[PATCH] Implement support for command line argument parsing using <argp.h>

[Sergio Durigan Junior]

Oi de novo :-),

Eu sou um fã da <argp.h>, uso ela em vários projetos pessoais, e achei
que fosse uma boa adição ao rnetclient.  Eu optei por criar um switch
chamado -d|--declaration pra que o usuário possa passar o nome do
arquivo da declaração, mas também mantive a compatibilidade com versões
anteriores que aceitam o arquivo passado diretamente (i.e., sem switches
nem nada).

O patch é simples, não tem muito truque, mas reviews são obviamente bem
vindos.  Queria vê-lo incluído antes do release de hoje :-).

Falou!

-- 
Sergio

commit 28a8c5807a9fdfff747d9a8e95d6cb986f56e681
Author: Sergio Durigan Junior <sergiodj en sergiodj.net>
Date:   Sat Mar 15 16:28:39 2014 -0300

    Implement argument parsing via argp.h.
    
    This commit implements argument parsing from the command line via
    argp.h. So far, I have added only one parameter ('-d', or
    '--declaracao') which is used for providing the filename of the
    declaration.  I have also marked this argument as optional, so that the
    user will still be able to provide the filename without using '-d'.
    
    As an auxiliary support, I enabled the generation of the config.h header
    file, so that the program can obtain the package version and the bug
    report address directly from configure.ac.

diff --git a/.gitignore b/.gitignore
index c037aae..c62646f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,6 +8,7 @@ build-aux
 config.log
 config.status
 configure
+config.h*
 
 # Object files
 *.o
diff --git a/bootstrap.sh b/bootstrap.sh
index 41e9823..1bf9968 100755
--- a/bootstrap.sh
+++ b/bootstrap.sh
@@ -10,5 +10,6 @@ AUX_DIR=build-aux
 test -d $AUX_DIR || mkdir -p $AUX_DIR
 
 aclocal
+autoheader
 autoconf
 automake --add-missing --copy --force --foreign
diff --git a/configure.ac b/configure.ac
index c7a85dc..e06ecdf 100644
--- a/configure.ac
+++ b/configure.ac
@@ -7,4 +7,5 @@ PKG_CHECK_MODULES(GNUTLS, gnutls >= 1.4.0, , AC_MSG_ERROR(Could not find gnutls)
 AM_PATH_LIBGCRYPT(,,AC_MSG_ERROR(Could not find gcrypt))
 LIBS="$LIBGCRYPT_LIBS $GNUTLS_LIBS $LIBS -lz"
 CFLAGS="$LIBGCRYPT_CFLAGS $GNUTLS_CFLAGS $CFLAGS"
+AC_CONFIG_HEADERS([config.h])
 AC_OUTPUT(Makefile)
diff --git a/rnetclient.c b/rnetclient.c
index d264c72..eb5a391 100644
--- a/rnetclient.c
+++ b/rnetclient.c
@@ -27,10 +27,81 @@
 #include <netdb.h>
 #include <gnutls/gnutls.h>
 #include <zlib.h>
+#include <argp.h>
+#include "config.h"
 #include "decfile.h"
 #include "rnet_message.h"
 #include "rnet_encode.h"
 
+/* Program version and bug report address.  */
+
+const char *argp_program_version = PACKAGE_VERSION;
+const char *argp_program_bug_address = PACKAGE_BUGREPORT;
+
+/* Documentation strings.  */
+
+static const char rnetclient_doc[] =
+	"Send the Brazilian Income Tax Declaration to the Brazilian "
+	"Tax Authority";
+static const char rnetclient_args_doc[] =
+	"[-d|--declaration] FILE";
+
+/* Description and definition of each option accepted by the program.  */
+
+static const struct argp_option rnetclient_options_desc[] = {
+	{ "declaration", 'd', "FILE", OPTION_ARG_OPTIONAL,
+	  "The Income Tax Declaration file that will be sent.",
+	  0 },
+
+	{ NULL },
+};
+
+struct rnetclient_args {
+	/* File representing the declaration.  */
+	char *file;
+};
+
+/* Parser for command line arguments.  */
+
+static error_t rnetclient_parse_opt(int key, char *arg, struct argp_state *state)
+{
+	struct rnetclient_args *a = state->input;
+	switch (key) {
+	case 'd':
+		/* The user has explicitly provided a filename through
+		   the '-d' switch.  */
+		a->file = arg;
+		break;
+
+	case ARGP_KEY_ARG:
+		/* The user has possibly provided a filename without
+		   using any switches (e.g., by running './rnetclient
+		   file').  */
+		a->file = arg;
+		break;
+
+	case ARGP_KEY_END:
+		/* We have reached the end of the argument parsing.
+		   Let's check if the user has provided a filename.  */
+		if (arg == NULL && a->file == NULL)
+			argp_error(state,
+				   "You need to provide the Income Tax Declaration "
+				   "filename.");
+	}
+
+	return 0;
+}
+
+/* Control struct used by argp.  */
+
+static struct argp rnetclient_argp = {
+	rnetclient_options_desc,
+	rnetclient_parse_opt,
+	rnetclient_args_doc,
+	rnetclient_doc,
+	NULL, NULL, NULL
+};
+
 static size_t chars2len (unsigned char buf[2]) {
 	return (buf[0] << 8 | buf[1]);
 }
@@ -172,12 +243,6 @@ static int handshake(int c)
 	return 0;
 }
 
-static void usage(void)
-{
-	fprintf(stderr, "rnetclient [filename]\n");
-	exit(1);
-}
-
 static int rnet_send(gnutls_session_t session, char *buffer, size_t len, int header)
 {
 	int r = 0;
@@ -329,17 +394,17 @@ int main(int argc, char **argv)
 	int r;
 	struct rnet_decfile *decfile;
 	struct rnet_message *message = NULL;
+	struct rnetclient_args rnet_args;
 	gnutls_session_t session;
 	int finish = 0;
 	char *cpf;
 	
-	if (argc < 2) {
-		usage();
-	}
+	memset (&rnet_args, 0, sizeof (rnet_args));
+	argp_parse (&rnetclient_argp, argc, argv, 0, NULL, &rnet_args);
 
-	decfile = rnet_decfile_open(argv[1]);
+	decfile = rnet_decfile_open(rnet_args.file);
 	if (!decfile) {
-		fprintf(stderr, "could not parse %s: %s\n", argv[1], strerror(errno));
+		fprintf(stderr, "could not parse file \"%s\": %s\n", rnet_args.file, strerror(errno));
 		exit(1);
 	}