Re: [PATCH v2 5/9] gpg-interface: introduce an abstraction for multiple gpg formats
On Tue, Jul 10, 2018 at 10:52:27AM +0200, Henning Schild wrote:
> Create a struct that holds the format details for the supported formats.
> At the moment that is still just "openpgp". This commit prepares for the
> introduction of more formats, that might use other programs and match
> other signatures.
Great, this looks like a good incremental step.
Show 9 quoted lines
> static char *configured_signing_key;
> -static const char *gpg_format = "openpgp";
> -static const char *gpg_program = "gpg";
> +struct gpg_format_data {
> + const char *format;
> + const char *program;
> + const char *extra_args_verify[1];
> + const char *sigs[2];
> +};These magic numbers are at a weird distance from where we fill them in:
Show 6 quoted lines
> +struct gpg_format_data gpg_formats[] = {
> + { .format = "openpgp", .program = "gpg",
> + .extra_args_verify = { "--keyid-format=long" },
> + .sigs = { PGP_SIGNATURE, PGP_MESSAGE }
> + },
> +};I'm not sure if we can easily do any better in C, though. Declaring the struct with an open-ended "[]" would make the compiler unhappy. We could do something like:
struct gpg_format_data {
...
const char **extra_args_verify;
};
...
static const char *openpgp_verify_args[] = {
"--key-id-format=long"
};
...
static struct gpg_format_data gpg_formats[] = {
{ ...
.extra_args_verify = openpgp_verify_args
}
};I'm not sure if that's more horrible or less. It's worse to write in the first place, but it's slightly easier to maintain going forward. I dunno.
> +enum gpgformats { PGP_FMT };Looks like we use this only for indexing the gpg_formats array. I know that C guarantees 0-indexing, but if we're depending on it, it might be worth writing out "PGP_FMT = 0" explicitly. And probably adding a comment that this needs to remain in sync with the array.
The other alternative is that we could simply use get_format_data("openpgp"), though that does add a minor runtime cost.
Show 6 quoted lines
> +struct gpg_format_data gpg_formats[] = {
> + { .format = "openpgp", .program = "gpg",
> + .extra_args_verify = { "--keyid-format=long" },
> + .sigs = { PGP_SIGNATURE, PGP_MESSAGE }
> + },
> +};This array should be marked static, I think.
Show 8 quoted lines
> +static struct gpg_format_data *get_format_data(const char *str)
> +{
> + int i;
> + for (i = 0; i < ARRAY_SIZE(gpg_formats); i++)
> + if (!strcasecmp(gpg_formats[i].format, str))
> + return gpg_formats + i;
> + return NULL;
> +}This looks much nicer than the assert()-ing version from v1.
Show 11 quoted lines
> +static struct gpg_format_data *get_format_data_by_sig(const char *sig)
> +{
> + int i, j;
> + for (i = 0; i < ARRAY_SIZE(gpg_formats); i++)
> + for (j = 0; j < ARRAY_SIZE(gpg_formats[i].sigs); j++)
> + if (gpg_formats[i].sigs[j] &&
> + !strncmp(gpg_formats[i].sigs[j], sig,
> + strlen(gpg_formats[i].sigs[j])))
> + return gpg_formats + i;
> + return NULL;
> +}This might be a little more readable with:
starts_with(sig, gpg_formats[i].sigs[j])
instead of the strncmp. It may also be more efficient, as we don't have to compute the strlen of the prefix for each non-matching line (the compiler _might_ be smart enough to realize these are all string literals, but it's pretty buried).
I also wondered if our prefix matching here is overly loose. We have to do a prefix match, since "sig" isn't terminated at the line buffer. So I think we'd match:
--- BEGIN PGP MESSAGE --- AND SOME OTHER STUFF ---
on a line. But I think that's no different than the current code. If we care, I guess we could look for '\n' or '\0' immediately after.
Show 6 quoted lines
> static int is_gpg_start(const char *line)
> {
> - return starts_with(line, PGP_SIGNATURE) ||
> - starts_with(line, PGP_MESSAGE);
> + return (get_format_data_by_sig(line) != NULL);
> }I don't know if we've ever discussed this style explicitly, but we'd usually omit the unnecessary parentheses for the return here.
Show 9 quoted lines
> @@ -140,18 +173,14 @@ int git_gpg_config(const char *var, const char *value, void *cb)
> }
>
> if (!strcmp(var, "gpg.format")) {
> - if (strcasecmp(value, "openpgp"))
> + if (!get_format_data(value))
> return error("malformed value for %s: %s", var, value);
> return git_config_string(&gpg_format, var, value);
> }Show 12 quoted lines
> @@ -165,12 +194,16 @@ const char *get_signing_key(void)
> int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
> {
> struct child_process gpg = CHILD_PROCESS_INIT;
> + struct gpg_format_data *fmt;
> int ret;
> size_t i, j, bottom;
> struct strbuf gpg_status = STRBUF_INIT;
>
> + fmt = get_format_data(gpg_format);
> + if (!fmt)
> + BUG("bad gpg_format '%s'", gpg_format);This makes sense as a BUG, because we would already have validated it when parsing gpg.format earlier. That does make me wonder if we should simply be storing a "struct gpg_format_data" instead of a string, though. I.e., at the top-level:
/* default to signing with openpgp */
static struct gpg_format_data *gpg_format = &gpg_formats[0];
Show 6 quoted lines
> @@ -223,10 +257,18 @@ int verify_signed_buffer(const char *payload, size_t payload_size,
> return -1;
> }
>
> + fmt = get_format_data_by_sig(signature);
> + assert(fmt);
Is this assert() right? The signature data comes from the user. I guess to get here we'll already have matched their signature via is_gpg_start(), and this is just a cross-check? If so, then it's OK to assert, but a BUG() with a descriptive message would be better still.
I also wonder if whoever parses the signature should get back a gpg_format_data and just pass it in here, so we don't have to reparse. That's what my earlier series did. It requires tweaking the function signatures, but IMHO the result was a lot more obvious.
> + argv_array_pushl(&gpg.args,
> + fmt->program, NULL);
If you're just pushing one thing, you don't need pushl(). You can just:
argv_array_push(&gpg.args, fmt->program);
> + for (i = 0; i < ARRAY_SIZE(fmt->extra_args_verify); i++)
> + if (fmt->extra_args_verify[i])
> + argv_array_pushl(&gpg.args,
> + fmt->extra_args_verify[i], NULL);
Likewise here. Though if you made extra_args_verify a NULL-terminated list, this whole loop could become:
argv_array_pushv(&gpg.args, fmt->extra_args_verify);
It's not _that_ much code, but I think using NULL-terminated lists in a situation like this is more idiomatic for our code base.
-Peff
Henning Schild
