diff mbox

[v3,1/5] QJSON: Add JSON writer

Message ID 1419604968-87437-2-git-send-email-agraf@suse.de
State New
Headers show

Commit Message

Alexander Graf Dec. 26, 2014, 2:42 p.m. UTC 
To support programmatic JSON assembly while keeping the code that generates it
readable, this patch introduces a simple JSON writer. It emits JSON serially
into a buffer in memory.

The nice thing about this writer is its simplicity and low memory overhead.
Unlike the QMP JSON writer, this one does not need to spawn QObjects for every
element it wants to represent.

This is a prerequisite for the migration stream format description generator.

Signed-off-by: Alexander Graf <agraf@suse.de>
---
 Makefile.objs   |  1 +
 include/qjson.h | 28 +++++++++++++++++
 qjson.c         | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 126 insertions(+)
 create mode 100644 include/qjson.h
 create mode 100644 qjson.c

Comments

Eric Blake Jan. 6, 2015, 3:41 p.m. UTC | #1 
On 12/26/2014 07:42 AM, Alexander Graf wrote:
> To support programmatic JSON assembly while keeping the code that generates it
> readable, this patch introduces a simple JSON writer. It emits JSON serially
> into a buffer in memory.
> 
> The nice thing about this writer is its simplicity and low memory overhead.
> Unlike the QMP JSON writer, this one does not need to spawn QObjects for every
> element it wants to represent.
> 
> This is a prerequisite for the migration stream format description generator.
> 
> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
>  Makefile.objs   |  1 +
>  include/qjson.h | 28 +++++++++++++++++
>  qjson.c         | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 126 insertions(+)
>  create mode 100644 include/qjson.h
>  create mode 100644 qjson.c

> +struct QJSON {
> +    QString *str;
> +    bool omit_comma;
> +    unsigned long self_size_offset;

Would size_t be smarter for this field?

> +}
> +
> +const char *qjson_get_str(QJSON *json)
> +{
> +    return qstring_get_str(json->str);
> +}
> +
> +QJSON *qjson_new(void)
> +{
> +    QJSON *json = g_new(QJSON, 1);
> +    json->str = qstring_from_str("{ ");
> +    json->omit_comma = true;
> +    return json;

If I'm not mistaken, this creates an open-ended object, as in "{ ...".
Should qjson_get_str add the closing }?
Alexander Graf Jan. 6, 2015, 9:39 p.m. UTC | #2 
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On 06.01.15 16:41, Eric Blake wrote:
> On 12/26/2014 07:42 AM, Alexander Graf wrote:
>> To support programmatic JSON assembly while keeping the code that
>> generates it readable, this patch introduces a simple JSON
>> writer. It emits JSON serially into a buffer in memory.
>> 
>> The nice thing about this writer is its simplicity and low memory
>> overhead. Unlike the QMP JSON writer, this one does not need to
>> spawn QObjects for every element it wants to represent.
>> 
>> This is a prerequisite for the migration stream format
>> description generator.
>> 
>> Signed-off-by: Alexander Graf <agraf@suse.de> --- Makefile.objs
>> |  1 + include/qjson.h | 28 +++++++++++++++++ qjson.c         |
>> 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 3
>> files changed, 126 insertions(+) create mode 100644
>> include/qjson.h create mode 100644 qjson.c
> 
>> +struct QJSON { +    QString *str; +    bool omit_comma; +
>> unsigned long self_size_offset;
> 
> Would size_t be smarter for this field?

Turns out the smartest thing to do is to remove the field - it was
unused :).


Btw, thanks a lot for the review!

Alex
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diff mbox

Patch

diff --git a/Makefile.objs b/Makefile.objs
index abeb902..28999d3 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -51,6 +51,7 @@  common-obj-$(CONFIG_LINUX) += fsdev/
 common-obj-y += migration/
 common-obj-y += qemu-char.o #aio.o
 common-obj-y += page_cache.o
+common-obj-y += qjson.o
 
 common-obj-$(CONFIG_SPICE) += spice-qemu-char.o
 
diff --git a/include/qjson.h b/include/qjson.h
new file mode 100644
index 0000000..8f8c145
--- /dev/null
+++ b/include/qjson.h
@@ -0,0 +1,28 @@ 
+/*
+ * QEMU JSON writer
+ *
+ * Copyright Alexander Graf
+ *
+ * Authors:
+ *  Alexander Graf <agraf@suse.de
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+#ifndef QEMU_QJSON_H
+#define QEMU_QJSON_H
+
+typedef struct QJSON QJSON;
+
+QJSON *qjson_new(void);
+void json_prop_str(QJSON *json, const char *name, const char *str);
+void json_prop_int(QJSON *json, const char *name, int64_t val);
+void json_end_array(QJSON *json);
+void json_start_array(QJSON *json, const char *name);
+void json_end_object(QJSON *json);
+void json_start_object(QJSON *json, const char *name);
+const char *qjson_get_str(QJSON *json);
+void qjson_finish(QJSON *json);
+
+#endif /* QEMU_QJSON_H */
diff --git a/qjson.c b/qjson.c
new file mode 100644
index 0000000..7a7cd72
--- /dev/null
+++ b/qjson.c
@@ -0,0 +1,97 @@ 
+/*
+ * QEMU JSON writer
+ *
+ * Copyright Alexander Graf
+ *
+ * Authors:
+ *  Alexander Graf <agraf@suse.de
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#include <qapi/qmp/qstring.h>
+#include <stdbool.h>
+#include <glib.h>
+#include <qjson.h>
+
+struct QJSON {
+    QString *str;
+    bool omit_comma;
+    unsigned long self_size_offset;
+};
+
+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->str, "\"");
+        qstring_append(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;
+}
+
+void json_end_object(QJSON *json)
+{
+    qstring_append(json->str, " }");
+    json->omit_comma = false;
+}
+
+void json_start_array(QJSON *json, const char *name)
+{
+    json_emit_element(json, name);
+    qstring_append(json->str, "[ ");
+    json->omit_comma = true;
+}
+
+void json_end_array(QJSON *json)
+{
+    qstring_append(json->str, " ]");
+    json->omit_comma = false;
+}
+
+void json_prop_int(QJSON *json, const char *name, int64_t val)
+{
+    json_emit_element(json, name);
+    qstring_append_int(json->str, val);
+}
+
+void json_prop_str(QJSON *json, const char *name, const char *str)
+{
+    json_emit_element(json, name);
+    qstring_append_chr(json->str, '"');
+    qstring_append(json->str, str);
+    qstring_append_chr(json->str, '"');
+}
+
+const char *qjson_get_str(QJSON *json)
+{
+    return qstring_get_str(json->str);
+}
+
+QJSON *qjson_new(void)
+{
+    QJSON *json = g_new(QJSON, 1);
+    json->str = qstring_from_str("{ ");
+    json->omit_comma = true;
+    return json;
+}
+
+void qjson_finish(QJSON *json)
+{
+    json_end_object(json);
+}