golden/pdfxform a pdf rasterization server

go/pdf/poppler.go

Index: go/pdf/poppler.go
diff --git a/go/pdf/poppler.go b/go/pdf/poppler.go
new file mode 100644
index 0000000000000000000000000000000000000000..d76ae9d1dd4a76542aa21e484fe6ece763423b71
--- /dev/null
+++ b/go/pdf/poppler.go
@@ -0,0 +1,93 @@
+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()
+}