Support empty Cords with an expected checksum

PiperOrigin-RevId: 484578104
Change-Id: Ie4be3e4de27dc28d88395e16fd075fb10ab7a302

3 files changed, 17 insertions, 9 deletions

diff --git a/absl/strings/internal/cord_rep_crc.cc b/absl/strings/internal/cord_rep_crc.cc
index ee140354..7d7273ef 100644
--- a/absl/strings/internal/cord_rep_crc.cc
+++ b/absl/strings/internal/cord_rep_crc.cc
@@ -25,8 +25,7 @@ ABSL_NAMESPACE_BEGIN
 namespace cord_internal {
 
 CordRepCrc* CordRepCrc::New(CordRep* child, uint32_t crc) {
-  assert(child != nullptr);
-  if (child->IsCrc()) {
+  if (child != nullptr && child->IsCrc()) {
     if (child->refcount.IsOne()) {
       child->crc()->crc = crc;
       return child->crc();
@@ -37,7 +36,7 @@ CordRepCrc* CordRepCrc::New(CordRep* child, uint32_t crc) {
     CordRep::Unref(old);
   }
   auto* new_cordrep = new CordRepCrc;
-  new_cordrep->length = child->length;
+  new_cordrep->length = child != nullptr ? child->length : 0;
   new_cordrep->tag = cord_internal::CRC;
   new_cordrep->child = child;
   new_cordrep->crc = crc;
@@ -45,7 +44,9 @@ CordRepCrc* CordRepCrc::New(CordRep* child, uint32_t crc) {
 }
 
 void CordRepCrc::Destroy(CordRepCrc* node) {
-  CordRep::Unref(node->child);
+  if (node->child != nullptr) {
+    CordRep::Unref(node->child);
+  }
   delete node;
 }
 
diff --git a/absl/strings/internal/cord_rep_crc.h b/absl/strings/internal/cord_rep_crc.h
index 5294b0d1..455a1127 100644
--- a/absl/strings/internal/cord_rep_crc.h
+++ b/absl/strings/internal/cord_rep_crc.h
@@ -40,7 +40,7 @@ struct CordRepCrc : public CordRep {
   // If the specified `child` is itself a CordRepCrc node, then this method
   // either replaces the existing node, or directly updates the crc value in it
   // depending on the node being shared or not, i.e.: refcount.IsOne().
-  // `child` must not be null. Never returns null.
+  // `child` must only be null if the Cord is empty. Never returns null.
   static CordRepCrc* New(CordRep* child, uint32_t crc);
 
   // Destroys (deletes) the provided node. `node` must not be null.
diff --git a/absl/strings/internal/cord_rep_crc_test.cc b/absl/strings/internal/cord_rep_crc_test.cc
index d73ea7b3..42a9110b 100644
--- a/absl/strings/internal/cord_rep_crc_test.cc
+++ b/absl/strings/internal/cord_rep_crc_test.cc
@@ -27,14 +27,11 @@ namespace {
 
 using ::absl::cordrep_testing::MakeFlat;
 using ::testing::Eq;
+using ::testing::IsNull;
 using ::testing::Ne;
 
 #if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
 
-TEST(CordRepCrc, NewWithNullPtr) {
-  EXPECT_DEATH(CordRepCrc::New(nullptr, 0), "");
-}
-
 TEST(CordRepCrc, RemoveCrcWithNullptr) {
   EXPECT_DEATH(RemoveCrcNode(nullptr), "");
 }
@@ -82,6 +79,16 @@ TEST(CordRepCrc, NewExistingCrcShared) {
   CordRep::Unref(new_crc);
 }
 
+TEST(CordRepCrc, NewEmpty) {
+  CordRepCrc* crc = CordRepCrc::New(nullptr, 12345);
+  EXPECT_TRUE(crc->refcount.IsOne());
+  EXPECT_THAT(crc->child, IsNull());
+  EXPECT_THAT(crc->length, Eq(0u));
+  EXPECT_THAT(crc->crc, Eq(12345u));
+  EXPECT_TRUE(crc->refcount.IsOne());
+  CordRepCrc::Destroy(crc);
+}
+
 TEST(CordRepCrc, RemoveCrcNotCrc) {
   CordRep* rep = cordrep_testing::MakeFlat("Hello world");
   CordRep* nocrc = RemoveCrcNode(rep);