Proto

Another random excercise. I cannot remember if it was for an interview or some online code challenge.

Nonetheless. An example of code.

Your application must interface with an old-school mainframe MPS7 for payment processing. This means consuming a proprietary binary protocol format.

You must read in a file, 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.

MPS7 transaction log specification:

Header:

| 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.

Record:

| 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.