1 files changed, 41 insertions, 2 deletions

diff --git a/absl/strings/cord.h b/absl/strings/cord.h
index abef98fe..17341bda 100644
--- a/absl/strings/cord.h
+++ b/absl/strings/cord.h
@@ -78,6 +78,8 @@
 #include "absl/functional/function_ref.h"
 #include "absl/meta/type_traits.h"
 #include "absl/strings/internal/cord_internal.h"
+#include "absl/strings/internal/cord_rep_ring.h"
+#include "absl/strings/internal/cord_rep_ring_reader.h"
 #include "absl/strings/internal/resize_uninitialized.h"
 #include "absl/strings/internal/string_constant.h"
 #include "absl/strings/string_view.h"
@@ -361,6 +363,10 @@ class Cord {
     friend class CharIterator;
 
    private:
+    using CordRep = absl::cord_internal::CordRep;
+    using CordRepRing = absl::cord_internal::CordRepRing;
+    using CordRepRingReader = absl::cord_internal::CordRepRingReader;
+
     // Stack of right children of concat nodes that we have to visit.
     // Keep this at the end of the structure to avoid cache-thrashing.
     // TODO(jgm): Benchmark to see if there's a more optimal value than 47 for
@@ -385,6 +391,10 @@ class Cord {
     // Stack specific operator++
     ChunkIterator& AdvanceStack();
 
+    // Ring buffer specific operator++
+    ChunkIterator& AdvanceRing();
+    void AdvanceBytesRing(size_t n);
+
     // Iterates `n` bytes, where `n` is expected to be greater than or equal to
     // `current_chunk_.size()`.
     void AdvanceBytesSlowPath(size_t n);
@@ -398,6 +408,10 @@ class Cord {
     absl::cord_internal::CordRep* current_leaf_ = nullptr;
     // The number of bytes left in the `Cord` over which we are iterating.
     size_t bytes_remaining_ = 0;
+
+    // Cord reader for ring buffers. Empty if not traversing a ring buffer.
+    CordRepRingReader ring_reader_;
+
     // See 'Stack' alias definition.
     Stack stack_of_right_children_;
   };
@@ -1107,6 +1121,11 @@ inline bool Cord::StartsWith(absl::string_view rhs) const {
 }
 
 inline void Cord::ChunkIterator::InitTree(cord_internal::CordRep* tree) {
+  if (tree->tag == cord_internal::RING) {
+    current_chunk_ = ring_reader_.Reset(tree->ring());
+    return;
+  }
+
   stack_of_right_children_.push_back(tree);
   operator++();
 }
@@ -1126,13 +1145,33 @@ inline Cord::ChunkIterator::ChunkIterator(const Cord* cord)
   }
 }
 
+inline Cord::ChunkIterator& Cord::ChunkIterator::AdvanceRing() {
+  current_chunk_ = ring_reader_.Next();
+  return *this;
+}
+
+inline void Cord::ChunkIterator::AdvanceBytesRing(size_t n) {
+  assert(n >= current_chunk_.size());
+  bytes_remaining_ -= n;
+  if (bytes_remaining_) {
+    if (n == current_chunk_.size()) {
+      current_chunk_ = ring_reader_.Next();
+    } else {
+      size_t offset = ring_reader_.length() - bytes_remaining_;
+      current_chunk_ = ring_reader_.Seek(offset);
+    }
+  } else {
+    current_chunk_ = {};
+  }
+}
+
 inline Cord::ChunkIterator& Cord::ChunkIterator::operator++() {
   ABSL_HARDENING_ASSERT(bytes_remaining_ > 0 &&
                         "Attempted to iterate past `end()`");
   assert(bytes_remaining_ >= current_chunk_.size());
   bytes_remaining_ -= current_chunk_.size();
   if (bytes_remaining_ > 0) {
-    return AdvanceStack();
+    return ring_reader_ ? AdvanceRing() : AdvanceStack();
   } else {
     current_chunk_ = {};
   }
@@ -1174,7 +1213,7 @@ inline void Cord::ChunkIterator::AdvanceBytes(size_t n) {
   if (ABSL_PREDICT_TRUE(n < current_chunk_.size())) {
     RemoveChunkPrefix(n);
   } else if (n != 0) {
-    AdvanceBytesSlowPath(n);
+    ring_reader_ ? AdvanceBytesRing(n) : AdvanceBytesSlowPath(n);
   }
 }