diff --git a/adb/client/incremental.cpp b/adb/client/incremental.cpp
index 9765292..2814932 100644
--- a/adb/client/incremental.cpp
+++ b/adb/client/incremental.cpp
@@ -16,13 +16,13 @@
 
 #include "incremental.h"
 
-#include <android-base/endian.h>
+#include "incremental_utils.h"
+
 #include <android-base/file.h>
 #include <android-base/stringprintf.h>
 #include <openssl/base64.h>
 
 #include "adb_client.h"
-#include "adb_io.h"
 #include "adb_utils.h"
 #include "commandline.h"
 #include "sysdeps.h"
@@ -31,65 +31,8 @@
 
 namespace incremental {
 
-namespace {
-
-static constexpr auto IDSIG = ".idsig"sv;
-
 using android::base::StringPrintf;
 
-using Size = int64_t;
-
-static inline int32_t read_int32(borrowed_fd fd) {
-    int32_t result;
-    return ReadFdExactly(fd, &result, sizeof(result)) ? result : -1;
-}
-
-static inline void append_int(borrowed_fd fd, std::vector<char>* bytes) {
-    int32_t le_val = read_int32(fd);
-    auto old_size = bytes->size();
-    bytes->resize(old_size + sizeof(le_val));
-    memcpy(bytes->data() + old_size, &le_val, sizeof(le_val));
-}
-
-static inline void append_bytes_with_size(borrowed_fd fd, std::vector<char>* bytes) {
-    int32_t le_size = read_int32(fd);
-    if (le_size < 0) {
-        return;
-    }
-    int32_t size = int32_t(le32toh(le_size));
-    auto old_size = bytes->size();
-    bytes->resize(old_size + sizeof(le_size) + size);
-    memcpy(bytes->data() + old_size, &le_size, sizeof(le_size));
-    ReadFdExactly(fd, bytes->data() + old_size + sizeof(le_size), size);
-}
-
-static inline std::pair<std::vector<char>, int32_t> read_id_sig_headers(borrowed_fd fd) {
-    std::vector<char> result;
-    append_int(fd, &result);              // version
-    append_bytes_with_size(fd, &result);  // hashingInfo
-    append_bytes_with_size(fd, &result);  // signingInfo
-    auto le_tree_size = read_int32(fd);
-    auto tree_size = int32_t(le32toh(le_tree_size));  // size of the verity tree
-    return {std::move(result), tree_size};
-}
-
-static inline Size verity_tree_size_for_file(Size fileSize) {
-    constexpr int INCFS_DATA_FILE_BLOCK_SIZE = 4096;
-    constexpr int SHA256_DIGEST_SIZE = 32;
-    constexpr int digest_size = SHA256_DIGEST_SIZE;
-    constexpr int hash_per_block = INCFS_DATA_FILE_BLOCK_SIZE / digest_size;
-
-    Size total_tree_block_count = 0;
-
-    auto block_count = 1 + (fileSize - 1) / INCFS_DATA_FILE_BLOCK_SIZE;
-    auto hash_block_count = block_count;
-    for (auto i = 0; hash_block_count > 1; i++) {
-        hash_block_count = (hash_block_count + hash_per_block - 1) / hash_per_block;
-        total_tree_block_count += hash_block_count;
-    }
-    return total_tree_block_count * INCFS_DATA_FILE_BLOCK_SIZE;
-}
-
 // Read, verify and return the signature bytes. Keeping fd at the position of start of verity tree.
 static std::pair<unique_fd, std::vector<char>> read_signature(Size file_size,
                                                               std::string signature_file,
@@ -104,7 +47,7 @@
         return {};
     }
 
-    unique_fd fd(adb_open(signature_file.c_str(), O_RDONLY | O_CLOEXEC));
+    unique_fd fd(adb_open(signature_file.c_str(), O_RDONLY));
     if (fd < 0) {
         if (!silent) {
             fprintf(stderr, "Failed to open signature file: %s. Abort.\n", signature_file.c_str());
@@ -172,9 +115,8 @@
             return {};
         }
 
-        auto file_desc =
-                StringPrintf("%s:%lld:%s:%s", android::base::Basename(file).c_str(),
-                             (long long)st.st_size, std::to_string(i).c_str(), signature.c_str());
+        auto file_desc = StringPrintf("%s:%lld:%d:%s:1", android::base::Basename(file).c_str(),
+                                      (long long)st.st_size, i, signature.c_str());
         command_args.push_back(std::move(file_desc));
 
         signature_fds.push_back(std::move(signature_fd));
@@ -190,21 +132,9 @@
         return {};
     }
 
-    // Pushing verity trees for all installation files.
-    for (auto&& local_fd : signature_fds) {
-        if (!copy_to_file(local_fd.get(), connection_fd.get())) {
-            if (!silent) {
-                fprintf(stderr, "Failed to stream tree bytes: %s. Abort.\n", strerror(errno));
-            }
-            return {};
-        }
-    }
-
     return connection_fd;
 }
 
-}  // namespace
-
 bool can_install(const Files& files) {
     for (const auto& file : files) {
         struct stat st;
diff --git a/adb/client/incremental_server.cpp b/adb/client/incremental_server.cpp
index 4b87d0a..1a1361c 100644
--- a/adb/client/incremental_server.cpp
+++ b/adb/client/incremental_server.cpp
@@ -1,4 +1,4 @@
-/*
+﻿/*
  * Copyright (C) 2020 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -44,9 +44,10 @@
 
 namespace incremental {
 
-static constexpr int kBlockSize = 4096;
+static constexpr int kHashesPerBlock = kBlockSize / kDigestSize;
 static constexpr int kCompressedSizeMax = kBlockSize * 0.95;
 static constexpr int8_t kTypeData = 0;
+static constexpr int8_t kTypeHash = 1;
 static constexpr int8_t kCompressionNone = 0;
 static constexpr int8_t kCompressionLZ4 = 1;
 static constexpr int kCompressBound = std::max(kBlockSize, LZ4_COMPRESSBOUND(kBlockSize));
@@ -132,41 +133,64 @@
     CompressionType compression_type;  // 1 byte
     BlockIdx block_idx;                // 4 bytes
     BlockSize block_size;              // 2 bytes
+
+    static constexpr size_t responseSizeFor(size_t dataSize) {
+        return dataSize + sizeof(ResponseHeader);
+    }
+} __attribute__((packed));
+
+template <size_t Size = kBlockSize>
+struct BlockBuffer {
+    ResponseHeader header;
+    char data[Size];
 } __attribute__((packed));
 
 // Holds streaming state for a file
 class File {
   public:
     // Plain file
-    File(const char* filepath, FileId id, int64_t size, unique_fd fd) : File(filepath, id, size) {
+    File(const char* filepath, FileId id, int64_t size, unique_fd fd, int64_t tree_offset,
+         unique_fd tree_fd)
+        : File(filepath, id, size, tree_offset) {
         this->fd_ = std::move(fd);
+        this->tree_fd_ = std::move(tree_fd);
         priority_blocks_ = PriorityBlocksForFile(filepath, fd_.get(), size);
     }
-    int64_t ReadBlock(BlockIdx block_idx, void* buf, bool* is_zip_compressed,
-                      std::string* error) const {
-        char* buf_ptr = static_cast<char*>(buf);
+    int64_t ReadDataBlock(BlockIdx block_idx, void* buf, bool* is_zip_compressed) const {
         int64_t bytes_read = -1;
         const off64_t offsetStart = blockIndexToOffset(block_idx);
-        bytes_read = adb_pread(fd_, &buf_ptr[sizeof(ResponseHeader)], kBlockSize, offsetStart);
+        bytes_read = adb_pread(fd_, buf, kBlockSize, offsetStart);
+        return bytes_read;
+    }
+    int64_t ReadTreeBlock(BlockIdx block_idx, void* buf) const {
+        int64_t bytes_read = -1;
+        const off64_t offsetStart = tree_offset_ + blockIndexToOffset(block_idx);
+        bytes_read = adb_pread(tree_fd_, buf, kBlockSize, offsetStart);
         return bytes_read;
     }
 
-    const unique_fd& RawFd() const { return fd_; }
     const std::vector<BlockIdx>& PriorityBlocks() const { return priority_blocks_; }
 
     std::vector<bool> sentBlocks;
     NumBlocks sentBlocksCount = 0;
 
+    std::vector<bool> sentTreeBlocks;
+
     const char* const filepath;
     const FileId id;
     const int64_t size;
 
   private:
-    File(const char* filepath, FileId id, int64_t size) : filepath(filepath), id(id), size(size) {
+    File(const char* filepath, FileId id, int64_t size, int64_t tree_offset)
+        : filepath(filepath), id(id), size(size), tree_offset_(tree_offset) {
         sentBlocks.resize(numBytesToNumBlocks(size));
+        sentTreeBlocks.resize(verity_tree_blocks_for_file(size));
     }
     unique_fd fd_;
     std::vector<BlockIdx> priority_blocks_;
+
+    unique_fd tree_fd_;
+    const int64_t tree_offset_;
 };
 
 class IncrementalServer {
@@ -174,6 +198,8 @@
     IncrementalServer(unique_fd adb_fd, unique_fd output_fd, std::vector<File> files)
         : adb_fd_(std::move(adb_fd)), output_fd_(std::move(output_fd)), files_(std::move(files)) {
         buffer_.reserve(kReadBufferSize);
+        pendingBlocksBuffer_.resize(kChunkFlushSize + 2 * kBlockSize);
+        pendingBlocks_ = pendingBlocksBuffer_.data() + sizeof(ChunkHeader);
     }
 
     bool Serve();
@@ -208,7 +234,11 @@
     void erase_buffer_head(int count) { buffer_.erase(buffer_.begin(), buffer_.begin() + count); }
 
     enum class SendResult { Sent, Skipped, Error };
-    SendResult SendBlock(FileId fileId, BlockIdx blockIdx, bool flush = false);
+    SendResult SendDataBlock(FileId fileId, BlockIdx blockIdx, bool flush = false);
+
+    bool SendTreeBlock(FileId fileId, int32_t fileBlockIdx, BlockIdx blockIdx);
+    bool SendTreeBlocksForDataBlock(FileId fileId, BlockIdx blockIdx);
+
     bool SendDone();
     void RunPrefetching();
 
@@ -228,7 +258,10 @@
     int compressed_ = 0, uncompressed_ = 0;
     long long sentSize_ = 0;
 
-    std::vector<char> pendingBlocks_;
+    static constexpr auto kChunkFlushSize = 31 * kBlockSize;
+
+    std::vector<char> pendingBlocksBuffer_;
+    char* pendingBlocks_ = nullptr;
 
     // True when client notifies that all the data has been received
     bool servingComplete_;
@@ -250,7 +283,7 @@
 
         if (bcur > 0) {
             // output the rest.
-            WriteFdExactly(output_fd_, buffer_.data(), bcur);
+            (void)WriteFdExactly(output_fd_, buffer_.data(), bcur);
             erase_buffer_head(bcur);
         }
 
@@ -265,9 +298,10 @@
         auto res = adb_poll(&pfd, 1, blocking ? kPollTimeoutMillis : 0);
 
         if (res != 1) {
-            WriteFdExactly(output_fd_, buffer_.data(), buffer_.size());
+            auto err = errno;
+            (void)WriteFdExactly(output_fd_, buffer_.data(), buffer_.size());
             if (res < 0) {
-                D("Failed to poll: %s\n", strerror(errno));
+                D("Failed to poll: %s", strerror(err));
                 return false;
             }
             if (blocking) {
@@ -289,7 +323,7 @@
             continue;
         }
 
-        D("Failed to read from fd %d: %d. Exit\n", adb_fd_.get(), errno);
+        D("Failed to read from fd %d: %d. Exit", adb_fd_.get(), errno);
         break;
     }
     // socket is closed. print remaining messages
@@ -313,56 +347,113 @@
     return request;
 }
 
-auto IncrementalServer::SendBlock(FileId fileId, BlockIdx blockIdx, bool flush) -> SendResult {
+bool IncrementalServer::SendTreeBlocksForDataBlock(const FileId fileId, const BlockIdx blockIdx) {
+    auto& file = files_[fileId];
+    const int32_t data_block_count = numBytesToNumBlocks(file.size);
+
+    const int32_t total_nodes_count(file.sentTreeBlocks.size());
+    const int32_t leaf_nodes_count = (data_block_count + kHashesPerBlock - 1) / kHashesPerBlock;
+
+    const int32_t leaf_nodes_offset = total_nodes_count - leaf_nodes_count;
+
+    // Leaf level, sending only 1 block.
+    const int32_t leaf_idx = leaf_nodes_offset + blockIdx / kHashesPerBlock;
+    if (file.sentTreeBlocks[leaf_idx]) {
+        return true;
+    }
+    if (!SendTreeBlock(fileId, blockIdx, leaf_idx)) {
+        return false;
+    }
+    file.sentTreeBlocks[leaf_idx] = true;
+
+    // Non-leaf, sending EVERYTHING. This should be done only once.
+    if (leaf_nodes_offset == 0 || file.sentTreeBlocks[0]) {
+        return true;
+    }
+
+    for (int32_t i = 0; i < leaf_nodes_offset; ++i) {
+        if (!SendTreeBlock(fileId, blockIdx, i)) {
+            return false;
+        }
+        file.sentTreeBlocks[i] = true;
+    }
+    return true;
+}
+
+bool IncrementalServer::SendTreeBlock(FileId fileId, int32_t fileBlockIdx, BlockIdx blockIdx) {
+    const auto& file = files_[fileId];
+
+    BlockBuffer buffer;
+    const int64_t bytesRead = file.ReadTreeBlock(blockIdx, buffer.data);
+    if (bytesRead <= 0) {
+        fprintf(stderr, "Failed to get data for %s.idsig at blockIdx=%d.\n", file.filepath,
+                blockIdx);
+        return false;
+    }
+
+    buffer.header.compression_type = kCompressionNone;
+    buffer.header.block_type = kTypeHash;
+    buffer.header.file_id = toBigEndian(fileId);
+    buffer.header.block_size = toBigEndian(int16_t(bytesRead));
+    buffer.header.block_idx = toBigEndian(blockIdx);
+
+    Send(&buffer, ResponseHeader::responseSizeFor(bytesRead), /*flush=*/false);
+
+    return true;
+}
+
+auto IncrementalServer::SendDataBlock(FileId fileId, BlockIdx blockIdx, bool flush) -> SendResult {
     auto& file = files_[fileId];
     if (blockIdx >= static_cast<long>(file.sentBlocks.size())) {
-        fprintf(stderr, "Failed to read file %s at block %" PRId32 " (past end).\n", file.filepath,
-                blockIdx);
-        return SendResult::Error;
+        // may happen as we schedule some extra blocks for reported page misses
+        D("Skipped reading file %s at block %" PRId32 " (past end).", file.filepath, blockIdx);
+        return SendResult::Skipped;
     }
     if (file.sentBlocks[blockIdx]) {
         return SendResult::Skipped;
     }
-    std::string error;
-    char raw[sizeof(ResponseHeader) + kBlockSize];
-    bool isZipCompressed = false;
-    const int64_t bytesRead = file.ReadBlock(blockIdx, &raw, &isZipCompressed, &error);
-    if (bytesRead < 0) {
-        fprintf(stderr, "Failed to get data for %s at blockIdx=%d (%s).\n", file.filepath, blockIdx,
-                error.c_str());
+
+    if (!SendTreeBlocksForDataBlock(fileId, blockIdx)) {
         return SendResult::Error;
     }
 
-    ResponseHeader* header = nullptr;
-    char data[sizeof(ResponseHeader) + kCompressBound];
-    char* compressed = data + sizeof(*header);
+    BlockBuffer raw;
+    bool isZipCompressed = false;
+    const int64_t bytesRead = file.ReadDataBlock(blockIdx, raw.data, &isZipCompressed);
+    if (bytesRead < 0) {
+        fprintf(stderr, "Failed to get data for %s at blockIdx=%d (%d).\n", file.filepath, blockIdx,
+                errno);
+        return SendResult::Error;
+    }
+
+    BlockBuffer<kCompressBound> compressed;
     int16_t compressedSize = 0;
     if (!isZipCompressed) {
-        compressedSize =
-                LZ4_compress_default(raw + sizeof(*header), compressed, bytesRead, kCompressBound);
+        compressedSize = LZ4_compress_default(raw.data, compressed.data, bytesRead, kCompressBound);
     }
     int16_t blockSize;
+    ResponseHeader* header;
     if (compressedSize > 0 && compressedSize < kCompressedSizeMax) {
         ++compressed_;
         blockSize = compressedSize;
-        header = reinterpret_cast<ResponseHeader*>(data);
+        header = &compressed.header;
         header->compression_type = kCompressionLZ4;
     } else {
         ++uncompressed_;
         blockSize = bytesRead;
-        header = reinterpret_cast<ResponseHeader*>(raw);
+        header = &raw.header;
         header->compression_type = kCompressionNone;
     }
 
     header->block_type = kTypeData;
-
     header->file_id = toBigEndian(fileId);
     header->block_size = toBigEndian(blockSize);
     header->block_idx = toBigEndian(blockIdx);
 
     file.sentBlocks[blockIdx] = true;
     file.sentBlocksCount += 1;
-    Send(header, sizeof(*header) + blockSize, flush);
+    Send(header, ResponseHeader::responseSizeFor(blockSize), flush);
+
     return SendResult::Sent;
 }
 
@@ -388,7 +479,8 @@
         if (!priority_blocks.empty()) {
             for (auto& i = prefetch.priorityIndex;
                  blocksToSend > 0 && i < (BlockIdx)priority_blocks.size(); ++i) {
-                if (auto res = SendBlock(file.id, priority_blocks[i]); res == SendResult::Sent) {
+                if (auto res = SendDataBlock(file.id, priority_blocks[i]);
+                    res == SendResult::Sent) {
                     --blocksToSend;
                 } else if (res == SendResult::Error) {
                     fprintf(stderr, "Failed to send priority block %" PRId32 "\n", i);
@@ -396,7 +488,7 @@
             }
         }
         for (auto& i = prefetch.overallIndex; blocksToSend > 0 && i < prefetch.overallEnd; ++i) {
-            if (auto res = SendBlock(file.id, i); res == SendResult::Sent) {
+            if (auto res = SendDataBlock(file.id, i); res == SendResult::Sent) {
                 --blocksToSend;
             } else if (res == SendResult::Error) {
                 fprintf(stderr, "Failed to send block %" PRId32 "\n", i);
@@ -409,30 +501,25 @@
 }
 
 void IncrementalServer::Send(const void* data, size_t size, bool flush) {
-    constexpr auto kChunkFlushSize = 31 * kBlockSize;
-
-    if (pendingBlocks_.empty()) {
-        pendingBlocks_.resize(sizeof(ChunkHeader));
-    }
-    pendingBlocks_.insert(pendingBlocks_.end(), static_cast<const char*>(data),
-                          static_cast<const char*>(data) + size);
-    if (flush || pendingBlocks_.size() > kChunkFlushSize) {
+    pendingBlocks_ = std::copy_n(static_cast<const char*>(data), size, pendingBlocks_);
+    if (flush || pendingBlocks_ - pendingBlocksBuffer_.data() > kChunkFlushSize) {
         Flush();
     }
 }
 
 void IncrementalServer::Flush() {
-    if (pendingBlocks_.empty()) {
+    auto dataBytes = pendingBlocks_ - (pendingBlocksBuffer_.data() + sizeof(ChunkHeader));
+    if (dataBytes == 0) {
         return;
     }
 
-    *(ChunkHeader*)pendingBlocks_.data() =
-            toBigEndian<int32_t>(pendingBlocks_.size() - sizeof(ChunkHeader));
-    if (!WriteFdExactly(adb_fd_, pendingBlocks_.data(), pendingBlocks_.size())) {
-        fprintf(stderr, "Failed to write %d bytes\n", int(pendingBlocks_.size()));
+    *(ChunkHeader*)pendingBlocksBuffer_.data() = toBigEndian<int32_t>(dataBytes);
+    auto totalBytes = sizeof(ChunkHeader) + dataBytes;
+    if (!WriteFdExactly(adb_fd_, pendingBlocksBuffer_.data(), totalBytes)) {
+        fprintf(stderr, "Failed to write %d bytes\n", int(totalBytes));
     }
-    sentSize_ += pendingBlocks_.size();
-    pendingBlocks_.clear();
+    sentSize_ += totalBytes;
+    pendingBlocks_ = pendingBlocksBuffer_.data() + sizeof(ChunkHeader);
 }
 
 bool IncrementalServer::ServingComplete(std::optional<TimePoint> startTime, int missesCount,
@@ -443,7 +530,7 @@
     D("Streaming completed.\n"
       "Misses: %d, of those unique: %d; sent compressed: %d, uncompressed: "
       "%d, mb: %.3f\n"
-      "Total time taken: %.3fms\n",
+      "Total time taken: %.3fms",
       missesCount, missesSent, compressed_, uncompressed_, sentSize_ / 1024.0 / 1024.0,
       duration_cast<microseconds>(endTime - (startTime ? *startTime : endTime)).count() / 1000.0);
     return true;
@@ -510,9 +597,21 @@
                                 fileId, blockIdx);
                         break;
                     }
-                    // fprintf(stderr, "\treading file %d block %04d\n", (int)fileId,
-                    // (int)blockIdx);
-                    if (auto res = SendBlock(fileId, blockIdx, true); res == SendResult::Error) {
+
+                    if (VLOG_IS_ON(INCREMENTAL)) {
+                        auto& file = files_[fileId];
+                        auto posP = std::find(file.PriorityBlocks().begin(),
+                                              file.PriorityBlocks().end(), blockIdx);
+                        D("\tMISSING BLOCK: reading file %d block %04d (in priority: %d of %d)",
+                          (int)fileId, (int)blockIdx,
+                          posP == file.PriorityBlocks().end()
+                                  ? -1
+                                  : int(posP - file.PriorityBlocks().begin()),
+                          int(file.PriorityBlocks().size()));
+                    }
+
+                    if (auto res = SendDataBlock(fileId, blockIdx, true);
+                        res == SendResult::Error) {
                         fprintf(stderr, "Failed to send block %" PRId32 ".\n", blockIdx);
                     } else if (res == SendResult::Sent) {
                         ++missesSent;
@@ -536,7 +635,7 @@
                                 fileId);
                         break;
                     }
-                    D("Received prefetch request for file_id %" PRId16 ".\n", fileId);
+                    D("Received prefetch request for file_id %" PRId16 ".", fileId);
                     prefetches_.emplace_back(files_[fileId]);
                     break;
                 }
@@ -551,6 +650,43 @@
     }
 }
 
+static std::pair<unique_fd, int64_t> open_fd(const char* filepath) {
+    struct stat st;
+    if (stat(filepath, &st)) {
+        error_exit("inc-server: failed to stat input file '%s'.", filepath);
+    }
+
+    unique_fd fd(adb_open(filepath, O_RDONLY));
+    if (fd < 0) {
+        error_exit("inc-server: failed to open file '%s'.", filepath);
+    }
+
+    return {std::move(fd), st.st_size};
+}
+
+static std::pair<unique_fd, int64_t> open_signature(int64_t file_size, const char* filepath) {
+    std::string signature_file(filepath);
+    signature_file += IDSIG;
+
+    unique_fd fd(adb_open(signature_file.c_str(), O_RDONLY));
+    if (fd < 0) {
+        error_exit("inc-server: failed to open file '%s'.", signature_file.c_str());
+    }
+
+    auto [tree_offset, tree_size] = skip_id_sig_headers(fd);
+    if (auto expected = verity_tree_size_for_file(file_size); tree_size != expected) {
+        error_exit("Verity tree size mismatch in signature file: %s [was %lld, expected %lld].\n",
+                   signature_file.c_str(), (long long)tree_size, (long long)expected);
+    }
+
+    int32_t data_block_count = numBytesToNumBlocks(file_size);
+    int32_t leaf_nodes_count = (data_block_count + kHashesPerBlock - 1) / kHashesPerBlock;
+    D("Verity tree loaded: %s, tree size: %d (%d blocks, %d leafs)", signature_file.c_str(),
+      int(tree_size), int(numBytesToNumBlocks(tree_size)), int(leaf_nodes_count));
+
+    return {std::move(fd), tree_offset};
+}
+
 bool serve(int connection_fd, int output_fd, int argc, const char** argv) {
     auto connection_ufd = unique_fd(connection_fd);
     auto output_ufd = unique_fd(output_fd);
@@ -563,17 +699,11 @@
     for (int i = 0; i < argc; ++i) {
         auto filepath = argv[i];
 
-        struct stat st;
-        if (stat(filepath, &st)) {
-            fprintf(stderr, "Failed to stat input file %s. Abort.\n", filepath);
-            return {};
-        }
+        auto [file_fd, file_size] = open_fd(filepath);
+        auto [sign_fd, sign_offset] = open_signature(file_size, filepath);
 
-        unique_fd fd(adb_open(filepath, O_RDONLY));
-        if (fd < 0) {
-            error_exit("inc-server: failed to open file '%s'.", filepath);
-        }
-        files.emplace_back(filepath, i, st.st_size, std::move(fd));
+        files.emplace_back(filepath, i, file_size, std::move(file_fd), sign_offset,
+                           std::move(sign_fd));
     }
 
     IncrementalServer server(std::move(connection_ufd), std::move(output_ufd), std::move(files));
diff --git a/adb/client/incremental_utils.cpp b/adb/client/incremental_utils.cpp
index fa501e4..dd117d2 100644
--- a/adb/client/incremental_utils.cpp
+++ b/adb/client/incremental_utils.cpp
@@ -18,6 +18,7 @@
 
 #include "incremental_utils.h"
 
+#include <android-base/endian.h>
 #include <android-base/mapped_file.h>
 #include <android-base/strings.h>
 #include <ziparchive/zip_archive.h>
@@ -28,19 +29,98 @@
 #include <numeric>
 #include <unordered_set>
 
+#include "adb_io.h"
 #include "adb_trace.h"
 #include "sysdeps.h"
 
 using namespace std::literals;
 
-static constexpr int kBlockSize = 4096;
+namespace incremental {
 
 static constexpr inline int32_t offsetToBlockIndex(int64_t offset) {
     return (offset & ~(kBlockSize - 1)) >> 12;
 }
 
+Size verity_tree_blocks_for_file(Size fileSize) {
+    if (fileSize == 0) {
+        return 0;
+    }
+
+    constexpr int hash_per_block = kBlockSize / kDigestSize;
+
+    Size total_tree_block_count = 0;
+
+    auto block_count = 1 + (fileSize - 1) / kBlockSize;
+    auto hash_block_count = block_count;
+    for (auto i = 0; hash_block_count > 1; i++) {
+        hash_block_count = (hash_block_count + hash_per_block - 1) / hash_per_block;
+        total_tree_block_count += hash_block_count;
+    }
+    return total_tree_block_count;
+}
+
+Size verity_tree_size_for_file(Size fileSize) {
+    return verity_tree_blocks_for_file(fileSize) * kBlockSize;
+}
+
+static inline int32_t read_int32(borrowed_fd fd) {
+    int32_t result;
+    return ReadFdExactly(fd, &result, sizeof(result)) ? result : -1;
+}
+
+static inline int32_t skip_int(borrowed_fd fd) {
+    return adb_lseek(fd, 4, SEEK_CUR);
+}
+
+static inline void append_int(borrowed_fd fd, std::vector<char>* bytes) {
+    int32_t le_val = read_int32(fd);
+    auto old_size = bytes->size();
+    bytes->resize(old_size + sizeof(le_val));
+    memcpy(bytes->data() + old_size, &le_val, sizeof(le_val));
+}
+
+static inline void append_bytes_with_size(borrowed_fd fd, std::vector<char>* bytes) {
+    int32_t le_size = read_int32(fd);
+    if (le_size < 0) {
+        return;
+    }
+    int32_t size = int32_t(le32toh(le_size));
+    auto old_size = bytes->size();
+    bytes->resize(old_size + sizeof(le_size) + size);
+    memcpy(bytes->data() + old_size, &le_size, sizeof(le_size));
+    ReadFdExactly(fd, bytes->data() + old_size + sizeof(le_size), size);
+}
+
+static inline int32_t skip_bytes_with_size(borrowed_fd fd) {
+    int32_t le_size = read_int32(fd);
+    if (le_size < 0) {
+        return -1;
+    }
+    int32_t size = int32_t(le32toh(le_size));
+    return (int32_t)adb_lseek(fd, size, SEEK_CUR);
+}
+
+std::pair<std::vector<char>, int32_t> read_id_sig_headers(borrowed_fd fd) {
+    std::vector<char> result;
+    append_int(fd, &result);              // version
+    append_bytes_with_size(fd, &result);  // hashingInfo
+    append_bytes_with_size(fd, &result);  // signingInfo
+    auto le_tree_size = read_int32(fd);
+    auto tree_size = int32_t(le32toh(le_tree_size));  // size of the verity tree
+    return {std::move(result), tree_size};
+}
+
+std::pair<off64_t, ssize_t> skip_id_sig_headers(borrowed_fd fd) {
+    skip_int(fd);                            // version
+    skip_bytes_with_size(fd);                // hashingInfo
+    auto offset = skip_bytes_with_size(fd);  // signingInfo
+    auto le_tree_size = read_int32(fd);
+    auto tree_size = int32_t(le32toh(le_tree_size));  // size of the verity tree
+    return {offset + sizeof(le_tree_size), tree_size};
+}
+
 template <class T>
-T valueAt(int fd, off64_t offset) {
+static T valueAt(borrowed_fd fd, off64_t offset) {
     T t;
     memset(&t, 0, sizeof(T));
     if (adb_pread(fd, &t, sizeof(T), offset) != sizeof(T)) {
@@ -68,7 +148,7 @@
             v.end());
 }
 
-static off64_t CentralDirOffset(int fd, int64_t fileSize) {
+static off64_t CentralDirOffset(borrowed_fd fd, Size fileSize) {
     static constexpr int kZipEocdRecMinSize = 22;
     static constexpr int32_t kZipEocdRecSig = 0x06054b50;
     static constexpr int kZipEocdCentralDirSizeFieldOffset = 12;
@@ -103,7 +183,7 @@
 }
 
 // Does not support APKs larger than 4GB
-static off64_t SignerBlockOffset(int fd, int64_t fileSize) {
+static off64_t SignerBlockOffset(borrowed_fd fd, Size fileSize) {
     static constexpr int kApkSigBlockMinSize = 32;
     static constexpr int kApkSigBlockFooterSize = 24;
     static constexpr int64_t APK_SIG_BLOCK_MAGIC_HI = 0x3234206b636f6c42l;
@@ -132,7 +212,7 @@
     return signerBlockOffset;
 }
 
-static std::vector<int32_t> ZipPriorityBlocks(off64_t signerBlockOffset, int64_t fileSize) {
+static std::vector<int32_t> ZipPriorityBlocks(off64_t signerBlockOffset, Size fileSize) {
     int32_t signerBlockIndex = offsetToBlockIndex(signerBlockOffset);
     int32_t lastBlockIndex = offsetToBlockIndex(fileSize);
     const auto numPriorityBlocks = lastBlockIndex - signerBlockIndex + 1;
@@ -160,7 +240,7 @@
     return zipPriorityBlocks;
 }
 
-[[maybe_unused]] static ZipArchiveHandle openZipArchiveFd(int fd) {
+[[maybe_unused]] static ZipArchiveHandle openZipArchiveFd(borrowed_fd fd) {
     bool transferFdOwnership = false;
 #ifdef _WIN32
     //
@@ -179,20 +259,22 @@
         D("%s failed at DuplicateHandle: %d", __func__, (int)::GetLastError());
         return {};
     }
-    fd = _open_osfhandle((intptr_t)dupedHandle, _O_RDONLY | _O_BINARY);
-    if (fd < 0) {
+    int osfd = _open_osfhandle((intptr_t)dupedHandle, _O_RDONLY | _O_BINARY);
+    if (osfd < 0) {
         D("%s failed at _open_osfhandle: %d", __func__, errno);
         ::CloseHandle(handle);
         return {};
     }
     transferFdOwnership = true;
+#else
+    int osfd = fd.get();
 #endif
     ZipArchiveHandle zip;
-    if (OpenArchiveFd(fd, "apk_fd", &zip, transferFdOwnership) != 0) {
+    if (OpenArchiveFd(osfd, "apk_fd", &zip, transferFdOwnership) != 0) {
         D("%s failed at OpenArchiveFd: %d", __func__, errno);
 #ifdef _WIN32
         // "_close()" is a secret WinCRT name for the regular close() function.
-        _close(fd);
+        _close(osfd);
 #endif
         return {};
     }
@@ -200,7 +282,7 @@
 }
 
 static std::pair<ZipArchiveHandle, std::unique_ptr<android::base::MappedFile>> openZipArchive(
-        int fd, int64_t fileSize) {
+        borrowed_fd fd, Size fileSize) {
 #ifndef __LP64__
     if (fileSize >= INT_MAX) {
         return {openZipArchiveFd(fd), nullptr};
@@ -220,7 +302,7 @@
     return {zip, std::move(mapping)};
 }
 
-static std::vector<int32_t> InstallationPriorityBlocks(int fd, int64_t fileSize) {
+static std::vector<int32_t> InstallationPriorityBlocks(borrowed_fd fd, Size fileSize) {
     static constexpr std::array<std::string_view, 3> additional_matches = {
             "resources.arsc"sv, "AndroidManifest.xml"sv, "classes.dex"sv};
     auto [zip, _] = openZipArchive(fd, fileSize);
@@ -249,8 +331,9 @@
         if (entryName == "classes.dex"sv) {
             // Only the head is needed for installation
             int32_t startBlockIndex = offsetToBlockIndex(entry.offset);
-            appendBlocks(startBlockIndex, 1, &installationPriorityBlocks);
-            D("\tadding to priority blocks: '%.*s' 1", (int)entryName.size(), entryName.data());
+            appendBlocks(startBlockIndex, 2, &installationPriorityBlocks);
+            D("\tadding to priority blocks: '%.*s' (%d)", (int)entryName.size(), entryName.data(),
+              2);
         } else {
             // Full entries are needed for installation
             off64_t entryStartOffset = entry.offset;
@@ -273,9 +356,9 @@
     return installationPriorityBlocks;
 }
 
-namespace incremental {
-std::vector<int32_t> PriorityBlocksForFile(const std::string& filepath, int fd, int64_t fileSize) {
-    if (!android::base::EndsWithIgnoreCase(filepath, ".apk")) {
+std::vector<int32_t> PriorityBlocksForFile(const std::string& filepath, borrowed_fd fd,
+                                           Size fileSize) {
+    if (!android::base::EndsWithIgnoreCase(filepath, ".apk"sv)) {
         return {};
     }
     off64_t signerOffset = SignerBlockOffset(fd, fileSize);
@@ -291,4 +374,5 @@
     unduplicate(priorityBlocks);
     return priorityBlocks;
 }
+
 }  // namespace incremental
diff --git a/adb/client/incremental_utils.h b/adb/client/incremental_utils.h
index 8bcf6c0..d969d94 100644
--- a/adb/client/incremental_utils.h
+++ b/adb/client/incremental_utils.h
@@ -16,11 +16,31 @@
 
 #pragma once
 
-#include <stdint.h>
+#include "adb_unique_fd.h"
 
 #include <string>
+#include <string_view>
+#include <utility>
 #include <vector>
 
+#include <stdint.h>
+
 namespace incremental {
-std::vector<int32_t> PriorityBlocksForFile(const std::string& filepath, int fd, int64_t fileSize);
-}  // namespace incremental
\ No newline at end of file
+
+using Size = int64_t;
+constexpr int kBlockSize = 4096;
+constexpr int kSha256DigestSize = 32;
+constexpr int kDigestSize = kSha256DigestSize;
+
+constexpr std::string_view IDSIG = ".idsig";
+
+std::vector<int32_t> PriorityBlocksForFile(const std::string& filepath, borrowed_fd fd,
+                                           Size fileSize);
+
+Size verity_tree_blocks_for_file(Size fileSize);
+Size verity_tree_size_for_file(Size fileSize);
+
+std::pair<std::vector<char>, int32_t> read_id_sig_headers(borrowed_fd fd);
+std::pair<off64_t, ssize_t> skip_id_sig_headers(borrowed_fd fd);
+
+}  // namespace incremental