fix header comparison causing spurious http checks

Consul modifies (adds headers) the header map on the cached version
which makes it always fail the comparison (DeepEqual) test. This fixes
the comparison to ignore the fields Consul adds.

check.go

@@ -136,7 +136,7 @@ func (c *CheckRunner) updateCheckHTTP(
 		httpCheck, httpCheckExists := c.checksHTTP.Load(checkHash)
 		if httpCheckExists &&
 			httpCheck.HTTP == http.HTTP &&
-			reflect.DeepEqual(httpCheck.Header, http.Header) &&
+			headersAlmostEqual(httpCheck.Header, http.Header) &&
 			httpCheck.Method == http.Method &&
 			httpCheck.TLSClientConfig.InsecureSkipVerify == http.TLSClientConfig.InsecureSkipVerify &&
 			httpCheck.TLSClientConfig.ServerName == http.TLSClientConfig.ServerName &&
@@ -172,6 +172,22 @@ func (c *CheckRunner) updateCheckHTTP(
 	return true
 }
 
+// Compares headers, skipping ones automatically added by Consul
+// in consul/agent/checks/check.go
+func headersAlmostEqual(h1, h2 map[string][]string) bool {
+	skip := map[string]bool{"User-Agent": true, "Accept": true}
+	for k1, v1 := range h1 {
+		if skip[k1] {
+			continue
+		}
+		v2 := h2[k1]
+		if !reflect.DeepEqual(v1, v2) {
+			return false
+		}
+	}
+	return true
+}
+
 func (c *CheckRunner) updateCheckTCP(
 	latestCheck *api.HealthCheck, checkHash types.CheckID,
 	definition *api.HealthCheckDefinition, updated, added checkIDSet,

check_test.go

@@ -423,3 +423,50 @@ func TestCheck_NoFlapping(t *testing.T) {
 	assert.Equal(t, 1, currentCheck.successCounter)
 	assert.Equal(t, api.HealthCritical, currentCheck.Status)
 }
+
+func TestHeadersAlmostEqual(t *testing.T) {
+	type headers map[string][]string
+	type testCase struct {
+		h1, h2 headers
+		equal  bool
+	}
+	testCases := []testCase{
+		{
+			h1:    headers{},
+			h2:    headers{},
+			equal: true,
+		},
+		{
+			h1:    headers{"foo": {"foo"}},
+			h2:    headers{"bar": {"bar"}},
+			equal: false,
+		},
+		{
+			h1:    headers{"User-Agent": {"foo"}},
+			h2:    headers{"Accept": {"bar"}},
+			equal: true,
+		},
+		{
+			h1:    headers{"foo": {"foo"}, "User-Agent": {"foo"}},
+			h2:    headers{"Accept": {"bar"}},
+			equal: false,
+		},
+		{
+			h1:    headers{"foo": {"foo"}, "User-Agent": {"foo"}},
+			h2:    headers{"foo": {"foo"}, "Accept": {"bar"}},
+			equal: true,
+		},
+	}
+	for _, tc := range testCases {
+		switch eq := headersAlmostEqual(tc.h1, tc.h2); tc.equal {
+		case true:
+			if !eq {
+				t.Error("headers should be equal", tc.h1, tc.h2)
+			}
+		case false:
+			if eq {
+				t.Error("headers should NOT be equal", tc.h1, tc.h2)
+			}
+		}
+	}
+}