[v3,08/18] qjson: Simplify by using json-output-visitor

Commit Message

Eric Blake April 29, 2016, 4:23 a.m. UTC

Instead of rolling our own limited JSON outputter, we can just
wrap the more full-featured JSON output Visitor.

This slightly changes the output (different spacing), but the
result is still equivalent JSON contents.

Signed-off-by: Eric Blake <[e-mail]>

---
v3: rebase to master
v2: rebase to earlier changes
---
 qjson.c | 61 ++++++++++++++++++++++---------------------------------------
 1 file changed, 22 insertions(+), 39 deletions(-)

Comments

Markus Armbruster May 2, 2016, 12:45 p.m. UTC | #1

Eric Blake <[e-mail]> writes:

> Instead of rolling our own limited JSON outputter, we can just
> wrap the more full-featured JSON output Visitor.
>
> This slightly changes the output (different spacing), but the
> result is still equivalent JSON contents.
>
> Signed-off-by: Eric Blake <[e-mail]>

The file comment

  /*
   * QEMU JSON writer
   *

becomes misleading.  This isn't "the" QEMU JSON writer.  It's not even
"a" JSON writer anymore.  It's a (QOM) object to accumulate JSON in a
limited way.

Why it's a *QOM* object I can't see.

If I take the QOMness away, all that's left is a thin, trivial wrapper
around the visitor.  Why is it useful?

Markus Armbruster May 2, 2016, 12:49 p.m. UTC | #2

Markus Armbruster <[e-mail]> writes:

> Eric Blake <[e-mail]> writes:
>
>> Instead of rolling our own limited JSON outputter, we can just
>> wrap the more full-featured JSON output Visitor.
>>
>> This slightly changes the output (different spacing), but the
>> result is still equivalent JSON contents.
>>
>> Signed-off-by: Eric Blake <[e-mail]>
>
> The file comment
>
>   /*
>    * QEMU JSON writer
>    *
>
> becomes misleading.  This isn't "the" QEMU JSON writer.  It's not even
> "a" JSON writer anymore.  It's a (QOM) object to accumulate JSON in a
> limited way.
>
> Why it's a *QOM* object I can't see.
>
> If I take the QOMness away, all that's left is a thin, trivial wrapper
> around the visitor.  Why is it useful?

Oh, now I see: you asked yourself the same question, and PATCH 10+11 are
the result.

The weekend deleted the cover letter from my memory %-)

Patch

diff --git a/qjson.c b/qjson.c
index d172b1f..17cc962 100644
--- a/qjson.c
+++ b/qjson.c
@@ -12,102 +12,85 @@ 
  */

 #include "qemu/osdep.h"
-#include <qapi/qmp/qstring.h>
-#include <glib.h>
 #include <qjson.h>
 #include <qemu/module.h>
 #include <qom/object.h>
+#include "qapi/json-output-visitor.h"
+#include "qapi/error.h"

 struct QJSON {
     Object obj;
-    QString *str;
-    bool omit_comma;
+    JsonOutputVisitor *jov;
+    char *str;
 };

 #define QJSON(obj) OBJECT_CHECK(QJSON, (obj), TYPE_QJSON)

-static void json_emit_element(QJSON *json, const char *name)
-{
-    /* Check whether we need to print a , before an element */
-    if (json->omit_comma) {
-        json->omit_comma = false;
-    } else {
-        qstring_append(json->str, ", ");
-    }
-
-    if (name) {
-        qstring_append_json_string(json->str, name);
-        qstring_append(json->str, " : ");
-    }
-}
-
 void json_start_object(QJSON *json, const char *name)
 {
-    json_emit_element(json, name);
-    qstring_append(json->str, "{ ");
-    json->omit_comma = true;
+    Visitor *v = json_output_get_visitor(json->jov);
+    visit_start_struct(v, name, NULL, 0, &error_abort);
 }

 void json_end_object(QJSON *json)
 {
-    qstring_append(json->str, " }");
-    json->omit_comma = false;
+    Visitor *v = json_output_get_visitor(json->jov);
+    visit_check_struct(v, &error_abort);
+    visit_end_struct(v);
 }

 void json_start_array(QJSON *json, const char *name)
 {
-    json_emit_element(json, name);
-    qstring_append(json->str, "[ ");
-    json->omit_comma = true;
+    Visitor *v = json_output_get_visitor(json->jov);
+    visit_start_list(v, name, NULL, 0, &error_abort);
 }

 void json_end_array(QJSON *json)
 {
-    qstring_append(json->str, " ]");
-    json->omit_comma = false;
+    Visitor *v = json_output_get_visitor(json->jov);
+    visit_end_list(v);
 }

 void json_prop_int(QJSON *json, const char *name, int64_t val)
 {
-    json_emit_element(json, name);
-    qstring_append_format(json->str, "%" PRId64, val);
+    Visitor *v = json_output_get_visitor(json->jov);
+    visit_type_int(v, name, &val, &error_abort);
 }

 void json_prop_str(QJSON *json, const char *name, const char *str)
 {
-    json_emit_element(json, name);
-    qstring_append_json_string(json->str, str);
+    Visitor *v = json_output_get_visitor(json->jov);
+    visit_type_str(v, name, (char **)&str, &error_abort);
 }

 const char *qjson_get_str(QJSON *json)
 {
-    return qstring_get_str(json->str);
+    return json->str;
 }

 QJSON *qjson_new(void)
 {
     QJSON *json = QJSON(object_new(TYPE_QJSON));
+    json_start_object(json, NULL);
     return json;
 }

 void qjson_finish(QJSON *json)
 {
     json_end_object(json);
+    json->str = json_output_get_string(json->jov);
 }

 static void qjson_initfn(Object *obj)
 {
     QJSON *json = QJSON(obj);
-
-    json->str = qstring_from_str("{ ");
-    json->omit_comma = true;
+    json->jov = json_output_visitor_new();
 }

 static void qjson_finalizefn(Object *obj)
 {
     QJSON *json = QJSON(obj);
-
-    qobject_decref(QOBJECT(json->str));
+    g_free(json->str);
 }

 static const TypeInfo qjson_type_info = {