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Visual Studio Code for CS50

Visual Studio Code for CS50 is a web app at cs50.dev that adapts GitHub Codespaces for students and teachers. It automates the process of creating a repository inside of CS50's GitHub organization, pushing to it an initial .devcontainer.json, and creating a "codespace," which is a Docker "container" in the cloud (akin to your very own virtual server). Ultimately, it allows students to start programming with just a browser, without needing to install or configure anything locally on their own computer. Within their browser is a full-fledged version of Visual Studio Code, aka VS Code, including a tabbed text editor, terminal window (connected to a Docker container running cs50/codespace), and graphical file explorer.

You can also use VS Code locally, even offline without internet, particularly if feeling more comfortable.

Settings

VS Code supports quite a few settings via which you can customize a codespace:

  1. User settings, which "apply globally to any instance of VS Code you open" and can be applied to codespaces as well via Settings Sync.
  2. Remote settings, which are set by CS50 via .devcontainer.json file in a codespace. Remote settings override User settings.
  3. Workspace settings, which can be set by you via VS Code's GUI (or by editing .vscode/settings.json manually). Workspace settings override Remote settings.

In other words, Workspace settings override Remote settings, and Remote settings override User settings.

If you use VS Code outside of CS50, you might thus want to store most of your settings in User settings (and enable Settings Sync). And if you would like to override any of CS50's Remote settings, you can do so via Workspace settings.

Themes

See code.visualstudio.com/docs/getstarted/themes.

User Interface

See code.visualstudio.com/docs/getstarted/userinterface.

Shortcuts

VS Code Desktop

If feeling more comfortable, you can also use VS Code locally:

  • without Docker, but with internet access, so that you can connect to a codespace remotely
  • with Docker, via which you'd run a codespace-like container on your own computer, even without internet access

Online, without Docker

To use VS Code locally without Docker, but with internet access, connecting to a codespace remotely:

  1. Download and install VS Code itself on your computer.
  2. Install VS Code's GitHub Codespaces extension.
  3. Visit cs50.dev, check Open in VS Code desktop, and log in as usual; you should be prompted to open the codespace in VS Code itself.

Alternatively, if already logged into a codespace, click the codespace's "hamburger" menu (☰) and select Open in VS Code.

Alternatively still, if already logged into a codespace, open the codespace's command palette, as via Ctrl+Shift+P on Linux, ⇧⌘P on macOS, and Ctrl+Shift+P on Windows, select >Codespaces: Open in VS Code.

Offline, with Docker

To use VS Code locally with Docker, running a codespace-like container on your own computer, even without internet access, and opening a folder like foo therein:

  1. Download CS50's latest .devcontainer.json file from https://cs50.dev/.devcontainer.json, saving it in foo. Because the file's name starts with a dot (i.e., period), it might seem to "disappear" when you download it. But, in a terminal window on Linux or macOS, you should see it with ls -a, and at a command prompt in Windows, you should see it with dir /a.
  2. Download, install, and start Docker on your computer.
  3. Download and install VS Code itself on your computer.
  4. Install VS Code's Dev Containers extension.
  5. Open VS Code's command palette, as via Ctrl+Shift+P on Linux, ⇧⌘P on macOS, and Ctrl+Shift+P on Windows, select >Dev Containers - Open Folder in Container..., and open foo.

Alternatively, select >Dev Containers: Install devcontainer CLI, and then, in VS Code's terminal window, cd to foo and execute devcontainer open ..

Once the container finishes building and starting, you should find that foo is mounted within the container at /workspaces/foo.

Git

Because a codespace is already associated with a Git repository in CS50's code50 organization at https://github.com/code50, which is used for automated backups, CS50 effectively disables git anytime you're inside of /workspaces/$RepositoryName (which is a codespace's default directory), wherein $RepositoryName is your (numeric) GitHub ID.

However, you can still use git outside of that directory, as by cloning other repositories into /workspaces itself. For instance, if you'd like to clone https://github.com/octocat/Hello-World into a codespace, you could execute

cd /workspaces
git clone https://github.com/octocat/Hello-World
cd Hello-World

at which point you could use git within that /workspaces/Hello-World directory as usual. Note that only /workspaces/$RepositoryName will be automatically backed up to CS50's code50 organization; repositories that you clone into /workspaces will not.

gitignore

Currently, only these files will be backed up to your Codespace GitHub repository:

  • *.c
  • *.cpp
  • *.css
  • *.db
  • *.h
  • *.html
  • *.java
  • *.js
  • *.md
  • *.py
  • *.sql
  • *.ts
  • *.txt
  • Makefile

GitHub

Authorization

Visual Studio Code for CS50 is implemented as an OAuth App that "lets external applications request authorization to private details in a user's GitHub account without accessing their password." When you log into Visual Studio Code for CS50 using your GitHub account, CS50 receives, via a web application flow, an "access token" from GitHub (but not your password) via which CS50 can execute certain operations (i.e., API calls) on your behalf.

But you'll first be prompted to "authorize" CS50. Only then will that access token have certain permissions, limited by scopes. CS50 currently requests these scopes:

  • codespace, via which CS50 can create and manage codespaces on your behalf
  • read:org, so that you can use the GitHub CLI
  • repo, via which CS50 can manage a repository for you and accept your invitation thereto, and via which git can access repositories to which your GitHub account has access
  • user:email, via which CS50 can access the email address with which you've registered for GitHub, but not your actual emails

Note that scopes are not as granular as would be ideal. The codespace scope technically allows CS50 to manage any of your codespaces, not just the one(s) you use for CS50. And the repo scope technically allows CS50 to access any of your repositories, not just the one(s) you use for CS50. In practice, CS50 only uses those scopes to manage CS50-specific resources. But if you have any concerns, you are welcome to create a (separate) GitHub account that you only use for CS50!

Organization Access

When you log into Visual Studio Code for CS50, your codespace is configured with a "token" that has repo scope, which lets git access repositories to which your GitHub account has access.

If you try to access a repository that's owned by an organization that has not granted access to Visual Studio Code for CS50, though, git might err with "Repository not found." (And gh might err with "Could not resolve to a Repository.") To grant (or request) access for that organization, visit github.com/settings/connections/applications/d1a90a524497a69391fa. Alternatively, you can configure your codespace to use SSH or a personal access token instead, both of which would have access to any repositories to which your GitHub account has access, whether or not owned by an organization.

Domains

Visual Studio Code for CS50 is built atop GitHub Codespaces, which requires that you can also access these domains:

  • *.github.com
  • *.api.github.com
  • *.azureedge.net
  • *.github.dev
  • *.microsoft.com
  • *.msecnd.net
  • *.visualstudio.com
  • *.vscode-webview.net
  • *.windows.net

If on a corporate or school network that blocks any of the above, you might need to ask your IT department if they can "allowlist" all of the above.

Troubleshooting

Could not register service workers

If using Firefox, disable Enhanced Tracking Protection, or use a different browser.

The workbench failed to connect to the server

If using Firefox, disable Enhanced Tracking Protection, or use a different browser.

I'm seeing "Oh no, it looks like you are offline" error message.

First of all, make sure all the required domains are not blocked by your device or internet environment.

Check that you have a stable internet connection and that your home, school, or company network is not blocking the connection. If possible, check logging for rejected connections on your device.

Firewall and Network Configuration

  • Certificate Inspection: If the school's network is injecting TLS certificates, it could be flagged as a man-in-the-middle attack. This issue might be resolved by installing the school's root TLS certificate on students' local machines or by allowing traffic from trusted domains such as *.github.com, *.windows.net, and *.visualstudio.com.
  • Packet Inspection: Investigate the packet inspection settings on the firewall to ensure they are not inadvertently blocking or altering secure traffic required for Codespaces connections.

Browser Extensions and Local Network Configurations

  • Certain browser extensions or individual network configurations (e.g., VPNs, proxies) may be contributing to the problem.
  • Verifying the browsers, extensions, and network settings on affected student devices could help identify additional issues.

The issues are very likely correlated to the Connectivity V2 feature rolled out by GitHub. Please check their announcement and related troubleshooting guidelines: https://github.blog/changelog/2024-02-12-enhanced-codespaces-connection/

To inspect network activity in your browser, follow one of these instructions:

If you see rejected connections, make sure the domains documented by the /meta REST API endpoint are not blocked by your firewall. Again, in other words, none of these domains should be blocked.

Optional: For more information, see REST API endpoints for meta data.

You can run this command in your terminal to get the list of domains required by GitHub Codespaces:

curl -L \
  -H "Accept: application/vnd.github+json" \
  -H "Authorization: Bearer <YOUR-TOKEN>" \
  -H "X-GitHub-Api-Version: 2022-11-28" \
  https://api.github.com/meta

Follow this instruction to generate a GitHub personal access token.

Alternatively, to get the list of domains required by GitHub Codespaces, execute the following command using GitHub CLI:

gh api meta | jq .domains.codespaces

How to monitor global variables in debugger

In debug50's RUN AND DEBUG pane, there's a section labeled WATCH. You can add expressions to this section, and the debugger will show you the values of these expressions as you step through the program. The expressions can include global variables and array names.

Consider the plurality problem, for example. If the arrow to the left of the WATCH heading is pointing to the right >, click it to expand the section. Then click the plus sign in the section heading to insert a new expression to be watched.

For example, you could type this: candidates[0]@candidate_count. Though this is not a legal expression in C, the @ operator is specially treated by the debugger. This particular watch expression means display candidate_count elements of the candidates array, starting with the first (i.e., the element at index 0).

When the debugger stops at a breakpoint, it will show you the value of the expressions it's watching. In this example, the array elements are structs, so you may need to expand them using their individual > buttons.

I can't type anything in the terminal

If you can't type anything in the terminal, please do the following:

  1. Click the Settings icon (the gear icon on the bottom-left icon).
  2. Search for terminal.integrated.gpuAcceleration.
  3. Click Workspace.
  4. Set it to off.

Getting "command not found" error in terminal

First, double-check that you are typing in the command correctly. Not only must the command be typed exactly as instructed, but spaces and capitalization must be exact as well.

Second, if you are absolutely sure that you are typing the command exactly as it should be and you are still receiving a command not found notification, please make sure:

  • Your input method does not introduce special characters.
  • Your codespace is not currently in recovery mode.
  • You are using a codespace provided by CS50.

Codespaces run into recovery mode

Occasionally, your codespace might run into a "recovery mode" due to service outage, a container creation error, or the .devcontainer.json had been modified incorrectly. Most CS50 commands, such as check50 and submit50, will not work and you can't compile your code using CS50 libraries.

In recovery mode, your terminal prompt would look like:

@githubUserName -> /workspaces/githubId (master) $

Normally, your terminal prompt should look like a single dollar sign:

$

To get out of the recovery mode, please do the following:

  1. Confirming there is no ongoing GitHub outage: githubstatus.com
  2. Run this command (copy-paste it to your Codespace terminal): 
    curl https://cs50.dev/devcontainer.json > /workspaces/$RepositoryName/.devcontainer.json
  3. Click the "Extensions" icon on the left, search for the "GitHub Codespaces" extension and install it (if not installed)
  4. After installing "GitHub Codespaces" extension, press "Command + Shift + P" (if on macOS) or "Ctrl + Shift + P" (if on Windows), search for "Codespaces: Rebuild Container" then press Enter on the keyboard,select the Full Rebuild (not Rebuild) option to perform a codespace rebuild.
  5. Your codespace will be launched once the rebuild process is completed.

Creating a new Codespace

If your codespace repeatedly runs into recovery mode and the above steps do not resolve the issue, you might want to try creating a new codespace:

  1. Visit cs50.dev/codespaces.
  2. Click Create codespace on main (the green button).
  3. Wait for your codespace to launch.

Please do NOT delete your old codespace unless you are sure all your files have been synced properly with repository at cs50.dev/repo.

GitDoc failed to sync with backing repository

If GitDoc is showing a GitHub Authentication error, please do the following:

  1. Visit cs50.dev.
  2. Click Login via GitHub.
  3. Click to Authorize cs50.
  4. Once your codespace is launched, visit cs50.dev/restart.

Missing files in Codespace

If you believe some of your files might be missing on your current Codespace, please first check to see if you have more than one Codespace by visiting: https://github.com/codespaces and you should see a list of Codespaces under "Owned by code50".

Some of your files could exist on previous Codespaces, in which it is indicated as "Last used XXX hours/days ago". To access these Codespaces and retrieve the files, please do the followings:

  1. Click on the Codespace name to launch it
  2. Once your Codespace is launched, go to File Explorer
  3. Right-click a file or folder
  4. Click "Download..." to download files to your local computer

If you can't find your missing files in any of your codespaces, look for them in your repository at https://cs50.dev/repo instead.

Alternatively, if you have submitted any assignments via submit50, you can access those at https://github.com/me50. Or, if you have submitted any assignments via Gradescope, you can access those at https://www.gradescope.com/.

Other Common Questions

  1. Why is an extension not installable in the browser?
  2. How do I allow VS Code to access my clipboard for reading?
  3. How do I allow VS Code to always open new tabs and windows?
  4. How do I allow VS Code in a browser to access local files and folders?

See https://code.visualstudio.com/docs/remote/codespaces#_common-questions.

Deleting a Codespace

Deleting a codespace will delete all files and folders therein. If you are sure you want to delete a codespace:

  1. Visit cs50.dev/codespaces.
  2. Under Your codespaces, to the right of main, click ..., select Delete, and click OK.

You can then create a new codespace by logging back into cs50.dev.

Acknowledgements

Special thanks to CS50's friends at GitHub and Microsoft for their support of this app!