Re: [PATCH v3 2/5] fetch: use strbuf to format FETCH_HEAD updates

> This commit refactors `append_fetch_head()` to use a `struct strbuf` for
> formatting the update which we're about to append to the FETCH_HEAD
> file. While the refactoring doesn't have much of a benefit right now, it
> servers as a preparatory step to implement atomic fetches where we need
> to buffer all updates to FETCH_HEAD and only flush them out if all
> reference updates succeeded.
> 
> No change in behaviour is expected from this commit.

> ---
>  builtin/fetch.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/builtin/fetch.c b/builtin/fetch.c
> index 50f0306a92..1252f37493 100644
> --- a/builtin/fetch.c
> +++ b/builtin/fetch.c
> @@ -899,6 +899,7 @@ static int iterate_ref_map(void *cb_data, struct object_id *oid)
>  
>  struct fetch_head {
>  	FILE *fp;
> +	struct strbuf buf;
>  };
>  
>  static int open_fetch_head(struct fetch_head *fetch_head)
> @@ -909,6 +910,7 @@ static int open_fetch_head(struct fetch_head *fetch_head)
>  		fetch_head->fp = fopen(filename, "a");
>  		if (!fetch_head->fp)
>  			return error_errno(_("cannot open %s"), filename);
> +		strbuf_init(&fetch_head->buf, 0);
>  	} else {
>  		fetch_head->fp = NULL;
>  	}
> @@ -941,14 +943,17 @@ static void append_fetch_head(struct fetch_head *fetch_head,
>  			return;
>  	}
>  
> -	fprintf(fetch_head->fp, "%s\t%s\t%s",
> -		oid_to_hex_r(old_oid_hex, old_oid), merge_status_marker, note);
> +	strbuf_addf(&fetch_head->buf, "%s\t%s\t%s",
> +		    oid_to_hex_r(old_oid_hex, old_oid), merge_status_marker, note);
>  	for (i = 0; i < url_len; ++i)
>  		if ('\n' == url[i])
> -			fputs("\\n", fetch_head->fp);
> +			strbuf_addstr(&fetch_head->buf, "\\n");
>  		else
> -			fputc(url[i], fetch_head->fp);
> -	fputc('\n', fetch_head->fp);
> +			strbuf_addch(&fetch_head->buf, url[i]);
> +	strbuf_addch(&fetch_head->buf, '\n');
> +
> +	strbuf_write(&fetch_head->buf, fetch_head->fp);
> +	strbuf_reset(&fetch_head->buf);
>  }
>  
>  static void commit_fetch_head(struct fetch_head *fetch_head)
> @@ -962,6 +967,7 @@ static void close_fetch_head(struct fetch_head *fetch_head)
>  		return;
>  
>  	fclose(fetch_head->fp);
> +	strbuf_release(&fetch_head->buf);
>  }
>  
>  static const char warn_show_forced_updates[] =
> -- 
> 2.30.0
>