fix: minor refactor of base64 handling

Noticed how inelegant the base64 handling was, mostly due to needing to
hard code and handle the valid operations (encode and decode) in two
different functions.

httpbin/handlers.go

@@ -1051,21 +1051,9 @@ func (h *HTTPBin) UUID(w http.ResponseWriter, _ *http.Request) {
 
 // Base64 - encodes/decodes input data
 func (h *HTTPBin) Base64(w http.ResponseWriter, r *http.Request) {
-	b, err := newBase64Helper(r.URL.Path)
+	result, err := newBase64Helper(r.URL.Path, h.MaxBodySize).transform()
 	if err != nil {
-		writeError(w, http.StatusBadRequest, fmt.Errorf("invalid base64 data: %w", err))
-		return
-	}
-
-	var result []byte
-	if b.operation == "decode" {
-		result, err = b.Decode()
-	} else {
-		result, err = b.Encode()
-	}
-
-	if err != nil {
-		writeError(w, http.StatusBadRequest, fmt.Errorf("%s failed: %w", b.operation, err))
+		writeError(w, http.StatusBadRequest, err)
 		return
 	}
 	writeResponse(w, http.StatusOK, textContentType, result)

httpbin/handlers_test.go

@@ -2752,8 +2752,8 @@ func TestBase64(t *testing.T) {
 			"decode failed",
 		},
 		{
-			"/base64/decode/" + strings.Repeat("X", Base64MaxLen+1),
-			"Cannot handle input",
+			"/base64/decode/" + strings.Repeat("X", int(maxBodySize)+1),
+			"input data exceeds max length",
 		},
 		{
 			"/base64/",
@@ -2765,7 +2765,7 @@ func TestBase64(t *testing.T) {
 		},
 		{
 			"/base64/decode/dmFsaWRfYmFzZTY0X2VuY29kZWRfc3RyaW5n/extra",
-			"invalid URL",
+			"decode failed",
 		},
 		{
 			"/base64/unknown/dmFsaWRfYmFzZTY0X2VuY29kZWRfc3RyaW5n",

httpbin/helpers.go

@@ -20,9 +20,6 @@ import (
 	"time"
 )
 
-// Base64MaxLen - Maximum input length for Base64 functions
-const Base64MaxLen = 2000
-
 // requestHeaders takes in incoming request and returns an http.Header map
 // suitable for inclusion in our response data structures.
 //
@@ -385,60 +382,66 @@ func uuidv4() string {
 	return fmt.Sprintf("%x-%x-%x-%x-%x", buff[0:4], buff[4:6], buff[6:8], buff[8:10], buff[10:])
 }
 
-// base64Helper - describes the base64 operation (encode|decode) and input data
+// base64Helper encapsulates a base64 operation (encode or decode) and its input
+// data.
 type base64Helper struct {
+	maxLen    int64
 	operation string
 	data      string
 }
 
-// newbase64Helper - create a new base64Helper struct
-// Supports the following URL paths
-// - /base64/input_str
-// - /base64/encode/input_str
-// - /base64/decode/input_str
-func newBase64Helper(path string) (*base64Helper, error) {
-	parts := strings.Split(path, "/")
-
-	if len(parts) != 3 && len(parts) != 4 {
-		return nil, errors.New("invalid URL")
-	}
-
-	var b base64Helper
-
-	// Validation for - /base64/input_str
-	if len(parts) == 3 {
+// newBase64Helper creates a new base64Helper from a URL path, which should be
+// in one of two forms:
+// - /base64/<base64_encoded_data>
+// - /base64/<operation>/<base64_encoded_data>
+func newBase64Helper(path string, maxLen int64) *base64Helper {
+	parts := strings.SplitN(path, "/", 4)
+	b := &base64Helper{maxLen: maxLen}
+	switch len(parts) {
+	// Any other cases will be rejected when transform() is called
+	case 3:
+		// handle /base64/<base64_encoded_data>
 		b.operation = "decode"
 		b.data = parts[2]
-	} else {
-		// Validation for
-		// - /base64/encode/input_str
-		// - /base64/encode/input_str
+	case 4:
+		// handle /base64/<operation>/<base64_encoded_data>
 		b.operation = parts[2]
-		if b.operation != "encode" && b.operation != "decode" {
-			return nil, fmt.Errorf("invalid operation: %s", b.operation)
-		}
 		b.data = parts[3]
 	}
-	if len(b.data) == 0 {
+	return b
+}
+
+// transform performs the base64 operation on the input data.
+func (b *base64Helper) transform() ([]byte, error) {
+	if dataLen := int64(len(b.data)); dataLen == 0 {
 		return nil, errors.New("no input data")
-	}
-	if len(b.data) >= Base64MaxLen {
-		return nil, fmt.Errorf("input length - %d, Cannot handle input >= %d", len(b.data), Base64MaxLen)
+	} else if dataLen > b.maxLen {
+		return nil, fmt.Errorf("input data exceeds max length of %d", b.maxLen)
 	}
 
-	return &b, nil
+	switch b.operation {
+	case "encode":
+		return b.encode(), nil
+	case "decode":
+		result, err := b.decode()
+		if err != nil {
+			return nil, fmt.Errorf("base64 decode failed: %w", err)
+		}
+		return result, nil
+	default:
+		return nil, fmt.Errorf("invalid operation: %s", b.operation)
+	}
 }
 
-// Encode - encode data as URL-safe base64
-func (b *base64Helper) Encode() ([]byte, error) {
+func (b *base64Helper) encode() []byte {
+	// always encode using the URL-safe character set
 	buff := make([]byte, base64.URLEncoding.EncodedLen(len(b.data)))
 	base64.URLEncoding.Encode(buff, []byte(b.data))
-	return buff, nil
+	return buff
 }
 
-// Decode - decode data from base64, attempting both URL-safe and standard
-// encodings.
-func (b *base64Helper) Decode() ([]byte, error) {
+func (b *base64Helper) decode() ([]byte, error) {
+	// first, try URL-safe encoding, then std encoding
 	if result, err := base64.URLEncoding.DecodeString(b.data); err == nil {
 		return result, nil
 	}