golden/pdfxform a pdf rasterization server

go/pdf/poppler.go

+package pdf
+
+import (
+        "fmt"
+        "io"
+        "os"
+        "os/exec"
+        "time"
+)
+
+const (
+        pdftoppmExecutable = "pdftoppm" // provided by poppler-utils
+        pnmtopngExecutable = "pnmtopng" // provided by netpbm
+)
+
+type Poppler struct{}
+
+func (Poppler) String() string { return "Poppler" }
+
+func (Poppler) Enabled() bool {
+        return commandFound(pdftoppmExecutable) && commandFound(pnmtopngExecutable)
+}
+
+// This does the following:
+//   `pdftoppm -r 72 -f 1 -l 1 < $PDF 2>/dev/null | pnmtopng 2> /dev/null > $PNG`
+func (Poppler) Rasterize(pdfInputPath, pngOutputPath string) error {
+        if !(Poppler{}).Enabled() {
+                return fmt.Errorf("pdftoppm or pnmtopng is missing")
+        }
+
+        pdftoppm := exec.Command(pdftoppmExecutable, "-r", "72", "-f", "1", "-l", "1")
+        pnmtopng := exec.Command(pnmtopngExecutable)
+
+        defer processKiller(pdftoppm)
+        defer processKiller(pnmtopng)
+
+        pr, pw, err := os.Pipe()
+        if err != nil {
+                return err
+        }
+        defer fileCloser(pw)
+        defer fileCloser(pr)
+        pdftoppm.Stdout = pw
+        pnmtopng.Stdin = pr
+
+        iFile, err := os.Open(pdfInputPath)
+        if err != nil {
+                return err
+        }
+        defer iFile.Close()
+        pdftoppm.Stdin = iFile
+
+        oFile, err := os.Create(pngOutputPath)
+        if err != nil {
+                return err
+        }
+        defer oFile.Close()
+        pnmtopng.Stdout = oFile
+
+        if err := pdftoppm.Start(); err != nil {
+                return err
+        }
+        if err := pnmtopng.Start(); err != nil {
+                return err
+        }
+
+        go func() {
+                time.Sleep(5 * time.Second)
+                _ = pdftoppm.Process.Kill()
+        }()
+        if err := pdftoppm.Wait(); err != nil {
+                return err
+        }
+        if err := pw.Close(); err != nil {
+                return err
+        }
+        if err := pnmtopng.Wait(); err != nil {
+                return err
+        }
+        return nil
+}
+
+// Prevents zombie processes
+func processKiller(command *exec.Cmd) {
+        if command.Process != nil {
+                _ = command.Process.Kill()
+                _ = command.Wait()
+        }
+}
+
+func fileCloser(c io.Closer) {
+        _ = c.Close()
+}