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79 lines
2.4 KiB
Go
79 lines
2.4 KiB
Go
// GoToSocial
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// Copyright (C) GoToSocial Authors admin@gotosocial.org
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// SPDX-License-Identifier: AGPL-3.0-or-later
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//
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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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//
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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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//
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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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package text
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import (
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"strings"
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"golang.org/x/text/unicode/norm"
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)
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const (
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maximumHashtagLength = 100
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)
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// NormalizeHashtag normalizes the given hashtag text by
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// removing the initial '#' symbol, and then decomposing
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// and canonically recomposing chars + combining diacritics
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// in the text to single unicode characters, following
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// Normalization Form C (https://unicode.org/reports/tr15/).
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//
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// Finally, it will do a check on the normalized string to
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// ensure that it's below maximumHashtagLength chars, and
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// contains only letters, numbers, and underscores (and not
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// *JUST* underscores).
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//
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// If all this passes, returned bool will be true.
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func NormalizeHashtag(text string) (string, bool) {
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// This normalization is specifically to avoid cases
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// where visually-identical hashtags are stored with
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// different unicode representations (e.g. with combining
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// diacritics). It allows a tasteful number of combining
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// diacritics to be used, as long as they can be combined
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// with parent characters to form regular letter symbols.
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normalized := norm.NFC.String(strings.TrimPrefix(text, "#"))
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// Validate normalized result.
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var (
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notJustUnderscores = false
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onlyPermittedChars = true
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lengthOK = true
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)
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for i, r := range normalized {
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if r != '_' {
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// This isn't an underscore,
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// so the whole hashtag isn't
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// just underscores.
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notJustUnderscores = true
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}
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if i >= maximumHashtagLength {
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lengthOK = false
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break
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}
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if !isPermittedInHashtag(r) {
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onlyPermittedChars = false
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break
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}
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}
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return normalized, (lengthOK && onlyPermittedChars && notJustUnderscores)
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}
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