[libc] Fix strtok_r crash when src and *saveptr are both nullptr

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[sivachandra]

Couple of nits inline. I can submit this for you after you update.

libc/src/string/string_utils.h

79

Can we avoid this pattern and do it in two steps:

*src = '\0';
src++;

libc/test/src/string/strtok_r_test.cpp

89

May be add:

ASSERT_STREQ(reserver, nullptr);

May be that is what your intention was below, but not sure.

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[gAlfonso-bit]

libc/test/src/string/strtok_r_test.cpp

89

Yeah that is what I meant. Thank you!

[sivachandra]

Will submit shortly.

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

[sivachandra]

I need your name and email address to attribute this change to you.

[gAlfonso-bit]

This comment was removed by gAlfonso-bit.

libc/src/string/string_utils.h

 #ifndef LIBC_SRC_STRING_STRING_UTILS_H
 #define LIBC_SRC_STRING_STRING_UTILS_H
 
+#include "src/__support/common.h"
 #include "utils/CPP/Bitset.h"
 #include <stddef.h> // size_t
 

 static inline char *string_token(char *__restrict src,
                                  const char *__restrict delimiter_string,
                                  char **__restrict saveptr) {
+  // Return nullptr immediately if both src AND saveptr are nullptr
+  if (unlikely(src == nullptr && ((src = *saveptr) == nullptr)))
+    return nullptr;
+
   cpp::Bitset<256> delimiter_set;
-  for (; *delimiter_string; ++delimiter_string)
+  for (; *delimiter_string != '\0'; ++delimiter_string)
     delimiter_set.set(*delimiter_string);
 
-  src = src ? src : *saveptr;
-  for (; *src && delimiter_set.test(*src); ++src)
+  for (; *src != '\0' && delimiter_set.test(*src); ++src)
     ;
-  if (!*src) {
+  if (*src == '\0') {
     *saveptr = src;
     return nullptr;
   }
   char *token = src;
-  for (; *src && !delimiter_set.test(*src); ++src)
-    ;
-  if (*src) {
-    *src = '\0';
-    ++src;
+  for (; *src != '\0'; ++src) {
+    if (delimiter_set.test(*src)) {
+      *src = '\0';
+      ++src;
+      break;
+    }
   }
   *saveptr = src;
   return token;

libc/test/src/string/strtok_r_test.cpp

   ASSERT_STREQ(__llvm_libc::strtok_r(nullptr, ",", &reserve), nullptr);
 }
 
+TEST(LlvmLibcStrTokReentrantTest,
+     ShouldReturnNullptrWhenBothSrcAndSaveptrAreNull) {
+  char *src = nullptr;
+  char *reserve = nullptr;
+  // Ensure that instead of crashing if src and reserve are null, nullptr is
+  // returned
+  ASSERT_STREQ(__llvm_libc::strtok_r(src, ",", &reserve), nullptr);
+  // And that neither src nor reserve are changed when that happens
+  ASSERT_STREQ(src, nullptr);
+  ASSERT_STREQ(reserve, nullptr);
+}
+
 TEST(LlvmLibcStrTokReentrantTest,
      SubsequentCallsShouldFindFollowingDelimiters) {
   char src[] = "12,34.56";