hexdump: fix short file of zero butes treated as dup

function                                             old     new   delta
bb_dump_dump                                        1466    1491     +25

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

2 files changed, 27 insertions, 5 deletions

diff --git a/libbb/dump.c b/libbb/dump.c
index 5941ef902..b4b49d709 100644
--- a/libbb/dump.c
+++ b/libbb/dump.c
@@ -387,7 +387,10 @@ static unsigned char *get(priv_dumper_t *dumper)
                         if (need == blocksize) {
                                 return NULL;
                         }
-                        if (dumper->pub.dump_vflag != ALL && !memcmp(dumper->get__curp, dumper->get__savp, nread)) {
+                        if (dumper->pub.dump_vflag != ALL   /* not "show all"? */
+                         && dumper->pub.dump_vflag != FIRST /* not first line? */
+                         && memcmp(dumper->get__curp, dumper->get__savp, nread) == 0 /* same data? */
+                        ) {
                                 if (dumper->pub.dump_vflag != DUP) {
                                         puts("*");
                                 }
@@ -399,7 +402,7 @@ static unsigned char *get(priv_dumper_t *dumper)
                 }
                 n = fread(dumper->get__curp + nread, sizeof(unsigned char),
                                 dumper->pub.dump_length == -1 ? need : MIN(dumper->pub.dump_length, need), stdin);
-                if (!n) {
+                if (n == 0) {
                         if (ferror(stdin)) {
                                 bb_simple_perror_msg(dumper->argv[-1]);
                         }
@@ -411,9 +414,10 @@ static unsigned char *get(priv_dumper_t *dumper)
                         dumper->pub.dump_length -= n;
                 }
                 need -= n;
-                if (!need) {
-                        if (dumper->pub.dump_vflag == ALL || dumper->pub.dump_vflag == FIRST
-                         || memcmp(dumper->get__curp, dumper->get__savp, blocksize)
+                if (need == 0) {
+                        if (dumper->pub.dump_vflag == ALL   /* "show all"? */
+                         || dumper->pub.dump_vflag == FIRST /* first line? */
+                         || memcmp(dumper->get__curp, dumper->get__savp, blocksize) != 0 /* not same data? */
                         ) {
                                 if (dumper->pub.dump_vflag == DUP || dumper->pub.dump_vflag == FIRST) {
                                         dumper->pub.dump_vflag = WAIT;
diff --git a/testsuite/hexdump.tests b/testsuite/hexdump.tests
new file mode 100755
index 000000000..45a0c1300
--- /dev/null
+++ b/testsuite/hexdump.tests
@@ -0,0 +1,18 @@
+#!/bin/sh
+
+# Copyright 2018 by Denys Vlasenko <vda.linux@googlemail.com>
+# Licensed under GPLv2, see file LICENSE in this source tree.
+
+. ./testing.sh
+
+# testing "description" "command" "result" "infile" "stdin"
+testing 'hexdump -C with four NULs' \
+        'hexdump -C' \
+        "\
+00000000  00 00 00 00                                       |....|
+00000004
+" \
+        '' \
+        '\0\0\0\0'
+
+exit $FAILCOUNT