adb: fix front_size, front_data.

Bug: https://issuetracker.google.com/150827486
Test: adb_test
Change-Id: I3d2c73a20a703d793efb56e592cf33149815f89b

adb/types.cpp

@@ -51,7 +51,7 @@ void IOVector::drop_front(IOVector::size_type len) {
     auto dropped = 0u;
     while (dropped < len) {
         const auto next = chain_[start_index_].size() - begin_offset_;
-        if (dropped + next < len) {
+        if (dropped + next <= len) {
             pop_front_block();
             dropped += next;
         } else {

adb/types.h

@@ -155,7 +155,7 @@ struct IOVector {
             return nullptr;
         }
 
-        return chain_.front().data() + begin_offset_;
+        return chain_[start_index_].data() + begin_offset_;
     }
 
     size_type front_size() const {
@@ -163,7 +163,7 @@ struct IOVector {
             return 0;
         }
 
-        return chain_.front().size() - begin_offset_;
+        return chain_[start_index_].size() - begin_offset_;
     }
 
     size_type size() const { return chain_length_ - begin_offset_; }

adb/types_test.cpp

@@ -117,3 +117,20 @@ TEST(IOVector, misaligned_split) {
     ASSERT_EQ(1ULL, bc.size());
     ASSERT_EQ(create_block("x"), bc.coalesce());
 }
+
+TEST(IOVector, drop_front) {
+    IOVector vec;
+
+    vec.append(create_block('x', 2));
+    vec.append(create_block('y', 1000));
+    ASSERT_EQ(2U, vec.front_size());
+    ASSERT_EQ(1002U, vec.size());
+
+    vec.drop_front(1);
+    ASSERT_EQ(1U, vec.front_size());
+    ASSERT_EQ(1001U, vec.size());
+
+    vec.drop_front(1);
+    ASSERT_EQ(1000U, vec.front_size());
+    ASSERT_EQ(1000U, vec.size());
+}