Re: [PATCH v2 09/14] range-diff: split lines manually

[Thomas Gummerer <t.gummerer@gmail.com>]

On 07/05, Johannes Schindelin wrote:
> Hi Thomas,
> 
> 
> On Fri, 5 Jul 2019, Thomas Gummerer wrote:
> 
> > Currently range-diff uses the 'strbuf_getline()' function for doing
> > its line by line processing.  In a future patch we want to do parts of
> > that parsing using the 'parse_git_header()' function, which does
> 
> If you like my suggestion in patch 7/14, this commit message needs to talk
> about the new name, too.

Thanks for the reminder here!  I do indeed like the new name, but
would probably have forgotten to change it in the commit message here.

> > requires reading parts of the input from that function, which doesn't
> 
> s/requires/require/
> 
> > use strbufs.
> >
> > Switch range-diff to do our own line by line parsing, so we can re-use
> > the parse_git_header function later.
> >
> > Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
> > ---
> >
> > Longer term it might be better to have both range-diff and apply code
> > use strbufs.  However I didn't feel it's worth making that change for
> > this patch series.
> 
> Makes sense.
> 
> >  range-diff.c | 69 +++++++++++++++++++++++++++++-----------------------
> >  1 file changed, 39 insertions(+), 30 deletions(-)
> >
> > diff --git a/range-diff.c b/range-diff.c
> > index 9242b8975f..916afa44c0 100644
> > --- a/range-diff.c
> > +++ b/range-diff.c
> > @@ -24,6 +24,17 @@ struct patch_util {
> >  	struct object_id oid;
> >  };
> >
> > +static unsigned long linelen(const char *buffer, unsigned long size)
> 
> Shouldn't this be `size_t`?
> 
> > +{
> > +	unsigned long len = 0;
> 
> Likewise.
> 
> > +	while (size--) {
> > +		len++;
> > +		if (*buffer++ == '\n')
> > +			break;
> > +	}
> > +	return len;
> 
> How about
> 
> 	const char *eol = memchr(buffer, '\n', size);
> 
> 	return !eol ? size : eol + 1 - buffer;
> 
> instead?
> 
> For an extra brownie point, you could even rename this function to
> `find_end_of_line()` and replace the LF by a NUL:
> 
> 	if (!eol)
> 		return size;
> 
> 	*eol = '\0';
> 	return eol + 1 - buffer;

I like this, thank you!

> > +}
> > +
> >  /*
> >   * Reads the patches into a string list, with the `util` field being populated
> >   * as struct object_id (will need to be free()d).
> > @@ -31,10 +42,12 @@ struct patch_util {
> >  static int read_patches(const char *range, struct string_list *list)
> >  {
> >  	struct child_process cp = CHILD_PROCESS_INIT;
> > -	FILE *in;
> > -	struct strbuf buf = STRBUF_INIT, line = STRBUF_INIT;
> > +	struct strbuf buf = STRBUF_INIT, file = STRBUF_INIT;
> 
> This puzzled me. I'd like to suggest s/file/contents/

Thanks, will change.

> >  	struct patch_util *util = NULL;
> >  	int in_header = 1;
> > +	char *line;
> > +	int offset, len;
> > +	size_t size;
> >
> >  	argv_array_pushl(&cp.args, "log", "--no-color", "-p", "--no-merges",
> >  			"--reverse", "--date-order", "--decorate=no",
> > @@ -54,17 +67,15 @@ static int read_patches(const char *range, struct string_list *list)
> >
> >  	if (start_command(&cp))
> >  		return error_errno(_("could not start `log`"));
> > -	in = fdopen(cp.out, "r");
> > -	if (!in) {
> > -		error_errno(_("could not read `log` output"));
> > -		finish_command(&cp);
> > -		return -1;
> > -	}
> > +	strbuf_read(&file, cp.out, 0);
> 
> Shouldn't we handle a negative return value here, erroring out with "could
> not read `log` output" as before?

Yeah, that was an oversight, we should definitely still handle errors
here.

> >
> > -	while (strbuf_getline(&line, in) != EOF) {
> > +	line = strbuf_detach(&file, &size);
> 
> I strongly suspect this to leak, given that `line` is subsequently
> advanced, and there is no backup copy.
> 
> Maybe
> 
> 	line = file.buf;
> 	size = file.len;
> 
> would make more sense here?

Hmm good point, that makes more sense indeed.

> > +	for (offset = 0; size > 0; offset += len, size -= len, line += len) {
> >  		const char *p;
> >
> > -		if (skip_prefix(line.buf, "commit ", &p)) {
> > +		len = linelen(line, size);
> > +		line[len - 1] = '\0';
> > +		if (skip_prefix(line, "commit ", &p)) {
> >  			if (util) {
> >  				string_list_append(list, buf.buf)->util = util;
> >  				strbuf_reset(&buf);
> > @@ -75,8 +86,6 @@ static int read_patches(const char *range, struct string_list *list)
> >  				free(util);
> >  				string_list_clear(list, 1);
> >  				strbuf_release(&buf);
> > -				strbuf_release(&line);
> > -				fclose(in);
> 
> We should release the file contents in `file` (or `contents`, if you like
> my suggestions) here.

Yeah, I thought it was no longer necessary because of the
'strbuf_detach()' earlier, but that obviously leaks in a different way
as you pointed out.  Will release 'contents' here and below. 

> >  				finish_command(&cp);
> >  				return -1;
> >  			}
> > @@ -85,26 +94,28 @@ static int read_patches(const char *range, struct string_list *list)
> >  			continue;
> >  		}
> >
> > -		if (starts_with(line.buf, "diff --git")) {
> > +		if (starts_with(line, "diff --git")) {
> >  			in_header = 0;
> >  			strbuf_addch(&buf, '\n');
> >  			if (!util->diff_offset)
> >  				util->diff_offset = buf.len;
> >  			strbuf_addch(&buf, ' ');
> > -			strbuf_addbuf(&buf, &line);
> > +			strbuf_addstr(&buf, line);
> >  		} else if (in_header) {
> > -			if (starts_with(line.buf, "Author: ")) {
> > -				strbuf_addbuf(&buf, &line);
> > +			if (starts_with(line, "Author: ")) {
> > +				strbuf_addstr(&buf, line);
> >  				strbuf_addstr(&buf, "\n\n");
> > -			} else if (starts_with(line.buf, "    ")) {
> > -				strbuf_rtrim(&line);
> > -				strbuf_addbuf(&buf, &line);
> > +			} else if (starts_with(line, "    ")) {
> > +				p = line + len - 2;
> > +				while (isspace(*p) && p >= line)
> > +					p--;
> > +				strbuf_add(&buf, line, p - line + 1);
> >  				strbuf_addch(&buf, '\n');
> >  			}
> >  			continue;
> > -		} else if (starts_with(line.buf, "@@ "))
> > +		} else if (starts_with(line, "@@ "))
> >  			strbuf_addstr(&buf, "@@");
> > -		else if (!line.buf[0] || starts_with(line.buf, "index "))
> > +		else if (!line[0] || starts_with(line, "index "))
> >  			/*
> >  			 * A completely blank (not ' \n', which is context)
> >  			 * line is not valid in a diff.  We skip it
> > @@ -117,25 +128,23 @@ static int read_patches(const char *range, struct string_list *list)
> >  			 * we are not interested.
> >  			 */
> >  			continue;
> > -		else if (line.buf[0] == '>') {
> > +		else if (line[0] == '>') {
> >  			strbuf_addch(&buf, '+');
> > -			strbuf_add(&buf, line.buf + 1, line.len - 1);
> > -		} else if (line.buf[0] == '<') {
> > +			strbuf_addstr(&buf, line + 1);
> > +		} else if (line[0] == '<') {
> >  			strbuf_addch(&buf, '-');
> > -			strbuf_add(&buf, line.buf + 1, line.len - 1);
> > -		} else if (line.buf[0] == '#') {
> > +			strbuf_addstr(&buf, line + 1);
> > +		} else if (line[0] == '#') {
> >  			strbuf_addch(&buf, ' ');
> > -			strbuf_add(&buf, line.buf + 1, line.len - 1);
> > +			strbuf_addstr(&buf, line + 1);
> >  		} else {
> >  			strbuf_addch(&buf, ' ');
> > -			strbuf_addbuf(&buf, &line);
> > +			strbuf_addstr(&buf, line);
> >  		}
> >
> >  		strbuf_addch(&buf, '\n');
> >  		util->diffsize++;
> >  	}
> > -	fclose(in);
> > -	strbuf_release(&line);
> 
> We should release the file contents we previously read via `strbuf_read()` here.
> 
> Ciao,
> Dscho
> 
> >
> >  	if (util)
> >  		string_list_append(list, buf.buf)->util = util;
> > --
> > 2.22.0.510.g264f2c817a
> >
> >