[balsa/gtk3] Use a filter to quote html-only messages

[Peter Bloomfield <peterb src gnome org>]

commit 378f25a7efedab31e9a97ce82443367631065ec5
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Sun Jun 5 09:54:06 2016 -0400

    Use a filter to quote html-only messages
    
        * configure.ac: detect an html-to-text-or-markdown filter;
        * libbalsa/html.c (html2text), (libbalsa_html_to_string):
          use it.

 ChangeLog       |   10 +++++++++
 configure.ac    |   13 +++++++++++
 libbalsa/html.c |   61 +++++++++++++++++++++++++++++++++++++++++++++++++-----
 3 files changed, 78 insertions(+), 6 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 23cb5d5..5650294 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2016-06-05  Albrecht Dreß
+
+       As Webkit does not have a method to convert html to text,
+       we cannot quote html-only messages.
+       As a workaround, try to use html2text.
+
+       * configure.ac: detect an html-to-text-or-markdown filter;
+       * libbalsa/html.c (html2text), (libbalsa_html_to_string):
+         use it.
+
 2016-06-04  Albrecht Dreß
 
        Force proper icon sizes
diff --git a/configure.ac b/configure.ac
index f247038..d02cd36 100644
--- a/configure.ac
+++ b/configure.ac
@@ -367,6 +367,19 @@ case "$use_html_widget" in
             fi
         fi
         AC_DEFINE(HAVE_WEBKIT,1,[Defined when WebKit can be used.])
+        AC_PATH_PROGS(HTML2TEXT,
+                      [python-html2text  \
+                       html2markdown     \
+                       html2markdown.py2 \
+                       html2markdown.py3 \
+                       html2text],
+                      no)
+        if test x"$ac_cv_path_HTML2TEXT" != "xno" ; then
+            AC_DEFINE_UNQUOTED(HTML2TEXT, "$ac_cv_path_HTML2TEXT",
+                               [Path to html2text program.])
+               else
+                       AC_MSG_WARN([You cannot properly quote html-only messags.])
+               fi
     ;;
     no)
         AC_MSG_RESULT([none])
diff --git a/libbalsa/html.c b/libbalsa/html.c
index 2078eb0..1616840 100644
--- a/libbalsa/html.c
+++ b/libbalsa/html.c
@@ -79,6 +79,57 @@ lbh_get_body_content(LibBalsaMessageBody * body, gchar ** buf)
 }
 
 # if defined(HAVE_WEBKIT)
+
+#ifdef HTML2TEXT
+
+/* common function for all Webkit versions */
+static void
+html2text(gchar ** text, gsize len)
+{
+    gchar *html2text[] = { HTML2TEXT, NULL, NULL };
+    GFile *html_data;
+    GFileIOStream *stream;
+    GError *err = NULL;
+
+    html_data = g_file_new_tmp("balsa-conv-XXXXXX.html", &stream, &err);
+    if (html_data != NULL) {
+        gsize bytes_written;
+        GOutputStream *ostream =
+            g_io_stream_get_output_stream(G_IO_STREAM(stream));
+
+        if (g_output_stream_write_all(ostream, *text, len,
+                                      &bytes_written, NULL, &err)) {
+            gchar *result = NULL;
+
+            g_output_stream_flush(ostream, NULL, NULL);
+            html2text[1] = g_file_get_path(html_data);
+            if (g_spawn_sync(NULL, html2text, NULL,
+                             G_SPAWN_STDERR_TO_DEV_NULL, NULL, NULL,
+                             &result, NULL, NULL, &err)) {
+                g_free(*text);
+                *text = result;
+            }
+            g_free(html2text[1]);
+        }
+        g_output_stream_close(ostream, NULL, NULL);
+        g_object_unref(G_OBJECT(stream));
+        g_file_delete(html_data, NULL, NULL);
+        g_object_unref(G_OBJECT(html_data));
+    }
+    if (err != NULL) {
+        libbalsa_information(LIBBALSA_INFORMATION_ERROR,
+                             _("Could not convert HTML part to text: %s"),
+                             err ? err->message : "Unknown error");
+        g_error_free(err);
+    }
+}
+
+#else
+
+#define html2text(p, l)
+
+#endif
+
 #  if defined(USE_WEBKIT2)
 
 /*
@@ -607,9 +658,8 @@ libbalsa_html_new(LibBalsaMessageBody * body,
 void
 libbalsa_html_to_string(gchar ** text, size_t len)
 {
-    return; /* this widget does not support conversion to a string. The
-             * string won't be altered. Other alternative would be to set
-             * it to an empty string. */
+    /* this widget does not support conversion to a string. */
+    html2text(text, len);
 }
 
 /*
@@ -1259,9 +1309,8 @@ libbalsa_html_new(LibBalsaMessageBody * body,
 void
 libbalsa_html_to_string(gchar ** text, size_t len)
 {
-    return; /* this widget does not support conversion to a string. The
-             * string won't be altered. Other alternative would be to set
-             * it to an empty string. */
+    /* this widget does not support conversion to a string. */
+    html2text(text, len);
 }
 
 static gboolean