feat: add some skeleton classes

src/call-credentials.ts

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+export class CallCredentials {}

src/call-stream.ts

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+import * as stream from 'stream';
+import { Status } from './constants';
+
+/**
+ * This class represents a duplex stream associated with a single gRPC call.
+ */
+export class CallStream extends stream.Duplex {
+  /**
+   * Cancels the call associated with this stream with a given status.
+   */
+  cancelWithStatus(status: Status) {
+    throw new Error();
+  }
+}

src/channel-credentials.ts

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+import { CallCredentials } from './call-credentials';
+
+/**
+ * A class that contains credentials for communicating over a channel.
+ */
+export class ChannelCredentials {
+  private constructor() {}
+
+  static createSsl(rootCerts: Buffer, privateKey?: Buffer, certChain?: Buffer) : ChannelCredentials {
+    throw new Error();
+  }
+
+  static createInsecure() : ChannelCredentials {
+    throw new Error();
+  }
+
+  compose(callCredentials: CallCredentials) : ChannelCredentials {
+    throw new Error();
+  }
+}

src/channel.ts

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+import { CallStream } from './call-stream';
+import { ChannelCredentials } from './channel-credentials';
+import { Metadata } from './metadata';
+
+/**
+ * An interface that contains options used when initializing a Channel instance.
+ */
+export interface ChannelOptions {}
+
+/**
+ * A class that represents a communication channel to a server specified by a given address.
+ */
+export class Channel {
+  constructor(address: string, credentials?: ChannelCredentials, options?: ChannelOptions) {
+    throw new Error();
+  }
+
+  createStream(methodName: string, metadata: Metadata) : CallStream {
+    throw new Error();
+  }
+
+  close() {
+    throw new Error();
+  }
+}

src/constants.ts

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+export enum Status {
+  OK = 0,
+  CANCELLED,
+  UNKNOWN,
+  INVALID_ARGUMENT,
+  DEADLINE_EXCEEDED,
+  NOT_FOUND,
+  ALREADY_EXISTS,
+  PERMISSION_DENIED,
+  RESOURCE_EXHAUSTED,
+  FAILED_PRECONDITION,
+  ABORTED,
+  OUT_OF_RANGE,
+  UNIMPLEMENTED,
+  INTERNAL,
+  UNAVAILABLE,
+  DATA_LOSS,
+  UNAUTHENTICATED
+}

src/metadata.ts

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+export class Metadata {}