tests: rework the code fuzzing journald

This should make it easier to add a new fuzzer without a lot of
duplication.

src/fuzz/fuzz-journald-syslog.c

@@ -1,29 +1,10 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 
-#include "alloc-util.h"
 #include "fuzz.h"
-#include "journald-server.h"
+#include "fuzz-journald.h"
 #include "journald-syslog.h"
-#include "sd-event.h"
 
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
-        Server s = {};
-        char *label = NULL;
-        size_t label_len = 0;
-        struct ucred *ucred = NULL;
-        struct timeval *tv = NULL;
-
-        if (size == 0)
-                return 0;
-
-        assert_se(sd_event_default(&s.event) >= 0);
-        s.syslog_fd = s.native_fd = s.stdout_fd = s.dev_kmsg_fd = s.audit_fd = s.hostname_fd = s.notify_fd = -1;
-        s.buffer = memdup_suffix0(data, size);
-        assert_se(s.buffer);
-        s.buffer_size = size + 1;
-        s.storage = STORAGE_NONE;
-        server_process_syslog_message(&s, s.buffer, size, ucred, tv, label, label_len);
-        server_done(&s);
-
+        fuzz_journald_processing_function(data, size, server_process_syslog_message);
         return 0;
 }

src/fuzz/fuzz-journald.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+#pragma once
+
+#include "alloc-util.h"
+#include "journald-server.h"
+#include "sd-event.h"
+
+static void fuzz_journald_processing_function(
+                const uint8_t *data,
+                size_t size,
+                void (*f)(Server *s, const char *buf, size_t raw_len, const struct ucred *ucred, const struct timeval *tv, const char *label, size_t label_len)
+        ) {
+        Server s = {};
+        char *label = NULL;
+        size_t label_len = 0;
+        struct ucred *ucred = NULL;
+        struct timeval *tv = NULL;
+
+        if (size == 0)
+                return;
+
+        assert_se(sd_event_default(&s.event) >= 0);
+        s.syslog_fd = s.native_fd = s.stdout_fd = s.dev_kmsg_fd = s.audit_fd = s.hostname_fd = s.notify_fd = -1;
+        s.buffer = memdup_suffix0(data, size);
+        assert_se(s.buffer);
+        s.buffer_size = size + 1;
+        s.storage = STORAGE_NONE;
+        (*f)(&s, s.buffer, size, ucred, tv, label, label_len);
+        server_done(&s);
+}