Network permissions (--allow-net) in Deno - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to allow network access when running a Deno script.

Deno

deno run [1] script.ts

Drag options to blanks, or click blank then click option'

A--allow-env

B--allow-write

C--allow-read

D--allow-net

Attempts:

3 left

💡 Hint

Common Mistakes

Using --allow-read instead of --allow-net

Forgetting to add any permission flag

Using --allow-write which is for file writing

The --allow-net flag grants network access to the Deno script.

2fill in blank

medium

Complete the code to allow network access only to example.com.

Deno

deno run --allow-net=[1] script.ts

Drag options to blanks, or click blank then click option'

Alocalhost

Bgoogle.com

Cexample.com

Ddeno.land

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong domain like google.com

Not specifying any domain, which allows all

Using localhost when the task asks for example.com

Specifying --allow-net=example.com restricts network access to example.com only.

3fill in blank

hard

Fix the error in the command to allow network access to both example.com and api.example.com.

Deno

deno run --allow-net=[1] script.ts

Drag options to blanks, or click blank then click option'

Aexample.com,api.example.com

Bexample.com api.example.com

Cexample.com;api.example.com

Dexample.com|api.example.com

Attempts:

3 left

💡 Hint

Common Mistakes

Using spaces or semicolons instead of commas

Using pipes which are invalid separators

Not separating the hosts properly

Multiple hosts are separated by commas in --allow-net flag.

4fill in blank

hard

Fill both blanks to complete the command that allows network access to localhost and denies all other hosts.

Deno

deno run --allow-net=[1] script.ts # Only allow [2]

Drag options to blanks, or click blank then click option'

Alocalhost

Bexample.com

Cgoogle.com

Ddeno.land

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching the allowed host and comment

Using a different host in the comment

Allowing multiple hosts when only localhost is needed

Using --allow-net=localhost restricts network access to localhost only.

5fill in blank

hard

Fill all three blanks to create a command that allows network access to api.example.com, localhost, and deno.land.

Deno

deno run --allow-net=[1],[2],[3] script.ts

Drag options to blanks, or click blank then click option'

Alocalhost

Bapi.example.com

Cdeno.land

Dexample.com

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong host names

Separating hosts with spaces or other characters

Missing one or more hosts

The --allow-net flag accepts multiple hosts separated by commas in any order.

Practice

1. What does the --allow-net flag do when running a Deno program?

easy

A. It allows the program to access the network.

B. It disables all network access for the program.

C. It grants permission to read local files.

D. It enables debugging mode for the program.

Solution

1. Step 1: Understand the purpose of --allow-net

   This flag is used to grant network access to a Deno program, which is otherwise restricted for security.

2. Step 2: Compare options with the flag's function

   Only "It allows the program to access the network." correctly states that --allow-net allows network access. Other options describe unrelated permissions or features.

3. Final Answer:

   It allows the program to access the network. -> Option A

4. Quick Check:

   Network permission = Allow network access [OK]

Hint: Remember: --allow-net means allow network access [OK]

Common Mistakes:

• Confusing --allow-net with file permissions
• Thinking it disables network access
• Mixing it up with debugging flags

2. Which of the following is the correct way to allow network access only to example.com when running a Deno script named app.ts?

easy

A. deno run app.ts --allow-net=example.com

B. deno run --allow-net app.ts example.com

C. deno run --allow-net=example.com app.ts

D. deno run --allow-net example.com app.ts

Solution

1. Step 1: Identify correct flag syntax for domain restriction

   The correct syntax is --allow-net=domain placed before the script name.

2. Step 2: Check command order and placement

   deno run --allow-net=example.com app.ts correctly places --allow-net=example.com before app.ts. Other options have incorrect order or syntax.

3. Final Answer:

   deno run --allow-net=example.com app.ts -> Option C

4. Quick Check:

   Correct flag syntax = deno run --allow-net=example.com app.ts [OK]

Hint: Put --allow-net=domain before script name [OK]

Common Mistakes:

• Placing domain after script name
• Using space instead of '=' between flag and domain
• Putting script name before flags

3. Consider this Deno command and script:

deno run --allow-net=deno.land app.ts

And app.ts contains:

const response = await fetch('https://deno.land/std/http/file_server.ts');
console.log(response.status);

What will be the output?

medium

A. SyntaxError

B. PermissionDenied: network access to "deno.land" is not allowed

C. 404

D. 200

Solution

1. Step 1: Check network permission for the domain

   The command allows network access only to "deno.land", which matches the fetch URL domain.

2. Step 2: Understand fetch behavior with permission

   Since permission is granted, fetch succeeds and returns HTTP status 200 for a valid resource.

3. Final Answer:

   200 -> Option D

4. Quick Check:

   Allowed domain fetch = 200 status [OK]

Hint: Allowed domain fetch returns 200 status [OK]

Common Mistakes:

• Assuming permission error despite allowed domain
• Confusing 404 with permission issues
• Expecting syntax errors from fetch

4. You run this command:

deno run --allow-net=example.com app.ts

Inside app.ts you fetch https://google.com. What error will you get?

medium

A. PermissionDenied: network access to "google.com" is not allowed

B. No error, fetch succeeds

C. TypeError: Invalid URL

D. ReferenceError: fetch is not defined

Solution

1. Step 1: Analyze allowed domains

   The command only allows network access to "example.com" but the script tries to fetch "google.com".

2. Step 2: Understand Deno's permission enforcement

   Deno blocks network requests to domains not allowed, causing a PermissionDenied error.

3. Final Answer:

   PermissionDenied: network access to "google.com" is not allowed -> Option A

4. Quick Check:

   Disallowed domain fetch = PermissionDenied error [OK]

Hint: Fetch outside allowed domain causes PermissionDenied [OK]

Common Mistakes:

• Thinking fetch will succeed without permission
• Confusing permission error with URL or reference errors
• Ignoring domain restrictions in --allow-net

5. You want to run a Deno script that fetches data from both api.example.com and data.service.org. Which command correctly grants network access to both domains using a single --allow-net flag?

hard

A. deno run --allow-net=api.example.com --allow-net=data.service.org app.ts

B. deno run --allow-net=api.example.com,data.service.org app.ts

C. deno run --allow-net app.ts api.example.com data.service.org

D. deno run --allow-net=api.example.com;data.service.org app.ts

Solution

1. Step 1: Understand multiple domain syntax for --allow-net

   Deno accepts multiple domains separated by commas in a single --allow-net flag.

2. Step 2: Evaluate each option's correctness

   deno run --allow-net=api.example.com,data.service.org app.ts uses comma-separated domains correctly. deno run --allow-net=api.example.com --allow-net=data.service.org app.ts repeats the flag (not a single flag). deno run --allow-net app.ts api.example.com data.service.org misplaces domains as arguments. deno run --allow-net=api.example.com;data.service.org app.ts uses semicolon which is incorrect.

3. Final Answer:

   deno run --allow-net=api.example.com,data.service.org app.ts -> Option B

4. Quick Check:

   Multiple domains = comma-separated in one flag [OK]

Hint: Use commas to list multiple domains in --allow-net [OK]

Common Mistakes:

• Using multiple --allow-net flags
• Separating domains with semicolons
• Placing domains after script name