GConverterInputStream: fix an edge case

Reading from a GConverterInputStream with both input_buffer and
converted_buffer non-empty would return bogus data (the data from
converted_buffer would essentially get skipped over, though the
returned nread reflected what the count would be if it hadn't been).

This was never noticed before because (a) it can't happen if all of
your reads are at least as large as either the internal buffer size or
the remaining length of the stream (which covers most real-world use),
and (b) it can't happen if all of your reads are 1 byte (which covers
most of tests/converter-test). (And (c) it only happens for some
converters/input streams.) But this was happening occasionally in
libsoup when content-sniffing a gzipped response, because the
SoupContentSnifferStream would first read 512 bytes (to sniff), and
then pass through larger reads after that.

Fixed and added a test to converter-test.

https://bugzilla.gnome.org/show_bug.cgi?id=676478

gio/gconverterinputstream.c

@@ -415,6 +415,7 @@ read_internal (GInputStream *stream,
   buffer_read (&priv->converted_buffer, buffer, available);
 
   total_bytes_read = available;
+  buffer += available;
   count -= available;
 
   /* If there is no data to convert, and no pre-converted data,

gio/tests/converter-stream.c

@@ -564,6 +564,168 @@ test_compressor (void)
   g_object_unref (compressor);
 }
 
+#define LEFTOVER_SHORT_READ_SIZE 512
+
+#define G_TYPE_LEFTOVER_CONVERTER         (g_leftover_converter_get_type ())
+#define G_LEFTOVER_CONVERTER(o)           (G_TYPE_CHECK_INSTANCE_CAST ((o), G_TYPE_LEFTOVER_CONVERTER, GLeftoverConverter))
+#define G_LEFTOVER_CONVERTER_CLASS(k)     (G_TYPE_CHECK_CLASS_CAST((k), G_TYPE_LEFTOVER_CONVERTER, GLeftoverConverterClass))
+#define G_IS_LEFTOVER_CONVERTER(o)        (G_TYPE_CHECK_INSTANCE_TYPE ((o), G_TYPE_LEFTOVER_CONVERTER))
+#define G_IS_LEFTOVER_CONVERTER_CLASS(k)  (G_TYPE_CHECK_CLASS_TYPE ((k), G_TYPE_LEFTOVER_CONVERTER))
+#define G_LEFTOVER_CONVERTER_GET_CLASS(o) (G_TYPE_INSTANCE_GET_CLASS ((o), G_TYPE_LEFTOVER_CONVERTER, GLeftoverConverterClass))
+
+typedef struct _GLeftoverConverter       GLeftoverConverter;
+typedef struct _GLeftoverConverterClass  GLeftoverConverterClass;
+
+struct _GLeftoverConverterClass
+{
+  GObjectClass parent_class;
+};
+
+GType       g_leftover_converter_get_type (void) G_GNUC_CONST;
+GConverter *g_leftover_converter_new      (void);
+
+
+
+static void g_leftover_converter_iface_init          (GConverterIface *iface);
+
+struct _GLeftoverConverter
+{
+  GObject parent_instance;
+};
+
+G_DEFINE_TYPE_WITH_CODE (GLeftoverConverter, g_leftover_converter, G_TYPE_OBJECT,
+			 G_IMPLEMENT_INTERFACE (G_TYPE_CONVERTER,
+						g_leftover_converter_iface_init))
+
+static void
+g_leftover_converter_class_init (GLeftoverConverterClass *klass)
+{
+}
+
+static void
+g_leftover_converter_init (GLeftoverConverter *local)
+{
+}
+
+GConverter *
+g_leftover_converter_new (void)
+{
+  GConverter *conv;
+
+  conv = g_object_new (G_TYPE_LEFTOVER_CONVERTER, NULL);
+
+  return conv;
+}
+
+static void
+g_leftover_converter_reset (GConverter *converter)
+{
+}
+
+static GConverterResult
+g_leftover_converter_convert (GConverter *converter,
+			      const void *inbuf,
+			      gsize       inbuf_size,
+			      void       *outbuf,
+			      gsize       outbuf_size,
+			      GConverterFlags flags,
+			      gsize      *bytes_read,
+			      gsize      *bytes_written,
+			      GError    **error)
+{
+  if (outbuf_size == LEFTOVER_SHORT_READ_SIZE)
+    {
+      g_set_error_literal (error,
+			   G_IO_ERROR,
+			   G_IO_ERROR_PARTIAL_INPUT,
+			   "partial input");
+      return G_CONVERTER_ERROR;
+    }
+
+  if (inbuf_size < 100)
+    *bytes_read = *bytes_written = MIN (inbuf_size, outbuf_size);
+  else
+    *bytes_read = *bytes_written = MIN (inbuf_size - 10, outbuf_size);
+  memcpy (outbuf, inbuf, *bytes_written);
+
+  if (*bytes_read == inbuf_size && (flags & G_CONVERTER_INPUT_AT_END))
+    return G_CONVERTER_FINISHED;
+  return G_CONVERTER_CONVERTED;
+}
+
+static void
+g_leftover_converter_iface_init (GConverterIface *iface)
+{
+  iface->convert = g_leftover_converter_convert;
+  iface->reset = g_leftover_converter_reset;
+}
+
+#define LEFTOVER_BUFSIZE 8192
+#define INTERNAL_BUFSIZE 4096
+
+static void
+test_converter_leftover (void)
+{
+  gchar *orig, *converted;
+  gsize total_read;
+  gssize res;
+  goffset offset;
+  GInputStream *mem, *cstream;
+  GConverter *converter;
+  GError *error;
+  int i;
+
+  converter = g_leftover_converter_new ();
+
+  orig = g_malloc (LEFTOVER_BUFSIZE);
+  converted = g_malloc (LEFTOVER_BUFSIZE);
+  for (i = 0; i < LEFTOVER_BUFSIZE; i++)
+    orig[i] = i % 64 + 32;
+
+  mem = g_memory_input_stream_new_from_data (orig, LEFTOVER_BUFSIZE, NULL);
+  cstream = g_converter_input_stream_new (mem, G_CONVERTER (converter));
+  g_object_unref (mem);
+
+  total_read = 0;
+
+  error = NULL;
+  res = g_input_stream_read (cstream,
+			     converted, LEFTOVER_SHORT_READ_SIZE,
+			     NULL, &error);
+  g_assert_cmpint (res, ==, LEFTOVER_SHORT_READ_SIZE);
+  total_read += res;
+
+  offset = g_seekable_tell (G_SEEKABLE (mem));
+  g_assert_cmpint (offset, >, LEFTOVER_SHORT_READ_SIZE);
+  g_assert_cmpint (offset, <, LEFTOVER_BUFSIZE);
+
+  /* At this point, @cstream has both a non-empty input_buffer
+   * and a non-empty converted_buffer, which is the case
+   * we want to test.
+   */
+
+  while (TRUE)
+    {
+      error = NULL;
+      res = g_input_stream_read (cstream,
+				 converted + total_read,
+				 LEFTOVER_BUFSIZE - total_read,
+				 NULL, &error);
+      g_assert (res >= 0);
+      if (res == 0)
+	break;
+      total_read += res;
+  }
+
+  g_assert_cmpint (total_read, ==, LEFTOVER_BUFSIZE);
+  g_assert (memcmp (converted, orig, LEFTOVER_BUFSIZE)  == 0);
+
+  g_object_unref (cstream);
+  g_free (orig);
+  g_free (converted);
+  g_object_unref (converter);
+}
+
 #define DATA_LENGTH 1000000
 
 static void
@@ -973,6 +1135,7 @@ main (int   argc,
     g_test_add_data_func (charset_tests[i].path, &charset_tests[i], test_charset);
 
   g_test_add_func ("/converter-stream/pollable", test_converter_pollable);
+  g_test_add_func ("/converter-stream/leftover", test_converter_leftover);
 
   return g_test_run();
 }