Re: [PATCH v2 1/4] fetch: extract writing to FETCH_HEAD

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 8, 2021, 23:40 UTC
Message-ID: <xmqqmtxjgfq6.fsf@gitster.c.googlers.com>
In-Reply-To: <d80dbc5a9c9520621651541e418ee5216d164053.1610107599.git.ps@pks.im>

Patrick Steinhardt <ps@pks.im> writes:

Show 13 quoted lines

> +static int open_fetch_head(struct fetch_head *fetch_head)
> +{
> +	const char *filename = git_path_fetch_head(the_repository);
> +
> +	if (!write_fetch_head)
> +		return 0;
> +
> +	fetch_head->fp = fopen(filename, "a");
> +	if (!fetch_head->fp)
> +		return error_errno(_("cannot open %s"), filename);
> +
> +	return 0;
> +}

So the difference from the original, which used to have a writable filehandle to /dev/null in the dry-run mode, is that fetch_head->fp is left as-is (not even NULLed out).

> +static void append_fetch_head(struct fetch_head *fetch_head, const char *old_oid,

It is clear from the type these days but variable names like "old_oid" hint the readers that they are not a hexadecimal object name string but either an array of uchar[40] or a struct object_id; perhaps "old_oid_hex" would be less misleading.

If the caller does have struct object_id, then it would be even better to take it as-is as a parameter and use oid_to_hex_r() on it in this function when it is given to fprintf(). [Nit #1]

Show 7 quoted lines

> +			      const char *merge_status_marker, const char *note,
> +			      const char *url, size_t url_len)
> +{
> +	size_t i;
> +
> +	if (!write_fetch_head)
> +		return;

Presumably, this check is what makes sure that fetch_head->fp that is left uninitialized will never gets used.

Show 9 quoted lines

> +	fprintf(fetch_head->fp, "%s\t%s\t%s",
> +		old_oid, merge_status_marker, note);
> +	for (i = 0; i < url_len; ++i)
> +		if ('\n' == url[i])
> +			fputs("\\n", fetch_head->fp);
> +		else
> +			fputc(url[i], fetch_head->fp);
> +	fputc('\n', fetch_head->fp);
> +}

OK. This is the "case FETCH_HEAD_NOT_FOR_MERGE" and "case FETCH_HEAD_MERGE" parts in the original.

As an abstraction, it may be better to make the caller pass a boolean "is this for merge?" and keep the knowledge of what exact string is used for merge_status_marker to this function, instead of letting the caller passing it as a parameter in the string form. After all, we never allow anything other than an empty string or a fixed "not-for-merge" string in that place in the file format. [Nit #2]

Show 9 quoted lines

> +static void commit_fetch_head(struct fetch_head *fetch_head)
> +{
> +	/* Nothing to commit yet. */
> +}
> +
> +static void close_fetch_head(struct fetch_head *fetch_head)
> +{
> +	if (!write_fetch_head)
> +		return;

So is this check a protection against uninitialized fetch_head->fp. Both changes make sense.

> +	fclose(fetch_head->fp);
> +}

Show 6 quoted lines

> @@ -909,22 +959,19 @@ N_("It took %.2f seconds to check forced updates. You can use\n"
>  static int store_updated_refs(const char *raw_url, const char *remote_name,
>  			      int connectivity_checked, struct ref *ref_map)
>  {
> -	FILE *fp;
> +	struct fetch_head fetch_head;

And that is why this variable is left uninitialised on stack and it is OK. An alternative design would be to initialize fetch_head.fp to NULL, and return early with "if (!fetch_head->fp)" in the two functions that take fetch_head struct. That way, we have less reliance on the global variable write_fetch_head.

Show 18 quoted lines

>  	struct commit *commit;
>  	int url_len, i, rc = 0;
>  	struct strbuf note = STRBUF_INIT;
>  	const char *what, *kind;
>  	struct ref *rm;
>  	char *url;
> -	const char *filename = (!write_fetch_head
> -				? "/dev/null"
> -				: git_path_fetch_head(the_repository));
>  	int want_status;
>  	int summary_width = transport_summary_width(ref_map);
>  
> -	fp = fopen(filename, "a");
> -	if (!fp)
> -		return error_errno(_("cannot open %s"), filename);
> +	rc = open_fetch_head(&fetch_head);
> +	if (rc)
> +		return -1;

OK, we've already said "cannot open" in the open_fetch_head() function, so we just return an error silently.

Show 18 quoted lines

> @@ -1016,16 +1063,10 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
>  				merge_status_marker = "not-for-merge";
>  				/* fall-through */
>  			case FETCH_HEAD_MERGE:
> -				fprintf(fp, "%s\t%s\t%s",
> -					oid_to_hex(&rm->old_oid),
> -					merge_status_marker,
> -					note.buf);
> -				for (i = 0; i < url_len; ++i)
> -					if ('\n' == url[i])
> -						fputs("\\n", fp);
> -					else
> -						fputc(url[i], fp);
> -				fputc('\n', fp);
> +				append_fetch_head(&fetch_head,
> +						  oid_to_hex(&rm->old_oid),
> +						  merge_status_marker,
> +						  note.buf, url, url_len);

Here, we can lose merge_status_marker variable from this caller, and then this caller becomes:

		switch (rm->fetch_head_status) {
		case FETCH_HEAD_NOT_FOR_MERGE:
		case FETCH_HEAD_MERGE:
			append_fetch_head(&fetch_head, &rm->old_oid,
				rm->fetch_head_status == FETCH_HEAD_MERGE,
                                note.buf, url, url_len);

Note that I am passing "is this a ref to be merged?" boolean to keep the exact string of "not-for-merge" in the callee.

Show 18 quoted lines

> @@ -1060,6 +1101,9 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
>  		}
>  	}
>  
> +	if (!rc)
> +		commit_fetch_head(&fetch_head);
> +
>  	if (rc & STORE_REF_ERROR_DF_CONFLICT)
>  		error(_("some local refs could not be updated; try running\n"
>  		      " 'git remote prune %s' to remove any old, conflicting "
> @@ -1077,7 +1121,7 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
>   abort:
>  	strbuf_release(&note);
>  	free(url);
> -	fclose(fp);
> +	close_fetch_head(&fetch_head);
>  	return rc;
>  }

Other than the above two nits, this step looks good to me.

Thanks.