Add notebook open protocol handler (#6093)

Adds a protocol handler for notebook open, which can be used from browsers
Uses extension-based handler support so all URIs must start with `azuredatastudio://microsoft.notebook`

Adds 2 actions:
- `/new` opens a new empty notebook
- `/open` opens a HTTP/S file as an untitled notebook or text document

Sample URL:
```
azuredatastudio://microsoft.notebook/open?url=https%3A%2F%2Fraw.githubusercontent.com%2Fkevcunnane%2Fmsbuild_ads_demo%2Fmaster%2F0_YoAzdata.ipynb
```

extensions/notebook/src/protocol/notebookUriHandler.ts

@@ -0,0 +1,131 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as vscode from 'vscode';
+import * as azdata from 'azdata';
+
+import * as request from 'request';
+import * as path from 'path';
+import * as querystring from 'querystring';
+import * as nls from 'vscode-nls';
+const localize = nls.loadMessageBundle();
+import { IQuestion, QuestionTypes } from '../prompts/question';
+import CodeAdapter from '../prompts/adapter';
+import { getErrorMessage, isEditorTitleFree } from '../common/utils';
+
+export class NotebookUriHandler implements vscode.UriHandler {
+	private prompter = new CodeAdapter();
+
+	constructor() {
+	}
+
+	handleUri(uri: vscode.Uri): vscode.ProviderResult<void> {
+		switch (uri.path) {
+			case '/new':
+				vscode.commands.executeCommand('notebook.command.new');
+				break;
+			case '/open':
+				this.open(uri);
+				break;
+			default:
+				vscode.window.showErrorMessage(localize('notebook.unsupportedAction', "Action {0} is not supported for this handler", uri.path));
+		}
+	}
+
+	private open(uri: vscode.Uri): void {
+		const data = querystring.parse(uri.query);
+
+		if (!data.url) {
+			console.warn('Failed to open URI:', uri);
+		}
+
+		this.openNotebook(data.url);
+	}
+
+	private async openNotebook(url: string | string[]): Promise<void> {
+		try {
+			if (Array.isArray(url)) {
+				url = url[0];
+			}
+			url = decodeURI(url);
+			let uri = vscode.Uri.parse(url);
+			switch (uri.scheme) {
+				case 'http':
+				case 'https':
+					break;
+				default:
+					vscode.window.showErrorMessage(localize('unsupportedScheme', "Cannot open link {0} as only HTTP and HTTPS links are supported", url));
+					return;
+			}
+
+			let doOpen = await this.prompter.promptSingle<boolean>(<IQuestion>{
+				type: QuestionTypes.confirm,
+				message: localize('notebook.confirmOpen', "Download and open '{0}'?", url),
+				default: true
+			});
+			if (!doOpen) {
+				return;
+			}
+
+			let contents = await this.download(url);
+			let untitledUri = this.getUntitledUri(path.basename(uri.fsPath));
+			if (path.extname(uri.fsPath) === '.ipynb') {
+				await azdata.nb.showNotebookDocument(untitledUri, {
+					initialContent: contents,
+					preserveFocus: true
+				});
+			} else {
+				let doc = await vscode.workspace.openTextDocument(untitledUri);
+				let editor = await vscode.window.showTextDocument(doc, vscode.ViewColumn.Active, true);
+				await editor.edit(builder => {
+					builder.insert(new vscode.Position(0, 0), contents);
+				});
+			}
+		} catch (err) {
+			vscode.window.showErrorMessage(getErrorMessage(err));
+		}
+	}
+
+	private download(url: string): Promise<string> {
+		return new Promise<string>((resolve, reject) => {
+			request.get(url, { timeout: 10000 }, (error, response, body) => {
+				if (error) {
+					return reject(error);
+				}
+
+				if (response.statusCode === 404) {
+					return reject(localize('notebook.fileNotFound', "Could not find the specified file"));
+				}
+
+				if (response.statusCode !== 200) {
+					return reject(
+						localize('notebook.fileDownloadError',
+							"File open request failed with error: {0} {1}",
+							response.statusCode,
+							response.statusMessage));
+				}
+
+				resolve(body);
+			});
+		});
+	}
+
+	private getUntitledUri(originalTitle: string): vscode.Uri {
+		let title = originalTitle;
+		let nextVal = 0;
+		let ext = path.extname(title);
+		while (!isEditorTitleFree(title)) {
+			if (ext) {
+				// Need it to be `Readme-0.txt` not `Readme.txt-0`
+				let titleStart = originalTitle.slice(0, originalTitle.length - ext.length);
+				title = `${titleStart}-${nextVal}${ext}`;
+			} else {
+				title = `${originalTitle}-${nextVal}`;
+			}
+			nextVal++;
+		}
+		return vscode.Uri.parse(`untitled:${title}`);
+	}
+}