str: reject empty substr in find_*()

Empty substring should be rejected in find_*() API families.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: msune

CHANGELOG.md

@@ -24,6 +24,7 @@ Legend:
 - [B] set: fix `cdada_set_find()` returning `true` on internal error
 - [B] str: fix uint32_t overflow in `cdada_str_erase()` bounds check
 - [B] str: fix `cdada_str_find_count()`/`cdada_str_find_all()` not returning `CDADA_E_NOT_FOUND`
+- [B] str: reject empty `substr` in `cdada_str_find_count()`/`cdada_str_find_all()`
 - [O] tests: add coverage for `cdada_strerr()` valid, boundary and high invalid values
 - [O] tests: add `oom_create_test` coverage for create paths (`list`, `map`, `queue`, `set`, `stack`, `str`, `bbitmap`)
 - [O] tests: add coverage for `cdada_str_replace_all()` empty-match invalid input and self-overlap replacement

src/str.cc

@@ -206,7 +206,7 @@ int cdada_str_find_count(const cdada_str_t* str, const char* substr,
 
 	CDADA_CHECK_MAGIC(m);
 
-	if(!substr || !n)
+	if(!substr || !n || !*substr)
 		return CDADA_E_INVALID;
 
 	std::string& s = *m->str;
@@ -243,7 +243,7 @@ int cdada_str_find_all(const cdada_str_t* str, const char* substr,
 
 	CDADA_CHECK_MAGIC(m);
 
-	if(!substr || !poss || !size || !cnt)
+	if(!substr || !poss || !size || !cnt || !*substr)
 		return CDADA_E_INVALID;
 
 	std::string& s = *m->str;

test/str_test.c

@@ -110,6 +110,7 @@ int test_basics(){
 	int rv;
 	cdada_str_t * s;
 	const char* ptr;
+	uint32_t count, poss[2];
 
 	void* ptr_not_null = (void*)0x123;
 
@@ -168,6 +169,8 @@ int test_basics(){
 	rv = cdada_str_find_count(s, (const char*)ptr_not_null,
 						(uint32_t*)NULL);
 	TEST_ASSERT(rv == CDADA_E_INVALID);
+	rv = cdada_str_find_count(s, "", &count);
+	TEST_ASSERT(rv == CDADA_E_INVALID);
 
 	rv = cdada_str_find_all(NULL, (const char*)ptr_not_null, 123,
 						(uint32_t*)ptr_not_null,
@@ -189,6 +192,8 @@ int test_basics(){
 						(uint32_t*)ptr_not_null,
 						(uint32_t*)NULL);
 	TEST_ASSERT(rv == CDADA_E_INVALID);
+	rv = cdada_str_find_all(s, "", 2, poss, &count);
+	TEST_ASSERT(rv == CDADA_E_INVALID);
 
 	rv = cdada_str_first_c(NULL, (char*)ptr_not_null);
 	TEST_ASSERT(rv == CDADA_E_INVALID);