117 lines
2.9 KiB
Go
117 lines
2.9 KiB
Go
// Package rotate provides an io.Writer that changes the file it writes to based
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// on the current date. It always writes to a file inside of the directory it is
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// given, and only switches files once it has finished writing a line and the
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// date has changed. It is intended to be used with log.SetOutput().
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package rotate
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import "os"
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import "io"
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import "time"
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import "errors"
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import "path/filepath"
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type logger struct {
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directory string
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file io.WriteCloser
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previousDay int
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closed bool
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}
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// New returns a new logger that will always log to directory/YYYY-MM-DD.log.
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// When its close method is called, it will close any open file and stop
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// accepting calls to Write. A closed logger may not be re-opened.
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func New (directory string) (io.WriteCloser, error) {
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logger := &logger { directory: directory }
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err := logger.updateCurrentFile()
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if err != nil { return nil, err }
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return logger, nil
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}
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func (logger *logger) Write (buffer []byte) (n int, err error) {
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if logger.closed {
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return 0, errors.New("rotate: attempt to write to closed logger")
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}
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if logger.file == nil {
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err = logger. updateCurrentFile()
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if err != nil { return }
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}
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for buffer != nil {
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var outgoing []byte
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var justWrote int
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outgoing, buffer = splitLine(buffer)
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justWrote, err = logger.file.Write(outgoing)
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n += justWrote
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if err != nil { return }
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err = logger.updateCurrentFile()
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if err != nil { return }
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}
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return
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}
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func (logger *logger) Close () error {
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return logger.file.Close()
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}
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func (logger *logger) updateCurrentFile() (err error) {
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if logger.closed { return }
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// yes this is not a correct measure of days since 1970 but all we need
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// to know is "has the date changed?"
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now := time.Now()
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currentDay := (now.Year() - 1970) * 366 + now.YearDay()
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if currentDay > logger.previousDay || logger.file == nil {
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if logger.file != nil { logger.file.Close() }
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logger.file, err = os.OpenFile(
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filepath.Join(logger.directory, now.Format("2006-01-02.log")),
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os.O_WRONLY | os.O_APPEND | os.O_CREATE,
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0660)
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if err != nil { return }
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}
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logger.previousDay = currentDay
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return
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}
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func splitLine (buffer []byte) (left, right []byte) {
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index := indexOf(buffer, '\n')
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if index < 1 { return buffer, nil }
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index += 1
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return buffer[:index], buffer[index:]
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}
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func indexOf[T comparable] (haystack []T, needle T) int {
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for index, element := range haystack {
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if element == needle {
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return index
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}
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}
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return -1
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}
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type lineWriter struct {
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destination func (line []byte) (int, error)
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}
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func LineWriter (destination func (line []byte) (int, error)) io.Writer {
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return &lineWriter { destination: destination }
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}
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func (writer lineWriter) Write (buffer []byte) (n int, err error) {
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for buffer != nil {
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var outgoing []byte
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var justWrote int
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outgoing, buffer = splitLine(buffer)
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justWrote, err = writer.destination(outgoing)
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n += justWrote
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if err != nil { return }
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}
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return
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}
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