[Qemu-devel] [PATCH 06/11] qapi: Add qstring_append_format()

[Eric Blake]

Back in commit 764c1ca (Nov 2009), we added qstring_append_int().
However, it did not see any use until commit 190c882 (Jan 2015).
Furthermore, it has a rather limited use case - to print anything
else, callers still have to format into a temporary buffer, unless
we want to introduce an explosion of new qstring_append_* methods
for each useful type to print.

A much better approach is to add a wrapper that merges printf
behavior onto qstring_append, via the new qstring_append_format()
(and its vararg counterpart).  In fact, with that in place, we
no longer need qstring_append_int().

Other immediate uses for the new function include simplifying
an existing client of qstring_append() on a just-formatted
buffer, and the fact that we can take advantage of printf width
manipulations for more efficient indentation.

Signed-off-by: Eric Blake <address@hidden>
---
 include/qapi/qmp/qstring.h |  7 ++++++-
 qjson.c                    |  2 +-
 qobject/qobject-json.c     | 25 +++++--------------------
 qobject/qstring.c          | 23 +++++++++++++++++++----
 4 files changed, 31 insertions(+), 26 deletions(-)

diff --git a/include/qapi/qmp/qstring.h b/include/qapi/qmp/qstring.h
index cab1faf..1b1e130 100644
--- a/include/qapi/qmp/qstring.h
+++ b/include/qapi/qmp/qstring.h
@@ -14,6 +14,8 @@
 #define QSTRING_H

 #include <stdint.h>
+#include <stdarg.h>
+#include "qemu/compiler.h"
 #include "qapi/qmp/qobject.h"
 #include "qapi/error.h"

@@ -29,9 +31,12 @@ QString *qstring_from_str(const char *str);
 QString *qstring_from_substr(const char *str, int start, int end);
 size_t qstring_get_length(const QString *qstring);
 const char *qstring_get_str(const QString *qstring);
-void qstring_append_int(QString *qstring, int64_t value);
 void qstring_append(QString *qstring, const char *str);
 void qstring_append_chr(QString *qstring, int c);
+void qstring_append_format(QString *qstring, const char *fmt, ...)
+    GCC_FMT_ATTR(2, 3);
+void qstring_append_vformat(QString *qstring, const char *fmt, va_list ap)
+    GCC_FMT_ATTR(2, 0);
 void qstring_append_json_string(QString *qstring, const char *raw);
 void qstring_append_json_number(QString *qstring, double number, Error **errp);
 QString *qobject_to_qstring(const QObject *obj);
diff --git a/qjson.c b/qjson.c
index 25afaff..8c93c1b 100644
--- a/qjson.c
+++ b/qjson.c
@@ -70,7 +70,7 @@ void json_end_array(QJSON *json)
 void json_prop_int(QJSON *json, const char *name, int64_t val)
 {
     json_emit_element(json, name);
-    qstring_append_int(json->str, val);
+    qstring_append_format(json->str, "%" PRId64, val);
 }

 void json_prop_str(QJSON *json, const char *name, const char *str)
diff --git a/qobject/qobject-json.c b/qobject/qobject-json.c
index dbe0ab8..3a7b26b 100644
--- a/qobject/qobject-json.c
+++ b/qobject/qobject-json.c
@@ -79,16 +79,13 @@ static void to_json(const QObject *obj, QString *str, int 
pretty, int indent);
 static void to_json_dict_iter(const char *key, QObject *obj, void *opaque)
 {
     ToJsonIterState *s = opaque;
-    int j;

     if (s->count) {
         qstring_append(s->str, s->pretty ? "," : ", ");
     }

     if (s->pretty) {
-        qstring_append(s->str, "\n");
-        for (j = 0 ; j < s->indent ; j++)
-            qstring_append(s->str, "    ");
+        qstring_append_format(s->str, "\n%*s", 4 * s->indent, "");
     }

     qstring_append_json_string(s->str, key);
@@ -101,16 +98,13 @@ static void to_json_dict_iter(const char *key, QObject 
*obj, void *opaque)
 static void to_json_list_iter(QObject *obj, void *opaque)
 {
     ToJsonIterState *s = opaque;
-    int j;

     if (s->count) {
         qstring_append(s->str, s->pretty ? "," : ", ");
     }

     if (s->pretty) {
-        qstring_append(s->str, "\n");
-        for (j = 0 ; j < s->indent ; j++)
-            qstring_append(s->str, "    ");
+        qstring_append_format(s->str, "\n%*s", 4 * s->indent, "");
     }

     to_json(obj, s->str, s->pretty, s->indent);
@@ -125,10 +119,7 @@ static void to_json(const QObject *obj, QString *str, int 
pretty, int indent)
         break;
     case QTYPE_QINT: {
         QInt *val = qobject_to_qint(obj);
-        char buffer[1024];
-
-        snprintf(buffer, sizeof(buffer), "%" PRId64, qint_get_int(val));
-        qstring_append(str, buffer);
+        qstring_append_format(str, "%" PRId64, qint_get_int(val));
         break;
     }
     case QTYPE_QSTRING: {
@@ -147,10 +138,7 @@ static void to_json(const QObject *obj, QString *str, int 
pretty, int indent)
         qstring_append(str, "{");
         qdict_iter(val, to_json_dict_iter, &s);
         if (pretty) {
-            int j;
-            qstring_append(str, "\n");
-            for (j = 0 ; j < indent ; j++)
-                qstring_append(str, "    ");
+            qstring_append_format(str, "\n%*s", 4 * indent, "");
         }
         qstring_append(str, "}");
         break;
@@ -166,10 +154,7 @@ static void to_json(const QObject *obj, QString *str, int 
pretty, int indent)
         qstring_append(str, "[");
         qlist_iter(val, (void *)to_json_list_iter, &s);
         if (pretty) {
-            int j;
-            qstring_append(str, "\n");
-            for (j = 0 ; j < indent ; j++)
-                qstring_append(str, "    ");
+            qstring_append_format(str, "\n%*s", 4 * indent, "");
         }
         qstring_append(str, "]");
         break;
diff --git a/qobject/qstring.c b/qobject/qstring.c
index c83e63c..a348ae3 100644
--- a/qobject/qstring.c
+++ b/qobject/qstring.c
@@ -88,12 +88,27 @@ void qstring_append(QString *qstring, const char *str)
     qstring->string[qstring->length] = 0;
 }

-void qstring_append_int(QString *qstring, int64_t value)
+void qstring_append_format(QString *qstring, const char *fmt, ...)
 {
-    char num[32];
+    va_list ap;

-    snprintf(num, sizeof(num), "%" PRId64, value);
-    qstring_append(qstring, num);
+    va_start(ap, fmt);
+    qstring_append_vformat(qstring, fmt, ap);
+    va_end(ap);
+}
+
+void qstring_append_vformat(QString *qstring, const char *fmt, va_list ap)
+{
+    va_list ap2;
+    size_t len;
+
+    va_copy(ap2, ap);
+    len = vsnprintf(qstring->string + qstring->length, 0, fmt, ap2);
+    va_end(ap2);
+
+    capacity_increase(qstring, len);
+    vsnprintf(qstring->string + qstring->length, len + 1, fmt, ap);
+    qstring->length += len;
 }

 /**
-- 
2.4.3