Fix container ID extraction from /proc/self/mountinfo file

context.go

@@ -2,9 +2,7 @@ package dockergen
 
 import (
 	"bufio"
-	"bytes"
 	"fmt"
-	"io"
 	"os"
 	"regexp"
 	"sync"
@@ -169,43 +167,42 @@ func GetCurrentContainerID(filepaths ...string) (id string) {
 		filepaths = []string{"/proc/1/cpuset", "/proc/self/cgroup", "/proc/self/mountinfo"}
 	}
 
-	var files []io.Reader
-
+	// We try to match a 64 character hex string starting with the hostname first
 	for _, filepath := range filepaths {
 		file, err := os.Open(filepath)
 		if err != nil {
 			continue
 		}
 		defer file.Close()
-		files = append(files, file)
-	}
-
-	reader := io.MultiReader(files...)
-	var buffer bytes.Buffer
-	tee := io.TeeReader(reader, &buffer)
-
-	// We try to match a 64 character hex string starting with the hostname first
-	scanner := bufio.NewScanner(tee)
-	scanner.Split(bufio.ScanLines)
-	for scanner.Scan() {
-		_, lines, err := bufio.ScanLines([]byte(scanner.Text()), true)
-		if err == nil {
-			strLines := string(lines)
-			if id = matchContainerIDWithHostname(strLines); len(id) == 64 {
-				return
+		scanner := bufio.NewScanner(file)
+		scanner.Split(bufio.ScanLines)
+		for scanner.Scan() {
+			_, lines, err := bufio.ScanLines([]byte(scanner.Text()), true)
+			if err == nil {
+				strLines := string(lines)
+				if id = matchContainerIDWithHostname(strLines); len(id) == 64 {
+					return
+				}
 			}
 		}
 	}
 
 	// If we didn't get any ID that matches the hostname, fall back to matching the first 64 character hex string
-	scanner = bufio.NewScanner(&buffer)
-	scanner.Split(bufio.ScanLines)
-	for scanner.Scan() {
-		_, lines, err := bufio.ScanLines([]byte(scanner.Text()), true)
-		if err == nil {
-			strLines := string(lines)
-			if id = matchContainerID(strLines); len(id) == 64 {
-				return
+	for _, filepath := range filepaths {
+		file, err := os.Open(filepath)
+		if err != nil {
+			continue
+		}
+		defer file.Close()
+		scanner := bufio.NewScanner(file)
+		scanner.Split(bufio.ScanLines)
+		for scanner.Scan() {
+			_, lines, err := bufio.ScanLines([]byte(scanner.Text()), true)
+			if err == nil {
+				strLines := string(lines)
+				if id = matchContainerID("([[:alnum:]]{64})", strLines); len(id) == 64 {
+					return
+				}
 			}
 		}
 	}
@@ -219,22 +216,21 @@ func matchContainerIDWithHostname(lines string) string {
 
 	if re.MatchString(hostname) {
 		regex := fmt.Sprintf("(%s[[:alnum:]]{52})", hostname)
-		re := regexp.MustCompilePOSIX(regex)
 
-		if re.MatchString(lines) {
-			submatches := re.FindStringSubmatch(string(lines))
-			containerID := submatches[1]
-
-			return containerID
-		}
+		return matchContainerID(regex, lines)
 	}
 	return ""
 }
 
-func matchContainerID(lines string) string {
-	regex := "([[:alnum:]]{64})"
-	re := regexp.MustCompilePOSIX(regex)
+func matchContainerID(regex, lines string) string {
+	// Attempt to detect if we're on a line from a /proc/<pid>/mountinfo file and modify the regexp accordingly
+	// https://www.kernel.org/doc/Documentation/filesystems/proc.txt section 3.5
+	re := regexp.MustCompilePOSIX("^[0-9]+ [0-9]+ [0-9]+:[0-9]+ /")
+	if re.MatchString(lines) {
+		regex = fmt.Sprintf("containers/%v", regex)
+	}
 
+	re = regexp.MustCompilePOSIX(regex)
 	if re.MatchString(lines) {
 		submatches := re.FindStringSubmatch(string(lines))
 		containerID := submatches[1]

context_test.go

@@ -8,17 +8,20 @@ import (
 	"testing"
 )
 
-func TestGetCurrentContainerID(t *testing.T) {
-	hostname := os.Getenv("HOSTNAME")
-	defer os.Setenv("HOSTNAME", hostname)
-
-	ids := []string{
+var (
+	ids = []string{
 		"0fa939e22e6938e7517f663de83e79a5087a18b1b997a36e0c933a917cddb295",
 		"e881f8c51a72db7da515e9d5cab8ed105b869579eb9923fdcf4ee80933160802",
 		"eede6bd9e72f5d783a4bfb845bd71f310e974cb26987328a5d15704e23a8d6cb",
 	}
 
-	contents := map[string]string{
+	fileKeys = []string{
+		"cpuset",
+		"cgroup",
+		"mountinfo",
+	}
+
+	contents = map[string]string{
 		"cpuset": fmt.Sprintf("/docker/%v", ids[0]),
 		"cgroup": fmt.Sprintf(`13:name=systemd:/docker-ce/docker/%[1]v
 12:pids:/docker-ce/docker/%[1]v
@@ -61,16 +64,15 @@ func TestGetCurrentContainerID(t *testing.T) {
 674 706 0:111 / /proc/scsi ro,relatime - tmpfs tmpfs ro,inode64
 675 709 0:112 / /sys/firmware ro,relatime - tmpfs tmpfs ro,inode64`, ids[2]),
 	}
+)
 
-	keys := []string{
-		"cpuset",
-		"cgroup",
-		"mountinfo",
-	}
+func TestGetCurrentContainerID(t *testing.T) {
+	hostname := os.Getenv("HOSTNAME")
+	defer os.Setenv("HOSTNAME", hostname)
 
 	var filepaths []string
 	// Create temporary files with test content
-	for _, key := range keys {
+	for _, key := range fileKeys {
 		file, err := ioutil.TempFile("", key)
 		if err != nil {
 			log.Fatal(err)
@@ -96,3 +98,38 @@ func TestGetCurrentContainerID(t *testing.T) {
 		t.Fatalf("id mismatch with custom HOSTNAME: got %v, exp %v", got, exp)
 	}
 }
+
+func TestGetCurrentContainerIDMountInfo(t *testing.T) {
+	// Test specific to cases like https://github.com/nginx-proxy/docker-gen/issues/355
+	// where only the /proc/<pid>/mountinfo file contains information
+	hostname := os.Getenv("HOSTNAME")
+	defer os.Setenv("HOSTNAME", hostname)
+	os.Setenv("HOSTNAME", "customhostname")
+
+	id := ids[2]
+
+	content := map[string]string{
+		"cpuset":    "/",
+		"cgroup":    "0::/",
+		"mountinfo": contents["mountinfo"],
+	}
+
+	var filepaths []string
+	// Create temporary files with test content
+	for _, key := range fileKeys {
+		file, err := ioutil.TempFile("", key)
+		if err != nil {
+			log.Fatal(err)
+		}
+		defer os.Remove(file.Name())
+		if _, err = file.WriteString(content[key]); err != nil {
+			log.Fatal(err)
+		}
+		filepaths = append(filepaths, file.Name())
+	}
+
+	// We should match the correct 64 characters long ID in mountinfo, not the first encountered
+	if got, exp := GetCurrentContainerID(filepaths...), id; got != exp {
+		t.Fatalf("id mismatch on mountinfo: got %v, exp %v", got, exp)
+	}
+}