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CFE-4616: Fix control chars escaping in JSON serialization #260

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Merged
larsewi merged 1 commit into from
Dec 4, 2025
Merged

CFE-4616: Fix control chars escaping in JSON serialization #260

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57 changes: 56 additions & 1 deletion libutils/json.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1012,7 +1012,14 @@ void JsonEncodeStringWriter(
WriterWriteChar(writer, 't');
break;
default:
WriterWriteChar(writer, *c);
if (CharIsPrintableAscii(*c))
{
WriterWriteChar(writer, *c);
}
else
{
WriterWriteF(writer, "\\u%04x", (unsigned char) *c);
}
}
}
}
Expand All @@ -1026,6 +1033,41 @@ char *JsonEncodeString(const char *const unescaped_string)
return StringWriterClose(writer);
}

static bool HexStringToChar(const char *hex_string, char *res)
{
assert(hex_string != NULL);

const int hex_len = 4;
if (strlen(hex_string) < hex_len)
{
return false;
}

char tmp[hex_len + 1];
memcpy(tmp, hex_string, hex_len);
tmp[hex_len] = '\0';

for (int i = 0; i < hex_len; ++i)
{
if (!isdigit(tmp[i]) &&
!(tmp[i] >= 'A' && tmp[i] <= 'F') &&
!(tmp[i] >= 'a' && tmp[i] <= 'f'))
{
return false;
}
}

char *end;
long c = strtol(tmp, &end, 16);
if ((*end != '\0') || (c > 255) || (c < 0))
{
return false;
}

*res = (unsigned char) c;
return true;
}

static void JsonDecodeStringWriter(
const char *const escaped_string, Writer *const w)
{
Expand Down Expand Up @@ -1062,6 +1104,19 @@ static void JsonDecodeStringWriter(
WriterWriteChar(w, '\t');
c++;
break;
case 'u':
if (c[2] == '\0')
{
break;
}

char d;
if (HexStringToChar(c + 2, &d))
{
WriterWriteF(w, "%c", (unsigned char) d);
c += 5;
}
break;
default:
WriterWriteChar(w, *c);
break;
Expand Down
27 changes: 27 additions & 0 deletions tests/unit/json_test.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1846,6 +1846,33 @@ static void test_string_escape(void)
assert_json_strings_eq(
"Hello, world!\n'Blah', \"blah\".",
"Hello, world!\\n'Blah', \\\"blah\\\".");
assert_json_strings_eq(
"Hello blah",
"Hello \\u001bblah");

const char unescaped_short_hex[] = {
'B', 'l', 'a', 'h', '\\', 'u', '0', '0', '\0'};
const char escaped_short_hex[] = {
'B', 'l', 'a', 'h', '\\', '\\', 'u', '0', '0', '\0'};
assert_json_strings_eq(unescaped_short_hex, escaped_short_hex);

const char unescaped_invalid_u[] = {
'B', 'l', 'a', 'h', '\\', 'u', '\0'};
const char escaped_invalid_u[] = {
'B', 'l', 'a', 'h', '\\', '\\', 'u', '\0'};
assert_json_strings_eq(unescaped_invalid_u, escaped_invalid_u);

const char unescaped_valid_hex[] = {
'B', 'l', 'a', 'h', '\\', 'u', '0', '0', '1', 'b', '\0'};
const char escaped_valid_hex[] = {
'B', 'l', 'a', 'h', '\\', '\\', 'u', '0', '0', '1', 'b', '\0'};
assert_json_strings_eq(unescaped_valid_hex, escaped_valid_hex);

const char unescaped_invalid_hex[] = {
'B', 'l', 'a', 'h', '\\', 'u', '0', 'z', '1', 'b', '\0'};
const char escaped_invalid_hex[] = {
'B', 'l', 'a', 'h', '\\', '\\', 'u', '0', 'z', '1', 'b', '\0'};
assert_json_strings_eq(unescaped_invalid_hex, escaped_invalid_hex);
}

#define assert_json5_data_eq(_size, unescaped, escaped) \
Expand Down
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