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Pure Elixir HL7 v2.x toolkit — schema-driven parsing, typed segments, message builder, MLLP transport
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lib/hl7v2/mllp.ex
defmodule HL7v2.MLLP do
@moduledoc """
MLLP (Minimal Lower Layer Protocol) framing for HL7v2 messages.
MLLP wraps each HL7v2 message in a simple frame:
<SB>message<EB><CR>
Where:
- SB (Start Block) = `0x0B`
- EB (End Block) = `0x1C`
- CR (Carriage Return) = `0x0D`
See HL7 Implementation Technology Specification — Minimal Lower Layer Protocol.
"""
@compile {:inline, frame: 1}
@sb 0x0B
@eb 0x1C
@cr 0x0D
@doc """
Wraps a message binary in an MLLP frame.
## Examples
iex> HL7v2.MLLP.frame("MSH|...")
<<0x0B, "MSH|...", 0x1C, 0x0D>>
"""
@spec frame(binary()) :: binary()
def frame(message) when is_binary(message) do
<<@sb, message::binary, @eb, @cr>>
end
@doc """
Extracts the message from an MLLP frame.
Returns `{:ok, message}` when the binary starts with SB and ends with EB+CR.
Returns `{:error, :invalid_frame}` otherwise.
## Examples
iex> HL7v2.MLLP.unframe(<<0x0B, "MSH|...", 0x1C, 0x0D>>)
{:ok, "MSH|..."}
iex> HL7v2.MLLP.unframe("bad")
{:error, :invalid_frame}
"""
@spec unframe(binary()) :: {:ok, binary()} | {:error, :invalid_frame}
def unframe(<<@sb, rest::binary>>) do
case :binary.split(rest, <<@eb, @cr>>) do
[message, <<>>] -> {:ok, message}
_ -> {:error, :invalid_frame}
end
end
def unframe(_), do: {:error, :invalid_frame}
@doc """
Extracts complete MLLP messages from a buffer.
Returns `{messages, remaining_buffer}` where `messages` is a list of
extracted message binaries (without MLLP framing) and `remaining_buffer`
contains any incomplete data that needs more bytes.
## Examples
iex> HL7v2.MLLP.extract_messages(<<0x0B, "MSG1", 0x1C, 0x0D, 0x0B, "MSG2", 0x1C, 0x0D>>)
{["MSG1", "MSG2"], <<>>}
iex> HL7v2.MLLP.extract_messages(<<0x0B, "MSG1", 0x1C, 0x0D, 0x0B, "partial">>)
{["MSG1"], <<0x0B, "partial">>}
"""
@spec extract_messages(binary()) :: {[binary()], binary()}
def extract_messages(buffer) do
extract_messages(buffer, [])
end
defp extract_messages(<<@sb, rest::binary>> = buffer, acc) do
case :binary.split(rest, <<@eb, @cr>>) do
[message, remainder] ->
extract_messages(remainder, [message | acc])
[_incomplete] ->
{Enum.reverse(acc), buffer}
end
end
defp extract_messages(<<>>, acc) do
{Enum.reverse(acc), <<>>}
end
# Data before an SB byte — skip leading garbage
defp extract_messages(buffer, acc) do
case :binary.split(buffer, <<@sb>>) do
[_garbage, rest] ->
extract_messages(<<@sb, rest::binary>>, acc)
[_no_sb] ->
{Enum.reverse(acc), buffer}
end
end
end