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read.go
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read.go
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package main
import (
"errors"
"fmt"
"io/ioutil"
"os"
"strings"
)
const EmptyString = ``
var errMultiLineString = errors.New(`string has more than one line`)
func byteToStrAndValidate(b []byte) (string, error) {
s := strings.TrimSuffix(string(b), "\n") // Many editors puts an empty line at the end of file
if strings.Contains(s, "\n") {
return EmptyString, errMultiLineString
}
return s, nil
}
func readData() (string, error) {
fCont, errRF := readFile()
if errRF != nil {
return EmptyString, errRF
}
inCont, errIN := readSTDIN()
if errIN != nil {
return EmptyString, errIN
}
if fCont == EmptyString && inCont == EmptyString {
return EmptyString, errors.New(`I did not receive the data in the form of a file name nor as a stream on STDIN`)
}
if fCont != EmptyString && inCont != EmptyString {
return EmptyString, errors.New(`I received the data both as a file and as a stream on STDIN`)
}
if fCont != EmptyString {
return fCont, nil
}
return inCont, nil
}
func readFile() (string, error) {
argsWithoutProg := os.Args[1:]
if len(argsWithoutProg) == 0 {
return EmptyString, nil
}
if len(argsWithoutProg) > 1 {
return EmptyString, errors.New(`I got more call arguments than one`)
}
fName := argsWithoutProg[0]
fInfo, err := os.Stat(fName)
if errors.Is(err, os.ErrNotExist) {
return EmptyString, err
}
if fInfo.IsDir() {
return EmptyString, fmt.Errorf(`%s is a directrory, but not a file`, fName)
}
if fInfo.Size() == 0 {
return EmptyString, fmt.Errorf(`%s is empty`, fName)
}
buf, err := ioutil.ReadFile(fName)
if err != nil {
return EmptyString, err
}
s, err := byteToStrAndValidate(buf)
if errors.Is(err, errMultiLineString) {
return EmptyString, fmt.Errorf(`%s contains more than one line`, fName)
}
return s, nil
}
func readSTDIN() (string, error) {
fh := os.Stdin
fi, err := fh.Stat()
itIsAPipe := func() bool {
return (fi.Mode() & os.ModeNamedPipe) != 0
}
if !itIsAPipe() {
return EmptyString, nil
}
buf, err := ioutil.ReadAll(os.Stdin)
if err != nil {
return EmptyString, err
}
s, err := byteToStrAndValidate(buf)
if errors.Is(err, errMultiLineString) {
return EmptyString, errors.New(`on STDIN I got more than one line`)
}
return s, nil
}