adding PDFtk for merging PDF files < 1.7

LICENSE

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2018 TheCodingMachine
+Copyright (c) 2019 TheCodingMachine
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

build/base/Dockerfile

@@ -44,3 +44,13 @@ RUN pip3 install unoconv &&\
     # https://github.com/nextcloud/docker/issues/380
     mkdir -p /usr/share/man/man1mkdir -p /usr/share/man/man1 &&\
     apt-get -y install libreoffice
+
+# |--------------------------------------------------------------------------
+# | PDFtk
+# |--------------------------------------------------------------------------
+# |
+# | Installs PDFtk as an alternative to pdfcpu for merging PDFs.
+# | https://github.com/thecodingmachine/gotenberg/issues/29
+# |
+
+RUN apt-get -y install pdftk

internal/pkg/printer/printer.go

@@ -3,6 +3,7 @@ package printer
 import (
 	"fmt"
 	"io/ioutil"
+	"os/exec"
 
 	pdfcpuAPI "github.com/hhrutter/pdfcpu/pkg/api"
 	pdfcpuLog "github.com/hhrutter/pdfcpu/pkg/log"
@@ -23,9 +24,18 @@ type Printer interface {
 
 // Merge merges PDF files.
 func Merge(fpaths []string, destination string) error {
-	cmd := pdfcpuAPI.MergeCommand(fpaths, destination, pdfcpuConfig.NewDefaultConfiguration())
-	_, err := pdfcpuAPI.Merge(cmd)
-	return err
+	cmdcpu := pdfcpuAPI.MergeCommand(fpaths, destination, pdfcpuConfig.NewDefaultConfiguration())
+	_, err := pdfcpuAPI.Merge(cmdcpu)
+	if err == nil {
+		return nil
+	}
+	// if pdfcpu failed to merge PDF files...
+	// https://github.com/thecodingmachine/gotenberg/issues/29
+	var cmdArgs []string
+	cmdArgs = append(cmdArgs, fpaths...)
+	cmdArgs = append(cmdArgs, "cat", "output", destination)
+	cmd := exec.Command("pdftk", cmdArgs...)
+	return cmd.Run()
 }
 
 func writeBytesToFile(dst string, b []byte) error {