D.R.Y. up the input source fetching.

cmd/bfg/main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bufio"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -29,28 +30,15 @@ func main() {
 	var sourceBuf, inputBuf io.ByteReader
 	source := flag.Arg(0)
 	input := flag.Arg(1)
-	if source == "" {
-		fmt.Println("please provide a source file")
+	sourceBuf, err := inputReader(source, false)
+	if err != nil {
+		fmt.Println("error opening program: err:", err)
 		os.Exit(1)
-	} else if source == "-" {
-		sourceBuf = bufio.NewReader(os.Stdin)
-	} else {
-		sourceFile, err := os.Open(source)
-		if err != nil {
-			fmt.Println("error opening source file: err:", err)
-			os.Exit(1)
-		}
-		sourceBuf = bufio.NewReader(sourceFile)
 	}
-	if input == "" {
-		inputBuf = bufio.NewReader(os.Stdin)
-	} else {
-		file, err := os.Open(input)
-		if err != nil {
-			fmt.Println("error opening input file: err:", err)
-			os.Exit(1)
-		}
-		inputBuf = bufio.NewReader(file)
+	inputBuf, err = inputReader(input, true)
+	if err != nil {
+		fmt.Println("error opening input: err:", err)
+		os.Exit(1)
 	}
 	outputBuf := bufio.NewWriter(os.Stdout)
 	defer outputBuf.Flush()
@@ -66,3 +54,21 @@ func main() {
 		parser.Execute(program, inputBuf, outputBuf)
 	}
 }
+
+func inputReader(pathStr string, useDefault bool) (buff io.ByteReader, err error) {
+	if useDefault && pathStr == "" {
+		pathStr = "-"
+	}
+	if pathStr == "" {
+		return nil, errors.New("no path provided")
+	} else if pathStr == "-" {
+		buff = bufio.NewReader(os.Stdin)
+	} else {
+		sourceFile, err := os.Open(pathStr)
+		if err != nil {
+			return nil, err
+		}
+		buff = bufio.NewReader(sourceFile)
+	}
+	return
+}