[PATCH 4/4] strbuf_attach: prefer `strbuf_attachstr_len()`

["Martin Ågren" <martin.agren@gmail.com>]

After the last few commits, we don't have many users of
`strbuf_attach()`.

Convert the sites in builtin/am.c, strbuf.c and mailinfo.c. They pass in
the same length twice for `len` and `mem` and will eventually hit
`realloc(3)`, which will be a no-op. The string in am.c has been
constructed using the strbuf machinery in `read_commit_msg()`. In
strbuf.c, we've used `reencode_string_iconv()`.  In mailinfo.c, we used
`reencode_string_len()`. So in all cases, we really do have an extra
byte at the end with a NUL.

As explained in the previous commit, it's not just that we avoid calling
`realloc()` to make room for a single NUL byte that we already have, we
avoid asking it for 16 more bytes and another 50% on top of that.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
---
 builtin/am.c  | 2 +-
 fast-import.c | 2 +-
 mailinfo.c    | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/builtin/am.c b/builtin/am.c
index e3dfd93c25..d777855c98 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -1101,7 +1101,7 @@ static void am_append_signoff(struct am_state *state)
 {
 	struct strbuf sb = STRBUF_INIT;
 
-	strbuf_attach(&sb, state->msg, state->msg_len, state->msg_len);
+	strbuf_attachstr_len(&sb, state->msg, state->msg_len);
 	append_signoff(&sb, 0, 0);
 	state->msg = strbuf_detach(&sb, &state->msg_len);
 }
diff --git a/fast-import.c b/fast-import.c
index 202dda11a6..28fbc4792b 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -2946,7 +2946,7 @@ static void cat_blob(struct object_entry *oe, struct object_id *oid)
 	cat_blob_write("\n", 1);
 	if (oe && oe->pack_id == pack_id) {
 		last_blob.offset = oe->idx.offset;
-		strbuf_attach(&last_blob.data, buf, size, size);
+		strbuf_attachstr_len(&last_blob.data, buf, size);
 		last_blob.depth = oe->depth;
 	} else
 		free(buf);
diff --git a/mailinfo.c b/mailinfo.c
index c31991e621..942c363bfd 100644
--- a/mailinfo.c
+++ b/mailinfo.c
@@ -461,7 +461,7 @@ static int convert_to_utf8(struct mailinfo *mi,
 		return error("cannot convert from %s to %s",
 			     charset, mi->metainfo_charset);
 	}
-	strbuf_attach(line, out, out_len, out_len);
+	strbuf_attachstr_len(line, out, out_len);
 	return 0;
 }
 
-- 
2.26.1