The fetcher accepts image/svg+xml; internal/magic detects SVG. orig of an SVG at the orig size is the SVG unchanged, cached, with a Content-Security-Policy allowing only its styles and data: images; at another size, ErrSVGNotOriginalSize (400). Any other format renders it at the least size covering the output, at most 8192 on a side. Rendering refuses an SVG with a side over 8192 times the other (ErrSVGTooThin, 415), and the orig size of one above 8192 on a side (ErrSVGTooLargeForOrigSize, 400). Child processes of pixad read an SVG's size and render it, killed after 20 seconds and limited to 1 GiB; any failure there is ErrSVGRenderFailed (415). Tests pinning the SVG refusal now expect SVG. Model: opus-5-5
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package imageprocessor
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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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"io"
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"os"
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"os/exec"
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"strconv"
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"syscall"
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"time"
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"github.com/davidbyttow/govips/v2/vips"
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)
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// An SVG child process is the running program started again with one of
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// these arguments first, naming what it does. Its command line, after the
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// program's name, is one of:
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//
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// read-svg-size MEMORY_LIMIT
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// render-svg-as-png MEMORY_LIMIT WIDTH HEIGHT
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//
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// MEMORY_LIMIT is in bytes. The child reads the SVG on standard input. It
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// writes the SVG's size as WIDTH HEIGHT, or the SVG rendered at WIDTH x
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// HEIGHT as PNG, to standard output.
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const (
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readSVGSizeArgument = "read-svg-size"
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renderSVGAsPNGArgument = "render-svg-as-png"
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)
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// errSVGChildProcessArguments is returned for a command line that is not
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// that of an SVG child process.
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var errSVGChildProcessArguments = errors.New(
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"not the command line of an SVG child process")
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// IsSVGChildProcess reports whether args, a process's command line after the
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// program's name, are those of an SVG child process.
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func IsSVGChildProcess(args []string) bool {
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return len(args) > 0 &&
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(args[0] == readSVGSizeArgument || args[0] == renderSVGAsPNGArgument)
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}
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// RunAsSVGChildProcess runs this process as the SVG child process that args,
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// its command line after the program's name, ask for. It returns the status
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// to exit with: 0 once it has written its result, and 1 after writing an
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// error to standard error, which the parent discards.
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func RunAsSVGChildProcess(args []string) int {
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err := runAsSVGChildProcess(args, os.Stdin, os.Stdout)
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if err != nil {
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_, _ = fmt.Fprintln(os.Stderr, err)
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return 1
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}
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return 0
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}
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// runAsSVGChildProcess does the work of RunAsSVGChildProcess, reading the SVG
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// from stdin and writing the result to stdout. It sets the process's limits
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// before it reads the SVG.
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func runAsSVGChildProcess(
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args []string, stdin io.Reader, stdout io.Writer,
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) error {
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numbers, err := parseSVGChildProcessArguments(args)
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if err != nil {
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return err
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}
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err = setSVGChildProcessLimits(numbers[0])
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if err != nil {
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return err
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}
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initVips()
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svg, err := io.ReadAll(stdin)
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if err != nil {
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return fmt.Errorf("failed to read the SVG: %w", err)
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}
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if args[0] == readSVGSizeArgument {
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return writeSVGSize(svg, stdout)
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}
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return writeSVGAsPNG(svg, numbers[1], numbers[2], stdout)
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}
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// parseSVGChildProcessArguments returns the numbers on the command line of an
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// SVG child process, args: the memory limit, then the width and height for
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// render-svg-as-png.
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func parseSVGChildProcessArguments(args []string) ([]int, error) {
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wantArgs := 2
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if len(args) > 0 && args[0] == renderSVGAsPNGArgument {
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wantArgs = 4
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}
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if !IsSVGChildProcess(args) || len(args) != wantArgs {
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return nil, fmt.Errorf("%w: %q", errSVGChildProcessArguments, args)
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}
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numbers := make([]int, 0, len(args)-1)
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for _, arg := range args[1:] {
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number, err := strconv.Atoi(arg)
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if err != nil {
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return nil, fmt.Errorf("%w: %q: %w", errSVGChildProcessArguments,
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args, err)
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}
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numbers = append(numbers, number)
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}
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return numbers, nil
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}
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// setSVGChildProcessLimits sets this process's RLIMIT_DATA to memoryLimit
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// bytes, so that allocating heap or other private writable memory past it
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// fails. RLIMIT_AS would also count the address space the Go runtime reserves
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// but does not use. It also sets RLIMIT_CORE to 0: librsvg crashes when an
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// allocation fails, and the crash would write a core file of up to
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// memoryLimit bytes into pixad's working directory.
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func setSVGChildProcessLimits(memoryLimit int) error {
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if memoryLimit < 1 {
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return fmt.Errorf("%w: memory limit %d", errSVGChildProcessArguments,
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memoryLimit)
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}
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err := syscall.Setrlimit(syscall.RLIMIT_DATA, &syscall.Rlimit{
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Cur: uint64(memoryLimit),
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Max: uint64(memoryLimit),
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})
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if err != nil {
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return fmt.Errorf("failed to limit memory to %d bytes: %w",
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memoryLimit, err)
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}
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err = syscall.Setrlimit(syscall.RLIMIT_CORE, &syscall.Rlimit{})
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if err != nil {
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return fmt.Errorf("failed to turn off core files: %w", err)
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}
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return nil
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}
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// writeSVGSize writes the size of svg to stdout as WIDTH HEIGHT. librsvg
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// reads the whole SVG for it.
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func writeSVGSize(svg []byte, stdout io.Writer) error {
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img, err := vips.NewImageFromBuffer(svg)
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if err != nil {
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return fmt.Errorf("failed to read the SVG: %w", err)
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}
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defer img.Close()
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_, err = fmt.Fprintf(stdout, "%d %d\n", img.Width(), img.Height())
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return err
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}
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// writeSVGAsPNG renders svg at width x height and writes it to stdout as PNG.
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// libvips' thumbnail has librsvg render the SVG at that size directly, at
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// any scale: govips takes a density only in whole dots per inch, which cannot
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// render an SVG below 1/72 of its own size. Given the SVG as bytes with no
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// file name, librsvg loads no file or URL the SVG refers to.
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func writeSVGAsPNG(svg []byte, width, height int, stdout io.Writer) error {
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img, err := vips.NewThumbnailWithSizeFromBuffer(svg, width, height,
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vips.InterestingNone, vips.SizeBoth)
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if err != nil {
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return fmt.Errorf("failed to render the SVG: %w", err)
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}
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defer img.Close()
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png, err := exportPNG(img)
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if err != nil {
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return fmt.Errorf("failed to save the SVG as PNG: %w", err)
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}
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_, err = stdout.Write(png)
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return err
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}
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// readSVGSize reads the size of the SVG data in a child process that pixa
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// kills at deadline (see runSVGChildProcess).
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func (p *ImageProcessor) readSVGSize(
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ctx context.Context, deadline time.Time, data []byte,
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) (int, int, error) {
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output, err := p.runSVGChildProcess(ctx, deadline, data,
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readSVGSizeArgument)
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if err != nil {
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return 0, 0, err
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}
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var width, height int
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_, err = fmt.Sscan(string(output), &width, &height)
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if err != nil {
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return 0, 0, fmt.Errorf("failed to read the size %q an SVG child "+
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"process wrote: %w", output, err)
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}
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return width, height, nil
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}
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// runSVGChildProcess starts the running program again as an SVG child
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// process, with argument, p.maxSVGRenderMemory and extraArgs as its command
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// line, and waits for it. It gives the child data on standard input,
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// discards its standard error, and returns its standard output. pixa kills
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// the child at deadline. A child that fails or is killed is
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// ErrSVGRenderFailed, unless ctx has ended: runSVGChildProcess then returns
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// ctx's error. Failing to start the child is another error.
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func (p *ImageProcessor) runSVGChildProcess(
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ctx context.Context, deadline time.Time, data []byte,
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argument string, extraArgs ...string,
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) ([]byte, error) {
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executable, err := os.Executable()
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if err != nil {
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return nil, fmt.Errorf("failed to find the running program: %w", err)
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}
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childCtx, cancel := context.WithDeadline(ctx, deadline)
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defer cancel()
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args := append([]string{argument, strconv.Itoa(p.maxSVGRenderMemory)},
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extraArgs...)
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//nolint:gosec // the running program, with arguments pixa makes
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cmd := exec.CommandContext(childCtx, executable, args...)
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cmd.Stdin = bytes.NewReader(data)
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var stdout bytes.Buffer
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cmd.Stdout = &stdout
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err = cmd.Run()
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var exitError *exec.ExitError
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switch {
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case err == nil:
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return stdout.Bytes(), nil
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case ctx.Err() != nil:
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return nil, ctx.Err()
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case childCtx.Err() != nil:
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return nil, fmt.Errorf("%w: it took more than %v", ErrSVGRenderFailed,
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p.svgRenderTimeout)
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case errors.As(err, &exitError):
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return nil, fmt.Errorf("%w: %w", ErrSVGRenderFailed, err)
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default:
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return nil, fmt.Errorf("failed to run an SVG child process: %w", err)
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}
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}
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