From 2dfc02e67d1f45c184473bbd42c841daa0543cc6 Mon Sep 17 00:00:00 2001
From: omrzk <193513049+omrzk@users.noreply.github.com>
Date: Fri, 13 Nov 2026 09:12:43 -0600
Subject: [PATCH] Preserve binary data when copying file streams

Copy the bytes returned by fread instead of treating each input chunk as a NUL-terminated string. Preserve the public stream positions and report read and write failures rather than returning success after a partial copy. Add binary boundary, current-position, native pipe error and full-device regression coverage.
---
 src/copyfile.c   | 21 ++++++++---
 test/.gitignore  |  1 +
 test/Makefile.am |  1 +
 test/fcopyfile.c | 92 ++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 110 insertions(+), 5 deletions(-)
 create mode 100644 test/fcopyfile.c

diff --git a/src/copyfile.c b/src/copyfile.c
index 2abc6fd..2936daa 100644
--- a/src/copyfile.c
+++ b/src/copyfile.c
@@ -286,6 +286,8 @@ int movefile(const char *src, const char *dst)
 int fcopyfile(FILE *src, FILE *dst)
 {
 	char *buf;
+	size_t len;
+	int rc, saved_errno;
 
 	if (!src || !dst) {
 		errno = EINVAL;
@@ -296,12 +298,21 @@ int fcopyfile(FILE *src, FILE *dst)
 	if (!buf)
 		return -1;
 
-	while (fgets(buf, BUFSIZ, src))
-		fputs(buf, dst);
-	
-	free(buf);
+	rc = 0;
+	while ((len = fread(buf, 1, BUFSIZ, src)) > 0) {
+		if (fwrite(buf, 1, len, dst) != len) {
+			rc = -1;
+			break;
+		}
+	}
+	if (ferror(src))
+		rc = -1;
 
-	return 0;
+	saved_errno = errno;
+	free(buf);
+	errno = saved_errno;
+
+	return rc;
 }
 
 /**
diff --git a/test/.gitignore b/test/.gitignore
index b2ed0a7..7128afe 100644
--- a/test/.gitignore
+++ b/test/.gitignore
@@ -4,6 +4,7 @@
 .deps/
 /chomp
 /copyfile
+/fcopyfile
 /dir
 /fexist
 /fisdir
diff --git a/test/Makefile.am b/test/Makefile.am
index bfa461c..ef46bcc 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -19,6 +19,7 @@ clean-local:
 TESTS           =
 TESTS          += chomp
 TESTS          += copyfile
+TESTS          += fcopyfile
 TESTS          += dir
 TESTS          += fexist
 TESTS          += fisdir
diff --git a/test/fcopyfile.c b/test/fcopyfile.c
new file mode 100644
index 0000000..4e2aa8f
--- /dev/null
+++ b/test/fcopyfile.c
@@ -0,0 +1,92 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include "check.h"
+
+static void copy_binary(size_t len)
+{
+	unsigned char data[3 * BUFSIZ + 37], copied[sizeof(data)];
+	const char prefix[] = "destination prefix";
+	FILE *src = tmpfile(), *dst = tmpfile();
+	size_t i;
+
+	fail_unless(src && dst);
+	for (i = 0; i < sizeof(data); i++)
+		data[i] = i % 253;
+
+	/* Begin at the current stream positions, preserving the destination prefix. */
+	fail_unless(fwrite(prefix, 1, sizeof(prefix), src) == sizeof(prefix));
+	fail_unless(fwrite(data, 1, len, src) == len);
+	fail_unless(fseek(src, sizeof(prefix), SEEK_SET) == 0);
+	fail_unless(fwrite(prefix, 1, sizeof(prefix), dst) == sizeof(prefix));
+
+	fail_unless(fcopyfile(src, dst) == 0);
+	fail_unless(ftell(src) == (long)(sizeof(prefix) + len));
+	fail_unless(ftell(dst) == (long)(sizeof(prefix) + len));
+	fail_unless(fseek(dst, 0, SEEK_SET) == 0);
+	fail_unless(fread(copied, 1, sizeof(prefix), dst) == sizeof(prefix));
+	fail_unless(memcmp(copied, prefix, sizeof(prefix)) == 0);
+	fail_unless(fread(copied, 1, sizeof(copied), dst) == len);
+	fail_unless(memcmp(copied, data, len) == 0);
+	fail_unless(fgetc(dst) == EOF && feof(dst));
+	fail_unless(fclose(src) == 0);
+	fail_unless(fclose(dst) == 0);
+}
+
+static void read_error(int partial)
+{
+	const char data[] = "bytes before the read error";
+	char copied[sizeof(data)];
+	int fd[2];
+	FILE *src, *dst = tmpfile();
+
+	fail_unless(dst && pipe(fd) == 0);
+	fail_unless(fcntl(fd[0], F_SETFL, O_NONBLOCK) == 0);
+	if (partial)
+		fail_unless(write(fd[1], data, sizeof(data)) == sizeof(data));
+	src = fdopen(fd[0], "r");
+	fail_unless(src);
+	errno = 0;
+	fail_unless(fcopyfile(src, dst) == -1);
+	fail_unless(errno == EAGAIN || errno == EWOULDBLOCK);
+	fail_unless(ferror(src));
+	fail_unless(ftell(dst) == (long)(partial ? sizeof(data) : 0));
+	if (partial) {
+		rewind(dst);
+		fail_unless(fread(copied, 1, sizeof(copied), dst) == sizeof(data));
+		fail_unless(memcmp(copied, data, sizeof(data)) == 0);
+	}
+	fclose(src);
+	fclose(dst);
+	close(fd[1]);
+}
+
+int main(void)
+{
+	const size_t lengths[] = { 0, 1, BUFSIZ - 1, BUFSIZ, BUFSIZ + 1, 3 * BUFSIZ + 37 };
+	size_t i;
+
+	for (i = 0; i < NELEMS(lengths); i++)
+		copy_binary(lengths[i]);
+	read_error(0);
+	read_error(1);
+
+#ifdef __linux__
+	FILE *src = tmpfile();
+	FILE *dst = fopen("/dev/full", "w");
+	fail_unless(src && dst);
+	fail_unless(fputs("data", src) >= 0);
+	rewind(src);
+	fail_unless(setvbuf(dst, NULL, _IONBF, 0) == 0);
+	errno = 0;
+	fail_unless(fcopyfile(src, dst) == -1);
+	fail_unless(errno == ENOSPC);
+	fail_unless(ferror(dst));
+	fclose(src);
+	fclose(dst);
+#endif
+
+	errno = 0;
+	fail_unless(fcopyfile(NULL, NULL) == -1 && errno == EINVAL);
+	return 0;
+}