Add support for multiple exceptions with the same status code (#565)

* Add client files.

* Compile withExceptions code.

* Add exceptions by status code to pave the way for updating the template.

* Update logic for exceptions handling in HTTP clients.

* Add withexceptions sample endpoint.

* Run go fmt.

* Fix tests.

* Run gofmt.

* Update after generate.

* Add sort to preserve ordering.

* Update example endpoint and client to avoid test failures.

* Switch to use multierr.

* Shorten log statement per review request.

* Remove "= nil" from var initialization.

codegen/method.go

@@ -22,6 +22,7 @@ package codegen
 
 import (
 	"fmt"
+	"sort"
 	"strconv"
 	"strings"
 
@@ -101,14 +102,15 @@ type MethodSpec struct {
 	// ResHeaders needed, generated from "zanzibar.http.resHeaders"
 	ResHeaders []string
 
-	RequestType       string
-	ShortRequestType  string
-	ResponseType      string
-	ShortResponseType string
-	OKStatusCode      StatusCode
-	Exceptions        []ExceptionSpec
-	ExceptionsIndex   map[string]ExceptionSpec
-	ValidStatusCodes  []int
+	RequestType            string
+	ShortRequestType       string
+	ResponseType           string
+	ShortResponseType      string
+	OKStatusCode           StatusCode
+	Exceptions             []ExceptionSpec
+	ExceptionsByStatusCode map[int][]ExceptionSpec
+	ExceptionsIndex        map[string]ExceptionSpec
+	ValidStatusCodes       []int
 	// Additional struct generated from the bundle of request args.
 	RequestBoxed bool
 	// Thrift service name the method belongs to.
@@ -388,12 +390,16 @@ func (ms *MethodSpec) setOKStatusCode(statusCode string) error {
 }
 
 func (ms *MethodSpec) setValidStatusCodes() {
-	ms.ValidStatusCodes = make([]int, len(ms.Exceptions)+1)
+	ms.ValidStatusCodes = []int{
+		ms.OKStatusCode.Code,
+	}
 
-	ms.ValidStatusCodes[0] = ms.OKStatusCode.Code
-	for i := 0; i < len(ms.Exceptions); i++ {
-		ms.ValidStatusCodes[i+1] = ms.Exceptions[i].StatusCode.Code
+	for code := range ms.ExceptionsByStatusCode {
+		ms.ValidStatusCodes = append(ms.ValidStatusCodes, code)
 	}
+
+	// Prevents non-deterministic builds
+	sort.Ints(ms.ValidStatusCodes)
 }
 
 func (ms *MethodSpec) setExceptions(
@@ -402,13 +408,11 @@ func (ms *MethodSpec) setExceptions(
 	resultSpec *compile.ResultSpec,
 	h *PackageHelper,
 ) error {
-	seenStatusCodes := map[int]bool{
-		ms.OKStatusCode.Code: true,
-	}
 	ms.Exceptions = make([]ExceptionSpec, len(resultSpec.Exceptions))
 	ms.ExceptionsIndex = make(
 		map[string]ExceptionSpec, len(resultSpec.Exceptions),
 	)
+	ms.ExceptionsByStatusCode = map[int][]ExceptionSpec{}
 
 	for i, e := range resultSpec.Exceptions {
 		typeName, err := h.TypeFullName(e.Type)
@@ -430,6 +434,13 @@ func (ms *MethodSpec) setExceptions(
 			}
 			ms.Exceptions[i] = exception
 			ms.ExceptionsIndex[e.Name] = exception
+			if _, exists := ms.ExceptionsByStatusCode[exception.StatusCode.Code]; !exists {
+				ms.ExceptionsByStatusCode[exception.StatusCode.Code] = []ExceptionSpec{}
+			}
+			ms.ExceptionsByStatusCode[exception.StatusCode.Code] = append(
+				ms.ExceptionsByStatusCode[exception.StatusCode.Code],
+				exception,
+			)
 			continue
 		}
 
@@ -441,16 +452,6 @@ func (ms *MethodSpec) setExceptions(
 			)
 		}
 
-		if seenStatusCodes[code] && !isEndpoint {
-			return errors.Wrapf(
-				err,
-				"cannot have duplicate status code %s for exception %s",
-				ms.annotations.HTTPStatus,
-				e.Name,
-			)
-		}
-		seenStatusCodes[code] = true
-
 		exception := ExceptionSpec{
 			StructSpec: StructSpec{
 				Type:        typeName,
@@ -464,6 +465,13 @@ func (ms *MethodSpec) setExceptions(
 		}
 		ms.Exceptions[i] = exception
 		ms.ExceptionsIndex[e.Name] = exception
+		if _, exists := ms.ExceptionsByStatusCode[exception.StatusCode.Code]; !exists {
+			ms.ExceptionsByStatusCode[exception.StatusCode.Code] = []ExceptionSpec{}
+		}
+		ms.ExceptionsByStatusCode[exception.StatusCode.Code] = append(
+			ms.ExceptionsByStatusCode[exception.StatusCode.Code],
+			exception,
+		)
 	}
 	return nil
 }

codegen/module.go

@@ -610,6 +610,7 @@ func (system *ModuleSystem) ResolveModules(
 
 				classConfigPath, _, _ := getConfigFilePath(moduleDirAbs, className)
 				if classConfigPath == "" {
+					fmt.Printf("  no class config found in %s directory\n", moduleDirAbs)
 					// No class config found in this directory, skip over it
 					continue
 				}

codegen/templates/http_client.tmpl

@@ -288,14 +288,18 @@ func (c *{{$clientName}}) {{$methodName}}(
 			}
 
 			return respHeaders, nil
-		{{range $idx, $exception := .Exceptions}}
-		case {{$exception.StatusCode.Code}}:
-			var exception {{$exception.Type}}
-			err = res.ReadAndUnmarshalBody(&exception)
+		{{range $code, $exceptions := .ExceptionsByStatusCode -}}
+		case {{$code}}:
+			allOptions := []interface{}{
+				{{range $idx, $exception := $exceptions -}}
+				&{{$exception.Type}}{},
+				{{- end}}
+			}
+			v, err := res.ReadAndUnmarshalBodyMultipleOptions(allOptions)
 			if err != nil {
 				return respHeaders, err
 			}
-			return respHeaders, &exception
+			return respHeaders, v.(error)
 		{{end}}
 		default:
 			_, err = res.ReadAll()
@@ -317,14 +321,18 @@ func (c *{{$clientName}}) {{$methodName}}(
 			{{- end}}
 
 			return {{if isPointerType .ResponseType}}&{{end}}responseBody, respHeaders, nil
-		{{range $idx, $exception := .Exceptions}}
-		case {{$exception.StatusCode.Code}}:
-			var exception {{$exception.Type}}
-			err = res.ReadAndUnmarshalBody(&exception)
+		{{range $code, $exceptions := .ExceptionsByStatusCode -}}
+		case {{$code}}:
+			allOptions := []interface{}{
+				{{range $idx, $exception := $exceptions -}}
+				&{{$exception.Type}}{},
+				{{- end}}
+			}
+			v, err := res.ReadAndUnmarshalBodyMultipleOptions(allOptions)
 			if err != nil {
 				return defaultRes, respHeaders, err
 			}
-			return defaultRes, respHeaders, &exception
+			return defaultRes, respHeaders, v.(error)
 		{{end}}
 		default:
 			_, err = res.ReadAll()