+/* Structure for defining custom input streams. You will need to provide
+ * a callback function to read the bytes from your storage, which can be
+ * for example a file or a network socket.
+ *
+ * The callback must conform to these rules:
+ *
+ * 1) Return false on IO errors. This will cause decoding to abort.
+ * 2) You can use state to store your own data (e.g. buffer pointer),
+ * and rely on pb_read to verify that no-body reads past bytes_left.
+ * 3) Your callback may be used with substreams, in which case bytes_left
+ * is different than from the main stream. Don't use bytes_left to compute
+ * any pointers.
+ */
+struct _pb_istream_t
+{
+#ifdef PB_BUFFER_ONLY
+ /* Callback pointer is not used in buffer-only configuration.
+ * Having an int pointer here allows binary compatibility but
+ * gives an error if someone tries to assign callback function.
+ */
+ int *callback;
+#else
+ bool (*callback)(pb_istream_t *stream, uint8_t *buf, size_t count);
+#endif
+
+ void *state; /* Free field for use by callback implementation */
+ size_t bytes_left;
+
+#ifndef PB_NO_ERRMSG
+ const char *errmsg;
+#endif
+};
+