aws/request: Fix SDK's handling of endpoints ending in slash (#3926)

Fixes the SDK's handling of endpoints that end in a slash (`/`) causing
signature validation errors due to Request.HTTPRequest.URL.Path not
matching what was sent in the request.

CHANGELOG_PENDING.md

@@ -3,3 +3,5 @@
 ### SDK Enhancements
 
 ### SDK Bugs
+* `aws/request`: Fix handling of endpoints with trailing slashes
+  * Fixes the SDK's handling of endpoint URLs that contain a trailing slash when the API operation's modeled path is suffixed. Also ensures any endpoint URL query string is squashed consistently. 

aws/request/request.go

@@ -129,12 +129,27 @@ func New(cfg aws.Config, clientInfo metadata.ClientInfo, handlers Handlers,
 	httpReq, _ := http.NewRequest(method, "", nil)
 
 	var err error
-	httpReq.URL, err = url.Parse(clientInfo.Endpoint + operation.HTTPPath)
+	httpReq.URL, err = url.Parse(clientInfo.Endpoint)
 	if err != nil {
 		httpReq.URL = &url.URL{}
 		err = awserr.New("InvalidEndpointURL", "invalid endpoint uri", err)
 	}
 
+	if len(operation.HTTPPath) != 0 {
+		opHTTPPath := operation.HTTPPath
+		var opQueryString string
+		if idx := strings.Index(opHTTPPath, "?"); idx >= 0 {
+			opQueryString = opHTTPPath[idx+1:]
+			opHTTPPath = opHTTPPath[:idx]
+		}
+
+		if strings.HasSuffix(httpReq.URL.Path, "/") && strings.HasPrefix(opHTTPPath, "/") {
+			opHTTPPath = opHTTPPath[1:]
+		}
+		httpReq.URL.Path += opHTTPPath
+		httpReq.URL.RawQuery = opQueryString
+	}
+
 	r := &Request{
 		Config:     cfg,
 		ClientInfo: clientInfo,

aws/request/request_1_8_test.go

@@ -84,3 +84,71 @@ func TestRequest_FollowPUTRedirects(t *testing.T) {
 		t.Errorf("expect %d endpoint hits, got %d", e, a)
 	}
 }
+
+func TestNewRequest_JoinEndpointWithOperationPathQuery(t *testing.T) {
+	cases := map[string]struct {
+		HTTPPath    string
+		Endpoint    *string
+		ExpectQuery string
+		ExpectPath  string
+	}{
+		"no op HTTP Path": {
+			HTTPPath:    "",
+			Endpoint:    aws.String("https://foo.bar.aws/foo?bar=Baz"),
+			ExpectPath:  "/foo",
+			ExpectQuery: "bar=Baz",
+		},
+		"no trailing slash": {
+			HTTPPath:    "/",
+			Endpoint:    aws.String("https://foo.bar.aws"),
+			ExpectPath:  "/",
+			ExpectQuery: "",
+		},
+		"set query": {
+			HTTPPath:    "/?Foo=bar",
+			Endpoint:    aws.String("https://foo.bar.aws"),
+			ExpectPath:  "/",
+			ExpectQuery: "Foo=bar",
+		},
+		"squash query": {
+			HTTPPath:    "/?Foo=bar",
+			Endpoint:    aws.String("https://foo.bar.aws/?bar=Foo"),
+			ExpectPath:  "/",
+			ExpectQuery: "Foo=bar",
+		},
+		"trailing slash": {
+			HTTPPath:    "/",
+			Endpoint:    aws.String("https://foo.bar.aws/"),
+			ExpectPath:  "/",
+			ExpectQuery: "",
+		},
+		"trailing slash set query": {
+			HTTPPath:    "/?Foo=bar",
+			Endpoint:    aws.String("https://foo.bar.aws/"),
+			ExpectPath:  "/",
+			ExpectQuery: "Foo=bar",
+		},
+	}
+
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			client := awstesting.NewClient(&aws.Config{
+				Endpoint: c.Endpoint,
+			})
+
+			client.Handlers.Clear()
+			r := client.NewRequest(&request.Operation{
+				Name:       "FooBar",
+				HTTPMethod: "GET",
+				HTTPPath:   c.HTTPPath,
+			}, nil, nil)
+
+			if e, a := c.ExpectPath, r.HTTPRequest.URL.Path; e != a {
+				t.Errorf("expect %v path, got %v", e, a)
+			}
+			if e, a := c.ExpectQuery, r.HTTPRequest.URL.RawQuery; e != a {
+				t.Errorf("expect %v query, got %v", e, a)
+			}
+		})
+	}
+}