refactor: improve path of read error

src/binary/constant.ts

@@ -8,9 +8,17 @@ export const Fixed32 = 5; // 32-bit: float, fixed32, sfixed32
 export const SHIFT_LEFT_32 = (1 << 16) * (1 << 16);
 export const SHIFT_RIGHT_32 = 1 / SHIFT_LEFT_32;
 
-export const MapStruct = (item: FieldMap): Field => () => [
-  [1, 'key', item[1], 1],
-  [2, 'value', item[2], 1],
-];
+export function MapStruct(item: FieldMap): Field {
+  return function MapValue() {
+    return [
+      [1, 'key', item[1], 1],
+      [2, 'value', item[2], 1],
+    ];
+  };
+}
 
-export const WrapperStruct = (value: string): Field => () => [[1, 'value', value, 1]];
+export function WrapperStruct(value: string): Field {
+  return function Wrapper() {
+    return [[1, 'value', value, 1]];
+  };
+}

src/binary/index.ts

@@ -134,11 +134,19 @@ const GetDefault = (item: FieldType) =>
     ? getDefault(item[1])
     : undefined;
 
-function DecodeHelper<T extends Record<string, any>>(b: BufRead, struct: Field, result = {} as T, end?: number) {
+function DecodeHelper<T extends Record<string, any>>(
+  b: BufRead,
+  struct: Field,
+  result = {} as T,
+  path = '',
+  end?: number
+) {
   const { s } = GetStruct(struct);
 
   end = end || b.buf.length;
 
+  b.path = path;
+
   while (b.pos < end) {
     const val = readVarint(b);
     const tag = val >> 3;
@@ -147,8 +155,8 @@ function DecodeHelper<T extends Record<string, any>>(b: BufRead, struct: Field,
     b.type = val & 0x7;
 
     if (s[tag]) {
-      const [, nameField, item, , oneof] = s[tag];
-      DecodeRead(b, nameField, result, item);
+      const [id, nameField, item, , oneof] = s[tag];
+      DecodeRead(b, nameField, result, `${path ? `${path}.` : ''}${nameField}[${id}]`, item);
 
       if (oneof) {
         if (result[nameField]) {
@@ -167,13 +175,13 @@ function DecodeHelper<T extends Record<string, any>>(b: BufRead, struct: Field,
   return DecodeDefault(struct, result);
 }
 
-function DecodeRead(b: BufRead, fieldName: string, result: Record<string, unknown>, item: FieldType) {
+function DecodeRead(b: BufRead, fieldName: string, result: Record<string, unknown>, path: string, item: FieldType) {
   if (isString(item)) {
     if (readMap[item as ReadMapKeys]) {
       result[fieldName] = getDefault(item, readMap[item as ReadMapKeys](b));
     }
   } else if (isFunction(item)) {
-    result[fieldName] = DecodeHelper(b, item, {}, readVarint(b) + b.pos);
+    result[fieldName] = DecodeHelper(b, item, {}, path, readVarint(b) + b.pos);
   } else if (isArray(item)) {
     if (item[0] === 'repeated') {
       if (isString(item[1]) && PACKED[item[1]]) {
@@ -183,17 +191,17 @@ function DecodeRead(b: BufRead, fieldName: string, result: Record<string, unknow
         const m = isArray(mm) ? mm : [];
         result[fieldName] = m;
         const o = {} as { out: unknown };
-        DecodeRead(b, 'out', o, item[1]);
+        DecodeRead(b, 'out', o, path, item[1]);
         m.push(o.out);
       }
     } else if (item[0] === 'map') {
       const mm = result[fieldName];
       const m = isObject(mm) ? mm : {};
       result[fieldName] = m;
-      const o = DecodeHelper(b, MapStruct(item), {} as { key: string; value: unknown }, readVarint(b) + b.pos);
+      const o = DecodeHelper(b, MapStruct(item), {} as { key: string; value: unknown }, path, readVarint(b) + b.pos);
       m[o.key] = o.value;
     } else if (item[0] === 'wrapper') {
-      const o = DecodeHelper(b, WrapperStruct(item[1]), {} as { value: unknown }, readVarint(b) + b.pos);
+      const o = DecodeHelper(b, WrapperStruct(item[1]), {} as { value: unknown }, path, readVarint(b) + b.pos);
       result[fieldName] = o.value;
     }
   }

src/binary/read.ts

@@ -5,6 +5,7 @@ import { readUtf8 } from './utf8';
 export class BufRead {
   pos = 0;
   type = 0;
+  path = '';
 
   constructor(public buf: Uint8Array) {}
 }
@@ -20,7 +21,7 @@ export const skip = (b: BufRead, val: number) => {
   } else if (type === Fixed64) {
     b.pos += 8;
   } else {
-    throw new Error(`Unimplemented type: ${type}`);
+    throw new Error(`Unimplemented type: ${type} in path "${b.path}"`);
   }
 };
 
@@ -79,7 +80,7 @@ function readVarintRemainder(low: number, b: BufRead) {
     return [low, high];
   }
 
-  throw new Error('Expected varint not more than 10 bytes');
+  throw new Error(`Expected varint not more than 10 bytes in path "${b.path}"`);
 }
 
 const toNum = ([low, high]: number[], s: boolean) => {

src/generator/message.ts

@@ -120,9 +120,9 @@ function message(pack: string, out: MakeOuts, item: Message, list: List[], enums
   }
 
   out.dts.push(`export const ${baseName}: Field<${baseName}>;`);
-  out.js.push(`export const ${baseName} = () => [`);
+  out.js.push(`export function ${baseName} () { return [`);
   for (const field of runtime) {
     out.js.push(field);
   }
-  out.js.push('];');
+  out.js.push(']; }');
 }