Re: [PATCH v6 1/4] interpret-trailers: factor out buffer-based processing to process_trailers()

> Li Chen <me@linux.beauty> writes:
> 
>> From: Li Chen <chenl311@chinatelecom.cn>
>>
>> Extracted trailer processing into a helper that accumulates output in
>> a strbuf before writing.
>>
>> Updated interpret_trailers() to reuse the helper, buffer output, and
>> clean up both input and output buffers after writing.
> 
> Imperative?
> 
>>
>> Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
>> ---
>>   builtin/interpret-trailers.c | 51 ++++++++++++++++++++----------------
>>   1 file changed, 29 insertions(+), 22 deletions(-)
>>
>> diff --git a/builtin/interpret-trailers.c b/builtin/interpret-trailers.c
>> index 41b0750e5a..4c90580fff 100644
>> --- a/builtin/interpret-trailers.c
>> +++ b/builtin/interpret-trailers.c
>> @@ -136,32 +136,21 @@ static void read_input_file(struct strbuf *sb, const char *file)
>>   	strbuf_complete_line(sb);
>>   }
>>   
>> -static void interpret_trailers(const struct process_trailer_options *opts,
>> -			       struct list_head *new_trailer_head,
>> -			       const char *file)
>> +static void process_trailers(const struct process_trailer_options *opts,
>> +			     struct list_head *new_trailer_head,
>> +			     struct strbuf *sb, struct strbuf *out)
> 
> So we gained *out strbuf; in the preimage below I see fwrite(),
> fprintf(), etc. to outfile that is either stdout or tempfile, but
> presumably the output all will be captured in the strbuf instead,
> which makes sense.  It is a bit curious what the new paramater sb
> is, but this is a file-scope static helper, so it does not strictly
> require documenting.  Having a comment would still be nicer, though,
> unlike "struct process_trailer_options" that is very limited
> purpose, "strbuf" can be used for any string processing, so a good
> variable name like "out" that conveys what it is used for by
> implication is good, but "sb", which is obvious abbreviation for
> "Str Buf", conveys no useful information.

>>   {
>>   	LIST_HEAD(head);
>> -	struct strbuf sb = STRBUF_INIT;
>> -	struct strbuf trailer_block_sb = STRBUF_INIT;
> 
> We no longer need a separate strbuf only for trailer block; we will
> see why before we read through this helper function, hopefully.
> 
>>   	struct trailer_block *trailer_block;
>> -	FILE *outfile = stdout;
>> -
>> -	trailer_config_init();
>>   
>> -	read_input_file(&sb, file);
>> -
>> -	if (opts->in_place)
>> -		outfile = create_in_place_tempfile(file);
> 
> OK, so the original code read the input (either "file", or standard
> input) into a tempfile and prepared the output file stream.
> Presumably it is now the responsibility of the caller of this new
> function.  Initializing the trailer configuration is also what the
> caller of this function is reponsible for, as well.
> 
> So this answers one of the questions I had upon starting to read
> this function, i.e. "what is sb?"  It holds the input string, which
> is what?  Something that look like a commit message that has title,
> body and then a trailer block?  We may want to give the parameter a
> better name?  I dunno (as this is file-scope static, as long as it
> is obvious to the local caller, it may be OK, but on the other hand,
> the caller needs to differenciate two strbuf parameters to the
> helper function, one used for input and the other output, so if you
> are calling the latter "out", perhaps you would want to call it
> "in", or "input", perhaps?)
> 
>> -	trailer_block = parse_trailers(opts, sb.buf, &head);
>> +	trailer_block = parse_trailers(opts, sb->buf, &head);
> 
> So we parse existing trailers from the input strbuf that is supplied
> by the caller.  The rest of this hunk is rewriting FILE* I/O with
> strbuf addition.
> 
>> @@ -173,22 +162,40 @@ static void interpret_trailers(const struct process_trailer_options *opts,
>>   	}
>>   
>>   	/* Print trailer block. */
>> -	format_trailers(opts, &head, &trailer_block_sb);
>> +	format_trailers(opts, &head, out);
>>   	free_trailers(&head);
>> -	fwrite(trailer_block_sb.buf, 1, trailer_block_sb.len, outfile);
>> -	strbuf_release(&trailer_block_sb);
> 
> The format_trailers() helper function appends appends to the strbuf
> that is given to it, so instead of using an extra strbuf (and then
> appending that to the output), we just pass our output strbuf to it,
> which is why we no longer need the trailer_block_sb strbuf anymore.
> Makes sense.
> 
>>   	/* Print the lines after the trailer block as is. */
>>   	if (!opts->only_trailers)
>> -		fwrite(sb.buf + trailer_block_end(trailer_block), 1,
>> -		       sb.len - trailer_block_end(trailer_block), outfile);
>> +		strbuf_add(out, sb->buf + trailer_block_end(trailer_block),
>> +			   sb->len - trailer_block_end(trailer_block));
>>   	trailer_block_release(trailer_block);
>> +}
> 
> And again, FILE* I/O is replaced with appending to the output strbuf
> in the rest of this helper function.  Good.
> 
>> +static void interpret_trailers(const struct process_trailer_options *opts,
>> +			       struct list_head *new_trailer_head,
>> +			       const char *file)
> 
> So the original caller of interpret_trailers() now call this outer
> shell, which has the same name and the same function signature as
> the original.  Our new process_trailers() helper assumes a handful
> of preparatory steps are already done by the caller, so what we are
> going read here will be mostly those preparation, a call to our new
> helper, and then printing the result to "file" or standard output.
> 
>> +{
>> +	struct strbuf sb = STRBUF_INIT;
>> +	struct strbuf out = STRBUF_INIT;
>> +	FILE *outfile = stdout;
>> +
>> +	trailer_config_init();
>> +
>> +	read_input_file(&sb, file);
>> +	if (opts->in_place)
>> +		outfile = create_in_place_tempfile(file);
> 
> And these are exactly the lines we lost from the new helper.
> Looking good.
> 
>> +	process_trailers(opts, new_trailer_head, &sb, &out);
> 
> And our call.  "out" should have what we wanted to output to
> outfile, so ...
> 
>> +	fwrite(out.buf, out.len, 1, outfile);
> 
> ... we write it out.  Good.  For a single long string that can never
> have NUL in it, I'd personally find it more natural to call fputs(),
> though.  Use of fwrite() makes readers unnecessarily wonder if there
> is something unusual (like needing to be able to handle NULs in the
> buffer).
> 
>>   	if (opts->in_place)
>>   		if (rename_tempfile(&trailers_tempfile, file))
>>   			die_errno(_("could not rename temporary file to %s"), file);
>>
>>   	strbuf_release(&sb);
>> +	strbuf_release(&out);
> 
> OK.  We could release out a bit earlier, immediately after fwrite().
> 
> Looking mostly good.
> 
>>   }
>>   
>>   int cmd_interpret_trailers(int argc,
>