Calculate digest when missing from registry response headers (#188)

Closes #186

docker/data_source_docker_registry_image.go

@@ -1,6 +1,7 @@
 package docker
 
 import (
+	"crypto/sha256"
 	"crypto/tls"
 	"encoding/json"
 	"fmt"
@@ -119,7 +120,7 @@ func getImageDigest(registry, image, tag, username, password string, fallback bo
 	switch resp.StatusCode {
 	// Basic auth was valid or not needed
 	case http.StatusOK:
-		return resp.Header.Get("Docker-Content-Digest"), nil
+		return getDigestFromResponse(resp)
 
 	// Either OAuth is required or the basic auth creds were invalid
 	case http.StatusUnauthorized:
@@ -170,7 +171,7 @@ func getImageDigest(registry, image, tag, username, password string, fallback bo
 				return "", fmt.Errorf("Got bad response from registry: " + digestResponse.Status)
 			}
 
-			return digestResponse.Header.Get("Docker-Content-Digest"), nil
+			return getDigestFromResponse(digestResponse)
 		}
 
 		return "", fmt.Errorf("Bad credentials: " + resp.Status)
@@ -200,3 +201,18 @@ func parseAuthHeader(header string) map[string]string {
 
 	return opts
 }
+
+func getDigestFromResponse(response *http.Response) (string, error) {
+	header := response.Header.Get("Docker-Content-Digest")
+
+	if header == "" {
+		body, err := ioutil.ReadAll(response.Body)
+		if err != nil {
+			return "", fmt.Errorf("Error reading registry response body: %s", err)
+		}
+
+		return fmt.Sprintf("sha256:%x", sha256.Sum256(body)), nil
+	}
+
+	return header, nil
+}

docker/data_source_docker_registry_image_test.go

@@ -1,7 +1,10 @@
 package docker
 
 import (
+	"bytes"
 	"fmt"
+	"io/ioutil"
+	"net/http"
 	"regexp"
 	"testing"
 
@@ -82,3 +85,27 @@ data "docker_registry_image" "foobar" {
 	name = "%s"
 }
 `
+
+func TestGetDigestFromResponse(t *testing.T) {
+	headerContent := "sha256:2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae"
+	respWithHeaders := &http.Response{
+		Header: http.Header{
+			"Docker-Content-Digest": []string{headerContent},
+		},
+		Body: ioutil.NopCloser(bytes.NewReader([]byte("foo"))),
+	}
+
+	if digest, _ := getDigestFromResponse(respWithHeaders); digest != headerContent {
+		t.Errorf("Expected digest from header to be %s, but was %s", headerContent, digest)
+	}
+
+	bodyDigest := "sha256:fcde2b2edba56bf408601fb721fe9b5c338d10ee429ea04fae5511b68fbf8fb9"
+	respWithoutHeaders := &http.Response{
+		Header: make(http.Header),
+		Body:   ioutil.NopCloser(bytes.NewReader([]byte("bar"))),
+	}
+
+	if digest, _ := getDigestFromResponse(respWithoutHeaders); digest != bodyDigest {
+		t.Errorf("Expected digest calculated from body to be %s, but was %s", bodyDigest, digest)
+	}
+}