From c341aa0014c7a1b852ebe10f55a6c10ca7e5e8a3 Mon Sep 17 00:00:00 2001
From: Sharang Gupta <sharang@sharanggupta.dev>
Date: Wed, 28 Oct 2026 23:59:59 +0000
Subject: [PATCH] Encode JSON parameters in the connection charset

Since #1685 JSON parameters were always written as UTF-8, so a
connection with a non-UTF-8 collation received garbled text.

Signed-off-by: Sharang Gupta <sharang@sharanggupta.dev>
Assisted-by: Anthropic Claude (claude-opus-5-5)
---
 .../mysqlclient/impl/datatype/DataTypeCodec.java  |  9 +++++++--
 .../tests/mysqlclient/MySQLCollationTest.java     | 15 +++++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/vertx-mysql-client/src/main/java/io/vertx/mysqlclient/impl/datatype/DataTypeCodec.java b/vertx-mysql-client/src/main/java/io/vertx/mysqlclient/impl/datatype/DataTypeCodec.java
index d153e4cd57..c75914cefe 100644
--- a/vertx-mysql-client/src/main/java/io/vertx/mysqlclient/impl/datatype/DataTypeCodec.java
+++ b/vertx-mysql-client/src/main/java/io/vertx/mysqlclient/impl/datatype/DataTypeCodec.java
@@ -30,6 +30,7 @@
 
 import java.math.BigInteger;
 import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.time.Duration;
 import java.time.LocalDate;
 import java.time.LocalDateTime;
@@ -179,7 +180,7 @@ public static void encodeBinary(DataType dataType, Object value, Charset charset
       case VARSTRING:
       default:
         if (value instanceof JsonObject || value instanceof JsonArray) {
-          binaryEncodeJson(value, buffer);
+          binaryEncodeJson(value, buffer, charset);
           return;
         } else if (value == Tuple.JSON_NULL) {
           // we have to make JSON literal null send as a STRING data type
@@ -467,7 +468,11 @@ private static void binaryEncodeDatetime(LocalDateTime value, ByteBuf buffer) {
     }
   }
 
-  private static void binaryEncodeJson(Object value, ByteBuf buffer) {
+  private static void binaryEncodeJson(Object value, ByteBuf buffer, Charset charset) {
+    if (!StandardCharsets.UTF_8.equals(charset)) {
+      BufferUtils.writeLengthEncodedString(buffer, Json.encode(value), charset);
+      return;
+    }
     ByteBuf tmp = buffer.alloc().buffer();
     try {
       Json.encodeTo(value, new ByteBufOutputStream(tmp));
diff --git a/vertx-mysql-client/src/test/java/io/vertx/tests/mysqlclient/MySQLCollationTest.java b/vertx-mysql-client/src/test/java/io/vertx/tests/mysqlclient/MySQLCollationTest.java
index 45482ed398..9390b467e4 100644
--- a/vertx-mysql-client/src/test/java/io/vertx/tests/mysqlclient/MySQLCollationTest.java
+++ b/vertx-mysql-client/src/test/java/io/vertx/tests/mysqlclient/MySQLCollationTest.java
@@ -12,6 +12,7 @@
 package io.vertx.tests.mysqlclient;
 
 import io.vertx.core.Vertx;
+import io.vertx.core.json.JsonObject;
 import io.vertx.ext.unit.TestContext;
 import io.vertx.ext.unit.junit.VertxUnitRunner;
 import io.vertx.mysqlclient.MySQLConnectOptions;
@@ -95,6 +96,20 @@ public void testConnectionCharset(TestContext ctx) {
     }));
   }
 
+  @Test
+  public void testJsonParameterWithConnectionCollation(TestContext ctx) {
+    MySQLConnectOptions connectOptions = options.setCollation("gbk_chinese_ci");
+    MySQLConnection.connect(vertx, connectOptions).onComplete(ctx.asyncAssertSuccess(conn -> {
+      conn
+        .preparedQuery("SELECT JSON_UNQUOTE(JSON_EXTRACT(CAST(? AS JSON), '$.city')) AS city")
+        .execute(Tuple.of(new JsonObject().put("city", "\u5317\u4EAC")))
+        .onComplete(ctx.asyncAssertSuccess(res -> {
+        ctx.assertEquals("\u5317\u4EAC", res.iterator().next().getString("city"));
+        conn.close();
+      }));
+    }));
+  }
+
   @Test
   public void testTableCollationBinary(TestContext ctx) {
     testBinary(ctx, PREPARE_TESTING_TABLE_DATA);