sendmail: make -f optional, document its default value

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/mailutils/sendmail.c b/mailutils/sendmail.c
index b5aa1d17bc1d159b8500f9119396dad626cbcc60..824109d99fbd5408bcbccbcbcef032cd33921abd 100644 (file)
--- a/mailutils/sendmail.c
+++ b/mailutils/sendmail.c
@@ -15,7 +15,8 @@
 //usage:       "Read email from stdin and send it\n"
 //usage:     "\nStandard options:"
 //usage:     "\n       -t              Read additional recipients from message body"
-//usage:     "\n       -f SENDER       Sender (required)"
+//usage:     "\n       -f SENDER       For use in MAIL FROM:<sender>. Can be empty string"
+//usage:     "\n                       Default: -auUSER, or username of current UID"
 //usage:     "\n       -o OPTIONS      Various options. -oi implied, others are ignored"
 //usage:     "\n       -i              -oi synonym. implied and ignored"
 //usage:     "\n"
@@ -40,6 +41,52 @@
 //usage:     "\nUse makemime to create emails with attachments"
 //usage:       )
 
+/* Currently we don't sanitize or escape user-supplied SENDER and RECIPIENT_EMAILs.
+ * We may need to do so. For one, '.' in usernames seems to require escaping!
+ *
+ * From http://cr.yp.to/smtp/address.html:
+ *
+ * SMTP offers three ways to encode a character inside an address:
+ *
+ * "safe": the character, if it is not <>()[].,;:@, backslash,
+ *  double-quote, space, or an ASCII control character;
+ * "quoted": the character, if it is not \012, \015, backslash,
+ *   or double-quote; or
+ * "slashed": backslash followed by the character.
+ *
+ * An encoded box part is either (1) a sequence of one or more slashed
+ * or safe characters or (2) a double quote, a sequence of zero or more
+ * slashed or quoted characters, and a double quote. It represents
+ * the concatenation of the characters encoded inside it.
+ *
+ * For example, the encoded box parts
+ *     angels
+ *     \a\n\g\e\l\s
+ *     "\a\n\g\e\l\s"
+ *     "angels"
+ *     "ang\els"
+ * all represent the 6-byte string "angels", and the encoded box parts
+ *     a\,comma
+ *     \a\,\c\o\m\m\a
+ *     "a,comma"
+ * all represent the 7-byte string "a,comma".
+ *
+ * An encoded address contains
+ *     the byte <;
+ *     optionally, a route followed by a colon;
+ *     an encoded box part, the byte @, and a domain; and
+ *     the byte >.
+ *
+ * It represents an Internet mail address, given by concatenating
+ * the string represented by the encoded box part, the byte @,
+ * and the domain. For example, the encoded addresses
+ *     <God@heaven.af.mil>
+ *     <\God@heaven.af.mil>
+ *     <"God"@heaven.af.mil>
+ *     <@gateway.af.mil,@uucp.local:"\G\o\d"@heaven.af.mil>
+ * all represent the Internet mail address "God@heaven.af.mil".
+ */
+
 #include "libbb.h"
 #include "mail.h"
 
@@ -163,7 +210,7 @@ int sendmail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int sendmail_main(int argc UNUSED_PARAM, char **argv)
 {
        char *opt_connect = opt_connect;
-       char *opt_from;
+       char *opt_from = NULL;
        char *s;
        llist_t *list = NULL;
        char *host = sane_address(safe_gethostname());
@@ -199,8 +246,8 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
        G.fp0 = xfdopen_for_read(3);
 
        // parse options
-       // -v is a counter, -f is required. -H and -S are mutually exclusive, -a is a list
-       opt_complementary = "vv:f:w+:H--S:S--H:a::";
+       // -v is a counter, -H and -S are mutually exclusive, -a is a list
+       opt_complementary = "vv:w+:H--S:S--H:a::";
        // N.B. since -H and -S are mutually exclusive they do not interfere in opt_connect
        // -a is for ssmtp (http://downloads.openwrt.org/people/nico/man/man8/ssmtp.8.html) compatibility,
        // it is still under development.
@@ -304,13 +351,11 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
        //      Since reading from console may defeat usability, the solution is either to read from a predefined
        //      file descriptor (e.g. 4), or again from a secured file.
 
-       // got no sender address? -> use system username as a resort
-       // N.B. we marked -f as required option!
-       //if (!G.user) {
-       //      // N.B. IMHO getenv("USER") can be way easily spoofed!
-       //      G.user = xuid2uname(getuid());
-       //      opt_from = xasprintf("%s@%s", G.user, domain);
-       //}
+       // got no sender address? use auth name, then UID username as a last resort
+       if (!opt_from) {
+               opt_from = G.user ? G.user : xuid2uname(getuid());
+       }
+
        smtp_checkp("MAIL FROM:<%s>", opt_from, 250);
 
        // process message