// PrefersHTML returns true if the request was made by something that looks like a browser, or can receive HTML
func PrefersHTML(req *http.Request) bool {
accepts := goautoneg.ParseAccept(req.Header.Get("Accept"))
acceptsHTML := false
acceptsJSON := false
for _, accept := range accepts {
if accept.Type == "text" && accept.SubType == "html" {
acceptsHTML = true
} else if accept.Type == "application" && accept.SubType == "json" {
acceptsJSON = true
}
}
// If HTML is accepted, return true
if acceptsHTML {
return true
}
// If JSON was specifically requested, return false
// This gives browsers a way to make requests and add an "Accept" header to request JSON
if acceptsJSON {
return false
}
// In Intranet/Compatibility mode, IE sends an Accept header that does not contain "text/html".
if strings.HasPrefix(req.UserAgent(), "Mozilla") {
return true
}
return false
}
func chooseEncoder(req *http.Request) (encoder, string) {
accepts := goautoneg.ParseAccept(req.Header.Get(acceptHeader))
for _, accept := range accepts {
switch {
case accept.Type == "application" &&
accept.SubType == "vnd.google.protobuf" &&
accept.Params["proto"] == "io.prometheus.client.MetricFamily":
switch accept.Params["encoding"] {
case "delimited":
return text.WriteProtoDelimited, DelimitedTelemetryContentType
case "text":
return text.WriteProtoText, ProtoTextTelemetryContentType
case "compact-text":
return text.WriteProtoCompactText, ProtoCompactTextTelemetryContentType
default:
continue
}
case accept.Type == "text" &&
accept.SubType == "plain" &&
(accept.Params["version"] == "0.0.4" || accept.Params["version"] == ""):
return text.MetricFamilyToText, TextTelemetryContentType
default:
continue
}
}
return text.MetricFamilyToText, TextTelemetryContentType
}
// If we know the location of the asset server, redirect to it when / is requested
// and the Accept header supports text/html
func assetServerRedirect(handler http.Handler, assetPublicURL string) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
if req.URL.Path == "/" {
accepts := goautoneg.ParseAccept(req.Header.Get("Accept"))
for _, accept := range accepts {
if accept.Type == "text" && accept.SubType == "html" {
http.Redirect(w, req, assetPublicURL, http.StatusFound)
return
}
}
}
// Dispatch to the next handler
handler.ServeHTTP(w, req)
})
}
// Negotiate returns the Content-Type based on the given Accept header.
// If no appropriate accepted type is found, FmtText is returned.
func Negotiate(h http.Header) Format {
for _, ac := range goautoneg.ParseAccept(h.Get(hdrAccept)) {
// Check for protocol buffer
if ac.Type == ProtoType && ac.SubType == ProtoSubType && ac.Params["proto"] == ProtoProtocol {
switch ac.Params["encoding"] {
case "delimited":
return FmtProtoDelim
case "text":
return FmtProtoText
case "compact-text":
return FmtProtoCompact
}
}
// Check for text format.
ver := ac.Params["version"]
if ac.Type == "text" && ac.SubType == "plain" && (ver == TextVersion || ver == "") {
return FmtText
}
}
return FmtText
}
// negotiate the most appropriate content type given the accept header and a list of
// alternatives.
func negotiate(header string, alternatives []string) (goautoneg.Accept, bool) {
alternates := make([][]string, 0, len(alternatives))
for _, alternate := range alternatives {
alternates = append(alternates, strings.SplitN(alternate, "/", 2))
}
for _, clause := range goautoneg.ParseAccept(header) {
for _, alternate := range alternates {
if clause.Type == alternate[0] && clause.SubType == alternate[1] {
return clause, true
}
if clause.Type == alternate[0] && clause.SubType == "*" {
clause.SubType = alternate[1]
return clause, true
}
if clause.Type == "*" && clause.SubType == "*" {
clause.Type = alternate[0]
clause.SubType = alternate[1]
return clause, true
}
}
}
return goautoneg.Accept{}, false
}
// negotiateMediaTypeOptions returns the most appropriate content type given the accept header and
// a list of alternatives along with the accepted media type parameters.
func negotiateMediaTypeOptions(header string, accepted []acceptedMediaType, endpoint endpointRestrictions) (mediaTypeOptions, bool) {
if len(header) == 0 && len(accepted) > 0 {
return mediaTypeOptions{
accepted: &accepted[0],
}, true
}
clauses := goautoneg.ParseAccept(header)
for _, clause := range clauses {
for i := range accepted {
accepts := &accepted[i]
switch {
case clause.Type == accepts.Type && clause.SubType == accepts.SubType,
clause.Type == accepts.Type && clause.SubType == "*",
clause.Type == "*" && clause.SubType == "*":
// TODO: should we prefer the first type with no unrecognized options? Do we need to ignore unrecognized
// parameters.
return acceptMediaTypeOptions(clause.Params, accepts, endpoint)
}
}
}
return mediaTypeOptions{}, false
}