Release absl::CordBuffer

absl::CordBuffer holds data for eventual inclusion within an existing
absl::Cord. CordBuffers are useful for building large Cords that may
require custom allocation of its associated memory, a pattern that is
common in zero-copy APIs.
PiperOrigin-RevId: 453212229
Change-Id: I6a8adc3a8d206691cb1b0001a9161e5080dd1c5f

1 files changed, 68 insertions, 0 deletions

diff --git a/absl/strings/cord.cc b/absl/strings/cord.cc
index c6ec1ecf..04dc7b90 100644
--- a/absl/strings/cord.cc
+++ b/absl/strings/cord.cc
@@ -34,6 +34,7 @@
 #include "absl/base/port.h"
 #include "absl/container/fixed_array.h"
 #include "absl/container/inlined_vector.h"
+#include "absl/strings/cord_buffer.h"
 #include "absl/strings/escaping.h"
 #include "absl/strings/internal/cord_data_edge.h"
 #include "absl/strings/internal/cord_internal.h"
@@ -520,6 +521,46 @@ inline void Cord::AppendImpl(C&& src) {
   contents_.AppendTree(rep, CordzUpdateTracker::kAppendCord);
 }
 
+static CordRep::ExtractResult ExtractAppendBuffer(CordRep* rep,
+                                                  size_t min_capacity) {
+  switch (rep->tag) {
+    case cord_internal::BTREE:
+      return CordRepBtree::ExtractAppendBuffer(rep->btree(), min_capacity);
+    default:
+      if (rep->IsFlat() && rep->refcount.IsOne() &&
+          rep->flat()->Capacity() - rep->length >= min_capacity) {
+        return {nullptr, rep};
+      }
+      return {rep, nullptr};
+  }
+}
+
+static CordBuffer CreateAppendBuffer(InlineData& data, size_t capacity) {
+  // Watch out for overflow, people can ask for size_t::max().
+  const size_t size = data.inline_size();
+  capacity = (std::min)(std::numeric_limits<size_t>::max() - size, capacity);
+  CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(size + capacity);
+  cord_internal::SmallMemmove(buffer.data(), data.as_chars(), size);
+  buffer.SetLength(size);
+  data = {};
+  return buffer;
+}
+
+CordBuffer Cord::GetAppendBufferSlowPath(size_t capacity, size_t min_capacity) {
+  auto constexpr method = CordzUpdateTracker::kGetAppendBuffer;
+  CordRep* tree = contents_.tree();
+  if (tree != nullptr) {
+    CordzUpdateScope scope(contents_.cordz_info(), method);
+    CordRep::ExtractResult result = ExtractAppendBuffer(tree, min_capacity);
+    if (result.extracted != nullptr) {
+      contents_.SetTreeOrEmpty(result.tree, scope);
+      return CordBuffer(result.extracted->flat());
+    }
+    return CordBuffer::CreateWithDefaultLimit(capacity);
+  }
+  return CreateAppendBuffer(contents_.data_, capacity);
+}
+
 void Cord::Append(const Cord& src) {
   AppendImpl(src);
 }
@@ -572,6 +613,33 @@ void Cord::PrependArray(absl::string_view src, MethodIdentifier method) {
   contents_.PrependTree(rep, method);
 }
 
+void Cord::AppendPrecise(absl::string_view src, MethodIdentifier method) {
+  assert(!src.empty());
+  assert(src.size() <= cord_internal::kMaxFlatLength);
+  if (contents_.remaining_inline_capacity() >= src.size()) {
+    const size_t inline_length = contents_.inline_size();
+    memcpy(contents_.data_.as_chars() + inline_length, src.data(), src.size());
+    contents_.set_inline_size(inline_length + src.size());
+  } else {
+    contents_.AppendTree(CordRepFlat::Create(src), method);
+  }
+}
+
+void Cord::PrependPrecise(absl::string_view src, MethodIdentifier method) {
+  assert(!src.empty());
+  assert(src.size() <= cord_internal::kMaxFlatLength);
+  if (contents_.remaining_inline_capacity() >= src.size()) {
+    const size_t inline_length = contents_.inline_size();
+    char data[InlineRep::kMaxInline + 1] = {0};
+    memcpy(data, src.data(), src.size());
+    memcpy(data + src.size(), contents_.data(), inline_length);
+    memcpy(contents_.data_.as_chars(), data, InlineRep::kMaxInline + 1);
+    contents_.set_inline_size(inline_length + src.size());
+  } else {
+    contents_.PrependTree(CordRepFlat::Create(src), method);
+  }
+}
+
 template <typename T, Cord::EnableIfString<T>>
 inline void Cord::Prepend(T&& src) {
   if (src.size() <= kMaxBytesToCopy) {