feat: allow overriding bytes as string

Allows interperting a `bytes` field as a `string` type in JavaScript:

```protobuf
message MyMessage {
  bytes field = 1 [jstype = JS_STRING];
}
```

packages/protons/src/index.ts

@@ -244,14 +244,26 @@ const types: Record<string, string> = {
   uint64: 'bigint'
 }
 
-const jsTypeOverrides: Record<string, 'number' | 'string'> = {
-  JS_NUMBER: 'number',
-  JS_STRING: 'string'
+const jsTypeOverrides: Record<string, { type: 'number' | 'string', allowed: string[] }> = {
+  JS_NUMBER: {
+    type: 'number',
+    allowed: ['int64', 'uint64', 'sint64', 'fixed64', 'sfixed64']
+  },
+  JS_STRING: {
+    type: 'string',
+    allowed: ['int64', 'uint64', 'sint64', 'fixed64', 'sfixed64', 'bytes']
+  }
 }
 
 const encoderGenerators: Record<string, (val: string, jsTypeOverride?: 'number' | 'string') => string> = {
   bool: (val) => `w.bool(${val})`,
-  bytes: (val) => `w.bytes(${val})`,
+  bytes: (val, jsTypeOverride) => {
+    if (jsTypeOverride === 'string') {
+      return `w.int64String(${val})`
+    }
+
+    return `w.bytes(new TextEncoder().encode(${val}))`
+  },
   double: (val) => `w.double(${val})`,
   fixed32: (val) => `w.fixed32(${val})`,
   fixed64: (val, jsTypeOverride) => {
@@ -319,7 +331,13 @@ const encoderGenerators: Record<string, (val: string, jsTypeOverride?: 'number'
 
 const decoderGenerators: Record<string, (jsTypeOverride?: 'number' | 'string') => string> = {
   bool: () => 'reader.bool()',
-  bytes: () => 'reader.bytes()',
+  bytes: (jsTypeOverride) => {
+    if (jsTypeOverride === 'string') {
+      return 'new TextDecoder().decode(reader.bytes())'
+    }
+
+    return 'reader.bytes()'
+  },
   double: () => 'reader.double()',
   fixed32: () => 'reader.fixed32()',
   fixed64: (jsTypeOverride) => {
@@ -432,12 +450,14 @@ const defaultValueTestGeneratorsJsTypeOverrides: Record<string, (field: string)
 }
 
 function findJsTypeOverride (defaultType: string, fieldDef: FieldDef): 'number' | 'string' | undefined {
-  if (fieldDef.options?.jstype != null && jsTypeOverrides[fieldDef.options?.jstype] != null) {
-    if (!['int64', 'uint64', 'sint64', 'fixed64', 'sfixed64'].includes(defaultType)) {
-      throw new Error(`jstype is only allowed on int64, uint64, sint64, fixed64 or sfixed64 fields - got "${defaultType}"`)
+  const override = jsTypeOverrides[fieldDef.options?.jstype]
+
+  if (override != null) {
+    if (!override.allowed.includes(defaultType)) {
+      throw new Error(`jstype is only allowed on ${override.allowed.join(', ')} fields - got "${defaultType}"`)
     }
 
-    return jsTypeOverrides[fieldDef.options?.jstype]
+    return override.type
   }
 }
 
@@ -517,7 +537,7 @@ function createDefaultObject (fields: Record<string, FieldDef>, messageDef: Mess
           defaultValueGenerator = defaultValueGeneratorsJsTypeOverrides[jsTypeOverride]
         }
 
-        if (type === 'bytes') {
+        if (type === 'bytes' && jsTypeOverride !== 'string') {
           moduleDef.addImport('uint8arrays/alloc', 'alloc', 'uint8ArrayAlloc')
         }
 

packages/protons/test/custom-options.spec.ts

@@ -25,7 +25,8 @@ describe('custom options', () => {
       ui64: '5',
       si64: '5',
       f64: '5',
-      sf64: '5'
+      sf64: '5',
+      bytes: ''
     }
 
     expect(CustomOptionString.decode(CustomOptionString.encode(obj)))

packages/protons/test/fixtures/custom-option-jstype.proto

@@ -16,4 +16,5 @@ message CustomOptionString {
   sint64 si64 = 4 [jstype = JS_STRING];
   fixed64 f64 = 5 [jstype = JS_STRING];
   sfixed64 sf64 = 6 [jstype = JS_STRING];
+  bytes bytes = 7 [jstype = JS_STRING];
 }

packages/protons/test/fixtures/custom-option-jstype.ts

@@ -129,6 +129,7 @@ export interface CustomOptionString {
   si64: string
   f64: string
   sf64: string
+  bytes: string
 }
 
 export namespace CustomOptionString {
@@ -171,6 +172,11 @@ export namespace CustomOptionString {
           w.sfixed64String(obj.sf64)
         }
 
+        if ((obj.bytes != null && obj.bytes !== '')) {
+          w.uint32(58)
+          w.int64String(obj.bytes)
+        }
+
         if (opts.lengthDelimited !== false) {
           w.ldelim()
         }
@@ -181,7 +187,8 @@ export namespace CustomOptionString {
           ui64: '',
           si64: '',
           f64: '',
-          sf64: ''
+          sf64: '',
+          bytes: ''
         }
 
         const end = length == null ? reader.len : reader.pos + length
@@ -214,6 +221,10 @@ export namespace CustomOptionString {
               obj.sf64 = reader.sfixed64String()
               break
             }
+            case 7: {
+              obj.bytes = new TextDecoder().decode(reader.bytes())
+              break
+            }
             default: {
               reader.skipType(tag & 7)
               break