🐛fix: update getOffer to consider quality and specificity

ctx_test.go

@@ -45,6 +45,10 @@ func Test_Ctx_Accepts(t *testing.T) {
 	utils.AssertEqual(t, "", c.Accepts())
 	utils.AssertEqual(t, ".xml", c.Accepts(".xml"))
 	utils.AssertEqual(t, "", c.Accepts(".john"))
+	utils.AssertEqual(t, "application/xhtml+xml", c.Accepts("application/xml", "application/xml+rss", "application/yml", "application/xhtml+xml"), "must use client-preferred mime type")
+
+	c.Request().Header.Set(HeaderAccept, "application/json, text/plain, */*;q=0")
+	utils.AssertEqual(t, "", c.Accepts("html"), "must treat */*;q=0 as not acceptable")
 
 	c.Request().Header.Set(HeaderAccept, "text/*, application/json")
 	utils.AssertEqual(t, "html", c.Accepts("html"))

docs/api/ctx.md

@@ -24,19 +24,31 @@ func (c *Ctx) AcceptsLanguages(offers ...string) string
 ```
 
 ```go title="Example"
-// Accept: text/*, application/json
+// Accept: text/html, application/json; q=0.8, text/plain; q=0.5; charset="utf-8"
 
 app.Get("/", func(c *fiber.Ctx) error {
   c.Accepts("html")             // "html"
   c.Accepts("text/html")        // "text/html"
   c.Accepts("json", "text")     // "json"
   c.Accepts("application/json") // "application/json"
+  c.Accepts("text/plain", "application/json") // "application/json", due to quality
   c.Accepts("image/png")        // ""
   c.Accepts("png")              // ""
   // ...
 })
 ```
 
+```go title="Example 2"
+// Accept: text/html, text/*, application/json, */*; q=0
+
+app.Get("/", func(c *fiber.Ctx) error {
+  c.Accepts("text/plain", "application/json") // "application/json", due to specificity
+  c.Accepts("application/json", "text/html") // "text/html", due to first match
+  c.Accepts("image/png")        // "", due to */* without q factor 0 is Not Acceptable
+  // ...
+})
+```
+
 Fiber provides similar functions for the other accept headers.
 
 ```go

helpers.go

@@ -25,6 +25,16 @@ import (
 	"github.com/valyala/fasthttp"
 )
 
+// acceptType is a struct that holds the parsed value of an Accept header
+// along with quality, specificity, and order.
+// used for sorting accept headers.
+type acceptedType struct {
+	spec        string
+	quality     float64
+	specificity int
+	order       int
+}
+
 // getTLSConfig returns a net listener's tls config
 func getTLSConfig(ln net.Listener) *tls.Config {
 	// Get listener type
@@ -263,40 +273,125 @@ func acceptsOfferType(spec, offerType string) bool {
 func getOffer(header string, isAccepted func(spec, offer string) bool, offers ...string) string {
 	if len(offers) == 0 {
 		return ""
-	} else if header == "" {
+	}
+	if header == "" {
 		return offers[0]
 	}
 
-	for _, offer := range offers {
-		if len(offer) == 0 {
-			continue
+	// Parse header and get accepted types with their quality and specificity
+	// See: https://www.rfc-editor.org/rfc/rfc9110#name-content-negotiation-fields
+	spec, commaPos, order := "", 0, 0
+	acceptedTypes := make([]acceptedType, 0, 20)
+	for len(header) > 0 {
+		order++
+
+		// Skip spaces
+		header = utils.TrimLeft(header, ' ')
+
+		// Get spec
+		commaPos = strings.IndexByte(header, ',')
+		if commaPos != -1 {
+			spec = utils.Trim(header[:commaPos], ' ')
+		} else {
+			spec = utils.TrimLeft(header, ' ')
 		}
-		spec, commaPos := "", 0
-		for len(header) > 0 && commaPos != -1 {
-			commaPos = strings.IndexByte(header, ',')
-			if commaPos != -1 {
-				spec = utils.Trim(header[:commaPos], ' ')
-			} else {
-				spec = utils.TrimLeft(header, ' ')
-			}
-			if factorSign := strings.IndexByte(spec, ';'); factorSign != -1 {
-				spec = spec[:factorSign]
-			}
 
-			// isAccepted if the current offer is accepted
-			if isAccepted(spec, offer) {
-				return offer
+		// Get quality
+		quality := 1.0
+		if factorSign := strings.IndexByte(spec, ';'); factorSign != -1 {
+			factor := utils.Trim(spec[factorSign+1:], ' ')
+			if strings.HasPrefix(factor, "q=") {
+				if q, err := fasthttp.ParseUfloat(utils.UnsafeBytes(factor[2:])); err == nil {
+					quality = q
+				}
 			}
+			spec = spec[:factorSign]
+		}
 
+		// Skip if quality is 0.0
+		// See: https://www.rfc-editor.org/rfc/rfc9110#quality.values
+		if quality == 0.0 {
 			if commaPos != -1 {
 				header = header[commaPos+1:]
+			} else {
+				break
+			}
+			continue
+		}
+
+		// Get specificity
+		specificity := 0
+		// check for wildcard this could be a mime */* or a wildcard character *
+		if spec == "*/*" || spec == "*" {
+			specificity = 1
+		} else if strings.HasSuffix(spec, "/*") {
+			specificity = 2
+		} else if strings.IndexByte(spec, '/') != -1 {
+			specificity = 3
+		} else {
+			specificity = 4
+		}
+
+		// Add to accepted types
+		acceptedTypes = append(acceptedTypes, acceptedType{spec, quality, specificity, order})
+
+		// Next
+		if commaPos != -1 {
+			header = header[commaPos+1:]
+		} else {
+			break
+		}
+	}
+
+	if len(acceptedTypes) > 1 {
+		// Sort accepted types by quality and specificity, preserving order of equal elements
+		sortAcceptedTypes(&acceptedTypes)
+	}
+
+	// Find the first offer that matches the accepted types
+	for _, acceptedType := range acceptedTypes {
+		for _, offer := range offers {
+			if len(offer) == 0 {
+				continue
+			}
+			if isAccepted(acceptedType.spec, offer) {
+				return offer
 			}
 		}
 	}
 
 	return ""
 }
 
+// sortAcceptedTypes sorts accepted types by quality and specificity, preserving order of equal elements
+//
+// Parameters are not supported, they are ignored when sorting by specificity.
+//
+// See: https://www.rfc-editor.org/rfc/rfc9110#name-content-negotiation-fields
+func sortAcceptedTypes(at *[]acceptedType) {
+	if at == nil || len(*at) < 2 {
+		return
+	}
+	acceptedTypes := *at
+
+	for i := 1; i < len(acceptedTypes); i++ {
+		lo, hi := 0, i-1
+		for lo <= hi {
+			mid := (lo + hi) / 2
+			if acceptedTypes[i].quality < acceptedTypes[mid].quality ||
+				(acceptedTypes[i].quality == acceptedTypes[mid].quality && acceptedTypes[i].specificity < acceptedTypes[mid].specificity) ||
+				(acceptedTypes[i].quality == acceptedTypes[mid].quality && acceptedTypes[i].specificity == acceptedTypes[mid].specificity && acceptedTypes[i].order > acceptedTypes[mid].order) {
+				lo = mid + 1
+			} else {
+				hi = mid - 1
+			}
+		}
+		for j := i; j > lo; j-- {
+			acceptedTypes[j-1], acceptedTypes[j] = acceptedTypes[j], acceptedTypes[j-1]
+		}
+	}
+}
+
 func matchEtag(s, etag string) bool {
 	if s == etag || s == "W/"+etag || "W/"+s == etag {
 		return true

helpers_test.go

@@ -62,6 +62,128 @@ func Test_Utils_ETag(t *testing.T) {
 	})
 }
 
+func Test_Utils_GetOffer(t *testing.T) {
+	t.Parallel()
+	utils.AssertEqual(t, "", getOffer("hello", acceptsOffer))
+	utils.AssertEqual(t, "1", getOffer("", acceptsOffer, "1"))
+	utils.AssertEqual(t, "", getOffer("2", acceptsOffer, "1"))
+
+	utils.AssertEqual(t, "", getOffer("", acceptsOfferType))
+	utils.AssertEqual(t, "", getOffer("text/html", acceptsOfferType))
+	utils.AssertEqual(t, "", getOffer("text/html", acceptsOfferType, "application/json"))
+	utils.AssertEqual(t, "", getOffer("text/html;q=0", acceptsOfferType, "text/html"))
+	utils.AssertEqual(t, "", getOffer("application/json, */*; q=0", acceptsOfferType, "image/png"))
+	utils.AssertEqual(t, "application/xml", getOffer("text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8", acceptsOfferType, "application/xml", "application/json"))
+	utils.AssertEqual(t, "text/html", getOffer("text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8", acceptsOfferType, "text/html"))
+	utils.AssertEqual(t, "application/pdf", getOffer("text/plain;q=0,application/pdf;q=0.9,*/*;q=0.000", acceptsOfferType, "application/pdf", "application/json"))
+	utils.AssertEqual(t, "application/pdf", getOffer("text/plain;q=0,application/pdf;q=0.9,*/*;q=0.000", acceptsOfferType, "application/pdf", "application/json"))
+
+	utils.AssertEqual(t, "", getOffer("utf-8, iso-8859-1;q=0.5", acceptsOffer))
+	utils.AssertEqual(t, "", getOffer("utf-8, iso-8859-1;q=0.5", acceptsOffer, "ascii"))
+	utils.AssertEqual(t, "utf-8", getOffer("utf-8, iso-8859-1;q=0.5", acceptsOffer, "utf-8"))
+	utils.AssertEqual(t, "iso-8859-1", getOffer("utf-8;q=0, iso-8859-1;q=0.5", acceptsOffer, "utf-8", "iso-8859-1"))
+
+	utils.AssertEqual(t, "deflate", getOffer("gzip, deflate", acceptsOffer, "deflate"))
+	utils.AssertEqual(t, "", getOffer("gzip, deflate;q=0", acceptsOffer, "deflate"))
+}
+
+func Benchmark_Utils_GetOffer(b *testing.B) {
+	headers := []string{
+		"text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
+		"application/json",
+		"utf-8, iso-8859-1;q=0.5",
+		"gzip, deflate",
+	}
+	offers := [][]string{
+		{"text/html", "application/xml", "application/xml+xhtml"},
+		{"application/json"},
+		{"utf-8"},
+		{"deflate"},
+	}
+	for n := 0; n < b.N; n++ {
+		for i, header := range headers {
+			getOffer(header, acceptsOfferType, offers[i]...)
+		}
+	}
+}
+
+func Test_Utils_SortAcceptedTypes(t *testing.T) {
+	t.Parallel()
+	acceptedTypes := []acceptedType{
+		{spec: "text/html", quality: 1, specificity: 3, order: 0},
+		{spec: "text/*", quality: 0.5, specificity: 2, order: 1},
+		{spec: "*/*", quality: 0.1, specificity: 1, order: 2},
+		{spec: "application/json", quality: 0.999, specificity: 3, order: 3},
+		{spec: "application/xml", quality: 1, specificity: 3, order: 4},
+		{spec: "application/pdf", quality: 1, specificity: 3, order: 5},
+		{spec: "image/png", quality: 1, specificity: 3, order: 6},
+		{spec: "image/jpeg", quality: 1, specificity: 3, order: 7},
+		{spec: "image/*", quality: 1, specificity: 2, order: 8},
+		{spec: "image/gif", quality: 1, specificity: 3, order: 9},
+		{spec: "text/plain", quality: 1, specificity: 3, order: 10},
+	}
+	sortAcceptedTypes(&acceptedTypes)
+	utils.AssertEqual(t, acceptedTypes, []acceptedType{
+		{spec: "text/html", quality: 1, specificity: 3, order: 0},
+		{spec: "application/xml", quality: 1, specificity: 3, order: 4},
+		{spec: "application/pdf", quality: 1, specificity: 3, order: 5},
+		{spec: "image/png", quality: 1, specificity: 3, order: 6},
+		{spec: "image/jpeg", quality: 1, specificity: 3, order: 7},
+		{spec: "image/gif", quality: 1, specificity: 3, order: 9},
+		{spec: "text/plain", quality: 1, specificity: 3, order: 10},
+		{spec: "image/*", quality: 1, specificity: 2, order: 8},
+		{spec: "application/json", quality: 0.999, specificity: 3, order: 3},
+		{spec: "text/*", quality: 0.5, specificity: 2, order: 1},
+		{spec: "*/*", quality: 0.1, specificity: 1, order: 2},
+	})
+}
+
+// go test -v -run=^$ -bench=Benchmark_Utils_SortAcceptedTypes_Sorted -benchmem -count=4
+func Benchmark_Utils_SortAcceptedTypes_Sorted(b *testing.B) {
+	acceptedTypes := make([]acceptedType, 3)
+	for n := 0; n < b.N; n++ {
+		acceptedTypes[0] = acceptedType{spec: "text/html", quality: 1, specificity: 1, order: 0}
+		acceptedTypes[1] = acceptedType{spec: "text/*", quality: 0.5, specificity: 1, order: 1}
+		acceptedTypes[2] = acceptedType{spec: "*/*", quality: 0.1, specificity: 1, order: 2}
+		sortAcceptedTypes(&acceptedTypes)
+	}
+	utils.AssertEqual(b, "text/html", acceptedTypes[0].spec)
+	utils.AssertEqual(b, "text/*", acceptedTypes[1].spec)
+	utils.AssertEqual(b, "*/*", acceptedTypes[2].spec)
+}
+
+// go test -v -run=^$ -bench=Benchmark_Utils_SortAcceptedTypes_Unsorted -benchmem -count=4
+func Benchmark_Utils_SortAcceptedTypes_Unsorted(b *testing.B) {
+	acceptedTypes := make([]acceptedType, 11)
+	for n := 0; n < b.N; n++ {
+		acceptedTypes[0] = acceptedType{spec: "text/html", quality: 1, specificity: 3, order: 0}
+		acceptedTypes[1] = acceptedType{spec: "text/*", quality: 0.5, specificity: 2, order: 1}
+		acceptedTypes[2] = acceptedType{spec: "*/*", quality: 0.1, specificity: 1, order: 2}
+		acceptedTypes[3] = acceptedType{spec: "application/json", quality: 0.999, specificity: 3, order: 3}
+		acceptedTypes[4] = acceptedType{spec: "application/xml", quality: 1, specificity: 3, order: 4}
+		acceptedTypes[5] = acceptedType{spec: "application/pdf", quality: 1, specificity: 3, order: 5}
+		acceptedTypes[6] = acceptedType{spec: "image/png", quality: 1, specificity: 3, order: 6}
+		acceptedTypes[7] = acceptedType{spec: "image/jpeg", quality: 1, specificity: 3, order: 7}
+		acceptedTypes[8] = acceptedType{spec: "image/*", quality: 1, specificity: 2, order: 8}
+		acceptedTypes[9] = acceptedType{spec: "image/gif", quality: 1, specificity: 3, order: 9}
+		acceptedTypes[10] = acceptedType{spec: "text/plain", quality: 1, specificity: 3, order: 10}
+		sortAcceptedTypes(&acceptedTypes)
+	}
+	utils.AssertEqual(b, acceptedTypes, []acceptedType{
+		{spec: "text/html", quality: 1, specificity: 3, order: 0},
+		{spec: "application/xml", quality: 1, specificity: 3, order: 4},
+		{spec: "application/pdf", quality: 1, specificity: 3, order: 5},
+		{spec: "image/png", quality: 1, specificity: 3, order: 6},
+		{spec: "image/jpeg", quality: 1, specificity: 3, order: 7},
+		{spec: "image/gif", quality: 1, specificity: 3, order: 9},
+		{spec: "text/plain", quality: 1, specificity: 3, order: 10},
+		{spec: "image/*", quality: 1, specificity: 2, order: 8},
+		{spec: "application/json", quality: 0.999, specificity: 3, order: 3},
+		{spec: "text/*", quality: 0.5, specificity: 2, order: 1},
+		{spec: "*/*", quality: 0.1, specificity: 1, order: 2},
+	})
+}
+
 // go test -v -run=^$ -bench=Benchmark_App_ETag -benchmem -count=4
 func Benchmark_Utils_ETag(b *testing.B) {
 	app := New()
@@ -221,13 +343,6 @@ func Test_Utils_Parse_Address(t *testing.T) {
 	}
 }
 
-func Test_Utils_GetOffset(t *testing.T) {
-	t.Parallel()
-	utils.AssertEqual(t, "", getOffer("hello", acceptsOffer))
-	utils.AssertEqual(t, "1", getOffer("", acceptsOffer, "1"))
-	utils.AssertEqual(t, "", getOffer("2", acceptsOffer, "1"))
-}
-
 func Test_Utils_TestConn_Deadline(t *testing.T) {
 	t.Parallel()
 	conn := &testConn{}