Add a TCP health checker

Also, add timeout and status code parameters to the HTTP checker, and
remove the threshold parameter for the file checker.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

health/checks/checks.go

@@ -2,15 +2,17 @@ package checks
 
 import (
 	"errors"
+	"net"
 	"net/http"
 	"os"
 	"strconv"
+	"time"
 
 	"github.com/docker/distribution/health"
 )
 
-// FileChecker checks the existence of a file and returns and error
-// if the file exists, taking the application out of rotation
+// FileChecker checks the existence of a file and returns an error
+// if the file exists.
 func FileChecker(f string) health.Checker {
 	return health.CheckFunc(func() error {
 		if _, err := os.Stat(f); err == nil {
@@ -20,18 +22,32 @@ func FileChecker(f string) health.Checker {
 	})
 }
 
-// HTTPChecker does a HEAD request and verifies if the HTTP status
-// code return is a 200, taking the application out of rotation if
-// otherwise
-func HTTPChecker(r string) health.Checker {
+// HTTPChecker does a HEAD request and verifies that the HTTP status code
+// returned matches statusCode.
+func HTTPChecker(r string, statusCode int, timeout time.Duration) health.Checker {
 	return health.CheckFunc(func() error {
-		response, err := http.Head(r)
+		client := http.Client{
+			Timeout: timeout,
+		}
+		response, err := client.Head(r)
 		if err != nil {
 			return errors.New("error while checking: " + r)
 		}
-		if response.StatusCode != http.StatusOK {
+		if response.StatusCode != statusCode {
 			return errors.New("downstream service returned unexpected status: " + strconv.Itoa(response.StatusCode))
 		}
 		return nil
 	})
 }
+
+// TCPChecker attempts to open a TCP connection.
+func TCPChecker(addr string, timeout time.Duration) health.Checker {
+	return health.CheckFunc(func() error {
+		conn, err := net.DialTimeout("tcp", addr, timeout)
+		if err != nil {
+			return errors.New("connection to " + addr + " failed")
+		}
+		conn.Close()
+		return nil
+	})
+}

health/checks/checks_test.go

@@ -15,11 +15,11 @@ func TestFileChecker(t *testing.T) {
 }
 
 func TestHTTPChecker(t *testing.T) {
-	if err := HTTPChecker("https://www.google.cybertron").Check(); err == nil {
+	if err := HTTPChecker("https://www.google.cybertron", 200, 0).Check(); err == nil {
 		t.Errorf("Google on Cybertron was expected as not exists")
 	}
 
-	if err := HTTPChecker("https://www.google.pt").Check(); err != nil {
+	if err := HTTPChecker("https://www.google.pt", 200, 0).Check(); err != nil {
 		t.Errorf("Google at Portugal was expected as exists, error:%v", err)
 	}
 }