TUN-8733: add log collection for docker

## Summary
Adds the log collector for docker based deployments

Closes TUN-8733

diagnostic/consts.go

@@ -10,5 +10,7 @@ const (
 	configurationCollectorName = "configuration"        // used for logging purposes
 	defaultTimeout             = 15 * time.Second       // timeout for the collectors
 	twoWeeksOffset             = -14 * 24 * time.Hour   // maximum offset for the logs
+	logFilename                = "cloudflared_logs.txt" // name of the output log file
 	configurationKeyUID        = "uid"                  // Key used to set and get the UID value from the configuration map
+	tailMaxNumberOfLines       = "10000"                // maximum number of log lines from a virtual runtime (docker or kubernetes)
 )

diagnostic/log_collector_docker.go

@@ -0,0 +1,83 @@
+package diagnostic
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"time"
+)
+
+type DockerLogCollector struct {
+	containerID string // This member identifies the container by identifier or name
+}
+
+func NewDockerLogCollector(containerID string) *DockerLogCollector {
+	return &DockerLogCollector{
+		containerID,
+	}
+}
+
+func (collector *DockerLogCollector) Collect(ctx context.Context) (*LogInformation, error) {
+	tmp := os.TempDir()
+
+	outputHandle, err := os.Create(filepath.Join(tmp, logFilename))
+	if err != nil {
+		return nil, fmt.Errorf("error opening output file: %w", err)
+	}
+
+	defer outputHandle.Close()
+
+	// Calculate 2 weeks ago
+	since := time.Now().Add(twoWeeksOffset).Format(time.RFC3339)
+
+	command := exec.CommandContext(
+		ctx,
+		"docker",
+		"logs",
+		"--tail",
+		tailMaxNumberOfLines,
+		"--since",
+		since,
+		collector.containerID,
+	)
+
+	stdoutReader, err := command.StdoutPipe()
+	if err != nil {
+		return nil, fmt.Errorf(
+			"error retrieving output from command '%s': %w",
+			command.String(),
+			err,
+		)
+	}
+
+	if err := command.Start(); err != nil {
+		return nil, fmt.Errorf(
+			"error running command '%s': %w",
+			command.String(),
+			err,
+		)
+	}
+
+	_, err = io.Copy(outputHandle, stdoutReader)
+	if err != nil {
+		return nil, fmt.Errorf(
+			"error copying output from %s to file %s: %w",
+			command.String(),
+			outputHandle.Name(),
+			err,
+		)
+	}
+
+	if err := command.Wait(); err != nil {
+		return nil, fmt.Errorf(
+			"error waiting from command '%s': %w",
+			command.String(),
+			err,
+		)
+	}
+
+	return NewLogInformation(outputHandle.Name(), true, false), nil
+}