Class: Aws::EventStream::Encoder

Inherits:
Object
  • Object
show all
Defined in:
lib/aws-eventstream/encoder.rb

Overview

This class provides #encode method for encoding Aws::EventStream::Message into binary.

  • #encode - encode Aws::EventStream::Message into binary when output IO-like object is provided, binary string would be written to IO. If not, the encoded binary string would be returned directly

## Examples

message = Aws::EventStream::Message.new(
  headers: {
    "foo" => Aws::EventStream::HeaderValue.new(
      value: "bar", type: "string"
     )
  },
  payload: "payload"
)
encoder = Aws::EventsStream::Encoder.new
file = Tempfile.new

# encode into IO ouput
encoder.encode(message, file)

# get encoded binary string
encoded_message = encoder.encode(message)

file.read == encoded_message
# => true

Constant Summary collapse

OVERHEAD_LENGTH =

bytes of total overhead in a message, including prelude and 4 bytes total message crc checksum

16
MAX_HEADERS_LENGTH =

Maximum header length allowed (after encode) 128kb

131072
MAX_PAYLOAD_LENGTH =

Maximum payload length allowed (after encode) 16mb

16777216

Instance Method Summary collapse

Instance Method Details

#encode(message, io = nil) ⇒ nil, String

Encodes Aws::EventStream::Message to output IO when

provided, else return the encoded binary string

Parameters:

  • message (Aws::EventStream::Message)
  • io (IO#write, nil) (defaults to: nil) —

    An IO-like object that responds to ‘#write`, encoded message will be written to this IO when provided

Returns:

  • (nil, String) —

    when output IO is provided, encoded message will be written to that IO, nil will be returned. Else, encoded binary string is returned.



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# File 'lib/aws-eventstream/encoder.rb', line 61

def encode(message, io = nil)
  encoded = encode_message(message).read
  if io
    io.write(encoded)
    io.close
  else
    encoded
  end
end

#encode_headers(msg) ⇒ Aws::EventStream::BytesBuffer

Encodes headers part of an Aws::EventStream::Message

into Aws::EventStream::BytesBuffer

Parameters:

Returns:



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# File 'lib/aws-eventstream/encoder.rb', line 107

def encode_headers(msg)
  buffer = BytesBuffer.new('')
  msg.headers.each do |k, v|
    # header key
    buffer << pack_uint8(k.bytesize)
    buffer << k

    # header value
    pattern, val_len, idx = Types.pattern[v.type]
    buffer << pack_uint8(idx)
    # boolean types doesn't need to specify value
    next if !!pattern == pattern
    buffer << pack_uint16(v.value.bytesize) unless val_len
    pattern ? buffer << [v.value].pack(pattern) :
      buffer << v.value
  end
  if buffer.bytesize > MAX_HEADERS_LENGTH
    raise Aws::EventStream::Errors::EventHeadersLengthExceedError.new
  end
  buffer
end

#encode_message(message) ⇒ Aws::EventStream::BytesBuffer

Encodes an Aws::EventStream::Message

into Aws::EventStream::BytesBuffer

Parameters:

Returns:



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# File 'lib/aws-eventstream/encoder.rb', line 77

def encode_message(message)
  # create context buffer with encode headers
  ctx_buffer = encode_headers(message)
  headers_len = ctx_buffer.bytesize
  # encode payload
  if message.payload.length > MAX_PAYLOAD_LENGTH
    raise Aws::EventStream::Errors::EventPayloadLengthExceedError.new
  end
  ctx_buffer << message.payload.read
  total_len = ctx_buffer.bytesize + OVERHEAD_LENGTH

  # create message buffer with prelude section
  buffer = prelude(total_len, headers_len)

  # append message context (headers, payload)
  buffer << ctx_buffer.read
  # append message checksum
  buffer << pack_uint32(Zlib.crc32(buffer.read))

  # write buffered message to io
  buffer.rewind
  buffer
end