feat: encoders accept strings

[kuhe]

Clients currently have two internal fields of type Encoder, currently Uint8Array => string.

These have been updated to be Uint8Array | string => string, to allow direct conversion of utf8 strings to base64, rather than requiring a Uint8Array input.

The Encoder type has been loosened, since it is public.

related issues:
aws/aws-sdk-js-v3#5745
aws/aws-sdk-js-v3#5240

[kuhe]

This will allow users to send strings as input for fields that otherwise require Uint8Array, which can be cumbersome to initialize.

Though it is as easy as writing Buffer.from('abcd'), discovering this is somewhat obscure because it's not obvious that Buffer is a Uint8Array.

[kuhe]

I verified this using SES

import * as sesClientModule from "@aws-sdk/client-ses";
import nodemailer from "nodemailer";

export const sendEmailWithAttachments = (from = "@email", to = "@email") => {
  const ses = new sesClientModule.SESClient({
    region: "us-west-2",
  });

  ses.middlewareStack.add(
    (next, context) => async (args: any) => {
      console.log("AWS SDK context", context.clientName, context.commandName);

      args.input.RawMessage.Data = args.input.RawMessage.Data.toString();
      console.log("AWS SDK request input", args.input);

      console.log("AWS SDK raw request", args.request);
      const result = await next(args);
    //   console.log("AWS SDK raw response", result.response);
      console.log("AWS SDK response metadata:", result.output.$metadata);
      // console.log("AWS SDK request output:", result.output);
      return result;
    },
    {
      name: "MyMiddleware",
      step: "build",
      override: true,
    }
  );

  const transporter = nodemailer.createTransport({
    SES: { ses, aws: sesClientModule },
  });

  return new Promise((resolve, reject) => {
    transporter.sendMail(
      {
        from,
        to,
        subject: "using string input for RawMessage",
        text: "using string input for RawMessage",
        attachments: [{ content: "Hello World!", filename: "hello.txt" }],
      },
      (err, info) => {
        if (err) {
          reject(err);
        } else {
          resolve(info);
        }
      }
    );
  });
};

sendEmailWithAttachments();

[syall]

For inputs that take Uint8Array | string, can we do a runtime check if it's not one of these types to restrict the types more?

I see typeof xxx === "string" is used, but can we use instanceof Uint8Array checks?