avoid additional buffer slice on string path

DataRowMessage.fields may now be either a string or a buffer slice
depending on the field format.

this relies on some assumption:

- fieldDescriptions is accurate when parseDataRowmessage is called. we
  make a similar assumption in pg/lib/result.js, so this seems fine.

Author: hjr3

packages/pg-protocol/src/inbound-parser.test.ts

@@ -301,7 +301,7 @@ describe('PgPacketStream', function () {
       testForMessage(oneFieldBuf, {
         name: 'dataRow',
         fieldCount: 1,
-        fields: [Buffer.from('test')],
+        fields: ['test'],
       })
     })
   })
@@ -524,7 +524,7 @@ describe('PgPacketStream', function () {
         name: 'dataRow',
         fieldCount: 1,
         length: 11,
-        fields: [Buffer.from('!')],
+        fields: ['!'],
       })
       assert.equal(messages[0].fields[0], '!')
       assert.deepEqual(messages[1], {

packages/pg-protocol/src/parser.ts

@@ -80,6 +80,7 @@ export class Parser {
   private bufferOffset: number = 0
   private reader = new BufferReader()
   private mode: Mode
+  private fieldDescriptions: Field[] = []
 
   constructor(opts?: StreamOptions) {
     if (opts?.mode === 'binary') {
@@ -253,6 +254,7 @@ export class Parser {
     for (let i = 0; i < fieldCount; i++) {
       message.fields[i] = this.parseField()
     }
+    this.fieldDescriptions = message.fields
     return message
   }
 
@@ -284,7 +286,12 @@ export class Parser {
     for (let i = 0; i < fieldCount; i++) {
       const len = this.reader.int32()
       // a -1 for length means the value of the field is null
-      fields[i] = len === -1 ? null : this.reader.bytes(len)
+      if (len === -1) {
+        fields[i] = null
+      } else {
+        const format = this.fieldDescriptions[i]?.format
+        fields[i] = format === 'binary' ? this.reader.bytes(len) : this.reader.string(len)
+      }
     }
     return new DataRowMessage(length, fields)
   }

packages/pg/lib/result.js

@@ -52,8 +52,7 @@ class Result {
     for (let i = 0, len = rowData.length; i < len; i++) {
       const rawValue = rowData[i]
       if (rawValue !== null) {
-        const v = this.fields[i].format !== 'binary' ? rawValue.toString('utf8') : rawValue
-        row[i] = this._parsers[i](v)
+        row[i] = this._parsers[i](rawValue)
       } else {
         row[i] = null
       }
@@ -67,8 +66,7 @@ class Result {
       const rawValue = rowData[i]
       const field = this.fields[i].name
       if (rawValue !== null) {
-        const v = this.fields[i].format !== 'binary' ? rawValue.toString('utf8') : rawValue
-        row[field] = this._parsers[i](v)
+        row[field] = this._parsers[i](rawValue)
       } else {
         row[field] = null
       }