wasm: Fix JSON parser to copy memory for strings and numbers

Previously the parser was constructing strings and numbers with
references to the input buffer memory. If that memory was freed after
the opa_json_parse() call, it would corrupt the strings and numbers
returned by the parse.

This commit just updates the parser to create a copy of the
string/number values. If this becomes a performance issue in the
future, we can introduce an optional API for callers that promise NOT
to free the input buffer.

Signed-off-by: Torin Sandall <torinsandall@gmail.com>

wasm/src/json.c

@@ -327,7 +327,14 @@ opa_value *opa_json_parse_string(int token, const char *buf, int len)
 {
     if (token == OPA_JSON_TOKEN_STRING)
     {
-        return opa_string(buf, len);
+        char *cpy = (char *)opa_malloc(len);
+
+        for (int i = 0; i < len; i++)
+        {
+            cpy[i] = buf[i];
+        }
+
+        return opa_string_allocated(cpy, len);
     }
 
     int max_len = opa_json_max_string_len(buf, len);
@@ -435,7 +442,14 @@ opa_value *opa_json_parse_string(int token, const char *buf, int len)
 
 opa_value *opa_json_parse_number(const char *buf, int len)
 {
-    return opa_number_ref(buf, len);
+    char *cpy = (char *)opa_malloc(len);
+
+    for (int i = 0; i < len; i++)
+    {
+        cpy[i] = buf[i];
+    }
+
+    return opa_number_ref_allocated(cpy, len);
 }
 
 opa_value *opa_json_parse_array(opa_json_lex *ctx)

wasm/src/value.c

@@ -662,7 +662,7 @@ void opa_value_free(opa_value *node)
         opa_free(opa_cast_boolean(node));
         return;
     case OPA_NUMBER:
-        opa_free(opa_cast_number(node));
+        opa_number_free(opa_cast_number(node));
         return;
     case OPA_STRING:
         opa_string_free(opa_cast_string(node));
@@ -881,9 +881,34 @@ opa_value *opa_number_ref(const char *s, size_t len)
     ret->repr = OPA_NUMBER_REPR_REF;
     ret->v.ref.s = s;
     ret->v.ref.len = len;
+    ret->v.ref.free = 0;
     return &ret->hdr;
 }
 
+opa_value *opa_number_ref_allocated(const char *s, size_t len)
+{
+    opa_number_t *ret = (opa_number_t *)opa_malloc(sizeof(opa_number_t));
+    ret->hdr.type = OPA_NUMBER;
+    ret->repr = OPA_NUMBER_REPR_REF;
+    ret->v.ref.s = s;
+    ret->v.ref.len = len;
+    ret->v.ref.free = 1;
+    return &ret->hdr;
+}
+
+void opa_number_free(opa_number_t *n)
+{
+    if (n->repr == OPA_NUMBER_REPR_REF)
+    {
+        if (n->v.ref.free)
+        {
+            opa_free((void *)n->v.ref.s);
+        }
+    }
+
+    opa_free(n);
+}
+
 int opa_number_try_int(opa_number_t *n, long long *i)
 {
     switch (n->repr)

wasm/src/value.h

@@ -34,6 +34,7 @@ typedef struct
 {
     const char *s;
     size_t len;
+    unsigned char free; // if set 's' is not a reference and should be freed
 } opa_number_ref_t;
 
 typedef struct
@@ -127,6 +128,7 @@ opa_value *opa_number_size(size_t v);
 opa_value *opa_number_int(long long v);
 opa_value *opa_number_float(double v);
 opa_value *opa_number_ref(const char *s, size_t len);
+opa_value *opa_number_ref_allocated(const char *s, size_t len);
 opa_value *opa_string(const char *v, size_t len);
 opa_value *opa_string_terminated(const char *v);
 opa_value *opa_string_allocated(const char *v, size_t len);
@@ -142,6 +144,7 @@ void opa_value_number_set_int(opa_value *v, long long i);
 
 int opa_number_try_int(opa_number_t *n, long long *i);
 double opa_number_as_float(opa_number_t *n);
+void opa_number_free(opa_number_t *n);
 
 void opa_string_free(opa_string_t *s);
 

wasm/tests/test.c

@@ -762,6 +762,27 @@ void test_opa_json_parse_composites()
     test("object nested", parse_crunch("{\"a\": {\"c\": 1, \"d\": 2}, \"b\": {\"e\": 3, \"f\": 4}}", &fixture_object2()->hdr));
 }
 
+void test_opa_json_parse_memory_ownership()
+{
+    char s[] = "[1,\"a\"]";
+
+    opa_value *result = opa_json_parse(s, sizeof(s));
+
+    opa_value *exp = opa_array();
+    opa_array_t *arr = opa_cast_array(exp);
+    opa_array_append(arr, opa_number_int(1));
+    opa_array_append(arr, opa_string("a", 1));
+
+    test("expected value", opa_value_compare(result, exp) == 0);
+
+    for (int i = 0; i < sizeof(s); i++)
+    {
+        s[i] = 0;
+    }
+
+    test("expected value after overwriting buffer", opa_value_compare(result, exp) == 0);
+}
+
 void test_opa_object_insert()
 {