add common lib
diff --git a/libasn1common/asn1_buffer.h b/libasn1common/asn1_buffer.h
new file mode 100644
index 0000000..464fc74
--- /dev/null
+++ b/libasn1common/asn1_buffer.h
@@ -0,0 +1,32 @@
+#ifndef ASN1_BUFFER_H
+#define ASN1_BUFFER_H
+
+/*
+ * Your typical dynamic character string buffer.
+ */
+typedef struct {
+ const char *buffer;
+ size_t length;
+ size_t size;
+} abuf;
+
+/*
+ * Create and destroy the buffer.
+ */
+abuf *abuf_new(void);
+void abuf_free(abuf *);
+
+/*
+ * Erase contents of the buffer (without destroying it).
+ */
+void abuf_clear(abuf *);
+
+/*
+ * Add characters to the buffer.
+ */
+void abuf_str(abuf *, const char *str);
+void abuf_buf(abuf *, const abuf *);
+void abuf_printf(abuf *, const char *fmt, ...)
+ __attribute__((format(printf, 2, 3)));
+
+#endif /* ASN1_BUFFER_H */