Add WithHeader enhancement to the Serve matcher to check for a return…

…ed header

matchers/serve.go

@@ -6,7 +6,9 @@ import (
 	"io"
 	"net/http"
 	"reflect"
+	"sort"
 	"strconv"
+	"strings"
 
 	"github.com/onsi/gomega/types"
 	"github.com/paketo-buildpacks/occam"
@@ -32,6 +34,18 @@ type ServeMatcher struct {
 	client   *http.Client
 }
 
+type Header struct {
+	key   string
+	value string
+}
+
+func WithHeader(key, value string) Header {
+	return Header{
+		key:   key,
+		value: value,
+	}
+}
+
 // OnPort sets the container port that is expected to be exposed.
 func (sm *ServeMatcher) OnPort(port int) *ServeMatcher {
 	sm.port = port
@@ -96,6 +110,12 @@ func (sm *ServeMatcher) Match(actual interface{}) (success bool, err error) {
 	}
 
 	if response != nil {
+		if header, ok := sm.expected.(Header); ok {
+			formatHeaders(sm, response)
+			sm.expected = fmt.Sprintf("Header '%s=%s'", header.key, header.value)
+			return response.Header.Get(header.key) == header.value, nil
+		}
+
 		defer response.Body.Close()
 		content, err := io.ReadAll(response.Body)
 		if err != nil {
@@ -116,6 +136,20 @@ func (sm *ServeMatcher) Match(actual interface{}) (success bool, err error) {
 	return false, nil
 }
 
+func formatHeaders(sm *ServeMatcher, response *http.Response) {
+	var keys []string
+	for key := range response.Header {
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+
+	sm.response = ""
+	for _, key := range keys {
+		sm.response += fmt.Sprintf("Header '%s=%s'\n\t", key, strings.Join(response.Header.Values(key), ", "))
+	}
+	sm.response = strings.TrimSpace(sm.response)
+}
+
 func (sm *ServeMatcher) compare(actual string, expected interface{}) (bool, error) {
 	if m, ok := expected.(types.GomegaMatcher); ok {
 		match, err := m.Match(actual)

matchers/serve_test.go

@@ -35,6 +35,8 @@ func testServe(t *testing.T, context spec.G, it spec.S) {
 				return
 			}
 
+			w.Header().Set("Date", "Sat, 17 Sep 2022 03:28:54 GMT")
+
 			switch req.URL.Path {
 			case "/":
 				w.WriteHeader(http.StatusOK)
@@ -240,6 +242,30 @@ func testServe(t *testing.T, context spec.G, it spec.S) {
 				})
 			})
 		})
+
+		context("WithHeader", func() {
+			it("returns true with the header is found", func() {
+				matcher = matchers.Serve(matchers.WithHeader("Content-Type", "text/plain; charset=utf-8"))
+
+				result, err := matcher.Match(occam.Container{
+					Ports: map[string]string{"8080": port},
+					Env:   map[string]string{"PORT": "8080"},
+				})
+				Expect(err).NotTo(HaveOccurred())
+				Expect(result).To(BeTrue())
+			})
+
+			it("returns false with the header is not found", func() {
+				matcher = matchers.Serve(matchers.WithHeader("Content-Type", "other"))
+
+				result, err := matcher.Match(occam.Container{
+					Ports: map[string]string{"8080": port},
+					Env:   map[string]string{"PORT": "8080"},
+				})
+				Expect(err).NotTo(HaveOccurred())
+				Expect(result).To(BeFalse())
+			})
+		})
 	})
 
 	context("when the matcher fails", func() {
@@ -284,6 +310,26 @@ Container logs:
 some logs
 	`)))
 			})
+
+			it("returns a useful error message for WithHeader", func() {
+				matcher = matchers.Serve(matchers.WithHeader("Content-Type", "other"))
+				_, _ = matcher.Match(occam.Container{
+					Ports: map[string]string{"8080": port},
+					Env:   map[string]string{"PORT": "8080"},
+				})
+
+				message := matcher.FailureMessage(actual)
+				Expect(message).To(ContainSubstring(strings.TrimSpace(`
+Expected the response from docker container some-container-id:
+
+	Header 'Content-Length=11'
+	Header 'Content-Type=text/plain; charset=utf-8'
+	Header 'Date=Sat, 17 Sep 2022 03:28:54 GMT'
+
+to contain:
+
+	Header 'Content-Type=other'`)))
+			})
 		})
 
 		context("NegatedFailureMessage", func() {
@@ -304,5 +350,25 @@ some logs
 	`)))
 			})
 		})
+
+		it("returns a useful error message for WithHeader", func() {
+			matcher = matchers.Serve(matchers.WithHeader("Content-Type", "other"))
+			_, _ = matcher.Match(occam.Container{
+				Ports: map[string]string{"8080": port},
+				Env:   map[string]string{"PORT": "8080"},
+			})
+
+			message := matcher.NegatedFailureMessage(actual)
+			Expect(message).To(ContainSubstring(strings.TrimSpace(`
+Expected the response from docker container some-container-id:
+
+	Header 'Content-Length=11'
+	Header 'Content-Type=text/plain; charset=utf-8'
+	Header 'Date=Sat, 17 Sep 2022 03:28:54 GMT'
+
+not to contain:
+
+	Header 'Content-Type=other'`)))
+		})
 	})
 }