Message Processor

Requirements

• Connect to an upstream router and wait for messages
  • Retry if connection closed with no message received
• Receive a message
• Decode message into a struct
• Write struct to stdout
• Repeat
• Strings are encoded as UTF-8
• Cleanly handle expected signals

Usage

st-proc [-v] [<hostname> [<port>]]

Description

st-proc connects to a server at <hostname>:<port> that supplies a data message requiring processing, decodes the data and writes to stdout. It blocks waiting for data from the server, stop with Ctrl-C or kill(1).

• <hostname> hostname can be a numerical IP or symbolic hostname. Default is data.salad.com.

• <port> port is a positive integer. Default is 5000.

flight Package

All of the specifics of handling the flight data are in the flight package. This primarily consists of the decoder and a header object that includes JSON Marshal() and Unmarshal() support for base64 encoding.

• Note that the specifications say the size of the floats are 4 bytes but also describes them as IEEE-754 64 bit (binary64). The binary buffer included uses 8 bytes for the float values so that is what is used in the code.

cmd Package

The cmd package contains the main processing loop and router connection handling.

The processing loop remains single-threaded since there is no requirement for parallel processing.

The RouterConn struct encapsulates the network info and configuration for connecting to the router and the retry logic for the Connect() method. It uses io.Copy and bytes.Buffer to dynamically size the receive buffer since the simple protocol only sends a single stream of data then closes the connection.

Building

• Get the source:

  git clone https://github.com/dtroyer/st-proc
  cd st-proc
  make setup

• Build, the executable will be in bin/st-proc:

  make build

• Run unit tests:

  make test

• Run locally: We can use netcat and base64 to simulate the server and run the processor locally for testing. Two shell sessions are required. To start the server, run in one session:

  base64 -d files/testPacket1 | nc -l 5000

  And in the other session run the processor client:

  bin/st-proc localhost

  Compare the JSON output with the testJson1 string in flight/message_test.go or with the string in the original spec. Note that the header field is included in this implementation.

  All 3 of the testPacketN messages are included in files/ base64 encoded.

See Also

Source on Github

Author

Dean Troyer dt-github@xr7.org

Known Issues

• The JSON output produces the header value as an integer array rather than a base64-encoded string. message.UnmarshalJSON() is not being called as expected.