t0021/rot13-filter: add packet_initialize()

diff --git a/strbuf.h b/strbuf.h
index 2075384e0b2df97a6d113acebcbcdcc853237166..0a74acb2369ac26cb56b05a953171330c3abe652 100644 (file)
--- a/strbuf.h
+++ b/strbuf.h
@@ -68,7 +68,7 @@ struct strbuf {
 };
 
 extern char strbuf_slopbuf[];
-#define STRBUF_INIT  { 0, 0, strbuf_slopbuf }
+#define STRBUF_INIT  { .alloc = 0, .len = 0, .buf = strbuf_slopbuf }
 
 /**
  * Life Cycle Functions
@@ -82,8 +82,12 @@ extern char strbuf_slopbuf[];
 extern void strbuf_init(struct strbuf *, size_t);
 
 /**
- * Release a string buffer and the memory it used. You should not use the
- * string buffer after using this function, unless you initialize it again.
+ * Release a string buffer and the memory it used. After this call, the
+ * strbuf points to an empty string that does not need to be free()ed, as
+ * if it had been set to `STRBUF_INIT` and never modified.
+ *
+ * To clear a strbuf in preparation for further use without the overhead
+ * of free()ing and malloc()ing again, use strbuf_reset() instead.
  */
 extern void strbuf_release(struct strbuf *);
 
@@ -91,6 +95,9 @@ extern void strbuf_release(struct strbuf *);
  * Detach the string from the strbuf and returns it; you now own the
  * storage the string occupies and it is your responsibility from then on
  * to release it with `free(3)` when you are done with it.
+ *
+ * The strbuf that previously held the string is reset to `STRBUF_INIT` so
+ * it can be reused after calling this function.
  */
 extern char *strbuf_detach(struct strbuf *, size_t *);
 
@@ -147,7 +154,10 @@ static inline void strbuf_setlen(struct strbuf *sb, size_t len)
        if (len > (sb->alloc ? sb->alloc - 1 : 0))
                die("BUG: strbuf_setlen() beyond buffer");
        sb->len = len;
-       sb->buf[len] = '\0';
+       if (sb->buf != strbuf_slopbuf)
+               sb->buf[len] = '\0';
+       else
+               assert(!strbuf_slopbuf[0]);
 }
 
 /**