gotosocial/internal/api/negotiate.go

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/*
GoToSocial
2021-12-20 18:42:19 +01:00
Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
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 api
import (
"errors"
"fmt"
"github.com/gin-gonic/gin"
)
// ActivityPubAcceptHeaders represents the Accept headers mentioned here:
var ActivityPubAcceptHeaders = []MIME{
AppActivityJSON,
AppActivityLDJSON,
}
// JSONAcceptHeaders is a slice of offers that just contains application/json types.
var JSONAcceptHeaders = []MIME{
AppJSON,
}
// HTMLOrJSONAcceptHeaders is a slice of offers that prefers TextHTML and will
// fall back to JSON 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 HTMLOrJSONAcceptHeaders = []MIME{
TextHTML,
AppJSON,
}
// HTMLAcceptHeaders is a slice of offers that just contains text/html types.
var HTMLAcceptHeaders = []MIME{
TextHTML,
}
// HTMLOrActivityPubHeaders matches text/html first, then activitypub types.
// This is useful for user URLs that a user might go to in their browser.
// https://www.w3.org/TR/activitypub/#retrieving-objects
var HTMLOrActivityPubHeaders = []MIME{
TextHTML,
AppActivityJSON,
AppActivityLDJSON,
}
// 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 ...MIME) (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 := c.NegotiateFormat(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
}