Issue #161: add a json_object_to_fd() function.

json_util.c

@@ -65,6 +65,8 @@ static int sscanf_is_broken = 0;
 static int sscanf_is_broken_testdone = 0;
 static void sscanf_is_broken_test(void);
 
+static int _json_object_to_fd(int fd, struct json_object *obj, int flags, const char *filename);
+
 static char _last_err[256] = "";
 
 const char *json_util_get_last_err()
@@ -126,42 +128,61 @@ struct json_object* json_object_from_file(const char *filename)
 
 int json_object_to_file_ext(const char *filename, struct json_object *obj, int flags)
 {
-  const char *json_str;
-  int fd, ret;
-  unsigned int wpos, wsize;
+	int fd, ret;
+	int saved_errno;
 
-  if(!obj) {
-    _set_last_err("json_object_to_file: object is null\n");
-    return -1;
-  }
+	if (!obj) {
+		_set_last_err("json_object_to_file: object is null\n");
+		return -1;
+	}
 
-  if((fd = open(filename, O_WRONLY | O_TRUNC | O_CREAT, 0644)) < 0) {
-    _set_last_err("json_object_to_file: error opening file %s: %s\n",
-	     filename, strerror(errno));
-    return -1;
-  }
+	if ((fd = open(filename, O_WRONLY | O_TRUNC | O_CREAT, 0644)) < 0) {
+		_set_last_err("json_object_to_file: error opening file %s: %s\n",
+		              filename, strerror(errno));
+		return -1;
+	}
+	ret = _json_object_to_fd(fd, obj, flags, filename);
+	saved_errno = errno;
+	close(fd);
+	errno = saved_errno;
+	return ret;
+}
 
-  if(!(json_str = json_object_to_json_string_ext(obj,flags))) {
-    close(fd);
-    return -1;
-  }
+int json_object_to_fd(int fd, struct json_object *obj, int flags)
+{
+	if (!obj) {
+		_set_last_err("json_object_to_fd: object is null\n");
+		return -1;
+	}
 
-  wsize = (unsigned int)(strlen(json_str) & UINT_MAX); /* CAW: probably unnecessary, but the most 64bit safe */
-  wpos = 0;
-  while(wpos < wsize) {
-    if((ret = write(fd, json_str + wpos, wsize-wpos)) < 0) {
-      close(fd);
-      _set_last_err("json_object_to_file: error writing file %s: %s\n",
-	     filename, strerror(errno));
-      return -1;
-    }
+	return _json_object_to_fd(fd, obj, flags, NULL);
+}
+static int _json_object_to_fd(int fd, struct json_object *obj, int flags, const char *filename)
+{
+	int ret;
+	const char *json_str;
+	unsigned int wpos, wsize;
 
-	/* because of the above check for ret < 0, we can safely cast and add */
-    wpos += (unsigned int)ret;
-  }
+	filename = filename ? filename : "(fd)";
 
-  close(fd);
-  return 0;
+	if (!(json_str = json_object_to_json_string_ext(obj,flags))) {
+		return -1;
+	}
+
+	wsize = (unsigned int)(strlen(json_str) & UINT_MAX); /* CAW: probably unnecessary, but the most 64bit safe */
+	wpos = 0;
+	while(wpos < wsize) {
+		if((ret = write(fd, json_str + wpos, wsize-wpos)) < 0) {
+		  _set_last_err("json_object_to_file: error writing file %s: %s\n",
+			 filename, strerror(errno));
+		  return -1;
+		}
+
+		/* because of the above check for ret < 0, we can safely cast and add */
+		wpos += (unsigned int)ret;
+	}
+
+	return 0;
 }
 
 // backwards compatible "format and write to file" function

json_util.h

@@ -67,7 +67,18 @@ 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);
 
 /**
- * Return the last error from json_object_to_file{,_ext} or
+ * Convert the json_object to a string and write it to the file descriptor.
+ * Handles partial writes and will keep writing until done, or an error
+ * occurs.
+ *
+ * @param flags flags to pass to json_object_to_json_string_ext()
+ * @return -1 if something fails.  See json_util_get_last_err() for details.
+ */
+extern int json_object_to_fd(int fd, struct json_object *obj, int flags);
+
+/**
+ * Return the last error from json_object_to_file{,_ext},
+ * json_object_to_fd() or
  * json_object_from_{file,fd}, or NULL if there is none.
  */
 const char *json_util_get_last_err(void);

tests/test_util_file.c

@@ -49,6 +49,25 @@ static void test_write_to_file()
 	       (rv == 0) ? "OK" : "FAIL", outfile2, rv);
 	if (rv == 0)
 		stat_and_cat(outfile2);
+
+	const char *outfile3 = "json3.out";
+	int d = open(outfile3, O_WRONLY|O_CREAT, 0600);
+	if (d < 0)
+	{
+		printf("FAIL: unable to open %s %s\n", outfile3, strerror(errno));
+		return;
+	}
+	rv = json_object_to_fd(d, jso, JSON_C_TO_STRING_PRETTY);
+	printf("%s: json_object_to_fd(%s, jso, JSON_C_TO_STRING_PRETTY)=%d\n",
+	       (rv == 0) ? "OK" : "FAIL", outfile3, rv);
+	// Write the same object twice
+	rv = json_object_to_fd(d, jso, JSON_C_TO_STRING_PLAIN);
+	printf("%s: json_object_to_fd(%s, jso, JSON_C_TO_STRING_PLAIN)=%d\n",
+	       (rv == 0) ? "OK" : "FAIL", outfile3, rv);
+	close(d);
+	if (rv == 0)
+		stat_and_cat(outfile3);
+
 	json_object_put(jso);
 }
 

tests/test_util_file.expected

@@ -19,3 +19,17 @@ file[json2.out], size=367, contents={
   "foo8":"abcdefghijklmnopqrstuvwxyz",
   "foo9":"abcdefghijklmnopqrstuvwxyz"
 }
+OK: json_object_to_fd(json3.out, jso, JSON_C_TO_STRING_PRETTY)=0
+OK: json_object_to_fd(json3.out, jso, JSON_C_TO_STRING_PLAIN)=0
+file[json3.out], size=703, contents={
+  "foo":1234,
+  "foo1":"abcdefghijklmnopqrstuvwxyz",
+  "foo2":"abcdefghijklmnopqrstuvwxyz",
+  "foo3":"abcdefghijklmnopqrstuvwxyz",
+  "foo4":"abcdefghijklmnopqrstuvwxyz",
+  "foo5":"abcdefghijklmnopqrstuvwxyz",
+  "foo6":"abcdefghijklmnopqrstuvwxyz",
+  "foo7":"abcdefghijklmnopqrstuvwxyz",
+  "foo8":"abcdefghijklmnopqrstuvwxyz",
+  "foo9":"abcdefghijklmnopqrstuvwxyz"
+}{"foo":1234,"foo1":"abcdefghijklmnopqrstuvwxyz","foo2":"abcdefghijklmnopqrstuvwxyz","foo3":"abcdefghijklmnopqrstuvwxyz","foo4":"abcdefghijklmnopqrstuvwxyz","foo5":"abcdefghijklmnopqrstuvwxyz","foo6":"abcdefghijklmnopqrstuvwxyz","foo7":"abcdefghijklmnopqrstuvwxyz","foo8":"abcdefghijklmnopqrstuvwxyz","foo9":"abcdefghijklmnopqrstuvwxyz"}