
+
       this.logger.info(`Handling stream with method (${method})`);
       let handlerResult: [JSONValue | undefined, ReadableStream<Uint8Array>];
       const headerWriter = rpcStream.writable.getWriter();

images/timeoutMiddlewareServerTimeout.svg

@@ -148,6 +148,13 @@ class ErrorRPCStreamEnded<T> extends ErrorRPCProtocol<T> {
 class ErrorRPCTimedOut<T> extends ErrorRPCProtocol<T> {
   static description = 'RPC handler has timed out';
   code = JSONRPCErrorCode.RPCTimedOut;
+  public toJSON(): JSONRPCError {
+    const json = super.toJSON();
+    if (typeof json === 'object' && !Array.isArray(json)) {
+      (json as POJO).type = this.constructor.name;
+    }
+    return json;
+  }
 }
 
 class ErrorUtilsUndefinedBehaviour<T> extends ErrorRPCProtocol<T> {

src/RPCServer.ts

@@ -4,7 +4,11 @@ import type {
   JSONRPCResponse,
   JSONRPCResponseResult,
   MiddlewareFactory,
+  JSONValue,
+  JSONRPCRequestMetadata,
+  JSONRPCResponseMetadata,
 } from './types';
+import type { ContextTimed } from '@matrixai/contexts';
 import { TransformStream } from 'stream/web';
 import { JSONParser } from '@streamparser/json';
 import * as utils from './utils';
@@ -75,6 +79,80 @@ function jsonMessageToBinaryStream(): TransformStream<
   });
 }
 
+function timeoutMiddlewareServer(
+  ctx: ContextTimed,
+  _cancel: (reason?: any) => void,
+  _meta: Record<string, JSONValue> | undefined,
+) {
+  const currentTimeout = ctx.timer.delay;
+  // Flags for tracking if the first message has been processed
+  let forwardFirst = true;
+  return {
+    forward: new TransformStream<
+      JSONRPCRequest<JSONRPCRequestMetadata>,
+      JSONRPCRequest<JSONRPCRequestMetadata>
+    >({
+      transform: (chunk, controller) => {
+        controller.enqueue(chunk);
+        if (forwardFirst) {
+          forwardFirst = false;
+          let clientTimeout = chunk.metadata?.timeout;
+          if (clientTimeout === undefined) return;
+          if (clientTimeout === null) clientTimeout = Infinity;
+          if (clientTimeout < currentTimeout) ctx.timer.reset(clientTimeout);
+        }
+      },
+    }),
+    reverse: new TransformStream<
+      JSONRPCResponse<JSONRPCResponseMetadata>,
+      JSONRPCResponse<JSONRPCResponseMetadata>
+    >({
+      transform: (chunk, controller) => {
+        // Passthrough chunk, no need for server to send ctx.timeout
+        controller.enqueue(chunk);
+      },
+    }),
+  };
+}
+
+/**
+ * This adds its own timeout to the forward metadata and updates it's timeout
+ * based on the reverse metadata.
+ * @param ctx
+ * @param _cancel
+ * @param _meta
+ */
+function timeoutMiddlewareClient(
+  ctx: ContextTimed,
+  _cancel: (reason?: any) => void,
+  _meta: Record<string, JSONValue> | undefined,
+) {
+  const currentTimeout = ctx.timer.delay;
+  // Flags for tracking if the first message has been processed
+  let forwardFirst = true;
+  return {
+    forward: new TransformStream<JSONRPCRequest, JSONRPCRequest>({
+      transform: (chunk, controller) => {
+        if (forwardFirst) {
+          forwardFirst = false;
+          if (chunk == null) chunk = { jsonrpc: '2.0', method: '' };
+          if (chunk.metadata == null) chunk.metadata = {};
+          (chunk.metadata as any).timeout = currentTimeout;
+        }
+        controller.enqueue(chunk);
+      },
+    }),
+    reverse: new TransformStream<
+      JSONRPCResponse<JSONRPCResponseMetadata>,
+      JSONRPCResponse<JSONRPCResponseMetadata>
+    >({
+      transform: (chunk, controller) => {
+        controller.enqueue(chunk); // Passthrough chunk, no need for client to set ctx.timeout
+      },
+    }),
+  };
+}
+
 /**
  * This function is a factory for creating a pass-through streamPair. It is used
  * as the default middleware for the middleware wrappers.
@@ -116,12 +194,14 @@ function defaultServerMiddlewareWrapper(
     >();
 
     const middleMiddleware = middlewareFactory(ctx, cancel, meta);
+    const timeoutMiddleware = timeoutMiddlewareServer(ctx, cancel, meta);
 
-    const forwardReadable = inputTransformStream.readable.pipeThrough(
-      middleMiddleware.forward,
-    ); // Usual middleware here
+    const forwardReadable = inputTransformStream.readable
+      .pipeThrough(timeoutMiddleware.forward) // Timeout middleware here
+      .pipeThrough(middleMiddleware.forward); // Usual middleware here
     const reverseReadable = outputTransformStream.readable
       .pipeThrough(middleMiddleware.reverse) // Usual middleware here
+      .pipeThrough(timeoutMiddleware.reverse) // Timeout middleware here
       .pipeThrough(jsonMessageToBinaryStream());
 
     return {
@@ -172,13 +252,15 @@ const defaultClientMiddlewareWrapper = (
       JSONRPCRequest
     >();
 
+    const timeoutMiddleware = timeoutMiddlewareClient(ctx, cancel, meta);
     const middleMiddleware = middleware(ctx, cancel, meta);
     const forwardReadable = inputTransformStream.readable
+      .pipeThrough(timeoutMiddleware.forward)
       .pipeThrough(middleMiddleware.forward) // Usual middleware here
       .pipeThrough(jsonMessageToBinaryStream());
-    const reverseReadable = outputTransformStream.readable.pipeThrough(
-      middleMiddleware.reverse,
-    ); // Usual middleware here
+    const reverseReadable = outputTransformStream.readable
+      .pipeThrough(middleMiddleware.reverse)
+      .pipeThrough(timeoutMiddleware.reverse); // Usual middleware here
 
     return {
       forward: {
@@ -196,6 +278,8 @@ const defaultClientMiddlewareWrapper = (
 export {
   binaryToJsonMessageStream,
   jsonMessageToBinaryStream,
+  timeoutMiddlewareClient,
+  timeoutMiddlewareServer,
   defaultMiddleware,
   defaultServerMiddlewareWrapper,
   defaultClientMiddlewareWrapper,

src/errors.ts

@@ -38,7 +38,7 @@ type JSONRPCRequestMessage<T extends JSONValue = JSONValue> = {
    *  SHOULD NOT contain fractional parts [2]
    */
   id: string | number | null;
-};
+} & JSONRPCRequestMetadata;
 
 /**
  * This is the JSON RPC notification object. this is used for a request that
@@ -60,7 +60,7 @@ type JSONRPCRequestNotification<T extends JSONValue = JSONValue> = {
    *  This member MAY be omitted.
    */
   params?: T;
-};
+} & JSONRPCRequestMetadata;
 
 /**
  * This is the JSON RPC response result object. It contains the response data for a
@@ -84,7 +84,7 @@ type JSONRPCResponseResult<T extends JSONValue = JSONValue> = {
    *  it MUST be Null.
    */
   id: string | number | null;
-};
+} & JSONRPCResponseMetadata;
 
 /**
  * This is the JSON RPC response Error object. It contains any errors that have
@@ -110,6 +110,34 @@ type JSONRPCResponseError = {
   id: string | number | null;
 };
 
+/**
+ * Used when an empty object is needed.
+ * Defined here with a linter override to avoid a false positive.
+ */
+// eslint-disable-next-line
+type ObjectEmpty = {};
+
+// Prevent overwriting the metadata type with `Omit<>`
+type JSONRPCRequestMetadata<T extends Record<string, JSONValue> = ObjectEmpty> =
+  {
+    metadata?: {
+      [Key: string]: JSONValue;
+    } & Partial<{
+      timeout: number | null;
+    }>;
+  } & Omit<T, 'metadata'>;
+
+// Prevent overwriting the metadata type with `Omit<>`
+type JSONRPCResponseMetadata<
+  T extends Record<string, JSONValue> = ObjectEmpty,
+> = {
+  metadata?: {
+    [Key: string]: JSONValue;
+  } & Partial<{
+    timeout: number | null;
+  }>;
+} & Omit<T, 'metadata'>;
+
 /**
  * This is a JSON RPC error object, it encodes the error data for the JSONRPCResponseError object.
  */
@@ -357,6 +385,8 @@ export type {
   JSONRPCRequestNotification,
   JSONRPCResponseResult,
   JSONRPCResponseError,
+  JSONRPCRequestMetadata,
+  JSONRPCResponseMetadata,
   JSONRPCError,
   JSONRPCRequest,
   JSONRPCResponse,

src/middleware.ts

@@ -278,6 +278,7 @@ const standardErrors: {
   URIError,
   AggregateError,
   AbstractError,
+  ErrorRPCTimedOut: errors.ErrorRPCTimedOut,
 };
 
 /**
@@ -342,6 +343,7 @@ function toError(
         let e: Error;
         switch (eClass) {
           case AbstractError:
+          case errors.ErrorRPCTimedOut:
             e = eClass.fromJSON(errorData);
             break;
           case AggregateError: