4 files changed, 215 insertions, 0 deletions
diff --git a/shard/lib/app/file.ex b/shard/lib/app/file.ex
new file mode 100644
index 0000000..a874222
--- /dev/null
+++ b/shard/lib/app/file.ex
@@ -0,0 +1,114 @@
+defmodule SApp.File do
+  @moduledoc"""
+  Shard application for a file identified by its infohash. The file cannot be modified.
+
+  The infohash is the hash of an info struct containing:
+
+      %Info{
+        merkle_root: hash
+        file_hash: hash
+        size: int
+        mime_type: string
+    }
+
+  The file is cut in blocks of 4kb that are collected in a 64-ary Merkle tree.
+  """
+
+  use GenServer
+
+  require Logger
+
+  alias SData.MerkleTree, as: MT
+
+  defmodule Manifest do
+    @moduledoc"""
+    Manifest for a file.
+    The file is identified by the root hash of its Merkle tree and by its mime type.
+    """
+    defstruct [:infohash]
+
+    defimpl Shard.Manifest do
+      def module(_m), do: SApp.File
+      def is_valid?(m) do
+        byte_size(m.infohash) == 32
+      end
+    end
+  end
+
+  defmodule Info do
+    @moduledoc"""
+    A file info struct.
+    """
+    defstruct [:merkle_root, :file_hash, :size, :mime_type]
+  end
+
+  defmodule State do
+    defstruct [:infohash, :id, :manifest, :netgroup, :info, :infobin, :store, :missing, :path]
+  end
+
+  def start_link(manifest) do
+    GenServer.start_link(__MODULE__, manifest)
+  end  
+
+  def init(manifest) do
+    %Manifest{infohash: infohash} = manifest
+    id = SData.term_hash manifest
+
+    Shard.Manager.dispatch_to(id, nil, self())
+    {infobin, info} = case Shard.Manager.load_state(id) do
+      nil -> {nil, nil}
+      infobin -> {infobin, SData.term_unbin infobin}
+    end
+    netgroup = %SNet.PubShardGroup{id: id}
+    SNet.Group.init_lookup(netgroup, self())
+
+    path = [Application.get_env(:shard, :data_path), "#{id|>Base.encode16}"] |> Path.join
+
+    {:ok, store} = SApp.PageStore.start_link(id, :meta, netgroup)
+
+    {:ok, %State{
+      id: id, infohash: infohash, manifest: manifest, netgroup: netgroup,
+      infobin: infobin, info: info, store: store, missing: nil, path: path
+    }}
+  end
+
+  def handle_cast({:init_with, file_path, infobin, mt}, state) do
+    info = SData.term_unbin(infobin)
+    for {k, v} <- mt.store do
+      {^k, _} = SData.PageStore.put(state.store, v)
+    end
+    File.copy!(file_path, state.path)
+    new_state = %{state |
+      infobin: infobin,
+      info: info,
+    }
+    {:noreply, new_state}
+  end
+
+  # TODO networking etc
+
+  # =========
+  # INTERFACE
+  # =========
+  
+  @doc"""
+  Create a File shard from a file path
+  """
+  def create(path, mime_type) do
+    %File.Stat{size: size} = File.stat!(path)
+    mt = MT.create(path)
+    hash = SData.file_hash(path)
+
+    info = %Info{
+      merkle_root: mt.root,
+      file_hash: hash,
+      size: size,
+      mime_type: mime_type,
+    }
+    infobin = SData.term_bin(info)
+    infohash = SData.bin_hash(infobin)
+    manifest = %Manifest{infohash: infohash}
+    pid = Shard.Manager.find_or_start(manifest)
+    GenServer.cast(pid, {:init_with, path, infobin, mt})
+  end
+end
diff --git a/shard/lib/data/data.ex b/shard/lib/data/data.ex
index 78c73cd..33dca09 100644
--- a/shard/lib/data/data.ex
+++ b/shard/lib/data/data.ex
@@ -26,6 +26,12 @@ defmodule SData do
     :crypto.hash(algo, bin)
   end
 
+  def file_hash(path, algo \\ :sha256) do
+    File.stream!(path, [], 65536)
+    |> Enum.reduce(:crypto.hash_init(algo), &(:crypto.hash_update(&2, &1)))
+    |> :crypto.hash_final()
+  end
+
   def term_unbin(bin) do
     :erlang.binary_to_term(bin, [:safe])
   end
diff --git a/shard/lib/data/merkletree.ex b/shard/lib/data/merkletree.ex
new file mode 100644
index 0000000..90361a3
--- /dev/null
+++ b/shard/lib/data/merkletree.ex
@@ -0,0 +1,93 @@
+defmodule SData.MerkleTree do
+  @moduledoc"""
+  A Merkle tree structure for storing metadata for a big file.
+  """
+
+  alias SData.PageStore, as: Store
+
+  @block_size 4096
+  @tree_arity 64
+
+  defstruct [:root, :store]
+
+  defmodule Page do
+    defstruct [:nblk, :child_nblk, :list]
+
+    defimpl SData.Page do
+      def refs(page) do
+        if page.child_nblk == 1 do
+          []
+        else
+          page.list
+        end
+      end
+    end
+  end
+
+  @doc"""
+  Create a Merkle tree for indexing a file.
+  """
+  def create(file, store \\ SData.LocalStore.new()) do
+    %File.Stat{size: size} = File.stat!(file)
+    nblk = div(size, @block_size) + (if rem(size, @block_size) == 0 do 0 else 1 end)
+    fh = File.open!(file, [:binary, :read])
+    create_file_aux(fh, store, 0, nblk, @tree_arity)
+  end
+
+  defp create_file_aux(fh, store, first_blk, nblk, divc) do
+    cond do
+      divc < nblk ->
+        create_file_aux(fh, store, first_blk, nblk, divc * @tree_arity)
+      divc == @tree_arity and nblk <= divc ->
+        hashes = for i <- first_blk .. (first_blk + nblk - 1) do
+            {:ok, blk} = :file.pread(fh, i * @block_size, @block_size)
+            :crypto.hash(:sha256, blk)
+        end
+        page = %Page{nblk: nblk, child_nblk: 1, list: hashes}
+        {hash, store} = Store.put(store, page)
+        %__MODULE__{root: hash, store: store}
+      divc > @tree_arity and nblk <= divc ->
+        sub_divc = div(divc, @tree_arity)
+        n_sub_minus_one = div(nblk, sub_divc)
+        {sub_hashes, store} = Enum.reduce(0..n_sub_minus_one, {[], store}, fn i, {sh, store} ->
+          sub_first = first_blk + i * sub_divc
+          sub_n = (if i == n_sub_minus_one do rem(nblk, sub_divc) else sub_divc end)
+          %__MODULE__{root: hash, store: store} = create_file_aux(fh, store, sub_first, sub_n, sub_divc)
+          {[hash | sh], store}
+        end)
+        page = %Page{nblk: nblk, child_nblk: sub_divc, list: Enum.reverse(sub_hashes)}
+        {hash, store} = Store.put(store, page)
+        %__MODULE__{root: hash, store: store}
+    end
+  end
+
+  @doc"""
+  Get the number of blocks in the tree
+  """
+  def block_count(mt) do
+    %Page{nblk: nblk} = Store.get(mt.store, mt.root)
+    nblk
+  end
+
+  @doc"""
+  Get the hash of block number i
+  """
+  def get(mt, i) do
+    %Page{child_nblk: cn, list: list} = Store.get(mt.store, mt.root)
+    if cn == 1 do
+      Enum.fetch!(list, i)
+    else
+      pos = div(i, cn)
+      subtree = %{mt | root: Enum.fetch!(list, pos)}
+      subpos = rem(i, cn)
+      get(subtree, subpos)
+    end
+  end
+
+  @doc"""
+  Get the hashes of all blocks in a range
+  """
+  def get_range(mt, range) do
+    range |> Enum.map(&(get(mt, &1))) # TODO: do this efficiently
+  end
+end
diff --git a/shard/lib/net/manager.ex b/shard/lib/net/manager.ex
index 759c5f0..fb92f13 100644
--- a/shard/lib/net/manager.ex
+++ b/shard/lib/net/manager.ex
@@ -90,6 +90,8 @@ defmodule SNet.Manager do
 
   @doc"""
   Connect to a peer specified by ip address and port
+
+    peer_info := {:inet, ip, port}
   """
   def add_peer(peer_info, opts \\ []) do
     GenServer.call(__MODULE__, {:add_peer, peer_info, opts[:auth], opts[:callback]})