Trailing slash normalization in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this nginx rewrite rule?

Given the nginx configuration snippet below, what will be the final URL after a client requests http://example.com/path/?

Nginx

location /path/ {
    rewrite ^/(.*)/$ /$1 permanent;
}

A Redirects to http://example.com/path (without trailing slash)

B Redirects to http://example.com/path/ (no change)

C Returns 404 Not Found

D Redirects to http://example.com//path (double slash)

💡 Hint

Look at the rewrite regex and replacement carefully.

The rewrite rule removes the trailing slash by matching any path ending with a slash and redirecting to the same path without it.

❓ Configuration

intermediate

Choose the correct nginx config to add trailing slash if missing

Which nginx configuration snippet will redirect http://example.com/path to http://example.com/path/ (adding trailing slash) using a 301 redirect?

A rewrite ^/(.*)$ /$1/ permanent;

B rewrite ^([^.]*[^/])$ $1/ permanent;

C rewrite ^/(.*)/$ /$1 permanent;

D rewrite ^([^.]*[^/])$ /$1 permanent;

💡 Hint

Focus on matching URLs without trailing slash and not containing a dot.

Option B matches URLs that do not end with a slash and do not contain a dot (to exclude files), then adds a trailing slash with a permanent redirect.

❓ Troubleshoot

advanced

Why does this trailing slash removal rule cause a redirect loop?

Consider this nginx config:

location /app/ {
    rewrite ^/(.*)/$ /$1 permanent;
    proxy_pass http://backend/;
}

Why might this cause a redirect loop when accessing /app/?

A Because the rewrite removes the slash but the location requires it, causing repeated redirects

B Because proxy_pass is missing a trailing slash, causing wrong backend path

C Because permanent redirects are cached and never updated

D Because the regex does not match the URL path

💡 Hint

Think about how location matching and rewrite interact.

The rewrite removes the trailing slash, but the location block matches only URLs with trailing slash, so nginx redirects again, causing a loop.

✅ Best Practice

advanced

Which approach is best for consistent trailing slash handling in nginx?

You want all URLs to have no trailing slash except for directories which must have it. Which nginx config approach is best?

A Use proxy_pass without any rewrite rules and handle trailing slashes in backend

B Use a single rewrite rule to remove all trailing slashes unconditionally

C Use separate location blocks for directories and files with rewrite rules to add or remove slashes accordingly

D Use rewrite rules to add trailing slashes to all URLs regardless of type

💡 Hint

Think about how nginx distinguishes directories and files.

Separate location blocks allow precise control: directories get trailing slash, files do not, avoiding redirect loops and confusion.

🧠 Conceptual

expert

What is the effect of this nginx config on URL normalization?

Analyze this nginx snippet:

if ($request_uri ~* ".+/$") {
    return 301 $scheme://$host$uri;
}

What does it do?

A Redirects URLs without a trailing slash to add one

B Does nothing because $uri is undefined

C Blocks access to URLs ending with a slash

D Redirects URLs ending with a slash to the same URL without the slash

💡 Hint

Look at the regex and the return statement carefully.

The if condition matches URLs ending with a slash and redirects to the same URL without the slash by using $uri which excludes the trailing slash.

Practice

1. What is the main purpose of trailing slash normalization in nginx?

easy

A. To disable URL rewriting completely

B. To block all URLs that end with a slash

C. To serve different content based on trailing slash presence

D. To ensure URLs are consistent by adding or removing trailing slashes

Solution

1. Step 1: Understand URL consistency

   Trailing slash normalization makes URLs uniform by either adding or removing the slash at the end.

2. Step 2: Identify nginx role

   nginx uses redirects to enforce this consistency, improving user experience and SEO.

3. Final Answer:

   To ensure URLs are consistent by adding or removing trailing slashes -> Option D

4. Quick Check:

   Trailing slash normalization = URL consistency [OK]

Hint: Normalization means making URLs uniform with or without slash [OK]

Common Mistakes:

• Thinking it blocks URLs ending with slash
• Confusing normalization with disabling rewriting
• Assuming different content is served based on slash

2. Which nginx directive is used to redirect URLs for trailing slash normalization?

easy

A. proxy_pass

B. return 301

C. listen

D. root

Solution

1. Step 1: Identify redirect directive

   nginx uses return 301 to send permanent redirects for URL changes.

2. Step 2: Confirm other directives' roles

   proxy_pass forwards requests, listen sets ports, root sets file paths, none redirect URLs.

3. Final Answer:

   return 301 -> Option B

4. Quick Check:

   Redirect = return 301 [OK]

Hint: Redirects use 'return 301' in nginx config [OK]

Common Mistakes:

• Using proxy_pass for redirects
• Confusing listen with redirect
• Using root directive incorrectly

3. Given this nginx snippet, what happens when a user visits /example/?

location /example {
  if ($request_uri ~ ".+/$") {
    return 301 $scheme://$host$uri;
  }
}

medium

A. The URL is redirected to /example without trailing slash

B. The URL stays as /example/ with trailing slash

C. The server returns a 404 error

D. The URL is redirected to /example// with double slash

Solution

1. Step 1: Analyze the if condition

   The condition checks if the URL ends with a slash using regex ".+/$".

2. Step 2: Understand the redirect

   If true, it returns a 301 redirect to the same URL but without the trailing slash (because $uri excludes query string and trailing slash).

3. Final Answer:

   The URL is redirected to /example without trailing slash -> Option A

4. Quick Check:

   Trailing slash removed by redirect = The URL is redirected to /example without trailing slash [OK]

Hint: If URL ends with slash, return 301 redirects to no slash [OK]

Common Mistakes:

• Assuming URL stays unchanged
• Thinking server returns 404
• Expecting double slashes in redirect

4. Identify the error in this nginx config for adding trailing slashes:

location / {
  if ($request_uri !~ "/$") {
    return 301 $scheme://$host$uri/;
  }
}

medium

A. Using $request_uri instead of $uri causes double query strings

B. Missing semicolon after return statement

C. The regex should check for trailing slash presence, not absence

D. Using if inside location is not allowed

Solution

1. Step 1: Understand variables used

   $request_uri includes query string, $uri does not. Adding slash to $uri is safer.

2. Step 2: Identify problem with $request_uri

   Appending slash to $request_uri can cause double query strings or malformed URLs.

3. Final Answer:

   Using $request_uri instead of $uri causes double query strings -> Option A

4. Quick Check:

   Use $uri for clean URL redirects [OK]

Hint: Use $uri, not $request_uri, to avoid query duplication [OK]

Common Mistakes:

• Thinking if inside location is forbidden
• Ignoring query string issues
• Misreading regex logic

5. How would you configure nginx to always add a trailing slash to URLs except for requests to files (like .html or .jpg)?

hard

A. Use proxy_pass to add trailing slash

B. Always append slash to all URLs unconditionally

C. Use an if condition to check if URI lacks slash and does not end with a file extension, then return 301 with slash

D. Disable trailing slash normalization for all URLs

Solution

1. Step 1: Define condition for adding slash

   Check if URL does not end with slash and does not match file extensions like .html, .jpg.

2. Step 2: Use if and return 301 for redirect

   Use nginx if directive with regex to exclude files, then redirect to URL with trailing slash.

3. Final Answer:

   Use an if condition to check if URI lacks slash and does not end with a file extension, then return 301 with slash -> Option C

4. Quick Check:

   Conditional redirect excluding files = Use an if condition to check if URI lacks slash and does not end with a file extension, then return 301 with slash [OK]

Hint: Exclude files by regex, redirect others with slash [OK]

Common Mistakes:

• Appending slash to all URLs including files
• Using proxy_pass for redirects
• Disabling normalization entirely