[pve-devel] [RFC PATCH mini-journalreader 2/2] include error in json output

[Dominik Csapak]

by using json-c and printing the string into a variable via `vasprintf`.
we use a json library to correctly escape and format the error string we
get, since we cannot be sure about the content.

Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
---
not sure if it's worth to include json-c here just for the error message...

 debian/control           |  2 +-
 src/Makefile             |  2 +-
 src/mini-journalreader.c | 33 +++++++++++++++++++++++++++------
 3 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/debian/control b/debian/control
index 8280f6d..d03772e 100644
--- a/debian/control
+++ b/debian/control
@@ -2,7 +2,7 @@ Source: proxmox-mini-journalreader
 Section: admin
 Priority: optional
 Maintainer: Proxmox Support Team <support at proxmox.com>
-Build-Depends: debhelper-compat (= 13), libsystemd-dev, pkg-config, scdoc,
+Build-Depends: debhelper-compat (= 13), libsystemd-dev, pkg-config, scdoc, libjson-c-dev
 Standards-Version: 4.6.2
 
 Package: proxmox-mini-journalreader
diff --git a/src/Makefile b/src/Makefile
index 449004f..adb2782 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -4,7 +4,7 @@ SOURCES=mini-journalreader.c
 BIN_DIR ?= $(DESTDIR)/usr/bin
 MAN1_DIR ?= $(DESTDIR)/usr/share/man/man1
 
-LIBS := libsystemd
+LIBS := libsystemd json-c
 CFLAGS += -Werror -Wall -Wextra -Wl,-z,relro -g -O2 --std=gnu11
 CFLAGS += -fstack-protector-strong -D_FORTIFY_SOURCE=2
 CFLAGS += $(shell pkg-config --cflags $(LIBS))
diff --git a/src/mini-journalreader.c b/src/mini-journalreader.c
index d934d43..62d8850 100644
--- a/src/mini-journalreader.c
+++ b/src/mini-journalreader.c
@@ -15,6 +15,10 @@
  * If not, see <https://www.gnu.org/licenses/>.
  */
 
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
 #include <errno.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -23,6 +27,7 @@
 #include <systemd/sd-journal.h>
 #include <time.h>
 #include <unistd.h>
+#include <json.h>
 
 #define BUFSIZE 4096
 
@@ -33,15 +38,31 @@ bool first_line = true;
 // helper to print errors on stderr
 // if we're in json mode, print closing json body if possible
 static void print_error_and_exit(const char *fmt, ...) {
+    fflush_unlocked(stdout);
+
     va_list args;
-    fprintf(stderr, fmt, args);
-    if (json) {
-        size_t r = fwrite_unlocked("],\"success\":0}", 1, 14, stdout);
-        if (r < 14) {
-            fprintf(stderr, "Failed to write closing json\n");
+    char *message;
+    va_start(args, fmt);
+    int r = vasprintf(&message, fmt, args);
+    if (r < 0) {
+        // could not allocate the string, so write it directly and don't
+        // include the error in the json output
+        fprintf(stderr, fmt, args);
+        if (json) {
+            fprintf(stdout, "],\"success\":0}");
         }
-        fflush_unlocked(stdout);
+        exit(1);
+    }
+    fprintf(stderr, "%s", message);
+    va_end(args);
+
+    if (json) {
+        struct json_object *obj = json_object_new_string(message);
+        const char *json_message = json_object_to_json_string(obj);
+        fprintf(stdout, "], \"error\":%s,\"success\":0}", json_message);
+        json_object_put(obj);
     }
+    free(message);
     exit(1);
 }
 
-- 
2.39.5