fix: compression priority (#1950)

* Initial update

* update remaining tests

* update .gitignore

* update another test, fix linting

* fix tests

* add missing Vary header

.gitignore

@@ -1,7 +1,8 @@
 tags
 *.pprof
-*.fasthttp.gz
 *.fasthttp.br
+*.fasthttp.zst
+*.fasthttp.gz
 .idea
 .vscode
 .DS_Store

fs.go

@@ -133,6 +133,7 @@ var (
 		GenerateIndexPages: true,
 		Compress:           true,
 		CompressBrotli:     true,
+		CompressZstd:       true,
 		AcceptByteRange:    true,
 	}
 	rootFSHandler RequestHandler
@@ -156,6 +157,7 @@ func ServeFS(ctx *RequestCtx, filesystem fs.FS, path string) {
 		GenerateIndexPages: true,
 		Compress:           true,
 		CompressBrotli:     true,
+		CompressZstd:       true,
 		AcceptByteRange:    true,
 	}
 	handler := f.NewRequestHandler()
@@ -321,13 +323,20 @@ type FS struct {
 	// absolute paths on any filesystem.
 	AllowEmptyRoot bool
 
-	// Uses brotli encoding and fallbacks to gzip in responses if set to true, uses gzip if set to false.
+	// Uses brotli encoding and fallbacks to zstd or gzip in responses if set to true, uses zstd or gzip if set to false.
 	//
 	// This value has sense only if Compress is set.
 	//
 	// Brotli encoding is disabled by default.
 	CompressBrotli bool
 
+	// Uses zstd encoding and fallbacks to gzip in responses if set to true, uses gzip if set to false.
+	//
+	// This value has sense only if Compress is set.
+	//
+	// zstd encoding is disabled by default.
+	CompressZstd bool
+
 	// Index pages for directories without files matching IndexNames
 	// are automatically generated if set.
 	//
@@ -487,6 +496,7 @@ func (fs *FS) initRequestHandler() {
 		generateIndexPages:     fs.GenerateIndexPages,
 		compress:               fs.Compress,
 		compressBrotli:         fs.CompressBrotli,
+		compressZstd:           fs.CompressZstd,
 		compressRoot:           compressRoot,
 		pathNotFound:           fs.PathNotFound,
 		acceptByteRange:        fs.AcceptByteRange,
@@ -518,6 +528,7 @@ type fsHandler struct {
 	generateIndexPages bool
 	compress           bool
 	compressBrotli     bool
+	compressZstd       bool
 	acceptByteRange    bool
 }
 
@@ -1049,14 +1060,14 @@ func (h *fsHandler) handleRequest(ctx *RequestCtx) {
 			mustCompress = true
 			fileCacheKind = brotliCacheKind
 			fileEncoding = "br"
+		case h.compressZstd && ctx.Request.Header.HasAcceptEncodingBytes(strZstd):
+			mustCompress = true
+			fileCacheKind = zstdCacheKind
+			fileEncoding = "zstd"
 		case ctx.Request.Header.HasAcceptEncodingBytes(strGzip):
 			mustCompress = true
 			fileCacheKind = gzipCacheKind
 			fileEncoding = "gzip"
-		case ctx.Request.Header.HasAcceptEncodingBytes(strZstd):
-			mustCompress = true
-			fileCacheKind = zstdCacheKind
-			fileEncoding = "zstd"
 		}
 	}
 
@@ -1122,10 +1133,13 @@ func (h *fsHandler) handleRequest(ctx *RequestCtx) {
 		switch fileEncoding {
 		case "br":
 			hdr.SetContentEncodingBytes(strBr)
+			hdr.addVaryBytes(strAcceptEncoding)
 		case "gzip":
 			hdr.SetContentEncodingBytes(strGzip)
+			hdr.addVaryBytes(strAcceptEncoding)
 		case "zstd":
 			hdr.SetContentEncodingBytes(strZstd)
+			hdr.addVaryBytes(strAcceptEncoding)
 		}
 	}