66 lines
1.5 KiB
Go
66 lines
1.5 KiB
Go
package main
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import (
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"io"
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"log"
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"os"
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"path/filepath"
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"strings"
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)
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// setupFileLogging tees the standard logger to a file alongside the config.
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// Returns the log file path. Stderr is kept as a secondary sink so dev runs
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// (linux, console) still print, while windowsgui builds rely on the file.
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func setupFileLogging(cfgDir string) (string, error) {
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if err := os.MkdirAll(cfgDir, 0755); err != nil {
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return "", err
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}
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p := filepath.Join(cfgDir, "companion.log")
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f, err := os.OpenFile(p, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
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if err != nil {
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return "", err
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}
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log.SetOutput(io.MultiWriter(f, os.Stderr))
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return p, nil
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}
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// tailLog returns the last n lines of the log file. Reads only the trailing
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// chunk of the file so the cost is bounded regardless of log size.
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func tailLog(p string, n int) ([]string, error) {
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const tailBytes = 32 * 1024
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f, err := os.Open(p)
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if err != nil {
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return nil, err
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}
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defer f.Close()
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info, err := f.Stat()
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if err != nil {
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return nil, err
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}
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size := info.Size()
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var off int64
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if size > tailBytes {
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off = size - tailBytes
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}
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buf := make([]byte, size-off)
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if _, err := f.ReadAt(buf, off); err != nil && err != io.EOF {
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return nil, err
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}
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s := string(buf)
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// Drop the (likely partial) first line when we didn't start at 0.
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if off > 0 {
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if i := strings.IndexByte(s, '\n'); i >= 0 {
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s = s[i+1:]
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}
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}
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s = strings.TrimRight(s, "\n")
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if s == "" {
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return nil, nil
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}
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lines := strings.Split(s, "\n")
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if len(lines) > n {
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lines = lines[len(lines)-n:]
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}
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return lines, nil
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}
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