From: Anthony PERARD <anthony.perard@vates.tech>

This reuse the "json_callback_*" implemented for the yajl parser as
they don't really need to be changed. It's just awkward to have to
cast between `unsigned char` and `char.`

Replace few strncpy() by memcpy() to let the compiler know we want to
copy the string without the terminating nul, as we are adding it just
after.

Also, it should be possible to keep using YAJL parser when json-c
library isn't available.

Signed-off-by: Anthony PERARD <anthony.perard@vates.tech>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
---
 tools/include/libxl_json.h    |   4 ++
 tools/libs/light/libxl_json.c | 120 ++++++++++++++++++++++++++++++++--
 2 files changed, 120 insertions(+), 4 deletions(-)

diff --git a/tools/include/libxl_json.h b/tools/include/libxl_json.h
index 3f97267eae..f0b4871e0e 100644
--- a/tools/include/libxl_json.h
+++ b/tools/include/libxl_json.h
@@ -42,6 +42,7 @@ yajl_gen_status libxl_ms_vm_genid_gen_json(yajl_gen hand, libxl_ms_vm_genid *p);
 #  define HAVE_YAJL_V2 1
 #endif
 
+#ifdef HAVE_LIBYAJL
 #ifdef HAVE_YAJL_V2
 
 typedef size_t libxl_yajl_length;
@@ -89,5 +90,8 @@ static inline yajl_gen libxl_yajl_gen_alloc(const yajl_alloc_funcs *allocFuncs)
 }
 
 #endif /* !HAVE_YAJL_V2 */
+#else
+typedef size_t libxl_yajl_length;
+#endif /* !HAVE_LIBYAJL */
 
 #endif /* LIBXL_JSON_H */
diff --git a/tools/libs/light/libxl_json.c b/tools/libs/light/libxl_json.c
index 9b8ef2cab9..44ee6e213f 100644
--- a/tools/libs/light/libxl_json.c
+++ b/tools/libs/light/libxl_json.c
@@ -16,7 +16,25 @@
 
 #include <math.h>
 
+#ifdef HAVE_LIBJSONC
+#include <json-c/json.h>
+#define USE_LIBJSONC_PARSER
+#endif
+
+#ifdef HAVE_LIBYAJL
+#  ifndef USE_LIBJSONC_PARSER
+#    define USE_LIBYAJL_PARSER
+#  endif
+#endif
+
+
+#ifdef USE_LIBJSONC_PARSER
+#include <json-c/json_visit.h>
+#endif
+
+#ifdef USE_LIBYAJL_PARSER
 #include <yajl/yajl_parse.h>
+#endif
 #include <yajl/yajl_gen.h>
 
 #include "libxl_internal.h"
@@ -25,7 +43,9 @@
 
 typedef struct libxl__yajl_ctx {
     libxl__gc *gc;
+#ifdef USE_LIBYAJL_PARSER
     yajl_handle hand;
+#endif
     libxl__json_object *head;
     libxl__json_object *current;
 #ifdef DEBUG_ANSWER
@@ -33,7 +53,7 @@ typedef struct libxl__yajl_ctx {
 #endif
 } libxl__yajl_ctx;
 
-#ifdef DEBUG_ANSWER
+#if defined(DEBUG_ANSWER) && defined(USE_LIBYAJL_PARSER)
 #if YAJL_VERSION < 20000
 #  define DEBUG_GEN_ALLOC(ctx)                  \
     if ((ctx)->g == NULL) {                     \
@@ -759,7 +779,7 @@ static int json_callback_number(void *opaque, const char *s, libxl_yajl_length l
     obj = libxl__json_object_alloc(ctx->gc, JSON_NUMBER);
 
     t = libxl__zalloc(ctx->gc, len + 1);
-    strncpy(t, s, len);
+    memcpy(t, s, len);
     t[len] = 0;
 
     obj->u.string = t;
@@ -806,7 +826,7 @@ static int json_callback_map_key(void *opaque, const unsigned char *str,
 
     DEBUG_GEN_STRING(ctx, str, len);
 
-    strncpy(t, (const char *) str, len);
+    memcpy(t, (const char *) str, len);
     t[len] = 0;
 
     if (libxl__json_object_is_map(obj)) {
@@ -890,6 +910,7 @@ static int json_callback_end_array(void *opaque)
     return 1;
 }
 
+#ifdef USE_LIBYAJL_PARSER
 static yajl_callbacks callbacks = {
     json_callback_null,
     json_callback_boolean,
@@ -903,28 +924,111 @@ static yajl_callbacks callbacks = {
     json_callback_start_array,
     json_callback_end_array
 };
+#endif
 
 static void yajl_ctx_free(libxl__yajl_ctx *yajl_ctx)
 {
+#ifdef USE_LIBYAJL_PARSER
     if (yajl_ctx->hand) {
         yajl_free(yajl_ctx->hand);
         yajl_ctx->hand = NULL;
     }
+#endif
     DEBUG_GEN_FREE(yajl_ctx);
 }
 
+#ifdef USE_LIBJSONC_PARSER
+static int jso_visiter(json_object *jso,
+                       int flags,
+                       json_object *parent_jso,
+                       const char *jso_key,
+                       size_t *jso_index,
+                       void *userarg)
+{
+    enum json_type type;
+    int r;
+
+    if (jso_key && flags != JSON_C_VISIT_SECOND) {
+        json_callback_map_key(userarg, (const unsigned char*)jso_key, strlen(jso_key));
+    }
+    type = json_object_get_type(jso);
+    switch (type) {
+    case json_type_null:
+        r = json_callback_null(userarg);
+        break;
+    case json_type_boolean:
+        r = json_callback_boolean(userarg, json_object_get_boolean(jso));
+        break;
+    case json_type_int:
+    case json_type_double: {
+        // it might be better to use on of
+        // json_object_get_{int,int64,uint64,double} instead.
+        // but would need to replace json_callback_number().
+        const char *s = json_object_get_string(jso);
+        r = json_callback_number(userarg, s, strlen(s));
+        break;
+    }
+    case json_type_object:
+        if (flags != JSON_C_VISIT_SECOND) {
+            r = json_callback_start_map(userarg);
+        } else {
+            r = json_callback_end_map(userarg);
+        }
+        break;
+    case json_type_array:
+        if (flags != JSON_C_VISIT_SECOND) {
+            r = json_callback_start_array(userarg);
+        } else {
+            r = json_callback_end_array(userarg);
+        }
+        break;
+    case json_type_string: {
+        const char *s = json_object_get_string(jso);
+        const int len = json_object_get_string_len(jso);
+        r = json_callback_string(userarg, (const unsigned char*)s, len);
+        break;
+    }
+    default:
+        /* error */
+        r = 0;
+    }
+    if (r == 0)
+        return JSON_C_VISIT_RETURN_ERROR;
+    return JSON_C_VISIT_RETURN_CONTINUE;
+}
+#endif
+
 libxl__json_object *libxl__json_parse(libxl__gc *gc, const char *s)
 {
+#ifdef USE_LIBYAJL_PARSER
     yajl_status status;
+    unsigned char *str = NULL;
+#endif
     libxl__yajl_ctx yajl_ctx;
     libxl__json_object *o = NULL;
-    unsigned char *str = NULL;
+#ifdef USE_LIBJSONC_PARSER
+    json_object *jso;
+    enum json_tokener_error error;
+
+    jso = json_tokener_parse_verbose(s, &error);
+    if (!jso) {
+        LOG(ERROR, "json-c parse error: %s", json_tokener_error_desc(error));
+        goto out;
+    }
+#endif
 
     memset(&yajl_ctx, 0, sizeof (yajl_ctx));
     yajl_ctx.gc = gc;
 
     DEBUG_GEN_ALLOC(&yajl_ctx);
 
+#ifdef USE_LIBJSONC_PARSER
+    int r = json_c_visit(jso, 0, jso_visiter, &yajl_ctx);
+    if (r < 0) {
+        LOG(ERROR, "json_c_visit failed");
+        goto out;
+    }
+#elif defined(USE_LIBYAJL_PARSER)
     if (yajl_ctx.hand == NULL) {
         yajl_ctx.hand = libxl__yajl_alloc(&callbacks, NULL, &yajl_ctx);
     }
@@ -935,6 +1039,7 @@ libxl__json_object *libxl__json_parse(libxl__gc *gc, const char *s)
     status = yajl_complete_parse(yajl_ctx.hand);
     if (status != yajl_status_ok)
         goto out;
+#endif
 
     o = yajl_ctx.head;
 
@@ -943,13 +1048,20 @@ libxl__json_object *libxl__json_parse(libxl__gc *gc, const char *s)
     yajl_ctx.head = NULL;
 
     yajl_ctx_free(&yajl_ctx);
+#ifdef USE_LIBJSONC_PARSER
+    json_object_put(jso);
+#endif
     return o;
 
 out:
+#ifdef USE_LIBJSONC_PARSER
+    json_object_put(jso);
+#elif defined(USE_LIBYAJL_PARSER)
     str = yajl_get_error(yajl_ctx.hand, 1, (const unsigned char*)s, strlen(s));
 
     LIBXL__LOG(libxl__gc_owner(gc), LIBXL__LOG_ERROR, "yajl error: %s", str);
     yajl_free_error(yajl_ctx.hand, str);
+#endif
     yajl_ctx_free(&yajl_ctx);
     return NULL;
 }
-- 
Anthony PERARD

On 29.09.2025 14:07, Anthony PERARD wrote:
> --- a/tools/libs/light/libxl_json.c
> +++ b/tools/libs/light/libxl_json.c
> @@ -16,7 +16,25 @@
>  
>  #include <math.h>
>  
> +#ifdef HAVE_LIBJSONC
> +#include <json-c/json.h>
> +#define USE_LIBJSONC_PARSER
> +#endif
> +
> +#ifdef HAVE_LIBYAJL
> +#  ifndef USE_LIBJSONC_PARSER
> +#    define USE_LIBYAJL_PARSER
> +#  endif
> +#endif
> +
> +
> +#ifdef USE_LIBJSONC_PARSER
> +#include <json-c/json_visit.h>
> +#endif

The version of json-c one of my systems is using also doesn't have this header.

Plus (uses originating from other patches in this series)
json_object_object_add() returns void there. Plus of course any number of further
issues I'm going to see. The checking configure.ac is doing right now looks to be
insufficient overall.

Jan

On Thu, Oct 16, 2025 at 12:45:57PM +0200, Jan Beulich wrote:
> On 29.09.2025 14:07, Anthony PERARD wrote:
> > --- a/tools/libs/light/libxl_json.c
> > +++ b/tools/libs/light/libxl_json.c
> > @@ -16,7 +16,25 @@
> >  
> >  #include <math.h>
> >  
> > +#ifdef HAVE_LIBJSONC
> > +#include <json-c/json.h>
> > +#define USE_LIBJSONC_PARSER
> > +#endif
> > +
> > +#ifdef HAVE_LIBYAJL
> > +#  ifndef USE_LIBJSONC_PARSER
> > +#    define USE_LIBYAJL_PARSER
> > +#  endif
> > +#endif
> > +
> > +
> > +#ifdef USE_LIBJSONC_PARSER
> > +#include <json-c/json_visit.h>
> > +#endif
> 
> The version of json-c one of my systems is using also doesn't have this header.

Looks like this was introduced in 0.13, with json_c_visit().

> Plus (uses originating from other patches in this series)
> json_object_object_add() returns void there. Plus of course any number of further
> issues I'm going to see. The checking configure.ac is doing right now looks to be
> insufficient overall.

json_object_object_add() prototype was change in 0.13 it seems,
according to
https://github.com/json-c/json-c/blob/master/ChangeLog

Also, another patch (xenstat) was using a deprecated function
json_object_object_get(), but the deprecation seems to have been removed
in 0.13.

I've tried to build with our Ubuntu 20.04 docker image, on which we can
install json-c 0.13 and found other missing functions.

Both json_object_new_null() and json_object_new_uint64() are missing,
the first one isn't needed, but I think we need the second one. Both
were introduced in json-c 0.14.

And last one, json_object_new_array_ext() which was introduced in 0.15.
We could replace it by json_object_new_array() if needed.

Overall, is seems the current code needs json-c 0.15, so 
    -PKG_CHECK_MODULES([libjsonc], [json-c],
    +PKG_CHECK_MODULES([libjsonc], [json-c >= 0.15],

I'll prepare a patch.

Cheers,

-- 
Anthony PERARD