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This enables fwupdates to resume even after a reboot
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,101 @@ | ||
| defmodule NervesHubLinkCommon.Journal do | ||
| @moduledoc """ | ||
| Simple journaling structure backed by a file on the filesystem | ||
| Stores data in chunks in the following format: | ||
| <<length::32, hash::binary-size(32)-unit(8), data::binary-size(length)-unit(8)>> | ||
| as chunks are streamed with `save_chunk/2` the data is updated both on disk and | ||
| in the structure. This can be used to rehydrate stateful events after a reboot, such as | ||
| a firmware update for example. | ||
| When opening an existing journal (done automatically if the journal exists), | ||
| the structure will validate all the chunks on disk, stopping on either | ||
| * the first chunk to fail a hash check | ||
| * the end of the file | ||
| In either case, the journal is valid to use at this point | ||
| """ | ||
|
|
||
| defstruct [:fd, :content_length, :chunks] | ||
|
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| @type t :: %__MODULE__{ | ||
| fd: :file.fd(), | ||
| content_length: non_neg_integer(), | ||
| chunks: [binary()] | ||
| } | ||
|
|
||
| @doc "Open or create a journal for this meta" | ||
| @spec open(Path.t()) :: {:ok, t()} | {:error, File.posix()} | ||
| def open(filename) do | ||
| with {:ok, fd} <- :file.open(filename, [:write, :read, :binary]), | ||
| {:ok, 0} <- :file.position(fd, 0), | ||
| {:ok, journal} <- validate_and_seek(%__MODULE__{fd: fd, content_length: 0, chunks: []}) do | ||
| {:ok, journal} | ||
| end | ||
| end | ||
|
|
||
| @spec reload(Path.t()) :: {:ok, t()} | {:error, File.posix()} | ||
| def reload(filename) do | ||
| if File.exists?(filename) do | ||
| open(filename) | ||
| else | ||
| {:error, :enoent} | ||
| end | ||
| end | ||
|
|
||
| @spec validate_and_seek(t()) :: {:ok, t()} | {:error, File.posix()} | ||
| def validate_and_seek(%__MODULE__{fd: fd, content_length: content_length} = journal) do | ||
| with {:ok, <<length::32>>} <- :file.read(fd, 4), | ||
| {:ok, hash} <- :file.read(fd, 32), | ||
| {:ok, data} <- :file.read(fd, length), | ||
| {:hash, ^length, ^hash} <- {:hash, length, :crypto.hash(:sha256, data)} do | ||
| validate_and_seek(%__MODULE__{ | ||
| journal | ||
| | content_length: content_length + length, | ||
| chunks: journal.chunks ++ [data] | ||
| }) | ||
| else | ||
| # made it thru all chunks in the file | ||
| :eof -> | ||
| {:ok, journal} | ||
|
|
||
| # hash check failed. rewind and break | ||
| {:hash, length, _} -> | ||
| rewind(journal, length + 32 + 4) | ||
|
|
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| {:error, posix} -> | ||
| {:error, posix} | ||
| end | ||
| end | ||
|
|
||
| @spec rewind(t(), pos_integer()) :: {:ok, t()} | {:error, File.posix()} | ||
| def rewind(journal, length) do | ||
| with {:ok, _} <- :file.position(journal.fd, -length) do | ||
| {:ok, journal} | ||
| end | ||
| end | ||
|
|
||
| @spec close(t()) :: :ok | ||
| def close(%__MODULE__{fd: fd} = _journal) do | ||
| :ok = :file.close(fd) | ||
| end | ||
|
|
||
| @spec save_chunk(t(), iodata()) :: {:ok, t()} | {:error, File.posix()} | ||
| def save_chunk(%__MODULE__{fd: fd} = journal, data) when is_binary(data) do | ||
| hash = :crypto.hash(:sha256, data) | ||
| length = byte_size(data) | ||
| journal_entry = IO.iodata_to_binary([<<length::32>>, hash, data]) | ||
|
|
||
| with :ok <- :file.write(fd, journal_entry) do | ||
| {:ok, | ||
| %__MODULE__{ | ||
| journal | ||
| | chunks: journal.chunks ++ [data], | ||
| content_length: journal.content_length + length | ||
| }} | ||
| end | ||
| end | ||
| end |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,32 @@ | ||
| defmodule NervesHubLinkCommon.JournalTest do | ||
| use ExUnit.Case | ||
|
|
||
| alias NervesHubLinkCommon.Journal | ||
|
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||
| setup do | ||
| {:ok, [path: "/tmp/#{System.unique_integer([:positive])}.journal"]} | ||
| end | ||
|
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||
| test "journals data to the filesystem", %{path: path} do | ||
| {:ok, journal} = Journal.open(path) | ||
| {:ok, journal1} = Journal.save_chunk(journal, "hello") | ||
| assert journal1.content_length == byte_size("hello") | ||
| assert "hello" in journal1.chunks | ||
|
|
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| {:ok, journal2} = Journal.save_chunk(journal1, "world") | ||
| :ok = Journal.close(journal2) | ||
|
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| {:ok, journal} = Journal.open(path) | ||
| assert journal.chunks == ["hello", "world"] | ||
| end | ||
|
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||
| test "stops when journal chunk hashes don't match", %{path: path} do | ||
| hash = :crypto.hash(:sha256, "hello") | ||
| :ok = File.write!(path, [<<5::32>>, hash, "hello"]) | ||
| :ok = File.write!(path, [<<5::32>>, <<0::32>>, "world"], [:append]) | ||
| {:ok, journal} = Journal.open(path) | ||
| assert journal.content_length == 5 | ||
| assert "hello" in journal.chunks | ||
| refute "world" in journal.chunks | ||
| end | ||
| end |
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