gotosocial/internal/api/util/negotiate.go

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// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
package util
import (
"errors"
"fmt"
"strings"
"github.com/gin-gonic/gin"
)
// JSONAcceptHeaders is a slice of offers that just contains application/json types.
var JSONAcceptHeaders = []string{
AppJSON,
}
// WebfingerJSONAcceptHeaders is a slice of offers that prefers the
// jrd+json content type, but will be chill and fall back to app/json.
// This is to be used specifically for webfinger responses.
// See https://www.rfc-editor.org/rfc/rfc7033#section-10.2
var WebfingerJSONAcceptHeaders = []string{
AppJRDJSON,
AppJSON,
}
// JSONOrHTMLAcceptHeaders is a slice of offers that prefers AppJSON and will
// fall back to HTML if necessary. This is useful for error handling, since it can
// be used to serve a nice HTML page if the caller accepts that, or just JSON if not.
var JSONOrHTMLAcceptHeaders = []string{
AppJSON,
TextHTML,
}
// HTMLAcceptHeaders is a slice of offers that just contains text/html types.
var HTMLAcceptHeaders = []string{
TextHTML,
}
// HTMLOrActivityPubHeaders matches text/html first, then activitypub types.
// This is useful for user URLs that a user might go to in their browser,
// but which should also be able to serve ActivityPub as a fallback.
//
// https://www.w3.org/TR/activitypub/#retrieving-objects
var HTMLOrActivityPubHeaders = []string{
TextHTML,
AppActivityLDJSON,
AppActivityJSON,
}
// ActivityPubOrHTMLHeaders matches activitypub types first, then text/html.
// This is useful for URLs that should serve ActivityPub by default, but
// which a user might also go to in their browser sometimes.
//
// https://www.w3.org/TR/activitypub/#retrieving-objects
var ActivityPubOrHTMLHeaders = []string{
AppActivityLDJSON,
AppActivityJSON,
TextHTML,
}
// ActivityPubHeaders matches only activitypub Accept headers.
// This is useful for URLs should only serve ActivityPub.
//
// https://www.w3.org/TR/activitypub/#retrieving-objects
var ActivityPubHeaders = []string{
AppActivityLDJSON,
AppActivityJSON,
}
var HostMetaHeaders = []string{
AppXMLXRD,
AppXML,
}
// NegotiateAccept takes the *gin.Context from an incoming request, and a
// slice of Offers, and performs content negotiation for the given request
// with the given content-type offers. It will return a string representation
// of the first suitable content-type, or an error if something goes wrong or
// a suitable content-type cannot be matched.
//
// For example, if the request in the *gin.Context has Accept headers of value
// [application/json, text/html], and the provided offers are of value
// [application/json, application/xml], then the returned string will be
// 'application/json', which indicates the content-type that should be returned.
//
// If the length of offers is 0, then an error will be returned, so this function
// should only be called in places where format negotiation is actually needed.
//
// If there are no Accept headers in the request, then the first offer will be returned,
// under the assumption that it's better to serve *something* than error out completely.
//
// Callers can use the offer slices exported in this package as shortcuts for
// often-used Accept types.
//
// See https://developer.mozilla.org/en-US/docs/Web/HTTP/Content_negotiation#server-driven_content_negotiation
func NegotiateAccept(c *gin.Context, offers ...string) (string, error) {
if len(offers) == 0 {
return "", errors.New("no format offered")
}
strings := []string{}
for _, o := range offers {
strings = append(strings, string(o))
}
accepts := c.Request.Header.Values("Accept")
if len(accepts) == 0 {
// there's no accept header set, just return the first offer
return strings[0], nil
}
format := NegotiateFormat(c, strings...)
if format == "" {
return "", fmt.Errorf("no format can be offered for requested Accept header(s) %s; this endpoint offers %s", accepts, offers)
}
return format, nil
}
// This is the exact same thing as gin.Context.NegotiateFormat except it contains
// tsmethurst's fix to make it work properly with multiple accept headers.
//
// https://github.com/gin-gonic/gin/pull/3156
func NegotiateFormat(c *gin.Context, offered ...string) string {
if len(offered) == 0 {
panic("you must provide at least one offer")
}
if c.Accepted == nil {
for _, a := range c.Request.Header.Values("Accept") {
c.Accepted = append(c.Accepted, parseAccept(a)...)
}
}
if len(c.Accepted) == 0 {
return offered[0]
}
for _, accepted := range c.Accepted {
for _, offer := range offered {
// According to RFC 2616 and RFC 2396, non-ASCII characters are not allowed in headers,
// therefore we can just iterate over the string without casting it into []rune
i := 0
for ; i < len(accepted); i++ {
if accepted[i] == '*' || offer[i] == '*' {
return offer
}
if accepted[i] != offer[i] {
break
}
}
if i == len(accepted) {
return offer
}
}
}
return ""
}
// https://github.com/gin-gonic/gin/blob/4787b8203b79012877ac98d7806422da3a678ba2/utils.go#L103
func parseAccept(acceptHeader string) []string {
parts := strings.Split(acceptHeader, ",")
out := make([]string, 0, len(parts))
for _, part := range parts {
if i := strings.IndexByte(part, ';'); i > 0 {
part = part[:i]
}
if part = strings.TrimSpace(part); part != "" {
out = append(out, part)
}
}
return out
}