Re: [PATCH v2 5/9] gpg-interface: introduce an abstraction for multiple gpg formats

[Henning Schild <henning.schild@siemens.com>]

Am Tue, 10 Jul 2018 10:16:39 -0700
schrieb Junio C Hamano <gitster@pobox.com>:

> Henning Schild <henning.schild@siemens.com> writes:
> 
> > 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.
> >
> > Signed-off-by: Henning Schild <henning.schild@siemens.com>
> > ---
> >  gpg-interface.c | 74
> > ++++++++++++++++++++++++++++++++++++++++++++------------- 1 file
> > changed, 58 insertions(+), 16 deletions(-)
> >
> > diff --git a/gpg-interface.c b/gpg-interface.c
> > index ed0e55917..0a8d1bff3 100644
> > --- a/gpg-interface.c
> > +++ b/gpg-interface.c
> > @@ -7,12 +7,46 @@
> >  #include "tempfile.h"
> >  
> >  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];
> > +};  
> 
> Do you use identifier "gpg_format" elsewhere as a structure name?  A
> structure is there always to hold "data", so often "_data" suffix is
> meaningless in a structure type name like this.

i renamed the struct to "gpg_format" and what was "gpg_format" before,
a const char* holding the format we use for signing, is now a pointer
into gpg_formats and called "current_format"
 
> >  #define PGP_SIGNATURE "-----BEGIN PGP SIGNATURE-----"
> >  #define PGP_MESSAGE "-----BEGIN PGP MESSAGE-----"
> >  
> > +enum gpgformats { PGP_FMT };
> > +struct gpg_format_data gpg_formats[] = {
> > +	{ .format = "openpgp", .program = "gpg",
> > +	  .extra_args_verify = { "--keyid-format=long" },
> > +	  .sigs = { PGP_SIGNATURE, PGP_MESSAGE }
> > +	},
> > +};
> > +static const char *gpg_format = "openpgp";
> > +
> > +static struct gpg_format_data *get_format_data(const char *str)  
> 
> get_format_data_by_name() or something like that, for consistency
> with the next function, perhaps?

I went for get_format_by_name and also renamed "format" inside the
struct to be "name"

> > +{
> > +	int i;
> > +	for (i = 0; i < ARRAY_SIZE(gpg_formats); i++)
> > +		if (!strcasecmp(gpg_formats[i].format, str))
> > +			return gpg_formats + i;
> > +	return NULL;
> > +}
> > +
> > +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;
> > +}
> > +
> >  void signature_check_clear(struct signature_check *sigc)
> >  {
> >  	FREE_AND_NULL(sigc->payload);
> > @@ -104,8 +138,7 @@ void print_signature_buffer(const struct
> > signature_check *sigc, unsigned flags) 
> >  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);  
> 
> If this is still called "is_gpg_start()", then shouldn't the
> implementation be more like this?
> 
> 	struct gpg_format *found = get_format_data_by_sig(line);
> 
> 	return found && found == &gpg_formats[PGP_FMT];
> 
> It probably does not make much difference in the end, as you won't
> have functions is_(gpg|gpgsm|somethingelse|yetanother)_start() but
> either have a single function "does some x509 looking block start
> here?" or "I am expecting gpg and nothing else, does a block for
> that start here?" and at that point this will no longer be called
> is_gpg_start(), I would expect.

I dropped the whole thing since it is now a one-liner and only called
on one place.

> >  size_t parse_signature(const char *buf, size_t size)
> > @@ -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);  
> 
> This is a bug introduced in an earlier step in the series, but you
> will segfault when given a configuration that looks like this:
> 
> 	[gpg]
> 		format
> 
> Imitate the way how !value is diagnosed upfront for "gpg.program"
> below before this patch.

The next version will take care of this.

> >  	}
> >  
> > -	if (!strcmp(var, "gpg.program")) {
> > -		if (!value)
> > -			return config_error_nonbool(var);
> > -		gpg_program = xstrdup(value);
> > -		return 0;
> > -	}
> > -
> > +	if (!strcmp(var, "gpg.program"))
> > +		return
> > git_config_string(&gpg_formats[PGP_FMT].program, var,
> > +					 value);  
> 
> git_config_string() has its own "do not feed boolean 'true' to me"
> check, so this change does not introduce a regression.
> 
> > @@ -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);
> >  	argv_array_pushl(&gpg.args,
> > -			 gpg_program,
> > +			 fmt->program,
> >  			 "--status-fd=2",
> >  			 "-bsau", signing_key,
> >  			 NULL);
> > @@ -208,8 +241,9 @@ int verify_signed_buffer(const char *payload,
> > size_t payload_size, struct strbuf *gpg_output, struct strbuf
> > *gpg_status) {
> >  	struct child_process gpg = CHILD_PROCESS_INIT;
> > +	struct gpg_format_data *fmt;
> >  	struct tempfile *temp;
> > -	int ret;
> > +	int ret, i;
> >  	struct strbuf buf = STRBUF_INIT;
> >  
> >  	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
> > @@ -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);
> > +
> > +	argv_array_pushl(&gpg.args,
> > +			 fmt->program, NULL);
> > +	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);  
> 
> This loop allows us to extend .extra_args_verify when we need to
> support another variant that needs to take two arguments by making
> .extra_args field larger for all variants and stuffing a NULL to
> unused slots, and it even allows a nonsense like this
> 
> 	.extra_args_verify = { NULL, "--keyid-format=long" },
> 
> I cannot quite shake the feeling that .extra_args_verify and .sigs
> fields should not be of fixed sized array of strings, but rather be
> of type "const char **" that is NULL terminated.  Such a clean-up
> will make it harder to write initializers, so it may not be worth
> it, I guess.

I now have NULL terminated variable size arrays.

Thanks,
Henning
 
> >  	argv_array_pushl(&gpg.args,
> > -			 gpg_program,
> >  			 "--status-fd=1",
> > -			 "--keyid-format=long",
> >  			 "--verify", temp->filename.buf, "-",
> >  			 NULL);