Separate field iterator logic from pb_decode to pb_common.

pb_common.h

@@ -0,0 +1,40 @@
+/* pb_common.h: Common support functions for pb_encode.c and pb_decode.c.
+ * These functions are rarely needed by applications directly.
+ */
+
+#ifndef _PB_COMMON_H_
+#define _PB_COMMON_H_
+
+#include "pb.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Iterator for pb_field_t list */
+typedef struct {
+    const pb_field_t *start;       /* Start of the pb_field_t array */
+    const pb_field_t *pos;         /* Current position of the iterator */
+    unsigned required_field_index; /* Zero-based index that counts only the required fields */
+    void *dest_struct;             /* Pointer to the destination structure to decode to */
+    void *pData;                   /* Pointer where to store current field value */
+    void *pSize;                   /* Pointer where to store the size of current array field */
+} pb_field_iter_t;
+
+/* Initialize the field iterator structure to beginning. */
+void pb_field_iter_begin(pb_field_iter_t *iter, const pb_field_t *fields, void *dest_struct);
+
+/* Advance the iterator to the next field.
+ * Returns false when the iterator wraps back to the first field. */
+bool pb_field_iter_next(pb_field_iter_t *iter);
+
+/* Advance the iterator until it points at a field with the given tag.
+ * Returns false if no such field exists. */
+bool pb_field_iter_find(pb_field_iter_t *iter, uint32_t tag);
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif
+