Rewrite json_object_object_add to replace just the value if the key already exists so keys remain valid.

This is particularly useful when replacing values in a loop, since it allows
 the key used by json_object_object_foreach to continue to be used.

json_object.c

@@ -306,8 +306,20 @@ struct lh_table* json_object_get_object(struct json_object *jso)
 void json_object_object_add(struct json_object* jso, const char *key,
 			    struct json_object *val)
 {
-  lh_table_delete(jso->o.c_object, key);
-  lh_table_insert(jso->o.c_object, strdup(key), val);
+	// We lookup the entry and replace the value, rather than just deleting
+	// and re-adding it, so the existing key remains valid.
+	json_object *existing_value = NULL;
+	struct lh_entry *existing_entry;
+	existing_entry = lh_table_lookup_entry(jso->o.c_object, (void*)key);
+	if (!existing_entry)
+	{
+		lh_table_insert(jso->o.c_object, strdup(key), val);
+		return;
+	}
+	existing_value = (void *)existing_entry->v;
+	if (existing_value)
+		json_object_put(existing_value);
+	existing_entry->v = val;
 }
 
 struct json_object* json_object_object_get(struct json_object* jso, const char *key)

tests/Makefile.am

@@ -6,6 +6,7 @@ LIBJSON_LA=$(top_builddir)/libjson.la
 check_PROGRAMS = test1 test1Formatted 
 check_PROGRAMS += test2 test2Formatted
 check_PROGRAMS += test4
+check_PROGRAMS += testReplaceExisting
 check_PROGRAMS += test_parse_int64
 check_PROGRAMS += test_null
 check_PROGRAMS += test_cast
@@ -25,6 +26,8 @@ test2Formatted_CPPFLAGS = -DTEST_FORMATTED
 
 test4_LDADD = $(LIBJSON_LA)
 
+testReplaceExisting_LDADD = $(LIBJSON_LA)
+
 test_parse_int64_LDADD = $(LIBJSON_LA)
 
 test_null_LDADD = $(LIBJSON_LA)
@@ -33,7 +36,7 @@ test_cast_LDADD = $(LIBJSON_LA)
 
 test_parse_LDADD = $(LIBJSON_LA)
 
-TESTS = test1.test test2.test test4.test parse_int64.test test_null.test test_cast.test test_parse.test
+TESTS = test1.test test2.test test4.test testReplaceExisting.test parse_int64.test test_null.test test_cast.test test_parse.test
 
 TESTS+= test_printbuf.test
 check_PROGRAMS+=test_printbuf

tests/testReplaceExisting.c

@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <string.h>
+
+#include "json.h"
+
+int main(int argc, char **argv)
+{
+	MC_SET_DEBUG(1);
+
+	/*
+	 * Check that replacing an existing object keeps the key valid,
+	 * and that it keeps the order the same.
+	 */
+	json_object *my_object = json_object_new_object();
+	json_object_object_add(my_object, "foo1", json_object_new_string("bar1"));
+	json_object_object_add(my_object, "foo2", json_object_new_string("bar2"));
+	json_object_object_add(my_object, "foo3", json_object_new_string("bar3"));
+	const char *original_key = NULL;
+	int orig_count = 0;
+	json_object_object_foreach(my_object, key, val)
+	{
+		printf("Key at index %d is [%s]\n", orig_count, key);
+		orig_count++;
+		if (strcmp(key, "foo2") != 0)
+			continue;
+		printf("replacing value for key [%s]\n", key);
+		original_key = key;
+		json_object_object_add(my_object, key, json_object_new_string("zzz"));
+	}
+
+	printf("==== second loop starting ====\n");
+
+	int new_count = 0;
+	int retval = 0;
+	json_object_object_foreach(my_object, key2, val2)
+	{
+		printf("Key at index %d is [%s]\n", new_count, key2);
+		new_count++;
+		if (strcmp(key2, "foo2") != 0)
+			continue;
+		printf("pointer for key [%s] does %smatch\n", key2,
+		       (key2 == original_key) ? "" : "NOT ");
+		if (key2 != original_key)
+			retval = 1;
+	}
+	if (new_count != orig_count)
+	{
+		printf("mismatch between original count (%d) and new count (%d)\n",
+		       orig_count, new_count);
+		retval = 1;
+	}
+
+	return 0;
+}

tests/testReplaceExisting.expected

@@ -0,0 +1,9 @@
+Key at index 0 is [foo1]
+Key at index 1 is [foo2]
+replacing value for key [foo2]
+Key at index 2 is [foo3]
+==== second loop starting ====
+Key at index 0 is [foo1]
+Key at index 1 is [foo2]
+pointer for key [foo2] does match
+Key at index 2 is [foo3]

tests/testReplaceExisting.test

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+# Common definitions
+if test -z "$srcdir"; then
+    srcdir="${0%/*}"
+    test "$srcdir" = "$0" && srcdir=.
+    test -z "$srcdir" && srcdir=.
+fi
+. "$srcdir/test-defs.sh"
+
+run_output_test testReplaceExisting
+exit $?