Remove rcmail_html_page

The calling code replaced the $rcmail->output on the fly, which makes is
hardly testable.
Also that class was used only in the class `rcmail_action_mail_get`, and
it's a pretty thin layer on top of `rcmail_output_html`, which is not
necessary.

Author: pabzm

program/actions/mail/get.php

@@ -181,8 +181,7 @@ public function run($args = [])
                     }
                     // html warning with a button to load the file anyway
                     else {
-                        $rcmail->output = new rcmail_html_page();
-                        $rcmail->output->register_inline_warning(
+                        $inline_warning = $this->make_inline_warning(
                             $rcmail->gettext([
                                 'name' => 'attachmentvalidationerror',
                                 'vars' => [
@@ -193,8 +192,7 @@ public function run($args = [])
                             $rcmail->gettext('showanyway'),
                             $rcmail->url(array_merge($_GET, ['_nocheck' => 1]))
                         );
-
-                        $rcmail->output->write();
+                        $this->send_html('', $inline_warning);
                     }
 
                     $rcmail->output->sendExit();
@@ -223,7 +221,7 @@ public function run($args = [])
                 // embed.css and blocks loading other css files (though calling
                 // reset() in write()). Also we don't need all the processing that it
                 // brings.
-                $styles_path = $rcmail->output->get_skin_file('/styles/styles.css', $path, null, true);
+                $styles_path = $rcmail->output->get_skin_file('/styles/styles.css');
                 $body = html::tag('html', [],
                     html::tag('head', [], html::tag('link', ['rel' => 'stylesheet', 'href' => $styles_path]))
                     . html::tag('body', [], $body)
@@ -233,24 +231,19 @@ public function run($args = [])
 
             // deliver part content
             if ($mimetype == 'text/html' && empty($_GET['_download'])) {
-                $rcmail->output = new rcmail_html_page();
-                $out = '';
-
                 // Check if we have enough memory to handle the message in it
                 // #1487424: we need up to 10x more memory than the body
                 if (!rcube_utils::mem_check($attachment->size * 10)) {
-                    $rcmail->output->register_inline_warning(
+                    $inline_warning = $this->make_inline_warning(
                         $rcmail->gettext('messagetoobig'),
                         $rcmail->gettext('download'),
                         $rcmail->url(array_merge($_GET, ['_download' => 1]))
                     );
+                    $this->send_html('', $inline_warning);
                 } else {
                     // render HTML body
-                    $out = $attachment->html();
+                    $this->send_html($attachment->html());
                 }
-
-                $rcmail->output->write($out);
-                $rcmail->output->sendExit();
             }
 
             // add filename extension if missing
@@ -355,4 +348,62 @@ public static function message_part_frame($attrib)
 
         return html::iframe($attrib);
     }
+
+    /**
+     * @param $contents       string Content to send as HTTP body
+     * @param $inline_warning string Something to inject into the beginning of the content
+     */
+    protected function send_html($contents, $inline_warning = null): void
+    {
+        $rcmail = rcmail::get_instance();
+        $rcmail->output->reset(true);
+
+        // load embed.css from skin folder (if exists)
+        $embed_css = $rcmail->config->get('embed_css_location', '/embed.css');
+        if ($embed_css = $rcmail->output->get_skin_file($embed_css)) {
+            $rcmail->output->include_css($embed_css);
+        } else {  // set default styles for warning blocks inside the attachment part frame
+            $rcmail->output->add_header(html::tag('style', ['type' => 'text/css'],
+                '.rcmail-inline-message { font-family: sans-serif; border:2px solid #ffdf0e;'
+                                        . "background:#fef893; padding:0.6em 1em; margin-bottom:0.6em }\n" .
+                '.rcmail-inline-buttons { margin-bottom:0 }'
+            ));
+        }
+
+        if (empty($contents)) {
+            $contents = '<html><body></body></html>';
+        }
+
+        if ($inline_warning) {
+            $body_start = 0;
+            if ($body_pos = strpos($contents, '<body')) {
+                $body_start = strpos($contents, '>', $body_pos) + 1;
+            }
+
+            $contents = substr_replace($contents, $inline_warning, $body_start, 0);
+        }
+
+        $rcmail->output->write_blank_slate($contents);
+        $rcmail->output->sendExit();
+    }
+
+    /**
+     * @param $text         string Text content
+     * @param $button_label string Text for the optional button to append to the content
+     * @param $button_url   string URL of the button
+     *
+     * @return string HTML code as string
+     */
+    protected function make_inline_warning($text, $button_label = null, $button_url = null): string
+    {
+        $text = html::span(null, $text);
+
+        if ($button_label) {
+            $onclick = "location.href = '{$button_url}'";
+            $button = html::tag('button', ['onclick' => $onclick], rcube::Q($button_label));
+            $text .= html::p(['class' => 'rcmail-inline-buttons'], $button);
+        }
+
+        return html::div(['class' => 'rcmail-inline-message rcmail-inline-warning'], $text);
+    }
 }

program/include/rcmail_html_page.php

@@ -701,6 +701,21 @@ public function write($template = '')
         $this->_write($template);
     }
 
+    /**
+     * Write output on a blank slate: no env, no scripts, no injected
+     * stylesheets.
+     */
+    public function write_blank_slate($content): void
+    {
+        $this->scripts = [];
+        $this->script_files = [];
+        $this->header = '';
+        $this->footer = '';
+        $this->page_headers();
+        // call super method
+        $this->_write($content);
+    }
+
     /**
      * Send common page headers
      * For now it only (re)sets X-Frame-Options when needed