Add kpod logs command

Signed-off-by: Ryan Cole <rcyoalne@gmail.com>

libkpod/logs.go

@@ -0,0 +1,80 @@
+package libkpod
+
+import (
+	"path"
+	"strings"
+	"time"
+
+	"github.com/hpcloud/tail"
+)
+
+// LogOptions contains all of the options for displaying logs in kpod
+type LogOptions struct {
+	Details   bool
+	Follow    bool
+	SinceTime time.Time
+	Tail      uint64
+}
+
+// GetLogs gets each line of a log file and, if it matches the criteria in logOptions, sends it down logChan
+func (c *ContainerServer) GetLogs(container string, logChan chan string, opts LogOptions) error {
+	defer close(logChan)
+	// Get the full ID of the container
+	ctr, err := c.LookupContainer(container)
+	if err != nil {
+		return err
+	}
+
+	containerID := ctr.ID()
+	sandbox := ctr.Sandbox()
+	if sandbox == "" {
+		sandbox = containerID
+	}
+	// Read the log line by line and pass it into the pipe
+	logsFile := path.Join(c.config.LogDir, sandbox, containerID+".log")
+
+	seekInfo := &tail.SeekInfo{Offset: 0, Whence: 0}
+	if opts.Tail > 0 {
+		// seek to correct position in logs files
+		seekInfo.Offset = int64(opts.Tail)
+		seekInfo.Whence = 2
+	}
+
+	t, err := tail.TailFile(logsFile, tail.Config{Follow: false, ReOpen: false, Location: seekInfo})
+	for line := range t.Lines {
+		if since, err := logSinceTime(opts.SinceTime, line.Text); err != nil || since == false {
+			continue
+		}
+		logMessage := line.Text[secondSpaceIndex(line.Text):]
+		if opts.Details {
+			// add additional information to line
+		}
+		logChan <- logMessage
+	}
+	return err
+}
+
+func logSinceTime(sinceTime time.Time, logStr string) (bool, error) {
+	timestamp := strings.Split(logStr, " ")[0]
+	logTime, err := time.Parse("2006-01-02T15:04:05.999999999-07:00", timestamp)
+	if err != nil {
+		return false, err
+	}
+	return logTime.After(sinceTime) || logTime.Equal(sinceTime), nil
+}
+
+// secondSpaceIndex returns the index of the second space in a string
+// In a line of the logs, the first two tokens are a timestamp and stdout/stderr,
+// followed by the message itself.  This allows us to get the index of the message
+// and avoid sending the other information back to the caller of GetLogs()
+func secondSpaceIndex(line string) int {
+	index := strings.Index(line, " ")
+	if index == -1 {
+		return 0
+	}
+	index = strings.Index(line[index:], " ")
+	if index == -1 {
+		return 0
+	}
+	return index
+}