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a75360ccd6
This package handles cases where we need to truncate human-readable text to fit a length constraint without leaving "ragged" multi-byte rune fragments at the end of the truncated value. Change-Id: Id972135d1880485f41b1fedfb65c2b8cc012d416 Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>
32 lines
1.1 KiB
Go
32 lines
1.1 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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// Package truncate provides a utility function for safely truncating UTF-8
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// strings to a fixed length, respecting multi-byte codepoints.
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package truncate
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// String returns a prefix of a UTF-8 string s, having length no greater than n
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// bytes. If s exceeds this length, it is truncated at a point ≤ n so that the
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// result does not end in a partial UTF-8 encoding. If s is less than or equal
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// to this length, it is returned unmodified.
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func String(s string, n int) string {
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if n >= len(s) {
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return s
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}
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// Back up until we find the beginning of a UTF-8 encoding.
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for n > 0 && s[n-1]&0xc0 == 0x80 { // 0x10... is a continuation byte
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n--
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}
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// If we're at the beginning of a multi-byte encoding, back up one more to
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// skip it. It's possible the value was already complete, but it's simpler
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// if we only have to check in one direction.
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//
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// Otherwise, we have a single-byte code (0x00... or 0x01...).
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if n > 0 && s[n-1]&0xc0 == 0xc0 { // 0x11... starts a multibyte encoding
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n--
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}
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return s[:n]
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}
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