99 lines
3.8 KiB
Go
99 lines
3.8 KiB
Go
/*
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GoToSocial
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Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU Affero General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Affero General Public License for more details.
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You should have received a copy of the GNU Affero General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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package api
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import (
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"errors"
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"fmt"
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"github.com/gin-gonic/gin"
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)
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// Offer represents an offered mime-type.
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type Offer string
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const (
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AppJSON Offer = `application/json` // AppJSON is the mime type for 'application/json'.
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AppActivityJSON Offer = `application/activity+json` // AppActivityJSON is the mime type for 'application/activity+json'.
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AppActivityLDJSON Offer = `application/ld+json; profile="https://www.w3.org/ns/activitystreams"` // AppActivityLDJSON is the mime type for 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"'
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TextHTML Offer = `text/html` // TextHTML is the mime type for 'text/html'.
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)
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// ActivityPubAcceptHeaders represents the Accept headers mentioned here:
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// https://www.w3.org/TR/activitypub/#retrieving-objects
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var ActivityPubAcceptHeaders = []Offer{
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AppActivityJSON,
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AppActivityLDJSON,
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}
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// JSONAcceptHeaders is a slice of offers that just contains application/json types.
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var JSONAcceptHeaders = []Offer{
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AppJSON,
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}
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// HTMLAcceptHeaders is a slice of offers that just contains text/html types.
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var HTMLAcceptHeaders = []Offer{
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TextHTML,
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}
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// NegotiateAccept takes the *gin.Context from an incoming request, and a
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// slice of Offers, and performs content negotiation for the given request
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// with the given content-type offers. It will return a string representation
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// of the first suitable content-type, or an error if something goes wrong or
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// a suitable content-type cannot be matched.
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//
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// For example, if the request in the *gin.Context has Accept headers of value
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// [application/json, text/html], and the provided offers are of value
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// [application/json, application/xml], then the returned string will be
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// 'application/json', which indicates the content-type that should be returned.
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//
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// If the length of offers is 0, then an error will be returned, so this function
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// should only be called in places where format negotiation is actually needed.
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//
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// If there are no Accept headers in the request, then the first offer will be returned,
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// under the assumption that it's better to serve *something* than error out completely.
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//
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// Callers can use the offer slices exported in this package as shortcuts for
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// often-used Accept types.
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//
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// See https://developer.mozilla.org/en-US/docs/Web/HTTP/Content_negotiation#server-driven_content_negotiation
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func NegotiateAccept(c *gin.Context, offers ...Offer) (string, error) {
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if len(offers) == 0 {
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return "", errors.New("no format offered")
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}
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strings := []string{}
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for _, o := range offers {
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strings = append(strings, string(o))
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}
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accepts := c.Request.Header.Values("Accept")
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if len(accepts) == 0 {
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// there's no accept header set, just return the first offer
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return strings[0], nil
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}
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format := c.NegotiateFormat(strings...)
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if format == "" {
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return "", fmt.Errorf("no format can be offered for requested Accept header(s) %s; this endpoint offers %s", accepts, offers)
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}
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return format, nil
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}
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