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Fixed StringSubstring() case where the result is one character returns NULL #279

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Merged
craigcomstock merged 3 commits into from
Jun 24, 2026
Merged

Fixed StringSubstring() case where the result is one character returns NULL #279

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1fb9551
Fixed StringSubstring() case where one or zero characters should be r…
craigcomstock Jun 23, 2026
01977fb
Adjusted json.c HexStringToChar() to avoid gnu-folded-constant warnin…
craigcomstock Jun 23, 2026
8cbd0db
Adjusted expectations in one case where end is less than start, used …
craigcomstock Jun 23, 2026
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3 changes: 2 additions & 1 deletion libutils/json.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1043,7 +1043,8 @@ static bool HexStringToChar(const char *hex_string, char *res)
return false;
}

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

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4 changes: 2 additions & 2 deletions libutils/string_lib.c
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Expand Up @@ -418,9 +418,9 @@ char *StringSubstring(const char *source, size_t source_len, int start, int len)
start = source_len + start;
}

if (start >= end)
if (start > end)
{
return NULL;
return SafeStringDuplicate("");
}

char *result = xcalloc(end - start + 2, sizeof(char));
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55 changes: 54 additions & 1 deletion tests/unit/string_lib_test.c
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Expand Up @@ -369,6 +369,55 @@ static void test_substring_overshoot(void)
free(new_string);
}

static void test_substring_result_is_one_char(void)
{
{
char *new_string = StringSubstring("[1]", 3, 1, -1);
assert_string_equal(new_string, "1");
free(new_string);
}
{
char *new_string = StringSubstring("[1]", 3, 0, 1);
assert_string_equal(new_string, "[");
free(new_string);
}
{
char *new_string = StringSubstring("[1]", 3, 2, 1);
assert_string_equal(new_string, "]");
free(new_string);
}
{
char *new_string = StringSubstring("1", 1, 0, 1);
assert_string_equal(new_string, "1");
free(new_string);
}
{
char *new_string = StringSubstring("1", 1, 0, -1);
assert_string_equal(new_string, "1");
free(new_string);
}
{
char *new_string = StringSubstring("1", 1, 0, 0);
assert_string_equal(new_string, "");
free(new_string);
}
}

static void test_substring_empty_input(void)
{
char *new_string = StringSubstring("", 0, 0, 1);
assert_string_equal(new_string, "");
free(new_string);
}

Comment on lines +372 to +412

@olehermanse olehermanse Jun 22, 2026

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Cool, but let's maybe add a few more tests to be sure? I.e. what happens when the 1 char string is at the beginning or end? What happens when the input string is also 1 character? What about when the input or the result is 0 length?

static void test_substring_empty_output(void)
{
char *new_string = StringSubstring("\"\"", 2, 1, -1);
assert_string_equal(new_string, "");
free(new_string);
}


static void test_substring_positive(void)
{
char *new_string = StringSubstring("abcdef", 6, 2, 3);
Expand Down Expand Up @@ -396,8 +445,9 @@ static void test_substring_negative(void)
static void test_substring_evil(void)
{
char *new_string = StringSubstring("abcdef", 6, 4, -4);
assert_string_equal(new_string, "");
free(new_string);

assert_int_equal(new_string, NULL);
}

static void test_string_to_long(void)
Expand Down Expand Up @@ -1568,6 +1618,9 @@ int main()
unit_test(test_concatenate),

unit_test(test_substring_overshoot),
unit_test(test_substring_result_is_one_char),
unit_test(test_substring_empty_input),
unit_test(test_substring_empty_output),
unit_test(test_substring_positive),
unit_test(test_substring_negative_length),
unit_test(test_substring_negative),
Expand Down
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