Introduce json_object_from_fd

Also refactor json_object_from_file to use json_object_from_fd
internally.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

json_util.c

@@ -64,30 +64,30 @@ static int sscanf_is_broken = 0;
 static int sscanf_is_broken_testdone = 0;
 static void sscanf_is_broken_test(void);
 
-struct json_object* json_object_from_file(const char *filename)
+/*
+ * Create a JSON object from already opened file descriptor.
+ *
+ * This function can be helpful, when you opened the file already,
+ * e.g. when you have a temp file.
+ * Note, that the fd must be readable at the actual position, i.e.
+ * use lseek(fd, 0, SEEK_SET) before.
+ */
+struct json_object* json_object_from_fd(int fd)
 {
   struct printbuf *pb;
   struct json_object *obj;
   char buf[JSON_FILE_BUF_SIZE];
-  int fd, ret;
+  int ret;
 
-  if((fd = open(filename, O_RDONLY)) < 0) {
-    MC_ERROR("json_object_from_file: error opening file %s: %s\n",
-	     filename, strerror(errno));
-    return NULL;
-  }
   if(!(pb = printbuf_new())) {
-    close(fd);
     MC_ERROR("json_object_from_file: printbuf_new failed\n");
     return NULL;
   }
   while((ret = read(fd, buf, JSON_FILE_BUF_SIZE)) > 0) {
     printbuf_memappend(pb, buf, ret);
   }
-  close(fd);
   if(ret < 0) {
-    MC_ERROR("json_object_from_file: error reading file %s: %s\n",
-	     filename, strerror(errno));
+    MC_ERROR("json_object_from_fd: error reading fd %d: %s\n", fd, strerror(errno));
     printbuf_free(pb);
     return NULL;
   }
@@ -96,6 +96,21 @@ struct json_object* json_object_from_file(const char *filename)
   return obj;
 }
 
+struct json_object* json_object_from_file(const char *filename)
+{
+  struct json_object *obj;
+  int fd;
+
+  if((fd = open(filename, O_RDONLY)) < 0) {
+    MC_ERROR("json_object_from_file: error opening file %s: %s\n",
+	     filename, strerror(errno));
+    return NULL;
+  }
+  obj = json_object_from_fd(fd);
+  close(fd);
+  return obj;
+}
+
 /* extended "format and write to file" function */
 
 int json_object_to_file_ext(const char *filename, struct json_object *obj, int flags)

json_util.h

@@ -31,6 +31,7 @@ extern "C" {
 
 /* utility functions */
 extern struct json_object* json_object_from_file(const char *filename);
+extern struct json_object* json_object_from_fd(int fd);
 extern int json_object_to_file(const char *filename, struct json_object *obj);
 extern int json_object_to_file_ext(const char *filename, struct json_object *obj, int flags);
 extern int json_parse_int64(const char *buf, int64_t *retval);