Response compression for the Website service (#7)

This PR contains the work done to add response compression to the Website service by registering the `ResponseCompressionMiddleware` middleware so responses are compressed when the client advertises support and the body exceeds a minimum size.

To provide further details about the work done:

* Added the **HummingbirdCompression** package dependency.
* Integrated the `ResponseCompressionMiddleware` middleware into the router, ahead of the not-found and static file middleware.
* Made the `minimum-response-size-to-compress` threshold configurable, with a default.

Reviewed-on: rock-n-code/loud-amsterdam#7
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Services/Website/Sources/App/App+build.swift

@@ -1,12 +1,13 @@
 import Configuration
 import Hummingbird
+import HummingbirdCompression
 import Logging
 import WebsiteCore
 
 /// Builds the website application.
 ///
-/// Reads the log level, server name, and static files location from the configuration,
-/// then assembles the router, server configuration, and logger.
+/// Reads the log level, server name, static files location, and minimum response size to
+/// compress from the configuration, then assembles the router, server configuration, and logger.
 /// - Parameter reader: the configuration reader the values are read from.
 /// - Returns: the configured application, ready to run as a service.
 func application(
@@ -26,6 +27,10 @@ func application(
             default: .Cache.maxAgeDefault
         )
     )
+    let compressionMinResponseSize = reader.int(
+        forKey: .Compression.minResponseSize,
+        default: .Compression.minResponseSize
+    )
     let logLevel = reader.string(
         forKey: .Log.level,
         as: Logger.Level.self,
@@ -44,6 +49,7 @@ func application(
         router: router(
             staticFilesPath: staticFilesPath,
             cacheControl: cacheControl,
+            compressionMinResponseSize: compressionMinResponseSize,
             logLevel: logLevel
         ),
         configuration: ApplicationConfiguration(
@@ -102,24 +108,30 @@ private func logger(
 
 /// Builds the application's router.
 ///
-/// Registers the request-logging middleware, the not-found middleware that serves the error
-/// page, and the static file middleware that serves the contents of `staticFilesPath` (tagging
-/// responses with the given `cacheControl` directives), then adds the `RootController` routes
-/// that render the landing page.
+/// Registers the request-logging middleware, the response-compression middleware that compresses
+/// responses larger than `minimumResponseSizeToCompress` when the client advertises support, the
+/// not-found middleware that serves the error page, and the static file middleware that serves the
+/// contents of `staticFilesPath` (tagging responses with the given `cacheControl` directives), then
+/// adds the `RootController` routes that render the landing page.
 /// - Parameters:
 ///   - staticFilesPath: the folder, relative to the working directory, the static files are served from.
 ///   - cacheControl: the cache-control directives applied to the served static files.
+///   - compressionMinResponseSize: the minimum response body size, in bytes, before compression is applied.
 ///   - logLevel: the level the request-logging middleware logs at.
 /// - Returns: the configured router.
 private func router(
     staticFilesPath: String,
     cacheControl: CacheControl,
+    compressionMinResponseSize: Int,
     logLevel: Logger.Level
 ) -> Router<AppRequestContext> {
     let router = Router(context: AppRequestContext.self)
 
     router.addMiddleware {
         LogRequestsMiddleware(logLevel)
+        ResponseCompressionMiddleware(
+            minimumResponseSizeToCompress: compressionMinResponseSize
+        )
         NotFoundMiddleware()
         FileMiddleware(
             staticFilesPath,