mrambossekandClaude Opus 5
40e76c52ca
Enrolling a device that cannot reach the admin UI meant transcribing a 200-character link with a base64 pin in it — the step the link format exists to avoid, and the one where a pin wrong by one character fails later as an inscrutable TLS error. Rendered as inline SVG rather than a PNG data: URI, because the page's CSP is default-src 'none' and means it: a data: image would need img-src opened, markup needs nothing. One path rather than a rect per module, since a link this long encodes to about 60x60 and two thousand elements is a lot of DOM for a picture of a square. It is generated from the same validated value as the href, so a rejected link produces neither. This relaxes the stdlib-only rule, deliberately and recorded in CLAUDE.md. The rule bought one self-contained binary with no supply chain to audit, which one small pure-Go package barely dents; F-Droid never applied to the server, only the app ships there. A correct QR encoder is ~500 lines of Reed-Solomon that nobody should be hand-writing. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
59 lines
1.9 KiB
Go
59 lines
1.9 KiB
Go
// SPDX-FileCopyrightText: 2026 Echolot contributors
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// SPDX-License-Identifier: GPL-3.0-or-later
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package adminui
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import (
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"fmt"
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"html/template"
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"strings"
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qrcode "github.com/skip2/go-qrcode"
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)
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// qrSVG renders text as an inline SVG QR code, or empty if it will not encode.
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//
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// Inline SVG rather than a PNG data: URI because the page's CSP is `default-src 'none'` and means
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// it. A data: image would need img-src opened up; markup needs nothing, and the QR is generated
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// here from a boolean matrix, so nothing a user supplied reaches the output.
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//
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// Drawn as one path rather than a rect per module: a link of this length encodes to roughly 60x60
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// modules, and two thousand elements is a lot of DOM for a picture of a square.
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func qrSVG(text string) template.HTML {
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if text == "" {
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return ""
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}
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// Medium recovery: a phone camera reading a screen has no dirt or creases to survive, and
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// lower recovery keeps the module count down, which keeps it scannable on a small display.
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q, err := qrcode.New(text, qrcode.Medium)
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if err != nil {
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return "" // too long to encode; the link text below it still works
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}
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bitmap := q.Bitmap()
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n := len(bitmap)
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if n == 0 {
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return ""
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}
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var path strings.Builder
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for y, row := range bitmap {
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for x, dark := range row {
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if dark {
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fmt.Fprintf(&path, "M%d %dh1v1h-1z", x, y)
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}
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}
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}
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// A quiet zone is part of the spec, not decoration: without it a scanner cannot find the
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// symbol's edges against whatever is next to it on the page.
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var out strings.Builder
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fmt.Fprintf(&out,
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`<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 %d %d" `+
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`width="240" height="240" shape-rendering="crispEdges" role="img" `+
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`aria-label="Enrolment link as a QR code">`+
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`<rect width="%d" height="%d" fill="#fff"/>`+
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`<path d="%s" fill="#000"/></svg>`,
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n, n, n, n, path.String())
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return template.HTML(out.String())
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}
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