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Parse a custom protocol format

Your payment processing application must interface with an old-school mainframe format that we've named "MPS7". This means consuming a proprietary binary protocol format that no one on your team is familiar with yet.


You must read in a transaction log, txnlog.dat, and parse it according to the specification in Notes below.

You must answer the following questions:

  • What is the total amount in dollars of debits?
  • What is the total amount in dollars of credits?
  • How many autopays were started?
  • How many autopays were ended?
  • What is balance of user ID 2456938384156277127?

You must supply your source code as part of your answer. Write your code in your best programming language. We'll want to compile your code from source and run it, so please include the complete instructions for doing so in a COMMENTS file.


Because txnlog.dat is a binary file, it can't be read by a normal text editor like sublime or vim. Instead, you'll need to read it programatically and parse the data you read in from there.

This is how the transaction log is structured:


| 4 byte magic string "MPS7" | 1 byte version | 4 byte (uint32) # of records |

The header contains the canonical information about how the records should be processed. Note: there are fewer than 100 records in txnlog.dat.


| 1 byte record type enum | 4 byte (uint32) Unix timestamp | 8 byte (uint64) user ID |

Record type enum:

  • 0x00: Debit
  • 0x01: Credit
  • 0x02: StartAutopay
  • 0x03: EndAutopay

For Debit and Credit record types, there is an additional field, an 8 byte (float64) amount in dollars, at the end of the record.

All multi-byte fields are encoded in network byte order.

The first record in the file, when fully parsed, will have these values:

Record type Unix timestamp user ID amount in dollars
'Debit' 1393108945 4136353673894269217 604.274335557087

Included files

Here are the files we'll give to you to get you started. Download them when you are ready to begin.

Ready to submit?

Don't include anything in your files that could identify you. We assign submissions a random number when they are received so our team does not know whose homework they are evaluating. Multiple team members will review your submission before a decision is made.

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