ddtrace/tracer: add Datadog-Container-ID when information is available (

#472)

This change adds the container ID as a transport header, when the
information is available and can be extracted as part of the
/proc/self/cgroup file.

ddtrace/tracer/transport.go

@@ -6,11 +6,13 @@
 package tracer
 
 import (
+	"bufio"
 	"fmt"
 	"io"
 	"net"
 	"net/http"
 	"os"
+	"regexp"
 	"runtime"
 	"strconv"
 	"strings"
@@ -90,6 +92,13 @@ func newHTTPTransport(addr string, roundTripper http.RoundTripper) *httpTranspor
 		"Datadog-Meta-Tracer-Version":   version.Tag,
 		"Content-Type":                  "application/msgpack",
 	}
+	f, err := os.Open("/proc/self/cgroup")
+	if err == nil {
+		if id, ok := readContainerID(f); ok {
+			defaultHeaders["Datadog-Container-ID"] = id
+		}
+		f.Close()
+	}
 	return &httpTransport{
 		traceURL: fmt.Sprintf("http://%s/v0.4/traces", resolveAddr(addr)),
 		client: &http.Client{
@@ -100,6 +109,29 @@ func newHTTPTransport(addr string, roundTripper http.RoundTripper) *httpTranspor
 	}
 }
 
+var (
+	// expLine matches a line in the /proc/self/cgroup file. It has a submatch for the last element (path), which contains the container ID.
+	expLine = regexp.MustCompile(`^\d+:[^:]*:(.+)$`)
+	// expContainerID matches contained IDs and sources. Source: https://github.com/Qard/container-info/blob/master/index.js
+	expContainerID = regexp.MustCompile(`([0-9a-f]{8}[-_][0-9a-f]{4}[-_][0-9a-f]{4}[-_][0-9a-f]{4}[-_][0-9a-f]{12}|[0-9a-f]{64})(?:.scope)?$`)
+)
+
+// readContainerID finds the first container ID reading from r and returns it.
+func readContainerID(r io.Reader) (id string, ok bool) {
+	scn := bufio.NewScanner(r)
+	for scn.Scan() {
+		path := expLine.FindStringSubmatch(scn.Text())
+		if len(path) != 2 {
+			// invalid entry, continue
+			continue
+		}
+		if id := expContainerID.FindString(path[1]); id != "" {
+			return id, true
+		}
+	}
+	return "", false
+}
+
 func (t *httpTransport) send(p *payload) (body io.ReadCloser, err error) {
 	// prepare the client and send the payload
 	req, err := http.NewRequest("POST", t.traceURL, p)

ddtrace/tracer/transport_test.go

@@ -28,6 +28,35 @@ func TestMain(m *testing.M) {
 	os.Exit(m.Run())
 }
 
+func TestReadContainerID(t *testing.T) {
+	for in, out := range map[string]string{
+		`other_line
+10:hugetlb:/kubepods/burstable/podfd52ef25-a87d-11e9-9423-0800271a638e/8c046cb0b72cd4c99f51b5591cd5b095967f58ee003710a45280c28ee1a9c7fa
+9:cpuset:/kubepods/burstable/podfd52ef25-a87d-11e9-9423-0800271a638e/8c046cb0b72cd4c99f51b5591cd5b095967f58ee003710a45280c28ee1a9c7fa
+8:pids:/kubepods/burstable/podfd52ef25-a87d-11e9-9423-0800271a638e/8c046cb0b72cd4c99f51b5591cd5b095967f58ee003710a45280c28ee1a9c7fa
+7:freezer:/kubepods/burstable/podfd52ef25-a87d-11e9-9423-0800271a638e/8c046cb0b72cd4c99f51b5591cd5b095967f58ee003710a45280c28ee1a9c7fa
+6:cpu,cpuacct:/kubepods/burstable/podfd52ef25-a87d-11e9-9423-0800271a638e/8c046cb0b72cd4c99f51b5591cd5b095967f58ee003710a45280c28ee1a9c7fa
+5:perf_event:/kubepods/burstable/podfd52ef25-a87d-11e9-9423-0800271a638e/8c046cb0b72cd4c99f51b5591cd5b095967f58ee003710a45280c28ee1a9c7fa
+4:blkio:/kubepods/burstable/podfd52ef25-a87d-11e9-9423-0800271a638e/8c046cb0b72cd4c99f51b5591cd5b095967f58ee003710a45280c28ee1a9c7fa
+3:devices:/kubepods/burstable/podfd52ef25-a87d-11e9-9423-0800271a638e/8c046cb0b72cd4c99f51b5591cd5b095967f58ee003710a45280c28ee1a9c7fa
+2:net_cls,net_prio:/kubepods/burstable/podfd52ef25-a87d-11e9-9423-0800271a638e/8c046cb0b72cd4c99f51b5591cd5b095967f58ee003710a45280c28ee1a9c7fa`: "8c046cb0b72cd4c99f51b5591cd5b095967f58ee003710a45280c28ee1a9c7fa",
+		"10:hugetlb:/kubepods/burstable/podfd52ef25-a87d-11e9-9423-0800271a638e/8c046cb0b72cd4c99f51b5591cd5b095967f58ee003710a45280c28ee1a9c7fa": "8c046cb0b72cd4c99f51b5591cd5b095967f58ee003710a45280c28ee1a9c7fa",
+		"10:hugetlb:/kubepods": "",
+	} {
+		id, ok := readContainerID(strings.NewReader(in))
+		if id != out {
+			t.Fatalf("%q -> %q", in, out)
+		}
+		if out == "" {
+			if ok {
+				t.Fatalf("%q: got ok=true", in)
+			}
+		} else if !ok {
+			t.Fatalf("%q: got ok=false", in)
+		}
+	}
+}
+
 // getTestSpan returns a Span with different fields set
 func getTestSpan() *span {
 	return &span{