fix(client): support multipart encoding array formats (#342)

Author: stainless-app[bot]

Diff for: internal/apiform/encoder.go

@@ -20,16 +20,32 @@ import (
 var encoders sync.Map // map[encoderEntry]encoderFunc
 
 func Marshal(value interface{}, writer *multipart.Writer) error {
-	e := &encoder{dateFormat: time.RFC3339}
+	e := &encoder{
+		dateFormat: time.RFC3339,
+		arrayFmt:   "brackets",
+	}
 	return e.marshal(value, writer)
 }
 
 func MarshalRoot(value interface{}, writer *multipart.Writer) error {
-	e := &encoder{root: true, dateFormat: time.RFC3339}
+	e := &encoder{
+		root:       true,
+		dateFormat: time.RFC3339,
+		arrayFmt:   "brackets",
+	}
+	return e.marshal(value, writer)
+}
+
+func MarshalWithSettings(value interface{}, writer *multipart.Writer, arrayFormat string) error {
+	e := &encoder{
+		arrayFmt:   arrayFormat,
+		dateFormat: time.RFC3339,
+	}
 	return e.marshal(value, writer)
 }
 
 type encoder struct {
+	arrayFmt   string
 	dateFormat string
 	root       bool
 }
@@ -163,15 +179,40 @@ func (e *encoder) newPrimitiveTypeEncoder(t reflect.Type) encoderFunc {
 	}
 }
 
+func arrayKeyEncoder(arrayFmt string) func(string, int) string {
+	var keyFn func(string, int) string
+	switch arrayFmt {
+	case "comma", "repeat":
+		keyFn = func(k string, _ int) string { return k }
+	case "brackets":
+		keyFn = func(key string, _ int) string { return key + "[]" }
+	case "indices:dots":
+		keyFn = func(k string, i int) string {
+			if k == "" {
+				return strconv.Itoa(i)
+			}
+			return k + "." + strconv.Itoa(i)
+		}
+	case "indices:brackets":
+		keyFn = func(k string, i int) string {
+			if k == "" {
+				return strconv.Itoa(i)
+			}
+			return k + "[" + strconv.Itoa(i) + "]"
+		}
+	}
+	return keyFn
+}
+
 func (e *encoder) newArrayTypeEncoder(t reflect.Type) encoderFunc {
 	itemEncoder := e.typeEncoder(t.Elem())
-
+	keyFn := arrayKeyEncoder(e.arrayFmt)
 	return func(key string, v reflect.Value, writer *multipart.Writer) error {
-		if key != "" {
-			key = key + "."
+		if keyFn == nil {
+			return fmt.Errorf("apiform: unsupported array format")
 		}
 		for i := 0; i < v.Len(); i++ {
-			err := itemEncoder(key+strconv.Itoa(i), v.Index(i), writer)
+			err := itemEncoder(keyFn(key, i), v.Index(i), writer)
 			if err != nil {
 				return err
 			}

Diff for: internal/apiform/form_test.go

@@ -19,6 +19,13 @@ type Primitives struct {
 	F []int   `form:"f"`
 }
 
+// These aliases are necessary to bypass the cache.
+// This only relevant during testing.
+type int_ int
+type PrimitivesBrackets struct {
+	F []int_ `form:"f"`
+}
+
 type PrimitivePointers struct {
 	A *bool    `form:"a"`
 	B *int     `form:"b"`
@@ -169,6 +176,27 @@ Content-Disposition: form-data; name="f.3"
 `,
 		Primitives{A: false, B: 237628372683, C: uint(654), D: 9999.43, E: 43.76, F: []int{1, 2, 3, 4}},
 	},
+	"primitive_struct,brackets": {
+		`--xxx
+Content-Disposition: form-data; name="f[]"
+
+1
+--xxx
+Content-Disposition: form-data; name="f[]"
+
+2
+--xxx
+Content-Disposition: form-data; name="f[]"
+
+3
+--xxx
+Content-Disposition: form-data; name="f[]"
+
+4
+--xxx--
+`,
+		PrimitivesBrackets{F: []int_{1, 2, 3, 4}},
+	},
 
 	"slices": {
 		`--xxx
@@ -213,7 +241,6 @@ Content-Disposition: form-data; name="slices.0.f.3"
 			Slice: []Primitives{{A: false, B: 237628372683, C: uint(654), D: 9999.43, E: 43.76, F: []int{1, 2, 3, 4}}},
 		},
 	},
-
 	"primitive_pointer_struct": {
 		`--xxx
 Content-Disposition: form-data; name="a"
@@ -423,7 +450,13 @@ func TestEncode(t *testing.T) {
 			buf := bytes.NewBuffer(nil)
 			writer := multipart.NewWriter(buf)
 			writer.SetBoundary("xxx")
-			err := Marshal(test.val, writer)
+
+			var arrayFmt string = "indices:dots"
+			if tags := strings.Split(name, ","); len(tags) > 1 {
+				arrayFmt = tags[1]
+			}
+
+			err := MarshalWithSettings(test.val, writer, arrayFmt)
 			if err != nil {
 				t.Errorf("serialization of %v failed with error %v", test.val, err)
 			}