In my main function, I open a logging text file for writing with a defer close method to close it once the application quits. However, at the beginning of each new day I wish to start writing to the next day's log file, and I don't know how to close the previous day's file and start writing to the current one.
In my main function:
func main() {
f, err := os.OpenFile("2019-07-24.txt", os.O_RDWR | os.O_CREATE | os.O_APPEND, 0644)
if err != nil {
log.Fatalf("Error opening log file: %v", err)
}
defer f.Close()
log.SetOutput(f)
}
Now when I receive a message on a new day in another package:
func gateway() {
f, err := os.OpenFile("2019-07-25.txt", os.O_RDWR | os.O_CREATE | os.O_APPEND, 0644)
if err != nil {
log.Fatalf("Error opening log file: %v", err)
}
defer f.Close()
log.SetOutput(f)
}
How do I get a pointer to the previous day's log file from another package, and then close it (when a defer call will not be invoked unless the application completely closes?
Create a package that that manages the log output.
package logoutput
package main
import (
"io"
"log"
"sync"
)
var (
mu sync.Mutex
curr io.WriteCloser
)
func Set(w io.WriteCloser) {
mu.Lock()
defer mu.Unlock()
prev := curr
curr = w
log.SetOutput(curr)
if prev != nil {
prev.Close()
}
}
func Close() {
mu.Lock()
defer mu.Unlock()
log.SetOutput(os.Stderr) // revert to default
if curr != nil {
curr.Close()
}
curr = nil
}
Call the package from main and the gateway package.
f, err := os.OpenFile("2019-07-24.txt", os.O_RDWR | os.O_CREATE | os.O_APPEND, 0644)
if err != nil {
log.Fatalf("Error opening log file: %v", err)
}
logoutput.Set(f)
defer logoutput.Close() // call from main only