parsing header and records

cmd/root.go

@@ -3,15 +3,29 @@ package cmd
 import (
 	"flag"
 	"fmt"
+	"log"
 	"os"
-	"strconv"
+
+	"jxs.me/proto/mps"
 )
 
 func Root() error {
 	args := flag.NewFlagSet("root", flag.ExitOnError)
-	verbose := args.Bool("verbose", false, "Extra logging")
 	args.Parse(os.Args[1:])
 
-	fmt.Printf("Hi %s", strconv.FormatBool(*verbose))
-	return nil
+	source := args.Arg(0)
+	if source == "" {
+		return fmt.Errorf("File is required")
+	}
+
+	sourceFile, err := os.Open(source)
+	if err != nil {
+		return err
+	}
+	defer sourceFile.Close()
+	tx, err := mps.Parse(sourceFile)
+
+	log.Printf("Parsed %d records", tx.Header.RecordCount)
+
+	return err
 }

mps/parse.go

@@ -0,0 +1,85 @@
+package mps
+
+import (
+	"encoding/binary"
+	"io"
+)
+
+const (
+	DEBIT = byte(iota)
+	CREDIT
+	STARTAUTOPAY
+	ENDAUTOPAY
+)
+
+// | 4 byte magic string "MPS7" | 1 byte version | 4 byte (uint32) # of records |
+
+// | 1 byte record type enum | 4 byte (uint32) Unix timestamp | 8 byte (uint64) user ID |
+type Record struct {
+	Type   byte
+	Time   uint32
+	UserId uint64
+	Amount float64
+}
+
+type TransactionLog struct {
+	Header  Header
+	Records []Record
+}
+
+// | 4 byte magic string "MPS7" | 1 byte version | 4 byte (uint32) # of records |
+type Header struct {
+	Magic       [4]byte
+	Version     int8
+	RecordCount uint32
+}
+
+func parseHeader(r io.Reader, h *Header) error {
+	err := binary.Read(r, binary.BigEndian, h)
+	return err
+}
+
+func parseRecord(r io.Reader, record *Record) error {
+	err := binary.Read(r, binary.BigEndian, &record.Type)
+	if err != nil {
+		return err
+	}
+
+	err = binary.Read(r, binary.BigEndian, &record.Time)
+	if err != nil {
+		return err
+	}
+	err = binary.Read(r, binary.BigEndian, &record.UserId)
+
+	if err != nil {
+		return err
+	}
+
+	if record.Type == CREDIT || record.Type == DEBIT {
+		err = binary.Read(r, binary.BigEndian, &record.Amount)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func Parse(r io.Reader) (*TransactionLog, error) {
+	var tx TransactionLog
+	err := parseHeader(r, &tx.Header)
+	if err != nil {
+		return nil, err
+	}
+
+	for i := 0; i < int(tx.Header.RecordCount); i++ {
+		var record Record
+		err := parseRecord(r, &record)
+		if err != nil {
+			return nil, err
+		}
+		tx.Records = append(tx.Records, record)
+	}
+
+	return &tx, nil
+}