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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 middleware
import (
"strings"
"codeberg.org/gruf/go-debug"
"github.com/gin-gonic/gin"
)
func ContentSecurityPolicy(extraURIs ...string) gin.HandlerFunc {
csp := BuildContentSecurityPolicy(extraURIs...)
return func(c *gin.Context) {
// Inform the browser we only load
// CSS/JS/media using the given policy.
c.Header("Content-Security-Policy", csp)
}
}
func BuildContentSecurityPolicy(extraURIs ...string) string {
const (
defaultSrc = "default-src"
objectSrc = "object-src"
imgSrc = "img-src"
mediaSrc = "media-src"
frames = "frame-ancestors"
self = "'self'"
none = "'none'"
blob = "blob:"
)
// CSP values keyed by directive.
values := make(map[string][]string, 4)
/*
default-src
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/default-src
*/
if !debug.DEBUG {
// Restrictive 'self' policy
values[defaultSrc] = []string{self}
} else {
// If debug is enabled, allow
// serving things from localhost
// as well (regardless of port).
values[defaultSrc] = []string{
self,
"localhost:*",
"ws://localhost:*",
}
}
/*
object-src
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/object-src
*/
// Disallow object-src as recommended.
values[objectSrc] = []string{none}
/*
img-src
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/img-src
*/
// Restrictive 'self' policy,
// include extraURIs, and 'blob:'
// for previewing uploaded images
// (header, avi, emojis) in settings.
values[imgSrc] = append(
[]string{self, blob},
extraURIs...,
)
/*
media-src
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/media-src
*/
// Restrictive 'self' policy,
// include extraURIs.
values[mediaSrc] = append(
[]string{self},
extraURIs...,
)
/*
frame-ancestors
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/frame-ancestors
*/
// Don't allow embedding us in an iframe
values[frames] = []string{none}
/*
Assemble policy directives.
*/
// Iterate through an ordered slice rather than
// iterating through the map, since we want these
// policyDirectives in a determinate order.
policyDirectives := make([]string, 4)
for i, directive := range []string{
defaultSrc,
objectSrc,
imgSrc,
mediaSrc,
} {
// Each policy directive should look like:
// `[directive] [value1] [value2] [etc]`
// Get assembled values
// for this directive.
values := values[directive]
// Prepend values with
// the directive name.
directiveValues := append(
[]string{directive},
values...,
)
// Space-separate them.
policyDirective := strings.Join(directiveValues, " ")
// Done.
policyDirectives[i] = policyDirective
}
// Content-security-policy looks like this:
// `Content-Security-Policy: <policy-directive>; <policy-directive>`
// So join each policy directive appropriately.
return strings.Join(policyDirectives, "; ")
}
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