bug#23763: Bug report: Grep stops, if a text file contains a null character after 32768 bytes

[Bjoern Voigt]

Grep shows a bug, if it processes a text file with at least one embedded
0 (ASCII zero) character after byte 32768. Grep stops with the error
message "Binary file testfile.txt matches" and exit code 0. The error
message is written to standard output. Any line after the 0 character is
silently ignored in output.

Environment:
- grep-2.25
- no patches, no "configure" options
- openSUSE Tumbleweed 20160611 x86_64; glibc 2.23; libpcre 8.38

I saw this bug first, as I tried to filter out a line of the MySQL
backup utility "mysqldump". Because grep stopped at the 0 character, the
backups where incomplete.

# mysqldump --all-databases | grep -v '^-- Dump completed on'
[... around 240 lines of SQL output ...]
LOCK TABLES `PartTable` WRITE;
/*!40000 ALTER TABLE `PartTable` DISABLE KEYS */;
Binary file (standard input) matches
mysqldump: Got errno 32 on write

I found that the mysqldump output contains 0 characters in table PartTable.

I wrote the following test script, which shows the bug without a
dependency to MySQL:
--------------------------------------------------------
#!/bin/bash

testfile="testfile.txt"

# write a text file large enough (16384 lines is
# the minimum number for this test case)
for((i=1;i<=16384;i++)) do echo "A"; done > $testfile

# write a zero byte
echo -e '\0' >> $testfile

# write an end line
echo -e 'A ... the end' >> $testfile

# verify the file contents
ls -l $testfile
tail -n 10 $testfile

# use 'grep' to find all lines with the string "A"
grep "A" $testfile

# the last line is missing, the output ends with
# "Binary file testfile.txt matches"

# check the exit code
echo "Exit code of grep:" $?
--------------------------------------------------------

The last line "A ... the end" is missing in output of grep. The exit
code is 0:

# ./null-bug-testcase.txt
[...]
A
A
A
Binary file testfile.txt matches
Exit code of grep: 0

I also found this bug in older grep versions (e.g. Ubuntu 14.04; grep 2.16).

FreeBSD's version of grep (tested with 2.5.1-FreeBSD under FreeBSD
10.3-RELEASE-p4) does not show the bug:

#./null-bug-testcase.txt
[...]
A
A
A
A ... the end
Exit code of grep: 0

Regards,
Björn