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dbaf0b0472
Raw Linux consoles support UTF-8, but we cannot assume that all UTF-8 characters are available. The default Fixed and Terminus fonts don’t contain half-block characters (`▀` and `▄`), but do contain the full-block character (`█`). Sometimes, Linux doesn’t have a framebuffer, so it falls back to VGA. When this happens, the full-block character could be anywhere in extended ASCII block, because we don’t know which code page is active. This PR introduces `--qr-format=auto` which tries to heuristically detect when Tailscale is printing to a raw Linux console, whether UTF-8 is enabled, and which block characters have been mapped in the console font. If Unicode characters are unavailable, the new `--qr-format=ascii` formatter uses `#` characters instead of full-block characters. Fixes #12935 Signed-off-by: Simon Law <sfllaw@tailscale.com>
68 lines
1.5 KiB
Go
68 lines
1.5 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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// Package qrcodes formats QR codes according to the active terminal.
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package qrcodes
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import (
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"fmt"
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"io"
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"strings"
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qrcode "github.com/skip2/go-qrcode"
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)
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// --qr-format values
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type Format string
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const (
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FormatAuto Format = "auto"
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FormatASCII Format = "ascii"
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FormatLarge Format = "large"
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FormatSmall Format = "small"
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)
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// Fprintln formats s according to [Format] and writes to w and a newline is
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// appended. It returns the number of bytes written and any write error
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// encountered.
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func Fprintln(w io.Writer, format Format, s string) (n int, err error) {
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const inverse = false // Modern scanners can read QR codes of any colour.
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q, err := qrcode.New(s, qrcode.Medium)
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if err != nil {
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return 0, fmt.Errorf("QR code error: %w", err)
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}
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if format == FormatAuto {
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format, err = detectFormat(w, inverse)
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if err != nil {
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return 0, fmt.Errorf("QR code error: %w", err)
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}
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}
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var out string
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switch format {
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case FormatASCII:
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out = q.ToString(inverse)
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out = strings.ReplaceAll(out, "█", "#")
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case FormatLarge:
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out = q.ToString(inverse)
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case FormatSmall:
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out = q.ToSmallString(inverse)
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default:
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return 0, fmt.Errorf("unknown QR code format: %q", format)
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}
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return fmt.Fprintln(w, out)
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}
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// EncodePNG renders a QR code for s as a PNG, with a width and height of size
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// pixels.
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func EncodePNG(s string, size int) ([]byte, error) {
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q, err := qrcode.New(s, qrcode.Medium)
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if err != nil {
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return nil, err
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}
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return q.PNG(size)
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}
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