Initial Commit

node_modules/@grpc/grpc-js/src/picker.ts

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+/*
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+import { StatusObject } from './call-interface';
+import { Metadata } from './metadata';
+import { Status } from './constants';
+import { LoadBalancer } from './load-balancer';
+import { SubchannelInterface } from './subchannel-interface';
+
+export enum PickResultType {
+  COMPLETE,
+  QUEUE,
+  TRANSIENT_FAILURE,
+  DROP,
+}
+
+export interface PickResult {
+  pickResultType: PickResultType;
+  /**
+   * The subchannel to use as the transport for the call. Only meaningful if
+   * `pickResultType` is COMPLETE. If null, indicates that the call should be
+   * dropped.
+   */
+  subchannel: SubchannelInterface | null;
+  /**
+   * The status object to end the call with. Populated if and only if
+   * `pickResultType` is TRANSIENT_FAILURE.
+   */
+  status: StatusObject | null;
+  onCallStarted: (() => void) | null;
+  onCallEnded: ((statusCode: Status) => void) | null;
+}
+
+export interface CompletePickResult extends PickResult {
+  pickResultType: PickResultType.COMPLETE;
+  subchannel: SubchannelInterface | null;
+  status: null;
+  onCallStarted: (() => void) | null;
+  onCallEnded: ((statusCode: Status) => void) | null;
+}
+
+export interface QueuePickResult extends PickResult {
+  pickResultType: PickResultType.QUEUE;
+  subchannel: null;
+  status: null;
+  onCallStarted: null;
+  onCallEnded: null;
+}
+
+export interface TransientFailurePickResult extends PickResult {
+  pickResultType: PickResultType.TRANSIENT_FAILURE;
+  subchannel: null;
+  status: StatusObject;
+  onCallStarted: null;
+  onCallEnded: null;
+}
+
+export interface DropCallPickResult extends PickResult {
+  pickResultType: PickResultType.DROP;
+  subchannel: null;
+  status: StatusObject;
+  onCallStarted: null;
+  onCallEnded: null;
+}
+
+export interface PickArgs {
+  metadata: Metadata;
+  extraPickInfo: { [key: string]: string };
+}
+
+/**
+ * A proxy object representing the momentary state of a load balancer. Picks
+ * subchannels or returns other information based on that state. Should be
+ * replaced every time the load balancer changes state.
+ */
+export interface Picker {
+  pick(pickArgs: PickArgs): PickResult;
+}
+
+/**
+ * A standard picker representing a load balancer in the TRANSIENT_FAILURE
+ * state. Always responds to every pick request with an UNAVAILABLE status.
+ */
+export class UnavailablePicker implements Picker {
+  private status: StatusObject;
+  constructor(status?: Partial<StatusObject>) {
+    this.status = {
+      code: Status.UNAVAILABLE,
+      details: 'No connection established',
+      metadata: new Metadata(),
+      ...status,
+    };
+  }
+  pick(pickArgs: PickArgs): TransientFailurePickResult {
+    return {
+      pickResultType: PickResultType.TRANSIENT_FAILURE,
+      subchannel: null,
+      status: this.status,
+      onCallStarted: null,
+      onCallEnded: null,
+    };
+  }
+}
+
+/**
+ * A standard picker representing a load balancer in the IDLE or CONNECTING
+ * state. Always responds to every pick request with a QUEUE pick result
+ * indicating that the pick should be tried again with the next `Picker`. Also
+ * reports back to the load balancer that a connection should be established
+ * once any pick is attempted.
+ */
+export class QueuePicker {
+  private calledExitIdle = false;
+  // Constructed with a load balancer. Calls exitIdle on it the first time pick is called
+  constructor(private loadBalancer: LoadBalancer) {}
+
+  pick(pickArgs: PickArgs): QueuePickResult {
+    if (!this.calledExitIdle) {
+      process.nextTick(() => {
+        this.loadBalancer.exitIdle();
+      });
+      this.calledExitIdle = true;
+    }
+    return {
+      pickResultType: PickResultType.QUEUE,
+      subchannel: null,
+      status: null,
+      onCallStarted: null,
+      onCallEnded: null,
+    };
+  }
+}