sendmail: document and fix usage of fd #4, fix check for helper failure.

function                                             old     new   delta
packed_usage                                       25663   25694     +31
signal_handler                                       191     215     +24
kill_helper                                           22      31      +9
launch_helper                                        194     184     -10
get_cred_or_die                                      142     129     -13
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/2 up/down: 64/-23)             Total: 41 bytes

2 files changed, 28 insertions, 24 deletions

diff --git a/include/usage.h b/include/usage.h
index 3363e103f..de6f03767 100644
--- a/include/usage.h
+++ b/include/usage.h
@@ -3651,6 +3651,7 @@
      "\n        -H 'prog args'  Run connection helper. E.g. openssl for encryption:" \
      "\n                        -H 'exec openssl s_client -quiet -tls1 -starttls smtp" \
      "\n                                        -connect smtp.gmail.com:25' <email.txt" \
+     "\n                                        [4<username_and_passwd.txt]" \
      "\n        -S server[:port] Server" \
         ) \
         USE_FEATURE_SENDMAIL_MAILXX( \
diff --git a/mailutils/mail.c b/mailutils/mail.c
index f30984897..71f46c86f 100644
--- a/mailutils/mail.c
+++ b/mailutils/mail.c
@@ -11,9 +11,10 @@
 
 static void kill_helper(void)
 {
-        // TODO!!!: is there more elegant way to terminate child on program failure?
-        if (G.helper_pid > 0)
+        if (G.helper_pid > 0) {
                 kill(G.helper_pid, SIGTERM);
+                G.helper_pid = 0;
+        }
 }
 
 // generic signal handler
@@ -26,44 +27,50 @@ static void signal_handler(int signo)
         }
 
         // SIGCHLD. reap zombies
-        if (safe_waitpid(G.helper_pid, &err, WNOHANG) > 0)
+        if (safe_waitpid(G.helper_pid, &err, WNOHANG) > 0) {
+                if (WIFSIGNALED(err))
+                        bb_error_msg_and_die("helper killed by signal %u", WTERMSIG(err));
                 if (WIFEXITED(err)) {
                         G.helper_pid = 0;
                         if (WEXITSTATUS(err))
-                                bb_error_msg_and_die("child exited (%d)", WEXITSTATUS(err));
+                                bb_error_msg_and_die("helper exited (%u)", WEXITSTATUS(err));
                 }
+        }
 #undef err
 }
 
 void FAST_FUNC launch_helper(const char **argv)
 {
         // setup vanilla unidirectional pipes interchange
-        int idx;
+        int i;
         int pipes[4];
 
         xpipe(pipes);
-        xpipe(pipes+2);
+        xpipe(pipes + 2);
+
         G.helper_pid = vfork();
         if (G.helper_pid < 0)
                 bb_perror_msg_and_die("vfork");
-        idx = (!G.helper_pid) * 2;
-        xdup2(pipes[idx], STDIN_FILENO);
-        xdup2(pipes[3-idx], STDOUT_FILENO);
-        if (ENABLE_FEATURE_CLEAN_UP)
-                for (int i = 4; --i >= 0; )
-                        if (pipes[i] > STDOUT_FILENO)
-                                close(pipes[i]);
+
+        i = (!G.helper_pid) * 2; // for parent:0, for child:2
+        close(pipes[i + 1]); // 1 or 3 - closing one write end
+        close(pipes[2 - i]); // 2 or 0 - closing one read end
+        xmove_fd(pipes[i], STDIN_FILENO); // 0 or 2 - using other read end
+        xmove_fd(pipes[3 - i], STDOUT_FILENO); // 3 or 1 - other write end
+
         if (!G.helper_pid) {
                 // child: try to execute connection helper
                 BB_EXECVP(*argv, (char **)argv);
                 _exit(127);
         }
-        // parent: check whether child is alive
+
+        // parent
         bb_signals(0
                 + (1 << SIGCHLD)
                 + (1 << SIGALRM)
                 , signal_handler);
-        signal_handler(SIGCHLD);
+        // check whether child is alive
+        //redundant:signal_handler(SIGCHLD);
         // child seems OK -> parent goes on
         atexit(kill_helper);
 }
@@ -226,17 +233,13 @@ void FAST_FUNC decode_base64(FILE *src_stream, FILE *dst_stream)
  */
 void FAST_FUNC get_cred_or_die(int fd)
 {
-        // either from TTY
         if (isatty(fd)) {
-                G.user = xstrdup(bb_ask_stdin("User: "));
-                G.pass = xstrdup(bb_ask_stdin("Password: "));
-        // or from STDIN
+                G.user = xstrdup(bb_ask(fd, /* timeout: */ 0, "User: "));
+                G.pass = xstrdup(bb_ask(fd, /* timeout: */ 0, "Password: "));
         } else {
-                FILE *fp = fdopen(fd, "r");
-                G.user = xmalloc_fgetline(fp);
-                G.pass = xmalloc_fgetline(fp);
-                fclose(fp);
+                G.user = xmalloc_reads(fd, /* pfx: */ NULL, /* maxsize: */ NULL);
+                G.pass = xmalloc_reads(fd, /* pfx: */ NULL, /* maxsize: */ NULL);
         }
-        if (!G.user || !*G.user || !G.pass || !*G.pass)
+        if (!G.user || !*G.user || !G.pass)
                 bb_error_msg_and_die("no username or password");
 }