more readable and extensible error messages, support for chrome_path.

lib/pdf_generator.ex

@@ -84,6 +84,8 @@ defmodule PdfGenerator do
   ## Options
 
    * `:generator` – either `chrome` or `wkhtmltopdf` (default)
+   * `:prefer_system_executable` - set to `true` if you installed
+     chrome-headless-render-pdf globally
    * `:no_sandbox` – disable sandbox for chrome, required to run as root (read: _docker_)
    * `:page_size` - output page size, defaults to "A4"
    * `:open_password` - password required to open PDF. Will apply encryption to PDF
@@ -134,14 +136,15 @@ defmodule PdfGenerator do
     with {html_file, pdf_file}       <- make_file_paths(options),
          :ok                         <- maybe_write_html(content, html_file),
          {executable, arguments}     <- make_command(generator, options, content, {html_file, pdf_file}),
-         {console_stderr, exit_code} <- System.cmd(executable, arguments, stderr_to_stdout: true),       # unfortuantely wkhtmltopdf returns 0 on errors as well :-/
-         {:result_ok, true}          <- {:result_ok, result_ok(generator, console_stderr, exit_code)},   # so we inspect stderr instead
+         {:cmd, {stderr, exit_code}} <- {:cmd, System.cmd(executable, arguments, stderr_to_stdout: true)},       # unfortuantely wkhtmltopdf returns 0 on errors as well :-/
+         {:result_ok, true, stderr}  <- {:result_ok, result_ok(generator, stderr, exit_code), stderr},           # so we inspect stderr instead
          {:rm, :ok}                  <- {:rm, maybe_delete_temp(delete_temp, html_file)},
          {:ok, encrypted_pdf}        <- maybe_encrypt_pdf(pdf_file, open_password, edit_password) do
       {:ok, encrypted_pdf}
     else
-      {:error, reason} -> {:error, reason}
-      reason           -> {:error, reason}
+      {:error, reason}        -> {:error, reason}
+      {:result_ok, _, stderr} -> {:error, {:generator_failed, stderr}}
+      reason                  -> {:error, reason}
     end
   end
 

lib/pdf_generator_path_agent.ex

@@ -1,10 +1,14 @@
 defmodule PdfGenerator.PathAgent do
   require Logger
-  defstruct wkhtml_path: nil, pdftk_path: nil
+  defstruct [
+    wkhtml_path: nil,
+    pdftk_path: nil,
+    chrome: nil,
+  ]
 
   @moduledoc """
-  Will check system requirements on startup and keep
-  a path map as state in an Agent process.
+  Will check for system executables at startup time and store paths. If
+  configured as such, will raise an error when no usable executable was found.
   """
 
   @name __MODULE__
@@ -17,8 +21,9 @@ defmodule PdfGenerator.PathAgent do
     # options override system default paths
     options =
       [
-        wkhtml_path:    System.find_executable( "wkhtmltopdf" ),
-        pdftk_path:     System.find_executable( "pdftk" )
+        wkhtml_path: System.find_executable("wkhtmltopdf"),
+        pdftk_path:  System.find_executable("pdftk"),
+        chrome_path: System.find_executable("chrome-headless-render-pdf"),
       ]
       ++ paths_from_options
       |> Enum.dedup()
@@ -39,15 +44,24 @@ defmodule PdfGenerator.PathAgent do
   end
 
   def raise_or_continue(options) do
-    exe_exists       = File.exists?(Keyword.get(options, :wkhtml_path, ""))
-    raise_on_missing = Keyword.get(options, :raise_on_missing_wkhtmltopdf_binary, true)
-
-    case {exe_exists, raise_on_missing} do
-      {true, _} -> options
-      {false, true} -> raise "wkhtmltopdf executable was not found on your system"
-      {false, false} -> 
-        Logger.warn "wkhtmltopdf executable was not found on your system"
-        options
-    end
+    wkhtml_exists = File.exists?(options[:wkhtml_path])
+    chrome_exists = File.exists?(options[:chrome_path])
+
+    raise_on_wkhtml_missing = options[:raise_on_missing_wkhtmltopdf_binary]
+    raise_on_chrome_missing = options[:raise_on_missing_chrome_binary]
+    raise_on_any_missing =    options[:raise_on_missing_binaries]
+
+    maybe_raise(:wkhtml, raise_on_wkhtml_missing, wkhtml_exists)
+    maybe_raise(:chrome, raise_on_chrome_missing, chrome_exists)
+    maybe_raise(:any,    raise_on_any_missing, wkhtml_exists or chrome_exists)
   end
+
+  defp maybe_raise(generator, config_says_raise = true,  wkhtml_exists = false), do: generator |> missing_message() |> raise()
+  defp maybe_raise(generator, config_says_raise = false, wkhtml_exists = false), do: generator |> missing_message() |> Logger.warn()
+  defp maybe_raise(generator, config_says_raise = _,     wkhtml_exists = _    ), do: :noop
+
+  defp missing_message(:wkhtml), do: "wkhtmltopdf executable was not found on your system"
+  defp missing_message(:chrome), do: "chrome-headless-render-pdf executable was not found on your system"
+  defp missing_message(:any),    do: "neither wkhtmltopdf or chrome-headless-render-pdf executables were found on your system"
+
 end