From cdf6f34a2fd1448c5d1b75f4717c57b057dd51b2 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Thu, 13 Jun 2024 09:29:10 +0200
Subject: [PATCH] io-util: add new helper fputs_with_newline()

---
 src/basic/io-util.c | 16 ++++++++++++++++
 src/basic/io-util.h |  3 +++
 src/core/unit.c     |  6 ++----
 3 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/src/basic/io-util.c b/src/basic/io-util.c
index 6bcbef34136..e07e1a1e191 100644
--- a/src/basic/io-util.c
+++ b/src/basic/io-util.c
@@ -306,3 +306,19 @@ ssize_t sparse_write(int fd, const void *p, size_t sz, size_t run_length) {
 
         return q - (const uint8_t*) p;
 }
+
+int fputs_with_newline(const char *s, FILE *f) {
+        assert(s);
+        assert(f);
+
+        /* This is like fputs() but outputs a trailing newline char, but only if the string doesn't end in a
+         * newline anyway. Just like fputs() returns EOF on error. Otherwise returns 0 in case we didn't
+         * append a newline, > 0 otherwise. */
+
+        if (fputs(s, f) == EOF)
+                return EOF;
+        if (endswith(s, "\n"))
+                return 0;
+
+        return fputc('\n', f) == EOF ? EOF : 1;
+}
diff --git a/src/basic/io-util.h b/src/basic/io-util.h
index e027c1a878c..0d9007a304d 100644
--- a/src/basic/io-util.h
+++ b/src/basic/io-util.h
@@ -5,6 +5,7 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
+#include <stdio.h>
 #include <sys/types.h>
 
 #include "macro.h"
@@ -44,3 +45,5 @@ static inline bool FILE_SIZE_VALID_OR_INFINITY(uint64_t l) {
         return FILE_SIZE_VALID(l);
 
 }
+
+int fputs_with_newline(const char *s, FILE *f);
diff --git a/src/core/unit.c b/src/core/unit.c
index 35e790ebba5..99c1db3a1a6 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -33,6 +33,7 @@
 #include "format-util.h"
 #include "id128-util.h"
 #include "install.h"
+#include "io-util.h"
 #include "iovec-util.h"
 #include "label-util.h"
 #include "load-dropin.h"
@@ -4569,10 +4570,7 @@ int unit_write_setting(Unit *u, UnitWriteFlags flags, const char *name, const ch
         if (u->transient_file) {
                 /* When this is a transient unit file in creation, then let's not create a new drop-in but instead
                  * write to the transient unit file. */
-                fputs(data, u->transient_file);
-
-                if (!endswith(data, "\n"))
-                        fputc('\n', u->transient_file);
+                fputs_with_newline(data, u->transient_file);
 
                 /* Remember which section we wrote this entry to */
                 u->last_section_private = !!(flags & UNIT_PRIVATE);
-- 
2.47.3