latexgrambot: inline LaTeX bot for Telegram in Go
Renders LaTeX expressions into PNG pictures, PDF documents and native Telegram rich text messages, entirely locally with TeX Live and poppler. - Chat mode with /image, /pdf, /rich plus per-user preamble and DPI - Inline mode delivering picture, PDF and rich text results - Broad default package set preloaded into a TeX format at image build - MongoDB persistence: settings, users, groups, render statistics - Private S3-compatible bucket with short-lived presigned URLs - OpenTelemetry traces over OTLP - Kubernetes manifests and Argo CD application, Docker Compose, GitHub Actions CI, BSD 3-Clause license
This commit is contained in:
corrado.mulas
446
internal/render/render.go
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446
internal/render/render.go
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@@ -0,0 +1,446 @@
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// Package render turns LaTeX expressions into PNG and PDF files using a
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// locally installed TeX Live (pdflatex) and poppler (pdftoppm). No network
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// service is involved.
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package render
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import (
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"bytes"
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"context"
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"errors"
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"fmt"
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"image"
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_ "image/jpeg"
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_ "image/png"
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"math"
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"os"
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"os/exec"
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"path/filepath"
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"regexp"
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"strconv"
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"strings"
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"time"
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"latexgrambot/internal/rich"
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"go.opentelemetry.io/otel"
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"go.opentelemetry.io/otel/attribute"
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"go.opentelemetry.io/otel/codes"
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"go.opentelemetry.io/otel/trace"
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)
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var renderTracer = otel.Tracer("latexgrambot/render")
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const (
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// minRenderedSide is the minimum size of the smallest PNG side. Small
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// formulas rasterize to a few hundred pixels at any DPI; Telegram then
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// upscales and JPEG-recompresses them, blurring thin glyphs. Upscaling
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// the raster beforehand keeps the final picture crisp.
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minRenderedSide = 2560
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// maxRenderedSide guards against pathologically tall formulas.
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maxRenderedSide = 4096
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)
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// documentClass is the fixed preview layout: the standalone class crops
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// tightly around the content.
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const documentClass = `\documentclass[preview,varwidth,border=4pt]{standalone}`
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// defaultPackages is inserted into the document when the user has no custom
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// preamble: the broad standard package set so documents compile without a
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// custom preamble.
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const defaultPackages = `\usepackage[utf8]{inputenc}
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\usepackage[T1]{fontenc}
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\usepackage{lmodern}
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\usepackage{textcomp}
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\usepackage{amsmath}
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\usepackage{amssymb}
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\usepackage{amsfonts}
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\usepackage{amsthm}
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\usepackage{amscd}
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\usepackage{mathtools}
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\usepackage{mathrsfs}
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\usepackage{bm}
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\usepackage{cancel}
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\usepackage{braket}
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\usepackage{siunitx}
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\usepackage{mhchem}
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\usepackage{chemfig}
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\usepackage{systeme}
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\usepackage{polynom}
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\usepackage{wasysym}
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\usepackage{stmaryrd}
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\usepackage{pifont}
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\usepackage{eurosym}
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\usepackage{graphicx}
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\usepackage{xcolor}
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\usepackage{colortbl}
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\usepackage{tikz}
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\usepackage{pgfplots}
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\pgfplotsset{compat=1.18}
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\usepackage{tikz-cd}
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\usepackage{tcolorbox}
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\usepackage{qrcode}
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\usepackage{float}
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\usepackage{array}
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\usepackage{multirow}
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\usepackage{makecell}
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\usepackage{booktabs}
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\usepackage{tabularx}
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\usepackage{longtable}
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\usepackage{multicol}
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\usepackage{enumitem}
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\usepackage{caption}
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\usepackage{subcaption}
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\usepackage{wrapfig}
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\usepackage{rotating}
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\usepackage[normalem]{ulem}
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\usepackage{soul}
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\usepackage{listings}
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\usepackage{algorithm}
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\usepackage{algpseudocode}
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\usepackage{microtype}
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\usepackage{xspace}
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\usepackage{etoolbox}
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\usepackage{hyperref}`
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// DefaultPreamble returns the preamble file used at image build time to
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// preload the default class and packages into the "latexgrambot" TeX
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// format, so renders no longer pay the package-load cost.
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func DefaultPreamble() string {
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return documentClass + "\n" + defaultPackages + "\n\\endofdump\n"
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}
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// Result carries the compiled output. JPEG is used for URL-based Telegram
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// inline photos, while PNG is used for direct chat replies.
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type Result struct {
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PNG []byte
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JPEG []byte
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PDF []byte
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}
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// LatexError wraps a LaTeX compile failure and carries the log excerpt shown
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// to the user.
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type LatexError struct {
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Excerpt string
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}
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func (e *LatexError) Error() string { return "latex compilation failed" }
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// Renderer compiles LaTeX documents locally.
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type Renderer struct {
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Pdflatex string
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Pdftoppm string
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Timeout time.Duration
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WorkDir string // base directory for temp dirs; os.TempDir() when empty
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// Format is the preloaded TeX format (built from DefaultPreamble) used
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// when the default preamble is in effect. Empty disables it.
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Format string
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sem chan struct{}
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}
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// New creates a Renderer that allows at most maxConcurrent simultaneous
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// pdflatex runs.
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func New(pdflatex, pdftoppm string, timeout time.Duration, maxConcurrent int, workDir string) *Renderer {
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if maxConcurrent < 1 {
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maxConcurrent = 1
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}
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return &Renderer{
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Pdflatex: pdflatex,
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Pdftoppm: pdftoppm,
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Timeout: timeout,
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WorkDir: workDir,
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sem: make(chan struct{}, maxConcurrent),
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}
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}
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// dangerousCommands are TeX primitives that read or write files; user input
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// must never reach them.
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var dangerousCommands = regexp.MustCompile(`\\(input|include|openin|openout|write|read|catcode|newwrite|immediate)\b`)
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// normalizeExpression validates and trims user LaTeX without changing its
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// mode. The bot has already applied the RICH_DEFAULT_MATH policy before it
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// calls the renderer; wrapping everything here would incorrectly place text
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// commands such as \hyperlink and \section inside display math.
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func normalizeExpression(expression string) (string, error) {
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expr := strings.TrimSpace(expression)
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if expr == "" {
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return "", &LatexError{Excerpt: "the expression is empty"}
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}
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if dangerousCommands.MatchString(expr) {
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return "", &LatexError{Excerpt: "unsupported TeX command in the expression"}
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}
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return expr, nil
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}
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// stripOuterMathDelimiters removes matching outer math delimiters, so a
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// forced math retry never nests delimiters.
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func stripOuterMathDelimiters(expr string) string {
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for _, pair := range [][2]string{{`$$`, `$$`}, {`$`, `$`}, {`\[`, `\]`}, {`\(`, `\)`}} {
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if len(expr) >= len(pair[0])+len(pair[1]) &&
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strings.HasPrefix(expr, pair[0]) && strings.HasSuffix(expr, pair[1]) {
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return strings.TrimSpace(expr[len(pair[0]) : len(expr)-len(pair[1])])
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}
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}
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return expr
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}
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// Formats selects which outputs a render produces.
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type Formats uint8
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const (
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FormatPNG Formats = 1 << iota
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FormatJPEG
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FormatPDF
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)
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// Render compiles the expression and produces every format.
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func (r *Renderer) Render(ctx context.Context, preamble, expression string, dpi int) (*Result, error) {
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return r.RenderFormats(ctx, preamble, expression, dpi, FormatPNG|FormatJPEG|FormatPDF)
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}
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// RenderFormats compiles the expression inside the given preamble and
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// produces only the requested formats, so callers never pay for
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// rasterization they do not use. The expression is normalised (math
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// delimiters stripped, plain expressions wrapped in math mode) and inserted
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// between \begin{document} and \end{document}.
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func (r *Renderer) RenderFormats(ctx context.Context, preamble, expression string, dpi int, formats Formats) (result *Result, err error) {
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normalized, err := normalizeExpression(expression)
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if err != nil {
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return nil, err
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}
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ctx, span := renderTracer.Start(ctx, "render",
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trace.WithAttributes(
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attribute.Int("dpi", dpi),
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attribute.Int("expression.length", len(expression)),
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attribute.Int("expression.normalized_length", len(normalized)),
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attribute.Int("preamble.length", len(preamble)),
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),
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)
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defer span.End()
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defer func() {
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if err != nil {
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span.RecordError(err)
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span.SetStatus(codes.Error, "render failed")
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}
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}()
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select {
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case r.sem <- struct{}{}:
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defer func() { <-r.sem }()
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case <-ctx.Done():
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return nil, ctx.Err()
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}
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workdir, err := os.MkdirTemp(r.WorkDir, "latexgrambot-")
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if err != nil {
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return nil, fmt.Errorf("create workdir: %w", err)
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}
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defer os.RemoveAll(workdir)
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texPath := filepath.Join(workdir, "document.tex")
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// Preloaded format: with the default preamble the class and packages
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// are already in the format, so only the body is compiled.
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useFormat := r.Format != "" && strings.TrimSpace(preamble) == ""
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compile := func(body string) error {
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document := buildDocument(preamble, body)
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if useFormat {
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document = "\\begin{document}\n" + body + "\n\\end{document}\n"
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}
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if err := os.WriteFile(texPath, []byte(document), 0o600); err != nil {
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return fmt.Errorf("write document: %w", err)
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}
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// -no-shell-escape is the default, spelled out here on purpose: the
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// \write18 escapes must never be enabled for user-supplied LaTeX.
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args := []string{
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"-interaction=nonstopmode", "-halt-on-error", "-no-shell-escape",
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"-output-directory=" + workdir,
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}
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if useFormat {
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args = append(args, "-fmt="+r.Format)
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}
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return r.run(ctx, workdir, r.Pdflatex, append(args, "document.tex")...)
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}
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// Entirely-math expressions are put into math mode up front: waiting
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// for the "Missing $ inserted" error would compile every formula twice.
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firstAttempt := normalized
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if rich.IsMathExpression(expression) && !rich.ContainsMathEnvironment(expression) {
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firstAttempt = `\[` + stripOuterMathDelimiters(strings.TrimSpace(normalized)) + `\]`
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}
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if err := compile(firstAttempt); err != nil {
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logContent, readErr := os.ReadFile(filepath.Join(workdir, "document.log"))
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if readErr != nil {
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return nil, err
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}
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// One retry for cases the up-front check missed: when the compiler
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// only complained about missing math delimiters and the whole
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// expression is math. If the retry fails too, the original error is
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// reported so the user decides what to do.
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if strings.Contains(string(logContent), "Missing $ inserted") &&
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rich.IsMathExpression(expression) && firstAttempt == normalized {
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forced := `\[` + stripOuterMathDelimiters(strings.TrimSpace(expression)) + `\]`
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for _, name := range []string{"document.aux", "document.log", "document.pdf"} {
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_ = os.Remove(filepath.Join(workdir, name))
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}
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if retryErr := compile(forced); retryErr != nil {
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return nil, &LatexError{Excerpt: extractError(string(logContent))}
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}
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} else {
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return nil, &LatexError{Excerpt: extractError(string(logContent))}
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}
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}
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pdfPath := filepath.Join(workdir, "document.pdf")
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result = &Result{}
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if formats&FormatPDF != 0 {
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result.PDF, err = os.ReadFile(pdfPath)
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if err != nil {
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return nil, fmt.Errorf("read compiled pdf: %w", err)
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}
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}
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if formats&FormatPNG != 0 {
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pngPath := filepath.Join(workdir, "document.png")
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if err := r.renderRaster(ctx, workdir, dpi, pdfPath, pngPath, "png"); err != nil {
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return nil, err
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}
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result.PNG, err = os.ReadFile(pngPath)
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if err != nil {
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return nil, fmt.Errorf("read rendered png: %w", err)
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}
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}
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if formats&FormatJPEG != 0 {
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jpegPath := filepath.Join(workdir, "document.jpg")
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if err := r.renderRaster(ctx, workdir, dpi, pdfPath, jpegPath, "jpeg"); err != nil {
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return nil, err
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}
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result.JPEG, err = os.ReadFile(jpegPath)
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if err != nil {
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return nil, fmt.Errorf("read rendered jpeg: %w", err)
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}
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}
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return result, nil
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}
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// renderRaster rasterizes the first PDF page to a PNG or JPEG, re-rendering
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// it upscaled when the natural size is too small for a crisp Telegram
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// display. Rasterizing the JPEG directly avoids decoding and re-encoding a
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// full-size PNG in Go.
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func (r *Renderer) renderRaster(ctx context.Context, workdir string, dpi int, pdfPath, outPath, format string) error {
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base := filepath.Join(workdir, "document")
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args := []string{"-" + format, "-r", strconv.Itoa(dpi), "-singlefile", "-f", "1", "-l", "1"}
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if err := r.run(ctx, workdir, r.Pdftoppm, append(args, pdfPath, base)...); err != nil {
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return err
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}
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width, height, err := imageSize(outPath)
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if err != nil {
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return fmt.Errorf("inspect rendered %s: %w", format, err)
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}
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small := min(width, height)
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large := max(width, height)
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scale := 1.0
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if small > 0 && small < minRenderedSide {
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scale = float64(minRenderedSide) / float64(small)
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if scale*float64(large) > maxRenderedSide {
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scale = float64(maxRenderedSide) / float64(large)
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}
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}
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if scale <= 1 {
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return nil
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}
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scaledWidth := int(math.Round(float64(width) * scale))
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args = append(args,
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"-scale-to-x", strconv.Itoa(scaledWidth), "-scale-to-y", "-1")
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return r.run(ctx, workdir, r.Pdftoppm, append(args, pdfPath, base)...)
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}
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func imageSize(path string) (int, int, error) {
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file, err := os.Open(path)
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if err != nil {
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return 0, 0, err
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}
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defer file.Close()
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config, _, err := image.DecodeConfig(file)
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if err != nil {
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return 0, 0, err
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}
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return config.Width, config.Height, nil
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}
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// buildDocument assembles the full .tex source. User preamble additions are
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// loaded after the broad default package set, so setting custom definitions
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// cannot accidentally remove core packages such as hyperref.
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func buildDocument(preamble, expression string) string {
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pkgs := defaultPackages
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if strings.TrimSpace(preamble) != "" {
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pkgs += "\n" + strings.TrimSpace(preamble)
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}
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return documentClass + "\n" +
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pkgs + "\n" +
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"\\begin{document}\n" +
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expression + "\n" +
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"\\end{document}\n"
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}
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// extractError pulls the first "! ..." error line and its "l.NN ..." context
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// line from the pdflatex log.
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func extractError(log string) string {
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var first, context string
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for _, line := range strings.Split(log, "\n") {
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trimmed := strings.TrimSpace(line)
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if first == "" && strings.HasPrefix(trimmed, "!") {
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first = trimmed
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continue
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}
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if first != "" && strings.HasPrefix(trimmed, "l.") {
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context = trimmed
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break
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}
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}
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if first == "" {
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return "compilation failed without an explicit error message"
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}
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if context == "" {
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return first
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}
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return first + "\n" + context
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}
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// run executes a command in dir, inheriting the timeout from ctx. Home,
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// TMPDIR and TEXMFOUTPUT point into the workdir so TeX never needs to write
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// outside it.
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func (r *Renderer) run(ctx context.Context, dir, bin string, args ...string) error {
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cmd := exec.CommandContext(ctx, bin, args...)
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cmd.Dir = dir
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cmd.Env = append(os.Environ(),
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"HOME="+dir,
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"TMPDIR="+dir,
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"TEXMFOUTPUT="+dir,
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)
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var output bytes.Buffer
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cmd.Stdout = &output
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cmd.Stderr = &output
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if err := cmd.Run(); err != nil {
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if ctx.Err() != nil {
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return fmt.Errorf("%s: %w", filepath.Base(bin), ctx.Err())
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}
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var execErr *exec.Error
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if errors.As(err, &execErr) {
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return fmt.Errorf("%s is not available: %w", bin, execErr)
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}
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return fmt.Errorf("%s failed: %w (%s)", filepath.Base(bin), err, firstLine(output.String()))
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}
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return nil
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}
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// firstLine returns the first non-empty line of s, or an empty string.
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func firstLine(s string) string {
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for _, line := range strings.Split(s, "\n") {
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if strings.TrimSpace(line) != "" {
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return strings.TrimSpace(line)
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}
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}
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return ""
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}
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Block a user