Author: asomers
Date: Mon Feb 19 22:09:49 2018
New Revision: 329606
URL: https://svnweb.freebsd.org/changeset/base/329606

Log:
  tail: fix "tail -r" for piped input that begins with '\n'
  
  A subtle logic bug, probably introduced in r311895, caused tail to print the
  first two lines of piped input in forward order, if the very first character
  was a newline.
  
  PR:           222671
  Reported by:  Jim Long <freebsd-bugzi...@umpquanet.com>, pproca...@gmail.com
  MFC after:    3 weeks
  Sponsored by: Spectra Logic Corp

Modified:
  head/usr.bin/tail/reverse.c
  head/usr.bin/tail/tests/tail_test.sh

Modified: head/usr.bin/tail/reverse.c
==============================================================================
--- head/usr.bin/tail/reverse.c Mon Feb 19 22:00:02 2018        (r329605)
+++ head/usr.bin/tail/reverse.c Mon Feb 19 22:09:49 2018        (r329606)
@@ -257,10 +257,13 @@ r_buf(FILE *fp, const char *fn)
                        if ((*p == '\n') || start) {
                                struct bfelem *tr;
 
-                               if (start && llen)
+                               if (llen && start && *p != '\n')
                                        WR(p, llen + 1);
-                               else if (llen)
+                               else if (llen) {
                                        WR(p + 1, llen);
+                                       if (start && *p == '\n')
+                                               WR(p, 1);
+                               }
                                tr = TAILQ_NEXT(tl, entries);
                                llen = 0;
                                if (tr != NULL) {

Modified: head/usr.bin/tail/tests/tail_test.sh
==============================================================================
--- head/usr.bin/tail/tests/tail_test.sh        Mon Feb 19 22:00:02 2018        
(r329605)
+++ head/usr.bin/tail/tests/tail_test.sh        Mon Feb 19 22:09:49 2018        
(r329606)
@@ -83,6 +83,27 @@ HERE
        atf_check cmp expectfile outpipe
 }
 
+# Regression test for PR 222671
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=222671
+atf_test_case pipe_leading_newline_r
+pipe_leading_newline_r_head()
+{
+       atf_set "descr" "Reverse a pipe whose first character is a newline"
+}
+pipe_leading_newline_r_body()
+{
+       cat > expectfile << HERE
+3
+2
+1
+
+HERE
+       printf '\n1\n2\n3\n' | tail -r > outfile
+       printf '\n1\n2\n3\n' | tail -r > outpipe
+       atf_check cmp expectfile outfile
+       atf_check cmp expectfile outpipe
+}
+
 atf_test_case file_rc28
 file_rc28_head()
 {
@@ -105,6 +126,28 @@ HERE
        atf_check cmp expectfile outpipe
 }
 
+atf_test_case file_rc28
+file_rc28_head()
+{
+       atf_set "descr" "Reverse a file and display the last 28 characters"
+}
+file_rc28_body()
+{
+       cat > infile <<HERE
+This is the first line
+This is the second line
+This is the third line
+HERE
+       cat > expectfile << HERE
+This is the third line
+line
+HERE
+       tail -rc28 infile > outfile
+       tail -rc28 < infile > outpipe
+       atf_check cmp expectfile outfile
+       atf_check cmp expectfile outpipe
+}
+
 atf_test_case longfile_r
 longfile_r_head()
 {
@@ -235,6 +278,7 @@ atf_init_test_cases()
        atf_add_test_case file_r
        atf_add_test_case file_rc28
        atf_add_test_case file_rn2
+       atf_add_test_case pipe_leading_newline_r
        # The longfile tests are designed to exercise behavior in r_buf(),
        # which operates on 128KB blocks
        atf_add_test_case longfile_r
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