feat: define default types during decode (#62)

Proto3 language guide [states](https://developers.google.com/protocol-buffers/docs/proto3#default):

> When a message is parsed, if the encoded message does not contain a particular singular element, the corresponding field in the parsed object is set to the default value for that field.

When decoding objects, create an object with all non-optional fields set to the default values, then overwrite them during decoding.

Given that we create arrays for repeated fields there's no need to check for their existence before returning the deserialized object.

The only weird part in all this is message fields.  The spec says that any non-optional field is required, but it also says that the default value for a sub-message is to be unset and that the actual value there is language-dependent and links to some language guides which don't include JavaScript - I've used `undefined` here.  The upshot of this is that you can have a non-optional field with a default value of `undefined` which essentially makes it optional.  Nice.  At the moment we throw if the sub-message is not present in the protobuf if the field is required though in a future change we may wish to ignore the spec and initialise the sub-message to an instance of it's type with default values set 🤷.

Refs #43

packages/protons-benchmark/src/protons/bench.ts

@@ -159,7 +159,9 @@ export namespace Yo {
           writer.ldelim()
         }
       }, (reader, length) => {
-        const obj: any = {}
+        const obj: any = {
+          lol: []
+        }
 
         const end = length == null ? reader.len : reader.pos + length
 
@@ -168,7 +170,6 @@ export namespace Yo {
 
           switch (tag >>> 3) {
             case 1:
-              obj.lol = obj.lol ?? []
               obj.lol.push(FOO.codec().decode(reader))
               break
             default:
@@ -177,12 +178,6 @@ export namespace Yo {
           }
         }
 
-        obj.lol = obj.lol ?? []
-
-        if (obj.lol == null) {
-          throw new Error('Protocol error: value for required field "lol" was not found in protobuf')
-        }
-
         return obj
       })
     }
@@ -230,7 +225,9 @@ export namespace Lol {
           writer.ldelim()
         }
       }, (reader, length) => {
-        const obj: any = {}
+        const obj: any = {
+          b: undefined
+        }
 
         const end = length == null ? reader.len : reader.pos + length
 

packages/protons-runtime/src/index.ts

@@ -180,12 +180,12 @@ export interface Reader {
   double: () => number
 
   /**
-   * Reads a sequence of bytes preceeded by its length as a varint
+   * Reads a sequence of bytes preceded by its length as a varint
    */
-  bytes: () => number
+  bytes: () => Uint8Array
 
   /**
-   * Reads a string preceeded by its byte length as a varint
+   * Reads a string preceded by its byte length as a varint
    */
   string: () => string
 

packages/protons/src/index.ts

@@ -39,7 +39,6 @@ const encoderGenerators: Record<string, (val: string) => string> = {
   bool: (val) => `writer.bool(${val})`,
   bytes: (val) => `writer.bytes(${val})`,
   double: (val) => `writer.double(${val})`,
-  // enumeration: (val) => `writer.double(${val})`,
   fixed32: (val) => `writer.fixed32(${val})`,
   fixed64: (val) => `writer.fixed64(${val})`,
   float: (val) => `writer.float(${val})`,
@@ -58,7 +57,6 @@ const decoderGenerators: Record<string, () => string> = {
   bool: () => 'reader.bool()',
   bytes: () => 'reader.bytes()',
   double: () => 'reader.double()',
-  // enumeration: () => `writer.double(${val})`,
   fixed32: () => 'reader.fixed32()',
   fixed64: () => 'reader.fixed64()',
   float: () => 'reader.float()',
@@ -73,6 +71,24 @@ const decoderGenerators: Record<string, () => string> = {
   uint64: () => 'reader.uint64()'
 }
 
+const defaultValueGenerators: Record<string, () => string> = {
+  bool: () => 'false',
+  bytes: () => 'new Uint8Array(0)',
+  double: () => '0',
+  fixed32: () => '0',
+  fixed64: () => '0n',
+  float: () => '0',
+  int32: () => '0',
+  int64: () => '0n',
+  sfixed32: () => '0',
+  sfixed64: () => '0n',
+  sint32: () => '0',
+  sint64: () => '0n',
+  string: () => "''",
+  uint32: () => '0',
+  uint64: () => '0n'
+}
+
 function findTypeName (typeName: string, classDef: MessageDef, moduleDef: ModuleDef): string {
   if (types[typeName] != null) {
     return types[typeName]
@@ -117,6 +133,65 @@ function findDef (typeName: string, classDef: MessageDef, moduleDef: ModuleDef):
   throw new Error(`Could not resolve type name "${typeName}"`)
 }
 
+function createDefaultObject (fields: Record<string, FieldDef>, messageDef: MessageDef, moduleDef: ModuleDef): string {
+  const output = Object.entries(fields)
+    .map(([name, fieldDef]) => {
+      if (fieldDef.repeated) {
+        return `${name}: []`
+      }
+
+      if (fieldDef.optional) {
+        return ''
+      }
+
+      const type: string = fieldDef.type
+      let defaultValue
+
+      if (defaultValueGenerators[type] != null) {
+        defaultValue = defaultValueGenerators[type]()
+      } else {
+        const def = findDef(fieldDef.type, messageDef, moduleDef)
+
+        if (isEnumDef(def)) {
+          // select lowest-value enum - should be 0 but it's not guaranteed
+          const val = Object.entries(def.values)
+            .sort((a, b) => {
+              if (a[1] < b[1]) {
+                return 1
+              }
+
+              if (a[1] > b[1]) {
+                return -1
+              }
+
+              return 0
+            })
+            .pop()
+
+          if (val == null) {
+            throw new Error(`Could not find default enum value for ${def.fullName}`)
+          }
+
+          defaultValue = `${def.name}.${val[0]}`
+        } else {
+          defaultValue = 'undefined'
+        }
+      }
+
+      return `${name}: ${defaultValue}`
+    })
+    .filter(Boolean)
+    .join(',\n          ')
+
+  if (output !== '') {
+    return `
+          ${output}
+        `
+  }
+
+  return ''
+}
+
 const encoders: Record<string, string> = {
   bool: 'bool',
   bytes: 'bytes',
@@ -259,7 +334,7 @@ export interface ${messageDef.name} {
     const ensureArrayProps = Object.entries(fields)
       .map(([name, fieldDef]) => {
         // make sure repeated fields have an array if not set
-        if (fieldDef.rule === 'repeated') {
+        if (fieldDef.optional && fieldDef.rule === 'repeated') {
           return `        obj.${name} = obj.${name} ?? []`
         }
 
@@ -269,7 +344,7 @@ export interface ${messageDef.name} {
     const ensureRequiredFields = Object.entries(fields)
       .map(([name, fieldDef]) => {
         // make sure required fields are set
-        if (!fieldDef.optional) {
+        if (!fieldDef.optional && !fieldDef.repeated) {
           return `
         if (obj.${name} == null) {
           throw new Error('Protocol error: value for required field "${name}" was not found in protobuf')
@@ -331,7 +406,7 @@ ${Object.entries(fields)
           writer.ldelim()
         }
       }, (reader, length) => {
-        const obj: any = {}
+        const obj: any = {${createDefaultObject(fields, messageDef, moduleDef)}}
 
         const end = length == null ? reader.len : reader.pos + length
 
@@ -360,8 +435,10 @@ ${Object.entries(fields)
                 }
 
                 return `case ${fieldDef.id}:${fieldDef.rule === 'repeated'
+? `${fieldDef.optional
 ? `
-              obj.${name} = obj.${name} ?? []
+              obj.${name} = obj.${name} ?? []`
+: ''}
               obj.${name}.push(${decoderGenerators[type] == null ? `${codec}.decode(reader${type === 'message' ? ', reader.uint32()' : ''})` : decoderGenerators[type]()})`
 : `
               obj.${name} = ${decoderGenerators[type] == null ? `${codec}.decode(reader${type === 'message' ? ', reader.uint32()' : ''})` : decoderGenerators[type]()}`}

packages/protons/test/fixtures/basic.proto

@@ -2,5 +2,5 @@ syntax = "proto3";
 
 message Basic {
   optional string foo = 1;
-  required int32 num = 2;
+  int32 num = 2;
 }

packages/protons/test/fixtures/basic.ts

@@ -36,7 +36,9 @@ export namespace Basic {
           writer.ldelim()
         }
       }, (reader, length) => {
-        const obj: any = {}
+        const obj: any = {
+          num: 0
+        }
 
         const end = length == null ? reader.len : reader.pos + length
 

packages/protons/test/fixtures/circuit.ts

@@ -112,7 +112,10 @@ export namespace CircuitRelay {
             writer.ldelim()
           }
         }, (reader, length) => {
-          const obj: any = {}
+          const obj: any = {
+            id: new Uint8Array(0),
+            addrs: []
+          }
 
           const end = length == null ? reader.len : reader.pos + length
 
@@ -124,7 +127,6 @@ export namespace CircuitRelay {
                 obj.id = reader.bytes()
                 break
               case 2:
-                obj.addrs = obj.addrs ?? []
                 obj.addrs.push(reader.bytes())
                 break
               default:
@@ -133,16 +135,10 @@ export namespace CircuitRelay {
             }
           }
 
-          obj.addrs = obj.addrs ?? []
-
           if (obj.id == null) {
             throw new Error('Protocol error: value for required field "id" was not found in protobuf')
           }
 
-          if (obj.addrs == null) {
-            throw new Error('Protocol error: value for required field "addrs" was not found in protobuf')
-          }
-
           return obj
         })
       }