Support passing additional arguments to Chrome from CLI

Dockerfile

@@ -54,6 +54,6 @@ USER node
 # https://github.com/jessfraz/dockerfiles/issues/65
 # https://github.com/jessfraz/dockerfiles/issues/156
 # https://github.com/jessfraz/dockerfiles/issues/341
-ENTRYPOINT ["node", "/decktape/decktape.js", "--no-sandbox", "--executablePath", "chromium-browser"]
+ENTRYPOINT ["node", "/decktape/decktape.js", "--chrome-path", "chromium-browser", "--chrome-arg=--no-sandbox"]
 
 CMD ["-h"]

README.adoc

@@ -125,6 +125,9 @@ Options:
    --screenshots-format <format>   Screenshots image format, one of [jpg, png]  [png]
    --slides <range>                Range of slides to be exported, a combination of slide indexes
                                    and ranges (e.g. '1-3,5,8')
+   --chrome-path <path>            Path to the Chromium or Chrome executable to run instead of the
+                                   bundled Chromium
+   --chrome-arg <arg>              Additional argument to pass to the Chrome instance, can be repeated
 
 Defaults to the automatic command.
 Iterates over the available plugins, picks the compatible one for presentation at the
@@ -281,6 +284,8 @@ $ docker rm `docker ps -lq`
 
 == FAQ
 
+==== Install
+
 * *_How to install prerequisites on Windows?_*
 +
 Open a Powershell prompt in _Run as administrator_ to install Visual Studio Build Tools and Python 2.7:
@@ -294,10 +299,37 @@ $ npm i -g --production windows-build-tools
 +
 Yes, it is available at https://aur.archlinux.org/packages/nodejs-decktape/.
 
-* *_I'm getting an error: No usable sandbox!_*
+==== Usage
+
+* *_Is it possible to pass arguments to Chrome?_*
++
+Yes, you can use the `--chrome-arg` option, e.g.:
++
+[source,shell]
+----
+$ decktape ... \
+  --chrome-arg=--proxy-server="proxy:8080" \
+  --chrome-arg=--allow-file-access-from-files 
+----
++
+The list of Chromium flags can be found https://peter.sh/experiments/chromium-command-line-switches/[here].
+
+==== Errors
+
+* *_No usable sandbox!_*
 +
 Arch Linux, among other Linux distributions may have the user namespace in the kernel disabled by default. You can verify this by accessing _chrome://sandbox_ in your chrom[e|ium] browser. You can find more about sandboxing, https://chromium.googlesource.com/chromium/src/+/master/docs/linux_sandboxing.md#User-namespaces-sandbox[here]. As a _temporary_ work-around, you can pass `--no-sandbox` as a CLI option.
 
+* *_Failed to read the 'rules' property from 'CSSStyleSheet': Cannot access rules_*
++
+Starting Chromium 64, accessing CSS rules in a stylesheet loaded from the local filesystem violates a CORS policy.
+As some Decktape plugins tweak the CSS rules for better PDF printing, you need to allow access to local files by setting the `--allow-file-access-from-files` flag option, e.g.:
++ 
+[source,shell]
+----
+$ decktape ... --chrome-arg=--allow-file-access-from-files
+----
+
 == Plugin API
 
 {icon-edit}

decktape.js

@@ -62,7 +62,7 @@ parser.script('decktape').options({
     default : 'screenshots',
     help    : 'Screenshots output directory',
   },
-  screenshotSize : {
+  screenshotSizes : {
     full      : 'screenshots-size',
     metavar   : '<size>',
     type      : 'string',
@@ -86,16 +86,18 @@ parser.script('decktape').options({
     help      : 'Range of slides to be exported, a combination of slide indexes and ranges (e.g. \'1-3,5,8\')',
   },
   // Chrome options
-  executablePath : {
-    full    : '--executablePath',
+  chromePath : {
+    full    : 'chrome-path',
     metavar : '<path>',
-    hidden  : true,
     type    : 'string',
+    help    : 'Path to the Chromium or Chrome executable to run instead of the bundled Chromium',
   },
-  noSandbox : {
-    full   : '--no-sandbox',
-    hidden : true,
-    flag   : true,
+  chromeArgs : {
+    full    : 'chrome-arg',
+    metavar : '<arg>',
+    type    : 'string',
+    list    : true,
+    help    : 'Additional argument to pass to the Chrome instance, can be repeated',
   },
 });
 
@@ -187,24 +189,11 @@ process.on('unhandledRejection', error => {
 (async () => {
 
   const browser = await puppeteer.launch({
-    headless : true,
+    headless       : true,
     // TODO: add a verbose option
-    // dumpio   : true,
-    executablePath: options.executablePath,
-    args     : Object.keys(options).reduce((args, option) => {
-      switch (option) {
-        case 'sandbox':
-          if (options.sandbox === false) args.push('--no-sandbox');
-          break;
-      }
-      return args;
-    },
-    [
-      '--disable-dev-shm-usage',
-      // Starting Chromium 64, accessing CSS rules in a stylesheet loaded from the local filesystem violates a CORS policy.
-      // Some Decktape plugins tweak the CSS rules for better PDF printing.
-      '--allow-file-access-from-files',
-    ])
+    // dumpio      : true,
+    executablePath : options.chromePath,
+    args           : options.chromeArgs,
   });
   const page = await browser.newPage();
   await page.emulateMedia('screen');
@@ -364,7 +353,7 @@ async function exportSlide(plugin, page, printer, context) {
   context.exportedSlides++;
 
   if (options.screenshots) {
-    for (let resolution of options.screenshotSize || [options.size]) {
+    for (let resolution of options.screenshotSizes || [options.size]) {
       await page.setViewport(resolution);
       // Delay page rendering to wait for the resize event to complete,
       // e.g. for impress.js (may be needed to be configurable)