diff: fix a bug in diffing against stdin. Closes 7784

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

2 files changed, 13 insertions, 1 deletions

diff --git a/editors/diff.c b/editors/diff.c
index a78a0ee28..c3ad31bf3 100644
--- a/editors/diff.c
+++ b/editors/diff.c
@@ -740,9 +740,10 @@ static int diffreg(char *file[2])
                         unlink(name);
                         if (bb_copyfd_eof(fd, fd_tmp) < 0)
                                 xfunc_die();
-                        if (fd) /* Prevents closing of stdin */
+                        if (fd != STDIN_FILENO)
                                 close(fd);
                         fd = fd_tmp;
+                        xlseek(fd, 0, SEEK_SET);
                 }
                 fp[i] = fdopen(fd, "r");
         }
diff --git a/testsuite/diff.tests b/testsuite/diff.tests
index 6de46483b..84d853852 100755
--- a/testsuite/diff.tests
+++ b/testsuite/diff.tests
@@ -44,6 +44,17 @@ testing "diff of stdin, twice" \
         "" \
         "stdin"
 
+testing "diff of empty file against stdin" \
+        "diff -u - input | $TRIM_TAB" \
+"\
+--- -
++++ input
+@@ -1 +0,0 @@
+-a
+" \
+        "" \
+        "a\n"
+
 testing "diff of empty file against nonempty one" \
         "diff -u - input | $TRIM_TAB" \
 "\