Re: [PATCH 3/8] http-fetch: support fetching packfiles by URL

[Jonathan Tan <jonathantanmy@google.com>]

> > -	if (argc != arg + 2 - commits_on_stdin)
> > +	if (argc != arg + 2 - (commits_on_stdin || packfile))
> >  		usage(http_fetch_usage);
> >  	if (commits_on_stdin) {
> >  		commits = walker_targets_stdin(&commit_id, &write_ref);
> > +	} else if (packfile) {
> > +		/* URL will be set later */
> 
> Prefer to see an empty statement spelled more explicitly, like this:
> 
> 		; /* URL will be set later */
> 
> Otherwise reader would be left wondering if a line was (or lines
> were) accidentally lost after this comment.

OK.

> The above probably want to be a single helper function.
> 
> The other side of if/else may also become another helper function.
> 
> That way, the flow of control would become clearer.  After all,
> these two branches do not share all that much.  Only http-init and
> http-cleanup and nothing else.
> 
> For that matter, even before introducing this new mode of operation,
> another patch to make a preparatory move of the original logic in
> this function to a helper function that would be called from the
> "else" side may make it easier to see what is going on.

OK.

> > diff --git a/http.c b/http.c
> > index 130e9d6259..ac66215ee6 100644
> > --- a/http.c
> > +++ b/http.c
> > @@ -2280,15 +2280,18 @@ int finish_http_pack_request(struct http_pack_request *preq)
> >  	int tmpfile_fd;
> >  	int ret = 0;
> >  
> > -	close_pack_index(p);
> > +	if (p)
> > +		close_pack_index(p);
> >  
> >  	fclose(preq->packfile);
> >  	preq->packfile = NULL;
> >  
> > -	lst = preq->lst;
> > -	while (*lst != p)
> > -		lst = &((*lst)->next);
> > -	*lst = (*lst)->next;
> > +	if (p) {
> > +		lst = preq->lst;
> > +		while (*lst != p)
> > +			lst = &((*lst)->next);
> > +		*lst = (*lst)->next;
> > +	}
> 
> This is quite ugly.  What is the original meaning of the target
> field of the pack_request structure again?  A packed_git structure
> that will be filled when we are done fetching the packfile from the
> other side and installed in our repository?  When we are (ab)using
> http_fetch code to fetch a single packfile, we do not install the
> packfile into the running process, because we are only (re)using the
> existing machinery as a poor-man's "curl | git index-pack --stdin"?
> 
> I do not think it is a bad idea to roll "curl | git index-pack
> --stdin" our own, but I do find this an ugly way to do so.  Perhaps
> a set of lower-level helper functions can be isolated out of the
> existing code before this new feature is added, and then a new "just
> fetch and pipe it to the index-pack" feature should be written using
> these helpers but with a separate set of entry points?  Would it be
> a good way to make the resulting code cleaner than this patch does?
> I dunno.

OK - I'll extract the functions as you suggested earlier in the email,
and then it might be more obvious if it can be done more cleanly.

> > diff --git a/http.h b/http.h
> > index a5b082f3ae..709dfa4c19 100644
> > --- a/http.h
> > +++ b/http.h
> > @@ -223,12 +223,21 @@ struct http_pack_request {
> >  	struct active_request_slot *slot;
> >  
> >  	/*
> > -	 * After calling new_http_pack_request(), point lst to the head of the
> > +	 * After calling new_http_pack_request(), if fetching a pack that
> > +	 * http_get_info_packs() told us about, point lst to the head of the
> >  	 * pack list that target is in. finish_http_pack_request() will remove
> >  	 * target from lst and call install_packed_git() on target.
> >  	 */
> >  	struct packed_git **lst;
> >  
> > +	/*
> > +	 * If this is true, finish_http_pack_request() will pass "--keep" to
> > +	 * index-pack, resulting in the creation of a keep file, and will not
> > +	 * suppress its stdout (that is, the "keep\t<hash>\n" line will be
> > +	 * printed to stdout).
> > +	 */
> > +	unsigned generate_keep : 1;
> > +
> 
> I suspect that this is a sign that this single patch is trying to
> do too many things at the same time.
> 
>  - Whether we are fetching a single packfile from a URL, or walking
>    to fetch all the packfiles in the repository at a given URL
> 
>  - Whether packfiles taken from outer space are marked with the
>    "keep" bit
> 
>  - Whether the obtained packfile(s) are internally "installed"
>    to the running process
> 
> are conceptually independent choices, but somehow mixed up, it
> seems.

You might be right...I needed another mode that does the opposite
choices in these 3 points and these points because options that could be
toggled independently. I'll see if there is a better way to do this.