fix: set UTF-8 client charset for SQL Server connections (#528)

* fix: set UTF-8 client charset for SQL Server connections

* fix: increase dbconvert buffer to handle multi-byte UTF-8 output

Author: datlechin

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- SQL Server: Unicode characters (Thai, CJK, etc.) in nvarchar/nchar/ntext columns displaying as question marks
 - Globe+F (fn+F) fullscreen shortcut not working in SwiftUI lifecycle app
 
 ## [0.26.0] - 2026-03-29

Plugins/MSSQLDriverPlugin/CFreeTDS/include/sybdb.h

@@ -49,6 +49,7 @@ typedef struct loginrec LOGINREC;
 #define DBSETUSER   2
 #define DBSETPWD    3
 #define DBSETAPP    5   // 4 is unused; real FreeTDS DBSETAPP = 5
+#define DBSETCHARSET 7  // Client charset for dbsetlname() — controls string encoding
 
 // Convenience macros (match FreeTDS sybdb.h)
 #define DBSETLHOST(x, y)    dbsetlname((x), (y), DBSETHOST)

Plugins/MSSQLDriverPlugin/MSSQLPlugin.swift

@@ -196,6 +196,7 @@ private final class FreeTDSConnection: @unchecked Sendable {
         _ = dbsetlname(login, user, Int32(DBSETUSER))
         _ = dbsetlname(login, password, Int32(DBSETPWD))
         _ = dbsetlname(login, "TablePro", Int32(DBSETAPP))
+        _ = dbsetlname(login, "UTF-8", Int32(DBSETCHARSET))
         _ = dbsetlversion(login, UInt8(DBVERSION_74))
 
         freetdsLastError = ""
@@ -371,10 +372,12 @@ private final class FreeTDSConnection: @unchecked Sendable {
             return String(bytes: UnsafeBufferPointer(start: ptr, count: Int(srcLen)), encoding: .utf8)
                 ?? String(bytes: UnsafeBufferPointer(start: ptr, count: Int(srcLen)), encoding: .isoLatin1)
         case Int32(SYBNCHAR), Int32(SYBNVARCHAR), Int32(SYBNTEXT):
-            let data = Data(bytes: ptr, count: Int(srcLen))
-            return String(data: data, encoding: .utf16LittleEndian)
+            // With client charset UTF-8, FreeTDS converts UTF-16 wire data to UTF-8
+            // but may still report the original nvarchar type token
+            return String(bytes: UnsafeBufferPointer(start: ptr, count: Int(srcLen)), encoding: .utf8)
+                ?? String(data: Data(bytes: ptr, count: Int(srcLen)), encoding: .utf16LittleEndian)
         default:
-            let bufSize: DBINT = 64
+            let bufSize: DBINT = 256
             var buf = [BYTE](repeating: 0, count: Int(bufSize))
             let converted = buf.withUnsafeMutableBufferPointer { bufPtr in
                 dbconvert(proc, srcType, ptr, srcLen, Int32(SYBCHAR), bufPtr.baseAddress, bufSize)