fix: typeCast string() parameters for JSON

lib/parsers/text_parser.js

@@ -85,8 +85,15 @@ function compile(fields, options, config) {
       db: field.schema,
       table: field.table,
       name: field.name,
-      string: function() {
-        return _this.packet.readLengthCodedString(field.encoding);
+      string: function(encoding = field.encoding) {
+        if (field.columnType === Types.JSON && encoding === field.encoding) {
+          // Since for JSON columns mysql always returns charset 63 (BINARY),
+          // we have to handle it according to JSON specs and use "utf8",
+          // see https://github.com/sidorares/node-mysql2/issues/1661
+          console.warn(`typeCast: JSON column "${field.name}" is interpreted as BINARY by default, recommended to manually set utf8 encoding: \`field.string("utf8")\``);
+        }
+
+        return _this.packet.readLengthCodedString(encoding);
       },
       buffer: function() {
         return _this.packet.readLengthCodedBuffer();
@@ -172,7 +179,7 @@ function compile(fields, options, config) {
       }  else {
         parserFn(`${lvalue} = ${readCode};`);
       }
-    }  
+    }
   }
 
   parserFn('return result;');
@@ -191,7 +198,7 @@ function compile(fields, options, config) {
   }
   if (typeof options.typeCast === 'function') {
     return parserFn.toFunction({wrap});
-  } 
+  }
   return parserFn.toFunction();
 }
 

test/unit/parsers/test-text-parser.js

@@ -0,0 +1,38 @@
+'use strict';
+
+const assert = require('assert');
+const common = require('../../common');
+
+const typeCastWrapper = function (...args) {
+  return function (field, next) {
+    if (field.type === 'JSON') {
+      return JSON.parse(field.string(...args));
+    }
+
+    return next();
+  }
+}
+
+const connection = common.createConnection();
+connection.query('CREATE TEMPORARY TABLE t (i JSON)');
+connection.query('INSERT INTO t values(\'{ "test": "😀" }\')');
+
+// JSON without encoding options - should result in unexpected behaviors
+connection.query({
+  sql: 'SELECT * FROM t',
+  typeCast: typeCastWrapper()
+}, (err, rows) => {
+  assert.ifError(err);
+  assert.notEqual(rows[0].i.test, "😀");
+});
+
+// JSON with encoding explicitly set to utf8
+connection.query({
+  sql: 'SELECT * FROM t',
+  typeCast: typeCastWrapper("utf8")
+}, (err, rows) => {
+  assert.ifError(err);
+  assert.equal(rows[0].i.test, "😀");
+});
+
+connection.end();