sendmail: support AUTH PLAIN in addition to AUTH LOGIN

Implement the -am argument to allow choosing an AUTH method.
For now only PLAIN and LOGIN are supported, but others can be added
easily in the future.

AUTH PLAIN required adding a new variant of encode_base64() capable of
handling NUL characters in the input string; the old function is now a
wrapper for the newer one.

function                                             old     new   delta
encode_n_base64                                        -     236    +236
sendmail_main                                       1199    1380    +181
packed_usage                                       32873   32877      +4
encode_base64                                        242      36    -206
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 2/1 up/down: 421/-206)          Total: 215 bytes

Signed-off-by: Raffaello D. Di Napoli <rafdev@dinapo.li>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

mailutils/mail.c

@@ -108,6 +108,17 @@ static char* FAST_FUNC parse_url(char *url, char **user, char **pass)
 */
 
 void FAST_FUNC encode_base64(char *fname, const char *text, const char *eol)
+{
+	size_t len = len;
+	if (text) {
+		// though we do not call uuencode(NULL, NULL) explicitly
+		// still we do not want to break things suddenly
+		len = strlen(text);
+	}
+	encode_n_base64(fname, text, len, eol);
+}
+
+void FAST_FUNC encode_n_base64(char *fname, const char *text, size_t len, const char *eol)
 {
 	enum {
 		SRC_BUF_SIZE = 57,  /* This *MUST* be a multiple of 3 */
@@ -116,17 +127,12 @@ void FAST_FUNC encode_base64(char *fname, const char *text, const char *eol)
 #define src_buf text
 	char src[SRC_BUF_SIZE];
 	FILE *fp = fp;
-	ssize_t len = len;
 	char dst_buf[DST_BUF_SIZE + 1];
 
 	if (fname) {
 		fp = (NOT_LONE_DASH(fname)) ? xfopen_for_read(fname) : (FILE *)text;
 		src_buf = src;
-	} else if (text) {
-		// though we do not call uuencode(NULL, NULL) explicitly
-		// still we do not want to break things suddenly
-		len = strlen(text);
-	} else
+	} else if (!text)
 		return;
 
 	while (1) {

mailutils/mail.h

@@ -35,3 +35,4 @@ void get_cred_or_die(int fd) FAST_FUNC;
 char *send_mail_command(const char *fmt, const char *param) FAST_FUNC;
 
 void encode_base64(char *fname, const char *text, const char *eol) FAST_FUNC;
+void encode_n_base64(char *fname, const char *text, size_t size, const char *eol) FAST_FUNC;

mailutils/sendmail.c

@@ -36,7 +36,9 @@
 //usage:     "\n		openssl s_client -quiet -tls1 -connect smtp.gmail.com:465"
 //usage:     "\n			$SMTP_ANTISPAM_DELAY: seconds to wait after helper connect"
 //usage:     "\n	-S HOST[:PORT]	Server (default $SMTPHOST or 127.0.0.1)"
-//usage:     "\n	-amLOGIN	Log in using AUTH LOGIN (-amCRAM-MD5 not supported)"
+//usage:     "\n	-amLOGIN	Log in using AUTH LOGIN"
+//usage:     "\n	-amPLAIN	or AUTH PLAIN"
+//usage:     "\n			(-amCRAM-MD5 not supported)"
 //usage:     "\n	-auUSER		Username for AUTH"
 //usage:     "\n	-apPASS 	Password for AUTH"
 //usage:     "\n"
@@ -248,6 +250,10 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
 		OPT_S = 1 << 6,         // specify connection string
 		OPT_a = 1 << 7,         // authentication tokens
 		OPT_v = 1 << 8,         // verbosity
+	//--- from -am
+		OPT_am_mask = 3 << 14,	// AUTH method
+		OPT_am_login = 0 << 14, // AUTH LOGIN (default)
+		OPT_am_plain = 1 << 14, // AUTH PLAIN
 	};
 
 	// init global variables
@@ -286,9 +292,12 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
 			G.user = xstrdup(a+1);
 		if ('p' == a[0])
 			G.pass = xstrdup(a+1);
-		// N.B. we support only AUTH LOGIN so far
-		//if ('m' == a[0])
-		//	G.method = xstrdup(a+1);
+		if ('m' == a[0]) {
+			if (strcasecmp("plain", a+1) == 0)
+				opts |= OPT_am_plain;
+			else if (strcasecmp("login", a+1) != 0)
+				bb_error_msg_and_die("unsupported AUTH method %s", a+1);
+		}
 	}
 	// N.B. list == NULL here
 	//bb_error_msg("OPT[%x] AU[%s], AP[%s], AM[%s], ARGV[%s]", opts, au, ap, am, *argv);
@@ -348,13 +357,28 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
 
 	// perform authentication
 	if (opts & OPT_a) {
-		smtp_check("AUTH LOGIN", 334);
 		// we must read credentials unless they are given via -a[up] options
 		if (!G.user || !G.pass)
 			get_cred_or_die(4);
-		encode_base64(NULL, G.user, NULL);
-		smtp_check("", 334);
-		encode_base64(NULL, G.pass, NULL);
+		if ((opts & OPT_am_mask) == OPT_am_plain) {
+			char *plain_auth;
+			size_t user_len, pass_len;
+			user_len = strlen(G.user);
+			pass_len = strlen(G.pass);
+			smtp_check("AUTH PLAIN", 334);
+			// use \1 as placeholders for \0 (format string is NUL-terminated)
+			plain_auth = xasprintf("\1%s\1%s", G.user, G.pass);
+			// substitute placeholders
+			plain_auth[0] = '\0';
+			plain_auth[1 + user_len] = '\0';
+			encode_n_base64(NULL, plain_auth, 1 + user_len + 1 + pass_len, NULL);
+			free(plain_auth);
+		} else if ((opts & OPT_am_mask) == OPT_am_login) {
+			smtp_check("AUTH LOGIN", 334);
+			encode_base64(NULL, G.user, NULL);
+			smtp_check("", 334);
+			encode_base64(NULL, G.pass, NULL);
+		}
 		smtp_check("", 235);
 	}