Code examples in Go
These code examples have an implementation in Go. To learn more about using Go with our Compute@Edge platform, see using Go.
NOTE: Some of the code examples here are also available in languages other than Go. Being able to see how the same solution can be achieved in other languages is often useful for migrations or learning, so where a code example has multiple implementations, we show all implementations together.
Verify if a web crawler accessing your server really is Googlebot
An implementation of Google's recommended mechanism for verifying googlebot
Add a new field to a JSON response
Decorate API responses in JSON format with new fields.
Geo-IP API at the edge
Create an API endpoint for fetching GeoIP data for the requesting browser, implemented 100% at the edge. The response should show your current approximate location, but no requests to any origin servers.
Tag requests with geolocation data
Add GeoIP data about the client browser as extra headers in any requests from Fastly to your origin.
Apply feature flags from an origin API
Park request, make a different request first, use the response to annotate the real origin request (or make decisions about how to route it).
Enforce a paywall using an origin API
Use a custom Paywall header to trigger preflight requests to authenticate every article view with a backend paywall service.
Detect leaked passwords
Detect requests that contain submitted passwords and use a service to determine whether the password has leaked before allowing the request to proceed to origin (data from haveibeenpwned).
Add www. to apex hostname and subdomains
Detect requests that don't include a www. prefix, and redirect to the equivalent path on a hostname that starts with www., usually to make sure there's only one canonical location for your content.
Override TTLs for path prefixes
Set TTLs at the edge based on looking up a path prefix in an edge dictionary.
Capture and aggregate log data from client devices
Collect and aggregate log data submitted from browsers directly into S3 or another log store without having to handle the traffic at your origin.
Use microservices to divide up a domain
Send request to different origin servers based on the URL path.
Replace origin errors with 'safe' responses
Detect specified response statuses from backends and instead serve a precomposed error page or error content generated at the edge.
Answer CORS OPTIONS preflight requests at the edge
Browsers send OPTIONS requests before performing cross-origin POSTs. You can answer these requests directly from the edge.
Apply HTTP basic auth to private endpoints
Store username/password list in an edge dictionary, authorize user at the edge, reject requests that don't have correct credentials.
Serve robots.txt from the edge
Serve full text of robots.txt as a synthetic response to avoid requests hitting your origin.
Load balance randomly across multiple backends
Load balance requests randomly across multiple backends, dropping them automatically if they become unhealthy.
Create self-destructing URLs for time-limited access
Make URLs expire after a configurable period.
Enable modern web security headers to all responses
Go from an F to an A grade on securityheaders.io by adding security policy headers to your responses at the edge.
Add, remove or change HTTP headers
Fastly can easily read and write HTTP headers at multiple stages of the request/response cycle.
Rewrite URL path
Receive a request for one path but request a different path from origin, without a redirect.
Filter query string parameters
Add, remove, and sort querystring parameters.
Change request method
Change PUT, DELETE, OPTIONS and others to POST, or vice versa, to help integrate incompatible client and server apps.
Add or remove cookies
Read individual cookies, set new cookies in response.
Filter cookies or other structured headers
Rewrite headers to keep only keys that you want to allow, similar to `querystring.filter_except` but for headers rather than querystrings.
Remove trailing slashes to normalize URLs
Treat URLs with and without suffixed slashes as equivalent, or redirect URLs with slashes to the version without.
Caching responses to POST requests
By default, Fastly does not cache responses to POST requests. But you can enable this if you wish.
Regular expression capturing patterns
Capture regex pattern groups to use in matching url segments and more.
Ban bad IPs for a fixed period
Block a list of IP addresses from accessing your service and include an expiry time.
Normalize requests to increase cache efficiency
Improve cache performance by normalizing requests. Filter and reorder query params, convert to lowercase, filter headers, and more.
Search and replace in strings
Use regular expression substitution functions to map paths, strip extraneous slashes, and more.
AWS S3 bucket origin (private)
Use AWS authenticated requests (signature version 4) to protect communication between your Fastly service and AWS.
Base64 POST body
Access the body of a POST request in Base64-encoded form.
Generate random whole numbers in a range.
Extract a substring from a string value
Isolate a portion of a string identified by a range of characters.
POST to GET rewrite using a Base64-encoded querystring
To allow caching of POST requests, consider rewriting them as GET requests at the edge.
Smoke test a new origin
Send a copy of your traffic to a test origin before returning a response from production.
Compute intersection of two lists
Useful for comparing capabilities with required permissions.
Prevent hotlinking of product images by third party websites
Detect and reject requests from third party websites that attempt to embed your images on their pages.
Decompress and read gzipped responses
When you need to work on API and text responses from backends that support gzip.
Prohibit browser caching
Ensure resources are not cached on the front end, while allowing caching within Fastly.
Clean backend responses
Remove headers added by backends that you don't want to emit to the browser, like amz- or goog- headers.
Follow redirects at the edge
Protect clients from redirects by chasing them internally at the edge, and then return the eventual non-redirect response.
Remove querystring from static assets
Use the new Sec-Fetch-Dest header or URL patterns to identify assets that should not allow querystrings to be part of the cache key.
Set Google Analytics _ga cookie
Auto retry a secondary backend
If primary backend fails, retry with a different backend without caching the failure or reducing cache efficiency.
Anonymize client IPs for logging
Strip the last octet or compute a hash of client IP address for anonymization.
Log the IP version (IPv4/IPv6)
Identify which type of IP address was used by the client connecting to your Fastly service.
Base64 URL path segments
Unknown data in URL paths can result in invalid URLs, but base64url is designed to be URL-safe.
Redirect old URLs at the edge
Use a dictionary of URL mappings to serve your redirects at lightning speed.
Perform multiple origin requests asynchronously
Handle third-party requests as they are resolved.
Validate domain on query string
Check the query string if it contains a valid domain.
All code on this page is provided under both the BSD and MIT open source licenses.