Re: [PATCH] pretty: add extra headers and MIME boundary directly

> The most correct way is that the caller of log_write_email_headers() and
> diff_flush() should have a function-local strbuf which holds the data,
> gets passed to diff_flush() as some kind opaque context, and then is
> freed afterwards. We don't have such a context, but if we were to abuse
> diff_options.stat_sep _temporarily_, that would still be a lot cleaner.
> I.e., something like this:
> 
>   struct strbuf stat_sep = STRBUF_INIT;
> 
>   /* may write into stat_sep, depending on options */
>   log_write_email_headers(..., &stat_sep);
>   opt->diffopt.stat_sep = stat_sep.buf;
> 
>   diff_flush(&opt->diffopt);
>   opt->diffopt.stat_sep = NULL;
>   strbuf_release(&stat_sep);
> 
> But it's a bit tricky because those two hunks happen in separate
> functions, which means passing the strbuf around.

> Anyway. Here's my attempt at the callback version of stat_sep.
> 
> ---
> diff --git a/diff.c b/diff.c
> index a628ac3a9..d061f9e18 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -4819,10 +4819,9 @@ void diff_flush(struct diff_options *options)
>  			fprintf(options->file, "%s%c",
>  				diff_line_prefix(options),
>  				options->line_termination);
> -			if (options->stat_sep) {
> -				/* attach patch instead of inline */
> -				fputs(options->stat_sep, options->file);
> -			}
> +			if (options->stat_sep)
> +				options->stat_sep(options->file,
> +						  options->stat_sep_data);
>  		}
>  
>  		for (i = 0; i < q->nr; i++) {
> diff --git a/diff.h b/diff.h
> index e9ccb38c2..4785f3b23 100644
> --- a/diff.h
> +++ b/diff.h
> @@ -154,9 +154,11 @@ struct diff_options {
>  	unsigned ws_error_highlight;
>  	const char *prefix;
>  	int prefix_length;
> -	const char *stat_sep;
>  	long xdl_opts;
>  
> +	void (*stat_sep)(FILE *, void *);
> +	void *stat_sep_data;
> +
>  	int stat_width;
>  	int stat_name_width;
>  	int stat_graph_width;
> diff --git a/log-tree.c b/log-tree.c
> index 7049a1778..5cf825c41 100644
> --- a/log-tree.c
> +++ b/log-tree.c
> @@ -348,6 +348,31 @@ void fmt_output_email_subject(struct strbuf *sb, struct rev_info *opt)
>  	}
>  }
>  
> +static void show_mime_attachment(FILE *out, void *data)
> +{
> +	struct rev_info *opt = data;
> +	struct strbuf filename = STRBUF_INIT;
> +
> +	if (opt->numbered_files)
> +		strbuf_addf(&filename, "%d", opt->nr);
> +	else
> +		fmt_output_commit(&filename, opt->commit_for_mime, opt);
> +
> +	fprintf(out,
> +		"\n--%s%s\n"
> +		"Content-Type: text/x-patch;"
> +		" name=\"%s\"\n"
> +		"Content-Transfer-Encoding: 8bit\n"
> +		"Content-Disposition: %s;"
> +		" filename=\"%s\"\n\n",
> +		mime_boundary_leader, opt->mime_boundary,
> +		filename.buf,
> +		opt->no_inline ? "attachment" : "inline",
> +		filename.buf);
> +
> +	strbuf_release(&filename);
> +}
> +
>  void log_write_email_headers(struct rev_info *opt, struct commit *commit,
>  			     int *need_8bit_cte_p)
>  {
> @@ -372,27 +397,10 @@ void log_write_email_headers(struct rev_info *opt, struct commit *commit,
>  		graph_show_oneline(opt->graph);
>  	}
>  	if (opt->mime_boundary) {
> -		static char buffer[1024];
> -		struct strbuf filename =  STRBUF_INIT;
>  		*need_8bit_cte_p = -1; /* NEVER */
> -
> -		if (opt->numbered_files)
> -			strbuf_addf(&filename, "%d", opt->nr);
> -		else
> -			fmt_output_commit(&filename, commit, opt);
> -		snprintf(buffer, sizeof(buffer) - 1,
> -			 "\n--%s%s\n"
> -			 "Content-Type: text/x-patch;"
> -			 " name=\"%s\"\n"
> -			 "Content-Transfer-Encoding: 8bit\n"
> -			 "Content-Disposition: %s;"
> -			 " filename=\"%s\"\n\n",
> -			 mime_boundary_leader, opt->mime_boundary,
> -			 filename.buf,
> -			 opt->no_inline ? "attachment" : "inline",
> -			 filename.buf);
> -		opt->diffopt.stat_sep = buffer;
> -		strbuf_release(&filename);
> +		opt->diffopt.stat_sep = show_mime_attachment;
> +		opt->diffopt.stat_sep_data = opt;
> +		opt->commit_for_mime = commit;
>  	}
>  }
>  
> diff --git a/revision.h b/revision.h
> index 14886ec92..46ca45d96 100644
> --- a/revision.h
> +++ b/revision.h
> @@ -156,6 +156,7 @@ struct rev_info {
>  	struct log_info *loginfo;
>  	int		nr, total;
>  	const char	*mime_boundary;
> +	struct commit *commit_for_mime;
>  	const char	*patch_suffix;
>  	int		numbered_files;
>  	int		reroll_count;