feat(ec2): introduce multipart user data

Add support for multiparat (MIME) user data for Linux environments. This
type is more versatile type of user data, and some AWS service
(i.e. AWS Batch) requires it in order to customize the launch
behaviour.

Change was tested in integ environment to check if all
user data parts has been executed correctly and with proper charset
encoding.

fixes aws#8315

Author: Radek Smogura

packages/@aws-cdk/aws-ec2/lib/user-data.ts

@@ -1,5 +1,7 @@
+import * as crypto from 'crypto';
+
 import { IBucket } from '@aws-cdk/aws-s3';
-import { CfnElement, Resource, Stack } from '@aws-cdk/core';
+import { CfnElement, Fn, Resource, Stack } from '@aws-cdk/core';
 import { OperatingSystemType } from './machine-image';
 
 /**
@@ -61,7 +63,7 @@ export interface ExecuteFileOptions {
 /**
  * Instance User Data
  */
-export abstract class UserData {
+export abstract class UserData implements IMultipartUserDataPartProducer {
   /**
    * Create a userdata object for Linux hosts
    */
@@ -108,6 +110,13 @@ export abstract class UserData {
    */
   public abstract render(): string;
 
+  /**
+   * Render the user data as a part for `MultipartUserData`. Not all subclasses supports this.
+   */
+  public renderAsMimePart(_renderOpts?: MultipartRenderOptions): MutlipartUserDataPart {
+    throw new Error('This class does not support rendering as MIME part');
+  }
+
   /**
    * Adds commands to download a file from S3
    *
@@ -151,6 +160,15 @@ class LinuxUserData extends UserData {
     return [shebang, ...(this.renderOnExitLines()), ...this.lines].join('\n');
   }
 
+  public renderAsMimePart(renderOpts?: MultipartRenderOptions): MutlipartUserDataPart {
+    const contentType = renderOpts?.contentType || 'text/x-shellscript';
+    return new MutlipartUserDataPart({
+      body: Fn.base64(this.render()), // Wrap into base64, to support UTF-8 encoding (actually decoding)
+      contentType: `${contentType}; charset="utf-8"`,
+      transferEncoding: 'base64',
+    });
+  }
+
   public addS3DownloadCommand(params: S3DownloadOptions): string {
     const s3Path = `s3://${params.bucket.bucketName}/${params.bucketKey}`;
     const localPath = ( params.localFile && params.localFile.length !== 0 ) ? params.localFile : `/tmp/${ params.bucketKey }`;
@@ -276,3 +294,164 @@ class CustomUserData extends UserData {
     throw new Error('CustomUserData does not support addSignalOnExitCommand, use UserData.forLinux() or UserData.forWindows() instead.');
   }
 }
+
+/**
+ * Options when creating `MutlipartUserDataPart`.
+ */
+export interface MutlipartUserDataPartOptions {
+  /**
+   * The body of message.
+   *
+   * @default undefined - body will not be added to part
+   */
+  readonly body?: string,
+
+  /**
+   * `Content-Type` header of this part.
+   *
+   * For Linux shell scripts use `text/x-shellscript`
+   */
+  readonly contentType: string;
+
+  /**
+   * `Content-Transfer-Encoding` header specifing part encoding.
+   *
+   * @default undefined - don't add this header
+   */
+  readonly transferEncoding?: string;
+}
+
+/**
+ * The raw part of multip-part user data, which can be added to {@link MultipartUserData}.
+ */
+export class MutlipartUserDataPart implements IMultipartUserDataPartProducer {
+  /** The body of this MIME part. */
+  public readonly body?: string;
+
+  /** `Content-Type` header of this part */
+  public readonly contentType: string;
+
+  /**
+   * `Content-Transfer-Encoding` header specifing part encoding.
+   *
+   * @default undefined - don't add this header
+   */
+  readonly transferEncoding?: string;
+
+  public constructor(props: MutlipartUserDataPartOptions) {
+    this.body = props.body;
+    this.contentType = props.contentType;
+    this.transferEncoding = props.transferEncoding;
+  }
+
+  renderAsMimePart(_renderOpts?: MultipartRenderOptions): MutlipartUserDataPart {
+    return this;
+  }
+}
+
+/**
+ * Render options for parts of multipart user data.
+ */
+export interface MultipartRenderOptions {
+  /**
+   * Can be used to override default content type (without charset part) used when producing
+   * part by `IMultipartUserDataPartProducer`.
+   *
+   * @default undefined - leave content type unchanged
+   */
+  readonly contentType?: string;
+}
+
+/**
+ * Class implementing this interface can produce `MutlipartUserDataPart` and can be added
+ * to `MultipartUserData`.
+ */
+export interface IMultipartUserDataPartProducer {
+  /**
+   * Creats the `MutlipartUserDataPart.
+   */
+  renderAsMimePart(renderOpts?: MultipartRenderOptions): MutlipartUserDataPart;
+}
+
+/**
+ * Mime multipart user data.
+ *
+ * This class represents MIME multipart user data, as described in.
+ * [Specifying Multiple User Data Blocks Using a MIME Multi Part Archive](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/bootstrap_container_instance.html#multi-part_user_data)
+ *
+ */
+export class MultipartUserData extends UserData {
+  private static readonly USE_PART_ERROR = 'MultipartUserData does not support this operation. Please add part using addPart.';
+
+  private parts: IMultipartUserDataPartProducer[] = [];
+
+  /**
+   * Adds a class which can producer `MutlipartUserDataPart`. I. e. `UserData.forLinux()`.
+   */
+  public addPart(producer: IMultipartUserDataPartProducer): this {
+    this.parts.push(producer);
+
+    return this;
+  }
+
+  public render(): string {
+    const renderedParts: MutlipartUserDataPart[] = this.parts.map(producer => producer.renderAsMimePart());
+
+    // Hash the message content, it will be used as boundry. The boundry should be
+    // so much unique not to be in message text, and stable so the text of archive will
+    // not be changed only due to change of boundry (may cause redeploys of resources)
+    const hash = crypto.createHash('sha256');
+    renderedParts.forEach(part => {
+      hash
+        .update(part.contentType)
+        .update(part.body || 'empty-body')
+        .update(part.transferEncoding || '');
+    });
+    hash.update('salt-boundary-rado');
+
+    const boundary = '-' + hash.digest('base64') + '-';
+
+    // Now build final MIME archive - there are few changes from MIME message which are accepted by cloud-init:
+    // - MIME RFC uses CRLF to separarte lines - cloud-init is fine with LF \n only
+    var resultArchive = `Content-Type: multipart/mixed; boundary="${boundary}"\n`;
+    resultArchive = resultArchive + 'MIME-Version: 1.0\n';
+
+    // Add parts - each part starts with boundry
+    renderedParts.forEach(part => {
+      resultArchive = resultArchive + '\n--' + boundary + '\n' + 'Content-Type: ' + part.contentType + '\n';
+
+      if (part.transferEncoding != null) {
+        resultArchive = resultArchive + `Content-Transfer-Encoding: ${part.transferEncoding}\n`;
+      }
+
+      if (part.body != null) {
+        resultArchive = resultArchive + '\n' + part.body;
+      }
+    });
+
+    // Add closing boundry
+    resultArchive = resultArchive + `\n--${boundary}--\n`;
+
+    return resultArchive;
+  }
+
+  public addS3DownloadCommand(_params: S3DownloadOptions): string {
+    throw new Error(MultipartUserData.USE_PART_ERROR);
+  }
+
+  public addExecuteFileCommand(_params: ExecuteFileOptions): void {
+    throw new Error(MultipartUserData.USE_PART_ERROR);
+  }
+
+  public addSignalOnExitCommand(_resource: Resource): void {
+    throw new Error(MultipartUserData.USE_PART_ERROR);
+  }
+
+  public addCommands(..._commands: string[]): void {
+    throw new Error(MultipartUserData.USE_PART_ERROR);
+  }
+
+  public addOnExitCommands(..._commands: string[]): void {
+    throw new Error(MultipartUserData.USE_PART_ERROR);
+  }
+}