[Toybox] [PATCH] syslogd: Ensure that socket sends are '\n'-terminated

[Anqi Dong via Toybox]

Hello! Apologies if this is formatted incorrectly; I have no experience
with emailing patches for review. Thanks!

From 834e956d017d8ef92d374ede9cd40c54b9ae4514 Mon Sep 17 00:00:00 2001
From: Anqi Dong <an...@google.com>
Date: Tue, 29 Jun 2021 16:50:27 -0700
Subject: [PATCH] syslogd: Ensure that socket sends are '\n'-terminated

The documentation for syslog states that "[t]he format string need not
include a terminating newline character", which implies that syslogd is
responsible for ensuring one. Busybox ensures this terminating newline
always, so add code to ensure it for the one case (sockets) where we
didn't.

Also, trim any trailing '\n' and '\0' characters from the read buffer,
to avoid (sometimes) printing multiple newlines.

---
 toys/pending/syslogd.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/toys/pending/syslogd.c b/toys/pending/syslogd.c
index 87aa228c..8c60dcd8 100644
--- a/toys/pending/syslogd.c
+++ b/toys/pending/syslogd.c
@@ -310,7 +310,7 @@ static int write_rotate(struct logfile *tf, int len)
   return write(tf->logfd, toybuf, len);
 }
 
-//Parse messege and write to file.
+//Parse message and write to file.
 static void logmsg(char *msg, int len)
 {
   time_t now;
@@ -321,7 +321,7 @@ static void logmsg(char *msg, int len)
 
   char *omsg = msg;
   int olen = len, fac, lvl;
-  
+
   if (*msg == '<') { // Extract the priority no.
     pri = (int) strtoul(msg + 1, &p, 10);
     if (*p == '>') msg = p + 1;
@@ -342,7 +342,7 @@ static void logmsg(char *msg, int len)
   fac = LOG_FAC(pri);
   lvl = LOG_PRI(pri);
 
-  if (toys.optflags & FLAG_K) len = sprintf(toybuf, "<%d> %s\n", pri, msg);
+  if (toys.optflags & FLAG_K) len = sprintf(toybuf, "<%d> %s", pri, msg);
   else {
     char facbuf[12], pribuf[12];
 
@@ -351,8 +351,8 @@ static void logmsg(char *msg, int len)
 
     p = "local";
     if (!uname(&uts)) p = uts.nodename;
-    if (toys.optflags & FLAG_S) len = sprintf(toybuf, "%s %s\n", ts, msg);
-    else len = sprintf(toybuf, "%s %s %s.%s %s\n", ts, p, facstr, lvlstr, msg);
+    if (toys.optflags & FLAG_S) len = sprintf(toybuf, "%s %s", ts, msg);
+    else len = sprintf(toybuf, "%s %s %s.%s %s", ts, p, facstr, lvlstr, msg);
   }
   if (lvl >= TT.log_prio) return;
 
@@ -454,7 +454,7 @@ init_jumpin:
     nfds++;
   }
   if (!nfds) {
-    error_msg("Can't open single socket for listenning.");
+    error_msg("Can't open single socket for listening.");
     goto clean_and_exit;
   }
 
@@ -524,8 +524,19 @@ init_jumpin:
       for (tsd = TT.lsocks; tsd; tsd = tsd->next) {
         int sd = tsd->sd;
         if (FD_ISSET(sd, &rfds)) {
-          int len = read(sd, buffer, 1023); //buffer is of 1K, hence readingonly 1023 bytes, 1 for NUL
+          // Buffer is of 1 KiB, hence reading only 1022 bytes, reserving 1
+          // for '\n' and 1 for '\0'
+          int len = read(sd, buffer, 1022);
+
+          // The syslog function's documentation says that a trailing '\n' is
+          // optional. We trim any that are present, and then append one.
+          while (len > 0 &&
+                 (buffer[len - 1] == '\n' || buffer[len - 1] == '\0')) {
+            --len;
+          }
+
           if (len > 0) {
+            buffer[len++] = '\n';
             buffer[len] = '\0';
             if((toys.optflags & FLAG_D) && (len == last_len))
               if (!memcmp(last_buf, buffer, len)) break;
-- 
2.32.0.554.ge1b32706d8-goog

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