log.go

package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"os"
	"strings"
)

// These are the environmental variables that determine if we log, and if
// we log whether or not the log should go to a file.
const EnvLog = "PACKER_LOG"          //Set to True
const EnvLogFile = "PACKER_LOG_PATH" //Set to a file

// logOutput determines where we should send logs (if anywhere).
func logOutput() (logOutput io.Writer, err error) {
	logOutput = nil
	if os.Getenv(EnvLog) != "" && os.Getenv(EnvLog) != "0" {
		logOutput = os.Stderr

		if logPath := os.Getenv(EnvLogFile); logPath != "" {
			var err error
			logOutput, err = os.Create(logPath)
			if err != nil {
				return nil, err
			}
		} else {
			// no path; do a little light filtering to avoid double-dipping UI
			// calls.
			r, w := io.Pipe()
			scanner := bufio.NewScanner(r)
			scanner.Split(ScanLinesSmallerThanBuffer)

			go func(scanner *bufio.Scanner) {
				for scanner.Scan() {
					if strings.Contains(scanner.Text(), "ui:") {
						continue
					}
					if strings.Contains(scanner.Text(), "ui error:") {
						continue
					}
					os.Stderr.WriteString(fmt.Sprint(scanner.Text() + "\n"))
				}
				if err := scanner.Err(); err != nil {
					os.Stderr.WriteString(err.Error())
					w.Close()
				}
			}(scanner)
			logOutput = w
		}
	}

	return
}

// The below functions come from bufio.Scanner with a small tweak, to fix an
// edgecase where the default ScanFunc fails: sometimes, if someone tries to
// log a line that is longer than 64*1024 bytes long before it contains a
// newline, the ScanLine will continue to return, requesting more data from the
// buffer, which can't increase in size anymore, causing a hang.
func dropCR(data []byte) []byte {
	if len(data) > 0 && data[len(data)-1] == '\r' {
		return data[0 : len(data)-1]
	}
	return data
}

func ScanLinesSmallerThanBuffer(data []byte, atEOF bool) (advance int, token []byte, err error) {
	if atEOF && len(data) == 0 {
		return 0, nil, nil
	}
	if i := bytes.IndexByte(data, '\n'); i >= 0 {
		// We have a full newline-terminated line.
		return i + 1, dropCR(data[0:i]), nil
	}
	// If we're at EOF, we have a final, non-terminated line. Return it.
	if atEOF {
		return len(data), dropCR(data), nil
	}

	// Our tweak:
	// Buffer is full, so we can't get more data. Just return what we have as
	// its own token so we can keep going, even though there's no newline.
	if len(data)+1 >= bufio.MaxScanTokenSize {
		return len(data), data[0 : len(data)-1], nil
	}

	// Request more data.
	return 0, nil, nil
}