elm_cnp: adjust image type to real format

we should never say that we have image/png etc. if we do not have the
respective format. Otherwise we are just confusing the other client.

With this you can copy things from elm to thunderbird / libreoffice
writer / firefox / telegram / chromium.

Please note if you test this: Start *a new xorg session* it was
discovered that xorg clients tent to be totally confused if there was a
protocol error before, or some wrong mime type was delivered before,
thunderbird even likes to crash if this is not done.

This should at some point be extended to more image types.

src/lib/elementary/elm_cnp.c

@@ -51,6 +51,47 @@ _elm_sel_format_to_mime_type(Elm_Sel_Format format)
    return ret;
 }
 
+typedef struct {
+  const unsigned char image_sequence[16];
+  size_t image_sequence_len;
+  const char *mimetype;
+} Mimetype_Content_Matcher;
+
+Mimetype_Content_Matcher matchers[] = {
+  {{0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A}, 8, "image/png"},
+  {{0xFF, 0xD8}, 2, "image/jpeg"},
+  {{0x42, 0x4D}, 2, "image/x-ms-bmp"},
+  {{0x47, 0x49, 0x46, 0x38, 0x37, 0x61}, 6, "image/gif"},
+  {{0x47, 0x49, 0x46, 0x38, 0x39, 0x61}, 6, "image/gif"},
+  {{0x49, 0x49, 0x2A, 00}, 4, "image/tiff"},
+  {{0x49, 0x4D, 0x00, 0x2A}, 4, "image/tiff"},
+  {{0},0, NULL}
+};
+
+static inline Eina_Array*
+_elm_sel_from_content_to_mime_type(const void *buf, size_t buflen)
+{
+   Eina_Array *ret = eina_array_new(10);
+
+   for (int i = 0; matchers[i].mimetype && eina_array_count(ret) == 0; ++i)
+     {
+        if (matchers[i].image_sequence_len >= buflen) continue;
+        for (size_t j = 0; j < matchers[i].image_sequence_len; ++j)
+          {
+             if (((const unsigned  char*)buf)[j] == matchers[i].image_sequence[j])
+               {
+                  eina_array_push(ret, matchers[i].mimetype);
+                  break;
+               }
+          }
+     }
+
+   if (eina_array_count(ret) != 1)
+     ERR("Specified mime type is not available");
+
+   return ret;
+}
+
 static inline Elm_Sel_Format
 _mime_type_to_elm_sel_format(const char *mime_type)
 {
@@ -100,7 +141,16 @@ elm_cnp_selection_set(Evas_Object *obj, Elm_Sel_Type selection,
 
    ee = ecore_evas_ecore_evas_get(evas_object_evas_get(obj));
 
-   tmp = _elm_sel_format_to_mime_type(format);
+   if (format == ELM_SEL_FORMAT_IMAGE)
+     {
+        tmp = _elm_sel_from_content_to_mime_type(buf, buflen);
+     }
+   else
+     {
+        tmp = _elm_sel_format_to_mime_type(format);
+     }
+
+
    if (eina_array_count(tmp) != 1)
      {
         ERR("You cannot specify more than one format when setting selection");