From 33a964ec6703eeed0ed90c0556f742faa7d11418 Mon Sep 17 00:00:00 2001
From: rillig <rillig@NetBSD.org>
Date: Sun, 22 May 2022 21:39:44 +0000
Subject: [PATCH] uncompress: if the source is broken, don't delete the target

Fixes the second half of PR bin/19722, reported by Giorgos Keramidas.
---
 tests/usr.bin/compress/t_pr_19722.sh |  9 ++++++---
 usr.bin/compress/compress.c          | 21 +++++++++++++++------
 2 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/tests/usr.bin/compress/t_pr_19722.sh b/tests/usr.bin/compress/t_pr_19722.sh
index b94f05909e40..bd3fabf3a6ef 100644
--- a/tests/usr.bin/compress/t_pr_19722.sh
+++ b/tests/usr.bin/compress/t_pr_19722.sh
@@ -1,4 +1,4 @@
-#	$NetBSD: t_pr_19722.sh,v 1.3 2022/05/22 21:16:50 rillig Exp $
+#	$NetBSD: t_pr_19722.sh,v 1.4 2022/05/22 21:39:44 rillig Exp $
 #
 # Copyright (c) 2022 The NetBSD Foundation, Inc.
 # All rights reserved.
@@ -148,6 +148,10 @@ atf_test_case 'uncompress_broken_source_existing_target'
 uncompress_broken_source_existing_target_body()
 {
 	# PR 19722: uncompressing a broken source removes existing target
+	#
+	# Before compress.c 1.29 from 2022-05-22, uncompress removed an
+	# existing target before checking that the source has the correct
+	# format.
 
 	echo 'broken' > file.Z
 	echo 'before' > file
@@ -158,8 +162,7 @@ uncompress_broken_source_existing_target_body()
 	    uncompress -f file.Z
 
 	atf_check -o 'inline:broken\n' cat file.Z
-	# FIXME: Must not be modified.
-	atf_check test ! -f file
+	atf_check -o 'inline:before\n' cat file
 }
 
 
diff --git a/usr.bin/compress/compress.c b/usr.bin/compress/compress.c
index 5a983579ac10..e772f8ac2e01 100644
--- a/usr.bin/compress/compress.c
+++ b/usr.bin/compress/compress.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: compress.c,v 1.28 2022/05/22 21:16:50 rillig Exp $	*/
+/*	$NetBSD: compress.c,v 1.29 2022/05/22 21:39:44 rillig Exp $	*/
 
 /*-
  * Copyright (c) 1992, 1993
@@ -39,7 +39,7 @@ __COPYRIGHT("@(#) Copyright (c) 1992, 1993\
 #if 0
 static char sccsid[] = "@(#)compress.c	8.2 (Berkeley) 1/7/94";
 #else
-__RCSID("$NetBSD: compress.c,v 1.28 2022/05/22 21:16:50 rillig Exp $");
+__RCSID("$NetBSD: compress.c,v 1.29 2022/05/22 21:39:44 rillig Exp $");
 #endif
 #endif /* not lint */
 
@@ -318,10 +318,6 @@ decompress(const char *in, const char *out, int bits)
 		cwarn("%s", in);
 		goto err;
 	}
-	if ((ofp = fopen(out, "w")) == NULL) {
-		cwarn("%s", out);
-		goto err;
-	}
 	if (!isstdin) {
 		if (stat(in, &sb)) {
 			cwarn("%s", in);
@@ -333,6 +329,19 @@ decompress(const char *in, const char *out, int bits)
 			isreg = 1;
 	} else
 		isreg = 0;
+	if ((nr = fread(buf, 1, sizeof(buf), ifp)) == 0) {
+		cwarn("%s", in);
+		goto err;
+	}
+
+	if ((ofp = fopen(out, "w")) == NULL) {
+		cwarn("%s", out);
+		goto err;
+	}
+	if (fwrite(buf, 1, nr, ofp) != nr) {
+		cwarn("%s", out);
+		goto err;
+	}
 
 	oreg <<= 1;
 	while ((nr = fread(buf, 1, sizeof(buf), ifp)) != 0)