Repository: traefik/traefik
File: pkg/middlewares/compress/acceptencoding.go (Go)

Code before:
)

type Encoding struct {
	Type   string
	Weight float64
}

func (c *compress) getCompressionEncoding(acceptEncoding []string) string {
	// RFC says: An Accept-Encoding header field with a field value that is empty implies that the user agent does not want any content coding in response.
	// https://datatracker.ietf.org/doc/html/rfc9110#name-accept-encoding
	if len(acceptEncoding) == 1 && acceptEncoding[0] == "" {
		return identityName
	}

	acceptableEncodings := parseAcceptableEncodings(acceptEncoding, c.supportedEncodings)

	// An empty Accept-Encoding header field would have been handled earlier.
	// If empty, it means no encoding is supported, we do not encode.
	if len(acceptableEncodings) == 0 {
		// TODO: return 415 status code instead of deactivating the compression, if the backend was not to compress as well.
		return notAcceptable
	}

	slices.SortFunc(acceptableEncodings, func(a, b Encoding) int {
		if a.Weight == b.Weight {
			// at same weight, we want to prioritize based on the encoding priority.
			// the lower the index, the higher the priority.
			return cmp.Compare(c.supportedEncodings[a.Type], c.supportedEncodings[b.Type])
		}
		return cmp.Compare(b.Weight, a.Weight)
	})

	if acceptableEncodings[0].Type == wildcardName {
		if c.defaultEncoding == "" {
			return c.encodings[0]
		}

		return c.defaultEncoding
	}

	return acceptableEncodings[0].Type
}

func parseAcceptableEncodings(acceptEncoding []string, supportedEncodings map[string]int) []Encoding {
	var encodings []Encoding

	for _, line := range acceptEncoding {
		for _, item := range strings.Split(strings.ReplaceAll(line, " ", ""), ",") {
			parsed := strings.SplitN(item, ";", 2)
			if len(parsed) == 0 {
				continue

Review comment (suggestion):
```suggestion
			// At same weight, we want to prioritize based on the encoding priority.
```

Code after:
)

type Encoding struct {
	Type   string
	Weight float64
}

func (c *compress) getCompressionEncoding(acceptEncoding []string) string {
	// RFC says: An Accept-Encoding header field with a field value that is empty implies that the user agent does not want any content coding in response.
	// https://datatracker.ietf.org/doc/html/rfc9110#name-accept-encoding
	if len(acceptEncoding) == 1 && acceptEncoding[0] == "" {
		return identityName
	}

	acceptableEncodings := parseAcceptableEncodings(acceptEncoding, c.supportedEncodings)

	// An empty Accept-Encoding header field would have been handled earlier.
	// If empty, it means no encoding is supported, we do not encode.
	if len(acceptableEncodings) == 0 {
		// TODO: return 415 status code instead of deactivating the compression, if the backend was not to compress as well.
		return notAcceptable
	}

	slices.SortFunc(acceptableEncodings, func(a, b Encoding) int {
		if a.Weight == b.Weight {
			// At same weight, we want to prioritize based on the encoding priority.
			// the lower the index, the higher the priority.
			return cmp.Compare(c.supportedEncodings[a.Type], c.supportedEncodings[b.Type])
		}
		return cmp.Compare(b.Weight, a.Weight)
	})

	if acceptableEncodings[0].Type == wildcardName {
		if c.defaultEncoding == "" {
			return c.encodings[0]
		}

		return c.defaultEncoding
	}

	return acceptableEncodings[0].Type
}

func parseAcceptableEncodings(acceptEncoding []string, supportedEncodings map[string]int) []Encoding {
	var encodings []Encoding

	for _, line := range acceptEncoding {
		for _, item := range strings.Split(strings.ReplaceAll(line, " ", ""), ",") {
			parsed := strings.SplitN(item, ";", 2)
			if len(parsed) == 0 {
				continue