3 files changed, 63 insertions, 63 deletions

diff --git a/absl/strings/internal/cord_rep_btree_reader.cc b/absl/strings/internal/cord_rep_btree_reader.cc
index 3ba4314..5dc7696 100644
--- a/absl/strings/internal/cord_rep_btree_reader.cc
+++ b/absl/strings/internal/cord_rep_btree_reader.cc
@@ -52,14 +52,14 @@ absl::string_view CordRepBtreeReader::Read(size_t n, size_t chunk_size,
   // data, calling `navigator_.Current()` is not safe before checking if we
   // already consumed all remaining data.
   const size_t consumed_by_read = n - chunk_size - result.n;
-  if (consumed_ + consumed_by_read >= length()) {
-    consumed_ = length();
+  if (consumed_by_read >= remaining_) {
+    remaining_ = 0;
     return {};
   }
 
   // We did not read all data, return remaining data from current edge.
   edge = navigator_.Current();
-  consumed_ += consumed_by_read + edge->length;
+  remaining_ -= consumed_by_read + edge->length;
   return CordRepBtree::EdgeData(edge).substr(result.n);
 }
 
diff --git a/absl/strings/internal/cord_rep_btree_reader.h b/absl/strings/internal/cord_rep_btree_reader.h
index c19fa43..66e97f5 100644
--- a/absl/strings/internal/cord_rep_btree_reader.h
+++ b/absl/strings/internal/cord_rep_btree_reader.h
@@ -31,9 +31,7 @@ namespace cord_internal {
 // References to the underlying data are returned as absl::string_view values.
 // The most typical use case is a forward only iteration over tree data.
 // The class also provides `Skip()`, `Seek()` and `Read()` methods similar to
-// CordRepBtreeNavigator that allow more advanced navigation. The class provides
-// a `consumed` property which contains the end offset of the chunk last
-// returned to the user which is useful in cord iteration logic.
+// CordRepBtreeNavigator that allow more advanced navigation.
 //
 // Example: iterate over all data inside a cord btree:
 //
@@ -61,9 +59,9 @@ namespace cord_internal {
 //     absl::string_view sv = reader.Next();
 //   }
 //
-// It is important to notice that `consumed` represents the end position of the
-// last data edge returned to the caller, not the cumulative data returned to
-// the caller which can be less in cases of skipping or seeking over data.
+// It is important to notice that `remaining` is based on the end position of
+// the last data edge returned to the caller, not the cumulative data returned
+// to the caller which can be less in cases of skipping or seeking over data.
 //
 // For example, consider a cord btree with five data edges: "abc", "def", "ghi",
 // "jkl" and "mno":
@@ -71,14 +69,12 @@ namespace cord_internal {
 //   absl::string_view sv;
 //   CordRepBtreeReader reader;
 //
-//   sv = reader.Init(tree); // sv = "abc", reader.consumed() = 3
-//   sv = reader.Skip(4);    // sv = "hi",  reader.consumed() = 9
-//   sv = reader.Skip(2);    // sv = "l",   reader.consumed() = 12
-//   sv = reader.Next();     // sv = "mno", reader.consumed() = 15
+//   sv = reader.Init(tree); // sv = "abc", remaining = 12
+//   sv = reader.Skip(4);    // sv = "hi",  remaining = 6
+//   sv = reader.Skip(2);    // sv = "l",   remaining = 3
+//   sv = reader.Next();     // sv = "mno", remaining = 0
+//   sv = reader.Seek(1);    // sv = "bc", remaining = 12
 //
-// In the above example, `reader.consumed()` reflects the data edges iterated
-// over or skipped by the reader, not the amount of data 'consumed' by the
-// caller.
 class CordRepBtreeReader {
  public:
   using ReadResult = CordRepBtreeNavigator::ReadResult;
@@ -98,13 +94,14 @@ class CordRepBtreeReader {
   // Requires that the current instance is not empty.
   size_t length() const;
 
-  // Returns the end offset of the last navigated to chunk, which represents the
-  // total bytes 'consumed' relative to the start of the tree. The returned
-  // value is never zero. For example, initializing a reader with a tree with a
-  // first data edge of 19 bytes will return `consumed() = 19`. See also the
-  // class comments on the meaning of `consumed`.
-  // Requires that the current instance is not empty.
-  size_t consumed() const;
+  // Returns the number of remaining bytes available for iteration, which is the
+  // number of bytes directly following the end of the last chunk returned.
+  // This value will be zero if we iterated over the last edge in the bound
+  // tree, in which case any call to Next() or Skip() will return an empty
+  // string_view reflecting the EOF state.
+  // Note that a call to `Seek()` resets `remaining` to a value based on the
+  // end position of the chunk returned by that call.
+  size_t remaining() const { return remaining_; }
 
   // Resets this instance to an empty value.
   void Reset() { navigator_.Reset(); }
@@ -157,7 +154,7 @@ class CordRepBtreeReader {
   absl::string_view Seek(size_t offset);
 
  private:
-  size_t consumed_;
+  size_t remaining_ = 0;
   CordRepBtreeNavigator navigator_;
 };
 
@@ -166,23 +163,18 @@ inline size_t CordRepBtreeReader::length() const {
   return btree()->length;
 }
 
-inline size_t CordRepBtreeReader::consumed() const {
-  assert(btree() != nullptr);
-  return consumed_;
-}
-
 inline absl::string_view CordRepBtreeReader::Init(CordRepBtree* tree) {
   assert(tree != nullptr);
   const CordRep* edge = navigator_.InitFirst(tree);
-  consumed_ = edge->length;
+  remaining_ = tree->length - edge->length;;
   return CordRepBtree::EdgeData(edge);
 }
 
 inline absl::string_view CordRepBtreeReader::Next() {
-  assert(consumed() < length());
+  if (remaining_ == 0) return {};
   const CordRep* edge = navigator_.Next();
   assert(edge != nullptr);
-  consumed_ += edge->length;
+  remaining_ -= edge->length;
   return CordRepBtree::EdgeData(edge);
 }
 
@@ -192,23 +184,23 @@ inline absl::string_view CordRepBtreeReader::Skip(size_t skip) {
   const size_t edge_length = navigator_.Current()->length;
   CordRepBtreeNavigator::Position pos = navigator_.Skip(skip + edge_length);
   if (ABSL_PREDICT_FALSE(pos.edge == nullptr)) {
-    consumed_ = length();
+    remaining_ = 0;
     return {};
   }
   // The combined length of all edges skipped before `pos.edge` is `skip -
   // pos.offset`, all of which are 'consumed', as well as the current edge.
-  consumed_ += skip - pos.offset + pos.edge->length;
+  remaining_ -= skip - pos.offset + pos.edge->length;
   return CordRepBtree::EdgeData(pos.edge).substr(pos.offset);
 }
 
 inline absl::string_view CordRepBtreeReader::Seek(size_t offset) {
   const CordRepBtreeNavigator::Position pos = navigator_.Seek(offset);
   if (ABSL_PREDICT_FALSE(pos.edge == nullptr)) {
-    consumed_ = length();
+    remaining_ = 0;
     return {};
   }
   absl::string_view chunk = CordRepBtree::EdgeData(pos.edge).substr(pos.offset);
-  consumed_ = offset + chunk.length();
+  remaining_ = length() - offset - chunk.length();
   return chunk;
 }
 
diff --git a/absl/strings/internal/cord_rep_btree_reader_test.cc b/absl/strings/internal/cord_rep_btree_reader_test.cc
index 44d3365..9b27a81 100644
--- a/absl/strings/internal/cord_rep_btree_reader_test.cc
+++ b/absl/strings/internal/cord_rep_btree_reader_test.cc
@@ -58,22 +58,26 @@ TEST(CordRepBtreeReaderTest, Next) {
     CordRepBtree* node = CordRepBtreeFromFlats(flats);
 
     CordRepBtreeReader reader;
+    size_t remaining = data.length();
     absl::string_view chunk = reader.Init(node);
     EXPECT_THAT(chunk, Eq(data.substr(0, chunk.length())));
 
-    size_t consumed = chunk.length();
-    EXPECT_THAT(reader.consumed(), Eq(consumed));
+    remaining -= chunk.length();
+    EXPECT_THAT(reader.remaining(), Eq(remaining));
 
-    while (consumed < data.length()) {
+    while (remaining > 0) {
+      const size_t offset = data.length() - remaining;
       chunk = reader.Next();
-      EXPECT_THAT(chunk, Eq(data.substr(consumed, chunk.length())));
+      EXPECT_THAT(chunk, Eq(data.substr(offset, chunk.length())));
 
-      consumed += chunk.length();
-      EXPECT_THAT(reader.consumed(), Eq(consumed));
+      remaining -= chunk.length();
+      EXPECT_THAT(reader.remaining(), Eq(remaining));
     }
 
-    EXPECT_THAT(consumed, Eq(data.length()));
-    EXPECT_THAT(reader.consumed(), Eq(data.length()));
+    EXPECT_THAT(reader.remaining(), Eq(0));
+
+    // Verify trying to read beyond EOF returns empty string_view
+    EXPECT_THAT(reader.Next(), testing::IsEmpty());
 
     CordRep::Unref(node);
   }
@@ -92,19 +96,22 @@ TEST(CordRepBtreeReaderTest, Skip) {
     for (size_t skip1 = 0; skip1 < data.length() - kChars; ++skip1) {
       for (size_t skip2 = 0; skip2 < data.length() - kChars; ++skip2) {
         CordRepBtreeReader reader;
+        size_t remaining = data.length();
         absl::string_view chunk = reader.Init(node);
-        size_t consumed = chunk.length();
+        remaining -= chunk.length();
 
         chunk = reader.Skip(skip1);
-        ASSERT_THAT(chunk, Eq(data.substr(consumed + skip1, chunk.length())));
-        consumed += chunk.length() + skip1;
-        ASSERT_THAT(reader.consumed(), Eq(consumed));
+        size_t offset = data.length() - remaining;
+        ASSERT_THAT(chunk, Eq(data.substr(offset + skip1, chunk.length())));
+        remaining -= chunk.length() + skip1;
+        ASSERT_THAT(reader.remaining(), Eq(remaining));
 
-        if (consumed >= data.length()) continue;
+        if (remaining == 0) continue;
 
-        size_t skip = std::min(data.length() - consumed - 1, skip2);
+        size_t skip = std::min(remaining - 1, skip2);
         chunk = reader.Skip(skip);
-        ASSERT_THAT(chunk, Eq(data.substr(consumed + skip, chunk.length())));
+        offset = data.length() - remaining;
+        ASSERT_THAT(chunk, Eq(data.substr(offset + skip, chunk.length())));
       }
     }
 
@@ -118,7 +125,7 @@ TEST(CordRepBtreeReaderTest, SkipBeyondLength) {
   CordRepBtreeReader reader;
   reader.Init(tree);
   EXPECT_THAT(reader.Skip(100), IsEmpty());
-  EXPECT_THAT(reader.consumed(), Eq(6));
+  EXPECT_THAT(reader.remaining(), Eq(0));
   CordRep::Unref(tree);
 }
 
@@ -138,7 +145,8 @@ TEST(CordRepBtreeReaderTest, Seek) {
       absl::string_view chunk = reader.Seek(seek);
       ASSERT_THAT(chunk, Not(IsEmpty()));
       ASSERT_THAT(chunk, Eq(data.substr(seek, chunk.length())));
-      ASSERT_THAT(reader.consumed(), Eq(seek + chunk.length()));
+      ASSERT_THAT(reader.remaining(),
+                  Eq(data.length() - seek - chunk.length()));
     }
 
     CordRep::Unref(node);
@@ -151,9 +159,9 @@ TEST(CordRepBtreeReaderTest, SeekBeyondLength) {
   CordRepBtreeReader reader;
   reader.Init(tree);
   EXPECT_THAT(reader.Seek(6), IsEmpty());
-  EXPECT_THAT(reader.consumed(), Eq(6));
+  EXPECT_THAT(reader.remaining(), Eq(0));
   EXPECT_THAT(reader.Seek(100), IsEmpty());
-  EXPECT_THAT(reader.consumed(), Eq(6));
+  EXPECT_THAT(reader.remaining(), Eq(0));
   CordRep::Unref(tree);
 }
 
@@ -171,7 +179,7 @@ TEST(CordRepBtreeReaderTest, Read) {
   chunk = reader.Read(0, chunk.length(), tree);
   EXPECT_THAT(tree, Eq(nullptr));
   EXPECT_THAT(chunk, Eq("abcde"));
-  EXPECT_THAT(reader.consumed(), Eq(5));
+  EXPECT_THAT(reader.remaining(), Eq(10));
   EXPECT_THAT(reader.Next(), Eq("fghij"));
 
   // Read in full
@@ -180,7 +188,7 @@ TEST(CordRepBtreeReaderTest, Read) {
   EXPECT_THAT(tree, Ne(nullptr));
   EXPECT_THAT(CordToString(tree), Eq("abcdefghijklmno"));
   EXPECT_THAT(chunk, Eq(""));
-  EXPECT_THAT(reader.consumed(), Eq(15));
+  EXPECT_THAT(reader.remaining(), Eq(0));
   CordRep::Unref(tree);
 
   // Read < chunk bytes
@@ -189,7 +197,7 @@ TEST(CordRepBtreeReaderTest, Read) {
   ASSERT_THAT(tree, Ne(nullptr));
   EXPECT_THAT(CordToString(tree), Eq("abc"));
   EXPECT_THAT(chunk, Eq("de"));
-  EXPECT_THAT(reader.consumed(), Eq(5));
+  EXPECT_THAT(reader.remaining(), Eq(10));
   EXPECT_THAT(reader.Next(), Eq("fghij"));
   CordRep::Unref(tree);
 
@@ -199,7 +207,7 @@ TEST(CordRepBtreeReaderTest, Read) {
   ASSERT_THAT(tree, Ne(nullptr));
   EXPECT_THAT(CordToString(tree), Eq("cd"));
   EXPECT_THAT(chunk, Eq("e"));
-  EXPECT_THAT(reader.consumed(), Eq(5));
+  EXPECT_THAT(reader.remaining(), Eq(10));
   EXPECT_THAT(reader.Next(), Eq("fghij"));
   CordRep::Unref(tree);
 
@@ -209,7 +217,7 @@ TEST(CordRepBtreeReaderTest, Read) {
   ASSERT_THAT(tree, Ne(nullptr));
   EXPECT_THAT(CordToString(tree), Eq("fgh"));
   EXPECT_THAT(chunk, Eq("ij"));
-  EXPECT_THAT(reader.consumed(), Eq(10));
+  EXPECT_THAT(reader.remaining(), Eq(5));
   EXPECT_THAT(reader.Next(), Eq("klmno"));
   CordRep::Unref(tree);
 
@@ -219,7 +227,7 @@ TEST(CordRepBtreeReaderTest, Read) {
   ASSERT_THAT(tree, Ne(nullptr));
   EXPECT_THAT(CordToString(tree), Eq("cdefghijklmn"));
   EXPECT_THAT(chunk, Eq("o"));
-  EXPECT_THAT(reader.consumed(), Eq(15));
+  EXPECT_THAT(reader.remaining(), Eq(0));
   CordRep::Unref(tree);
 
   // Read across chunks landing on exact edge boundary
@@ -228,7 +236,7 @@ TEST(CordRepBtreeReaderTest, Read) {
   ASSERT_THAT(tree, Ne(nullptr));
   EXPECT_THAT(CordToString(tree), Eq("cdefghij"));
   EXPECT_THAT(chunk, Eq("klmno"));
-  EXPECT_THAT(reader.consumed(), Eq(15));
+  EXPECT_THAT(reader.remaining(), Eq(0));
   CordRep::Unref(tree);
 
   CordRep::Unref(node);
@@ -264,7 +272,7 @@ TEST(CordRepBtreeReaderTest, ReadExhaustive) {
 
         consumed += n;
         remaining -= n;
-        EXPECT_THAT(reader.consumed(), Eq(consumed + chunk.length()));
+        EXPECT_THAT(reader.remaining(), Eq(remaining - chunk.length()));
 
         if (remaining > 0) {
           ASSERT_FALSE(chunk.empty());