[Qemu-devel] [PATCH v6 13/15] qobject: Implement qobject_to_json() atop JSON visitor

[Eric Blake <eblake@redhat.com>]

Rather than open-code two different JSON visitors, it's nicer to
make qobject_to_json() reuse the JSON output visitor.  The JSON
output visitor allowed us to separate formatting from walking
the tree, where the tree walk is normally done by the
QAPI-generated code for a "real" visit.  Now we can add another
tree walk of QObject, while reusing the formatting of the JSON
visitor, in a "virtual" visit.

Note that this virtual QObject tree walk can also be paired with
other visitors. The string output visitor isn't useful (it would
fail if structs are involved), but the (misnamed) QMP output
visitor could be used to perform a QObject deep clone.  However,
I did not find any obvious QObject clones in the current code
base that needed to use this trick.

Signed-off-by: Eric Blake <eblake@redhat.com>

---
v6: rebase, improve commit message, simplify iterators
[no v5 due to series split]
v4: new patch, inspired by discussion on v3 12/18
---
 include/qapi/qmp/qjson.h |   9 ++++
 qobject/qjson.c          | 113 +++++++++++++----------------------------------
 2 files changed, 40 insertions(+), 82 deletions(-)

diff --git a/include/qapi/qmp/qjson.h b/include/qapi/qmp/qjson.h
index 4b0e2b4..f8f4fcd 100644
--- a/include/qapi/qmp/qjson.h
+++ b/include/qapi/qmp/qjson.h
@@ -24,6 +24,15 @@ QObject *qobject_from_jsonv(const char *string, va_list *ap) GCC_FMT_ATTR(1, 0);
 /* Convert the object to QString; does not fail. */
 QString *qobject_to_json(const QObject *obj, bool pretty);

+/*
+ * Visit the object with an output visitor @v.
+ *
+ * @name represents the relationship of this object to any parent
+ * (ignored for a top-level visit, must be set if part of a
+ * dictionary, should be NULL if part of a list).
+ */
+void qobject_visit_output(Visitor *v, const char *name, const QObject *obj);
+
 int qstring_append_json_string(QString *qstring, const char *str);
 void qstring_append_json_number(QString *qstring, double number);

diff --git a/qobject/qjson.c b/qobject/qjson.c
index d45048b..4ce4b9a 100644
--- a/qobject/qjson.c
+++ b/qobject/qjson.c
@@ -19,6 +19,9 @@
 #include "qapi/qmp/qjson.h"
 #include "qapi/qmp/types.h"
 #include "qemu/unicode.h"
+#include "qapi/error.h"
+#include "qapi/visitor.h"
+#include "qapi/json-output-visitor.h"

 typedef struct JSONParsingState
 {
@@ -69,115 +72,59 @@ QObject *qobject_from_jsonf(const char *string, ...)
     return obj;
 }

-typedef struct ToJsonIterState
-{
-    int indent;
-    bool pretty;
-    int count;
-    QString *str;
-} ToJsonIterState;
-
-static void to_json(const QObject *obj, QString *str, bool pretty, int indent);
-
-static void to_json_dict_iter(const char *key, QObject *obj, void *opaque)
-{
-    ToJsonIterState *s = opaque;
-
-    if (s->count) {
-        qstring_append(s->str, s->pretty ? "," : ", ");
-    }
-
-    if (s->pretty) {
-        qstring_append_printf(s->str, "\n%*s", 4 * s->indent, "");
-    }
-
-    qstring_append_json_string(s->str, key);
-
-    qstring_append(s->str, ": ");
-    to_json(obj, s->str, s->pretty, s->indent);
-    s->count++;
-}
-
-static void to_json_list_iter(QObject *obj, void *opaque)
-{
-    ToJsonIterState *s = opaque;
-
-    if (s->count) {
-        qstring_append(s->str, s->pretty ? "," : ", ");
-    }
-
-    if (s->pretty) {
-        qstring_append_printf(s->str, "\n%*s", 4 * s->indent, "");
-    }
-
-    to_json(obj, s->str, s->pretty, s->indent);
-    s->count++;
-}
-
-static void to_json(const QObject *obj, QString *str, bool pretty, int indent)
+void qobject_visit_output(Visitor *v, const char *name, const QObject *obj)
 {
     switch (qobject_type(obj)) {
     case QTYPE_QNULL:
-        qstring_append(str, "null");
+        visit_type_null(v, name, &error_abort);
         break;
     case QTYPE_QINT: {
-        QInt *val = qobject_to_qint(obj);
-        qstring_append_printf(str, "%" PRId64, qint_get_int(val));
+        int64_t val = qint_get_int(qobject_to_qint(obj));
+
+        visit_type_int64(v, name, &val, &error_abort);
         break;
     }
     case QTYPE_QSTRING: {
-        QString *val = qobject_to_qstring(obj);
+        const char *str = qstring_get_str(qobject_to_qstring(obj));
+
         /* FIXME: no way inform user if we replaced invalid UTF-8
          * sequences to avoid invalid JSON */
-        qstring_append_json_string(str, qstring_get_str(val));
+        visit_type_str(v, name, (char **)&str, &error_abort);
         break;
     }
     case QTYPE_QDICT: {
-        ToJsonIterState s;
         QDict *val = qobject_to_qdict(obj);
+        const QDictEntry *ent;

-        s.count = 0;
-        s.str = str;
-        s.indent = indent + 1;
-        s.pretty = pretty;
-        qstring_append_chr(str, '{');
-        qdict_iter(val, to_json_dict_iter, &s);
-        if (pretty) {
-            qstring_append_printf(str, "\n%*s", 4 * indent, "");
+        visit_start_struct(v, name, NULL, 0, &error_abort);
+        for (ent = qdict_first(val); ent; ent = qdict_next(val, ent)) {
+            qobject_visit_output(v, ent->key, ent->value);
         }
-        qstring_append_chr(str, '}');
+        visit_check_struct(v, &error_abort);
+        visit_end_struct(v, NULL);
         break;
     }
     case QTYPE_QLIST: {
-        ToJsonIterState s;
         QList *val = qobject_to_qlist(obj);
+        const QListEntry *ent;

-        s.count = 0;
-        s.str = str;
-        s.indent = indent + 1;
-        s.pretty = pretty;
-        qstring_append_chr(str, '[');
-        qlist_iter(val, (void *)to_json_list_iter, &s);
-        if (pretty) {
-            qstring_append_printf(str, "\n%*s", 4 * indent, "");
+        visit_start_list(v, name, NULL, 0, &error_abort);
+        QTAILQ_FOREACH(ent, &val->head, next) {
+            qobject_visit_output(v, NULL, ent->value);
         }
-        qstring_append_chr(str, ']');
+        visit_end_list(v, NULL);
         break;
     }
     case QTYPE_QFLOAT: {
         double val = qfloat_get_double(qobject_to_qfloat(obj));

-        qstring_append_json_number(str, val);
+        visit_type_number(v, name, &val, &error_abort);
         break;
     }
     case QTYPE_QBOOL: {
-        QBool *val = qobject_to_qbool(obj);
+        bool val = qbool_get_bool(qobject_to_qbool(obj));

-        if (qbool_get_bool(val)) {
-            qstring_append(str, "true");
-        } else {
-            qstring_append(str, "false");
-        }
+        visit_type_bool(v, name, &val, &error_abort);
         break;
     }
     default:
@@ -187,11 +134,13 @@ static void to_json(const QObject *obj, QString *str, bool pretty, int indent)

 QString *qobject_to_json(const QObject *obj, bool pretty)
 {
-    QString *str = qstring_new();
+    char *str;
+    Visitor *v = json_output_visitor_new(pretty, &str);

-    to_json(obj, str, pretty, 0);
-
-    return str;
+    qobject_visit_output(v, NULL, obj);
+    visit_complete(v, &str);
+    visit_free(v);
+    return qstring_wrap_str(str);
 }

 /**
-- 
2.7.4