diff --git a/adb/Android.bp b/adb/Android.bp
index d605907..bd1f124 100644
--- a/adb/Android.bp
+++ b/adb/Android.bp
@@ -134,6 +134,7 @@
     "transport_fd.cpp",
     "transport_local.cpp",
     "transport_usb.cpp",
+    "types.cpp",
 ]
 
 libadb_posix_srcs = [
diff --git a/adb/daemon/usb.cpp b/adb/daemon/usb.cpp
index 1abae87..a9ad805 100644
--- a/adb/daemon/usb.cpp
+++ b/adb/daemon/usb.cpp
@@ -117,14 +117,18 @@
     }
 };
 
+template <class Payload>
 struct IoBlock {
     bool pending = false;
     struct iocb control = {};
-    std::shared_ptr<Block> payload;
+    Payload payload;
 
     TransferId id() const { return TransferId::from_value(control.aio_data); }
 };
 
+using IoReadBlock = IoBlock<Block>;
+using IoWriteBlock = IoBlock<std::shared_ptr<Block>>;
+
 struct ScopedAioContext {
     ScopedAioContext() = default;
     ~ScopedAioContext() { reset(); }
@@ -208,16 +212,17 @@
 
     virtual bool Write(std::unique_ptr<apacket> packet) override final {
         LOG(DEBUG) << "USB write: " << dump_header(&packet->msg);
-        Block header(sizeof(packet->msg));
-        memcpy(header.data(), &packet->msg, sizeof(packet->msg));
+        auto header = std::make_shared<Block>(sizeof(packet->msg));
+        memcpy(header->data(), &packet->msg, sizeof(packet->msg));
 
         std::lock_guard<std::mutex> lock(write_mutex_);
-        write_requests_.push_back(CreateWriteBlock(std::move(header), next_write_id_++));
+        write_requests_.push_back(
+                CreateWriteBlock(std::move(header), 0, sizeof(packet->msg), next_write_id_++));
         if (!packet->payload.empty()) {
             // The kernel attempts to allocate a contiguous block of memory for each write,
             // which can fail if the write is large and the kernel heap is fragmented.
             // Split large writes into smaller chunks to avoid this.
-            std::shared_ptr<Block> payload = std::make_shared<Block>(std::move(packet->payload));
+            auto payload = std::make_shared<Block>(std::move(packet->payload));
             size_t offset = 0;
             size_t len = payload->size();
 
@@ -464,16 +469,20 @@
         worker_thread_.join();
     }
 
-    void PrepareReadBlock(IoBlock* block, uint64_t id) {
+    void PrepareReadBlock(IoReadBlock* block, uint64_t id) {
         block->pending = false;
-        block->payload = std::make_shared<Block>(kUsbReadSize);
+        if (block->payload.capacity() >= kUsbReadSize) {
+            block->payload.resize(kUsbReadSize);
+        } else {
+            block->payload = Block(kUsbReadSize);
+        }
         block->control.aio_data = static_cast<uint64_t>(TransferId::read(id));
-        block->control.aio_buf = reinterpret_cast<uintptr_t>(block->payload->data());
-        block->control.aio_nbytes = block->payload->size();
+        block->control.aio_buf = reinterpret_cast<uintptr_t>(block->payload.data());
+        block->control.aio_nbytes = block->payload.size();
     }
 
-    IoBlock CreateReadBlock(uint64_t id) {
-        IoBlock block;
+    IoReadBlock CreateReadBlock(uint64_t id) {
+        IoReadBlock block;
         PrepareReadBlock(&block, id);
         block.control.aio_rw_flags = 0;
         block.control.aio_lio_opcode = IOCB_CMD_PREAD;
@@ -518,9 +527,9 @@
 
     void HandleRead(TransferId id, int64_t size) {
         uint64_t read_idx = id.id % kUsbReadQueueDepth;
-        IoBlock* block = &read_requests_[read_idx];
+        IoReadBlock* block = &read_requests_[read_idx];
         block->pending = false;
-        block->payload->resize(size);
+        block->payload.resize(size);
 
         // Notification for completed reads can be received out of order.
         if (block->id().id != needed_read_id_) {
@@ -531,7 +540,7 @@
 
         for (uint64_t id = needed_read_id_;; ++id) {
             size_t read_idx = id % kUsbReadQueueDepth;
-            IoBlock* current_block = &read_requests_[read_idx];
+            IoReadBlock* current_block = &read_requests_[read_idx];
             if (current_block->pending) {
                 break;
             }
@@ -540,19 +549,19 @@
         }
     }
 
-    void ProcessRead(IoBlock* block) {
-        if (!block->payload->empty()) {
+    void ProcessRead(IoReadBlock* block) {
+        if (!block->payload.empty()) {
             if (!incoming_header_.has_value()) {
-                CHECK_EQ(sizeof(amessage), block->payload->size());
-                amessage msg;
-                memcpy(&msg, block->payload->data(), sizeof(amessage));
+                CHECK_EQ(sizeof(amessage), block->payload.size());
+                amessage& msg = incoming_header_.emplace();
+                memcpy(&msg, block->payload.data(), sizeof(msg));
                 LOG(DEBUG) << "USB read:" << dump_header(&msg);
                 incoming_header_ = msg;
             } else {
                 size_t bytes_left = incoming_header_->data_length - incoming_payload_.size();
-                Block payload = std::move(*block->payload);
+                Block payload = std::move(block->payload);
                 CHECK_LE(payload.size(), bytes_left);
-                incoming_payload_.append(std::make_unique<Block>(std::move(payload)));
+                incoming_payload_.append(std::move(payload));
             }
 
             if (incoming_header_->data_length == incoming_payload_.size()) {
@@ -560,11 +569,15 @@
                 packet->msg = *incoming_header_;
 
                 // TODO: Make apacket contain an IOVector so we don't have to coalesce.
-                packet->payload = incoming_payload_.coalesce();
+                packet->payload = std::move(incoming_payload_).coalesce();
                 read_callback_(this, std::move(packet));
 
                 incoming_header_.reset();
-                incoming_payload_.clear();
+                // reuse the capacity of the incoming payload while we can.
+                auto free_block = incoming_payload_.clear();
+                if (block->payload.capacity() == 0) {
+                    block->payload = std::move(free_block);
+                }
             }
         }
 
@@ -572,7 +585,7 @@
         SubmitRead(block);
     }
 
-    bool SubmitRead(IoBlock* block) {
+    bool SubmitRead(IoReadBlock* block) {
         block->pending = true;
         struct iocb* iocb = &block->control;
         if (io_submit(aio_context_.get(), 1, &iocb) != 1) {
@@ -594,7 +607,7 @@
         std::lock_guard<std::mutex> lock(write_mutex_);
         auto it =
                 std::find_if(write_requests_.begin(), write_requests_.end(), [id](const auto& req) {
-                    return static_cast<uint64_t>(req->id()) == static_cast<uint64_t>(id);
+                    return static_cast<uint64_t>(req.id()) == static_cast<uint64_t>(id);
                 });
         CHECK(it != write_requests_.end());
 
@@ -605,27 +618,26 @@
         SubmitWrites();
     }
 
-    std::unique_ptr<IoBlock> CreateWriteBlock(std::shared_ptr<Block> payload, size_t offset,
-                                              size_t len, uint64_t id) {
-        auto block = std::make_unique<IoBlock>();
-        block->payload = std::move(payload);
-        block->control.aio_data = static_cast<uint64_t>(TransferId::write(id));
-        block->control.aio_rw_flags = 0;
-        block->control.aio_lio_opcode = IOCB_CMD_PWRITE;
-        block->control.aio_reqprio = 0;
-        block->control.aio_fildes = write_fd_.get();
-        block->control.aio_buf = reinterpret_cast<uintptr_t>(block->payload->data() + offset);
-        block->control.aio_nbytes = len;
-        block->control.aio_offset = 0;
-        block->control.aio_flags = IOCB_FLAG_RESFD;
-        block->control.aio_resfd = worker_event_fd_.get();
+    IoWriteBlock CreateWriteBlock(std::shared_ptr<Block> payload, size_t offset, size_t len,
+                                  uint64_t id) {
+        auto block = IoWriteBlock();
+        block.payload = std::move(payload);
+        block.control.aio_data = static_cast<uint64_t>(TransferId::write(id));
+        block.control.aio_rw_flags = 0;
+        block.control.aio_lio_opcode = IOCB_CMD_PWRITE;
+        block.control.aio_reqprio = 0;
+        block.control.aio_fildes = write_fd_.get();
+        block.control.aio_buf = reinterpret_cast<uintptr_t>(block.payload->data() + offset);
+        block.control.aio_nbytes = len;
+        block.control.aio_offset = 0;
+        block.control.aio_flags = IOCB_FLAG_RESFD;
+        block.control.aio_resfd = worker_event_fd_.get();
         return block;
     }
 
-    std::unique_ptr<IoBlock> CreateWriteBlock(Block payload, uint64_t id) {
-        std::shared_ptr<Block> block = std::make_shared<Block>(std::move(payload));
-        size_t len = block->size();
-        return CreateWriteBlock(std::move(block), 0, len, id);
+    IoWriteBlock CreateWriteBlock(Block&& payload, uint64_t id) {
+        size_t len = payload.size();
+        return CreateWriteBlock(std::make_shared<Block>(std::move(payload)), 0, len, id);
     }
 
     void SubmitWrites() REQUIRES(write_mutex_) {
@@ -642,9 +654,9 @@
 
         struct iocb* iocbs[kUsbWriteQueueDepth];
         for (int i = 0; i < writes_to_submit; ++i) {
-            CHECK(!write_requests_[writes_submitted_ + i]->pending);
-            write_requests_[writes_submitted_ + i]->pending = true;
-            iocbs[i] = &write_requests_[writes_submitted_ + i]->control;
+            CHECK(!write_requests_[writes_submitted_ + i].pending);
+            write_requests_[writes_submitted_ + i].pending = true;
+            iocbs[i] = &write_requests_[writes_submitted_ + i].control;
             LOG(VERBOSE) << "submitting write_request " << static_cast<void*>(iocbs[i]);
         }
 
@@ -689,7 +701,7 @@
     std::optional<amessage> incoming_header_;
     IOVector incoming_payload_;
 
-    std::array<IoBlock, kUsbReadQueueDepth> read_requests_;
+    std::array<IoReadBlock, kUsbReadQueueDepth> read_requests_;
     IOVector read_data_;
 
     // ID of the next request that we're going to send out.
@@ -699,7 +711,7 @@
     size_t needed_read_id_ = 0;
 
     std::mutex write_mutex_;
-    std::deque<std::unique_ptr<IoBlock>> write_requests_ GUARDED_BY(write_mutex_);
+    std::deque<IoWriteBlock> write_requests_ GUARDED_BY(write_mutex_);
     size_t next_write_id_ GUARDED_BY(write_mutex_) = 0;
     size_t writes_submitted_ GUARDED_BY(write_mutex_) = 0;
 
diff --git a/adb/sockets.cpp b/adb/sockets.cpp
index e78530c..7d5bf17 100644
--- a/adb/sockets.cpp
+++ b/adb/sockets.cpp
@@ -125,8 +125,7 @@
         if (rc > 0 && static_cast<size_t>(rc) == s->packet_queue.size()) {
             s->packet_queue.clear();
         } else if (rc > 0) {
-            // TODO: Implement a faster drop_front?
-            s->packet_queue.take_front(rc);
+            s->packet_queue.drop_front(rc);
             fdevent_add(s->fde, FDE_WRITE);
             return SocketFlushResult::TryAgain;
         } else if (rc == -1 && errno == EAGAIN) {
diff --git a/adb/transport_fd.cpp b/adb/transport_fd.cpp
index a93e68a..8d2ad66 100644
--- a/adb/transport_fd.cpp
+++ b/adb/transport_fd.cpp
@@ -93,8 +93,8 @@
 
                 if (pfds[0].revents & POLLIN) {
                     // TODO: Should we be getting blocks from a free list?
-                    auto block = std::make_unique<IOVector::block_type>(MAX_PAYLOAD);
-                    rc = adb_read(fd_.get(), &(*block)[0], block->size());
+                    auto block = IOVector::block_type(MAX_PAYLOAD);
+                    rc = adb_read(fd_.get(), &block[0], block.size());
                     if (rc == -1) {
                         *error = std::string("read failed: ") + strerror(errno);
                         return;
@@ -102,7 +102,7 @@
                         *error = "read failed: EOF";
                         return;
                     }
-                    block->resize(rc);
+                    block.resize(rc);
                     read_buffer_.append(std::move(block));
 
                     if (!read_header_ && read_buffer_.size() >= sizeof(amessage)) {
@@ -116,7 +116,7 @@
                         auto data_chain = read_buffer_.take_front(read_header_->data_length);
 
                         // TODO: Make apacket carry around a IOVector instead of coalescing.
-                        auto payload = data_chain.coalesce<apacket::payload_type>();
+                        auto payload = std::move(data_chain).coalesce();
                         auto packet = std::make_unique<apacket>();
                         packet->msg = *read_header_;
                         packet->payload = std::move(payload);
@@ -184,8 +184,7 @@
             return WriteResult::Error;
         }
 
-        // TODO: Implement a more efficient drop_front?
-        write_buffer_.take_front(rc);
+        write_buffer_.drop_front(rc);
         writable_ = write_buffer_.empty();
         if (write_buffer_.empty()) {
             return WriteResult::Completed;
@@ -199,10 +198,10 @@
         std::lock_guard<std::mutex> lock(write_mutex_);
         const char* header_begin = reinterpret_cast<const char*>(&packet->msg);
         const char* header_end = header_begin + sizeof(packet->msg);
-        auto header_block = std::make_unique<IOVector::block_type>(header_begin, header_end);
+        auto header_block = IOVector::block_type(header_begin, header_end);
         write_buffer_.append(std::move(header_block));
         if (!packet->payload.empty()) {
-            write_buffer_.append(std::make_unique<IOVector::block_type>(std::move(packet->payload)));
+            write_buffer_.append(std::move(packet->payload));
         }
 
         WriteResult result = DispatchWrites();
diff --git a/adb/types.cpp b/adb/types.cpp
new file mode 100644
index 0000000..26b77ab
--- /dev/null
+++ b/adb/types.cpp
@@ -0,0 +1,204 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "types.h"
+
+IOVector& IOVector::operator=(IOVector&& move) noexcept {
+    chain_ = std::move(move.chain_);
+    chain_length_ = move.chain_length_;
+    begin_offset_ = move.begin_offset_;
+    start_index_ = move.start_index_;
+
+    move.clear();
+    return *this;
+}
+
+IOVector::block_type IOVector::clear() {
+    chain_length_ = 0;
+    begin_offset_ = 0;
+    start_index_ = 0;
+    block_type res;
+    if (!chain_.empty()) {
+        res = std::move(chain_.back());
+    }
+    chain_.clear();
+    return res;
+}
+
+void IOVector::drop_front(IOVector::size_type len) {
+    if (len == 0) {
+        return;
+    }
+    if (len == size()) {
+        clear();
+        return;
+    }
+    CHECK_LT(len, size());
+
+    auto dropped = 0u;
+    while (dropped < len) {
+        const auto next = chain_[start_index_].size() - begin_offset_;
+        if (dropped + next < len) {
+            pop_front_block();
+            dropped += next;
+        } else {
+            const auto taken = len - dropped;
+            begin_offset_ += taken;
+            break;
+        }
+    }
+}
+
+IOVector IOVector::take_front(IOVector::size_type len) {
+    if (len == 0) {
+        return {};
+    }
+    if (len == size()) {
+        return std::move(*this);
+    }
+
+    CHECK_GE(size(), len);
+    IOVector res;
+    // first iterate over the blocks that completely go into the other vector
+    while (chain_[start_index_].size() - begin_offset_ <= len) {
+        chain_length_ -= chain_[start_index_].size();
+        len -= chain_[start_index_].size() - begin_offset_;
+        if (chain_[start_index_].size() > begin_offset_) {
+            res.append(std::move(chain_[start_index_]));
+            if (begin_offset_) {
+                res.begin_offset_ = std::exchange(begin_offset_, 0);
+            }
+        } else {
+            begin_offset_ = 0;
+        }
+        ++start_index_;
+    }
+
+    if (len > 0) {
+        // what's left is a single buffer that needs to be split between the |res| and |this|
+        // we know that it has to be split - there was a check for the case when it has to
+        // go away as a whole.
+        if (begin_offset_ != 0 || len < chain_[start_index_].size() / 2) {
+            // let's memcpy the data out
+            block_type block(chain_[start_index_].begin() + begin_offset_,
+                             chain_[start_index_].begin() + begin_offset_ + len);
+            res.append(std::move(block));
+            begin_offset_ += len;
+        } else {
+            CHECK_EQ(begin_offset_, 0u);
+            // move out the internal buffer out and copy only the tail of it back in
+            block_type block(chain_[start_index_].begin() + len, chain_[start_index_].end());
+            chain_length_ -= chain_[start_index_].size();
+            chain_[start_index_].resize(len);
+            res.append(std::move(chain_[start_index_]));
+            chain_length_ += block.size();
+            chain_[start_index_] = std::move(block);
+        }
+    }
+    return res;
+}
+
+void IOVector::trim_front() {
+    if ((begin_offset_ == 0 && start_index_ == 0) || chain_.empty()) {
+        return;
+    }
+    block_type& first_block = chain_[start_index_];
+    if (begin_offset_ == first_block.size()) {
+        ++start_index_;
+    } else {
+        memmove(first_block.data(), first_block.data() + begin_offset_,
+                first_block.size() - begin_offset_);
+        first_block.resize(first_block.size() - begin_offset_);
+    }
+    chain_length_ -= begin_offset_;
+    begin_offset_ = 0;
+    trim_chain_front();
+}
+
+void IOVector::trim_chain_front() {
+    if (start_index_) {
+        chain_.erase(chain_.begin(), chain_.begin() + start_index_);
+        start_index_ = 0;
+    }
+}
+
+void IOVector::pop_front_block() {
+    chain_length_ -= chain_[start_index_].size();
+    begin_offset_ = 0;
+    chain_[start_index_].clear();
+    ++start_index_;
+    if (start_index_ > std::max<size_t>(4, chain_.size() / 2)) {
+        trim_chain_front();
+    }
+}
+
+IOVector::block_type IOVector::coalesce() && {
+    // Destructive coalesce() may optimize for several cases when it doesn't need to allocate
+    // new buffer, or even return one of the existing blocks as is. The only guarantee is that
+    // after this call the IOVector is in some valid state. Nothing is guaranteed about the
+    // specifics.
+    if (size() == 0) {
+        return {};
+    }
+    if (begin_offset_ == chain_[start_index_].size() && chain_.size() == start_index_ + 2) {
+        chain_length_ -= chain_.back().size();
+        auto res = std::move(chain_.back());
+        chain_.pop_back();
+        return res;
+    }
+    if (chain_.size() == start_index_ + 1) {
+        chain_length_ -= chain_.back().size();
+        auto res = std::move(chain_.back());
+        chain_.pop_back();
+        if (begin_offset_ != 0) {
+            memmove(res.data(), res.data() + begin_offset_, res.size() - begin_offset_);
+            res.resize(res.size() - begin_offset_);
+            begin_offset_ = 0;
+        }
+        return res;
+    }
+    if (auto& firstBuffer = chain_[start_index_]; firstBuffer.capacity() >= size()) {
+        auto res = std::move(chain_[start_index_]);
+        auto size = res.size();
+        chain_length_ -= size;
+        if (begin_offset_ != 0) {
+            memmove(res.data(), res.data() + begin_offset_, res.size() - begin_offset_);
+            size -= begin_offset_;
+            begin_offset_ = 0;
+        }
+        for (auto i = start_index_ + 1; i < chain_.size(); ++i) {
+            memcpy(res.data() + size, chain_[i].data(), chain_[i].size());
+            size += chain_[i].size();
+        }
+        res.resize(size);
+        ++start_index_;
+        return res;
+    }
+    return const_cast<const IOVector*>(this)->coalesce<>();
+}
+
+std::vector<adb_iovec> IOVector::iovecs() const {
+    std::vector<adb_iovec> result;
+    result.reserve(chain_.size() - start_index_);
+    iterate_blocks([&result](const char* data, size_t len) {
+        adb_iovec iov;
+        iov.iov_base = const_cast<char*>(data);
+        iov.iov_len = len;
+        result.emplace_back(iov);
+    });
+
+    return result;
+}
diff --git a/adb/types.h b/adb/types.h
index 8bd66be..6b00224 100644
--- a/adb/types.h
+++ b/adb/types.h
@@ -19,9 +19,7 @@
 #include <string.h>
 
 #include <algorithm>
-#include <deque>
 #include <memory>
-#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -33,7 +31,7 @@
 struct Block {
     using iterator = char*;
 
-    Block() {}
+    Block() = default;
 
     explicit Block(size_t size) { allocate(size); }
 
@@ -43,24 +41,21 @@
     }
 
     Block(const Block& copy) = delete;
-    Block(Block&& move) noexcept {
-        std::swap(data_, move.data_);
-        std::swap(capacity_, move.capacity_);
-        std::swap(size_, move.size_);
-    }
+    Block(Block&& move) noexcept
+        : data_(std::exchange(move.data_, nullptr)),
+          capacity_(std::exchange(move.capacity_, 0)),
+          size_(std::exchange(move.size_, 0)) {}
 
     Block& operator=(const Block& copy) = delete;
     Block& operator=(Block&& move) noexcept {
         clear();
-
-        std::swap(data_, move.data_);
-        std::swap(capacity_, move.capacity_);
-        std::swap(size_, move.size_);
-
+        data_ = std::exchange(move.data_, nullptr);
+        capacity_ = std::exchange(move.capacity_, 0);
+        size_ = std::exchange(move.size_, 0);
         return *this;
     }
 
-    ~Block() { clear(); }
+    ~Block() = default;
 
     void resize(size_t new_size) {
         if (!data_) {
@@ -144,146 +139,63 @@
     using block_type = Block;
     using size_type = size_t;
 
-    IOVector() {}
+    IOVector() = default;
 
-    explicit IOVector(std::unique_ptr<block_type> block) {
-        append(std::move(block));
-    }
+    explicit IOVector(block_type&& block) { append(std::move(block)); }
 
     IOVector(const IOVector& copy) = delete;
     IOVector(IOVector&& move) noexcept : IOVector() { *this = std::move(move); }
 
     IOVector& operator=(const IOVector& copy) = delete;
-    IOVector& operator=(IOVector&& move) noexcept {
-        chain_ = std::move(move.chain_);
-        chain_length_ = move.chain_length_;
-        begin_offset_ = move.begin_offset_;
-        end_offset_ = move.end_offset_;
+    IOVector& operator=(IOVector&& move) noexcept;
 
-        move.chain_.clear();
-        move.chain_length_ = 0;
-        move.begin_offset_ = 0;
-        move.end_offset_ = 0;
-
-        return *this;
-    }
-
-    size_type size() const { return chain_length_ - begin_offset_ - end_offset_; }
+    size_type size() const { return chain_length_ - begin_offset_; }
     bool empty() const { return size() == 0; }
 
-    void clear() {
-        chain_length_ = 0;
-        begin_offset_ = 0;
-        end_offset_ = 0;
-        chain_.clear();
-    }
+    // Return the last block so the caller can still reuse its allocated capacity
+    // or it can be simply ignored.
+    block_type clear();
+
+    void drop_front(size_type len);
 
     // Split the first |len| bytes out of this chain into its own.
-    IOVector take_front(size_type len) {
-        IOVector head;
-
-        if (len == 0) {
-            return head;
-        }
-        CHECK_GE(size(), len);
-
-        std::shared_ptr<const block_type> first_block = chain_.front();
-        CHECK_GE(first_block->size(), begin_offset_);
-        head.append_shared(std::move(first_block));
-        head.begin_offset_ = begin_offset_;
-
-        while (head.size() < len) {
-            pop_front_block();
-            CHECK(!chain_.empty());
-
-            head.append_shared(chain_.front());
-        }
-
-        if (head.size() == len) {
-            // Head takes full ownership of the last block it took.
-            head.end_offset_ = 0;
-            begin_offset_ = 0;
-            pop_front_block();
-        } else {
-            // Head takes partial ownership of the last block it took.
-            size_t bytes_taken = head.size() - len;
-            head.end_offset_ = bytes_taken;
-            CHECK_GE(chain_.front()->size(), bytes_taken);
-            begin_offset_ = chain_.front()->size() - bytes_taken;
-        }
-
-        return head;
-    }
+    IOVector take_front(size_type len);
 
     // Add a nonempty block to the chain.
-    // The end of the chain must be a complete block (i.e. end_offset_ == 0).
-    void append(std::unique_ptr<const block_type> block) {
-        if (block->size() == 0) {
+    void append(block_type&& block) {
+        if (block.size() == 0) {
             return;
         }
-
-        CHECK_EQ(0ULL, end_offset_);
-        chain_length_ += block->size();
+        CHECK_NE(0ULL, block.size());
+        chain_length_ += block.size();
         chain_.emplace_back(std::move(block));
     }
 
-    void append(block_type&& block) { append(std::make_unique<block_type>(std::move(block))); }
-
-    void trim_front() {
-        if (begin_offset_ == 0) {
-            return;
-        }
-
-        const block_type* first_block = chain_.front().get();
-        auto copy = std::make_unique<block_type>(first_block->size() - begin_offset_);
-        memcpy(copy->data(), first_block->data() + begin_offset_, copy->size());
-        chain_.front() = std::move(copy);
-
-        chain_length_ -= begin_offset_;
-        begin_offset_ = 0;
-    }
+    void trim_front();
 
   private:
-    // append, except takes a shared_ptr.
-    // Private to prevent exterior mutation of blocks.
-    void append_shared(std::shared_ptr<const block_type> block) {
-        CHECK_NE(0ULL, block->size());
-        CHECK_EQ(0ULL, end_offset_);
-        chain_length_ += block->size();
-        chain_.emplace_back(std::move(block));
-    }
+    void trim_chain_front();
 
     // Drop the front block from the chain, and update chain_length_ appropriately.
-    void pop_front_block() {
-        chain_length_ -= chain_.front()->size();
-        begin_offset_ = 0;
-        chain_.pop_front();
-    }
+    void pop_front_block();
 
     // Iterate over the blocks with a callback with an operator()(const char*, size_t).
     template <typename Fn>
     void iterate_blocks(Fn&& callback) const {
-        if (chain_.size() == 0) {
+        if (size() == 0) {
             return;
         }
 
-        for (size_t i = 0; i < chain_.size(); ++i) {
-            const std::shared_ptr<const block_type>& block = chain_.at(i);
-            const char* begin = block->data();
-            size_t length = block->size();
+        for (size_t i = start_index_; i < chain_.size(); ++i) {
+            const auto& block = chain_[i];
+            const char* begin = block.data();
+            size_t length = block.size();
 
-            // Note that both of these conditions can be true if there's only one block.
-            if (i == 0) {
-                CHECK_GE(block->size(), begin_offset_);
+            if (i == start_index_) {
+                CHECK_GE(block.size(), begin_offset_);
                 begin += begin_offset_;
                 length -= begin_offset_;
             }
-
-            if (i == chain_.size() - 1) {
-                CHECK_GE(length, end_offset_);
-                length -= end_offset_;
-            }
-
             callback(begin, length);
         }
     }
@@ -291,7 +203,7 @@
   public:
     // Copy all of the blocks into a single block.
     template <typename CollectionType = block_type>
-    CollectionType coalesce() const {
+    CollectionType coalesce() const& {
         CollectionType result;
         if (size() == 0) {
             return result;
@@ -308,12 +220,13 @@
         return result;
     }
 
+    block_type coalesce() &&;
+
     template <typename FunctionType>
-    auto coalesced(FunctionType&& f) const ->
-        typename std::result_of<FunctionType(const char*, size_t)>::type {
-        if (chain_.size() == 1) {
+    auto coalesced(FunctionType&& f) const {
+        if (chain_.size() == start_index_ + 1) {
             // If we only have one block, we can use it directly.
-            return f(chain_.front()->data() + begin_offset_, size());
+            return f(chain_[start_index_].data() + begin_offset_, size());
         } else {
             // Otherwise, copy to a single block.
             auto data = coalesce();
@@ -322,23 +235,13 @@
     }
 
     // Get a list of iovecs that can be used to write out all of the blocks.
-    std::vector<adb_iovec> iovecs() const {
-        std::vector<adb_iovec> result;
-        iterate_blocks([&result](const char* data, size_t len) {
-            adb_iovec iov;
-            iov.iov_base = const_cast<char*>(data);
-            iov.iov_len = len;
-            result.emplace_back(iov);
-        });
-
-        return result;
-    }
+    std::vector<adb_iovec> iovecs() const;
 
   private:
     // Total length of all of the blocks in the chain.
     size_t chain_length_ = 0;
 
     size_t begin_offset_ = 0;
-    size_t end_offset_ = 0;
-    std::deque<std::shared_ptr<const block_type>> chain_;
+    size_t start_index_ = 0;
+    std::vector<block_type> chain_;
 };
diff --git a/adb/types_test.cpp b/adb/types_test.cpp
index 1fbd2ca..2c99f95 100644
--- a/adb/types_test.cpp
+++ b/adb/types_test.cpp
@@ -19,21 +19,21 @@
 #include <memory>
 #include "types.h"
 
-static std::unique_ptr<IOVector::block_type> create_block(const std::string& string) {
-    return std::make_unique<IOVector::block_type>(string.begin(), string.end());
+static IOVector::block_type create_block(const std::string& string) {
+    return IOVector::block_type(string.begin(), string.end());
 }
 
-static std::unique_ptr<IOVector::block_type> create_block(char value, size_t len) {
-    auto block = std::make_unique<IOVector::block_type>();
-    block->resize(len);
-    memset(&(*block)[0], value, len);
+static IOVector::block_type create_block(char value, size_t len) {
+    auto block = IOVector::block_type();
+    block.resize(len);
+    memset(&(block)[0], value, len);
     return block;
 }
 
 template <typename T>
-static std::unique_ptr<IOVector::block_type> copy_block(T&& block) {
-    auto copy = std::make_unique<IOVector::block_type>();
-    copy->assign(block->begin(), block->end());
+static IOVector::block_type copy_block(const T& block) {
+    auto copy = IOVector::block_type();
+    copy.assign(block.begin(), block.end());
     return copy;
 }
 
@@ -50,7 +50,7 @@
     bc.append(copy_block(block));
     ASSERT_EQ(100ULL, bc.size());
     auto coalesced = bc.coalesce();
-    ASSERT_EQ(*block, coalesced);
+    ASSERT_EQ(block, coalesced);
 }
 
 TEST(IOVector, single_block_split) {
@@ -60,8 +60,8 @@
     IOVector foo = bc.take_front(3);
     ASSERT_EQ(3ULL, foo.size());
     ASSERT_EQ(3ULL, bc.size());
-    ASSERT_EQ(*create_block("foo"), foo.coalesce());
-    ASSERT_EQ(*create_block("bar"), bc.coalesce());
+    ASSERT_EQ(create_block("foo"), foo.coalesce());
+    ASSERT_EQ(create_block("bar"), bc.coalesce());
 }
 
 TEST(IOVector, aligned_split) {
@@ -73,15 +73,15 @@
 
     IOVector foo = bc.take_front(3);
     ASSERT_EQ(3ULL, foo.size());
-    ASSERT_EQ(*create_block("foo"), foo.coalesce());
+    ASSERT_EQ(create_block("foo"), foo.coalesce());
 
     IOVector bar = bc.take_front(3);
     ASSERT_EQ(3ULL, bar.size());
-    ASSERT_EQ(*create_block("bar"), bar.coalesce());
+    ASSERT_EQ(create_block("bar"), bar.coalesce());
 
     IOVector baz = bc.take_front(3);
     ASSERT_EQ(3ULL, baz.size());
-    ASSERT_EQ(*create_block("baz"), baz.coalesce());
+    ASSERT_EQ(create_block("baz"), baz.coalesce());
 
     ASSERT_EQ(0ULL, bc.size());
 }
@@ -97,23 +97,23 @@
     // Aligned left, misaligned right, across multiple blocks.
     IOVector foob = bc.take_front(4);
     ASSERT_EQ(4ULL, foob.size());
-    ASSERT_EQ(*create_block("foob"), foob.coalesce());
+    ASSERT_EQ(create_block("foob"), foob.coalesce());
 
     // Misaligned left, misaligned right, in one block.
     IOVector a = bc.take_front(1);
     ASSERT_EQ(1ULL, a.size());
-    ASSERT_EQ(*create_block("a"), a.coalesce());
+    ASSERT_EQ(create_block("a"), a.coalesce());
 
     // Misaligned left, misaligned right, across two blocks.
     IOVector rba = bc.take_front(3);
     ASSERT_EQ(3ULL, rba.size());
-    ASSERT_EQ(*create_block("rba"), rba.coalesce());
+    ASSERT_EQ(create_block("rba"), rba.coalesce());
 
     // Misaligned left, misaligned right, across three blocks.
     IOVector zquxquu = bc.take_front(7);
     ASSERT_EQ(7ULL, zquxquu.size());
-    ASSERT_EQ(*create_block("zquxquu"), zquxquu.coalesce());
+    ASSERT_EQ(create_block("zquxquu"), zquxquu.coalesce());
 
     ASSERT_EQ(1ULL, bc.size());
-    ASSERT_EQ(*create_block("x"), bc.coalesce());
+    ASSERT_EQ(create_block("x"), bc.coalesce());
 }