Swig CSharp: Add additional support for UTF-8 strings (#14075)

Add UTF-8 encoding/decoding support to Gdal options functions

The following Gdal functions now accept UTF-8 strings for their `pszDefault` parameter and will return UTF-8 strings.
- GetConfigOption
- GetGlobalConfigOption
- GetThreadLocalConfigOption
- GetCredential
- GetPathSpecificOption

The following Gdal functions now accept UTF-8 strings for their `pszValue` parameter.
- SetConfigOption
- SetThreadLocalConfigOption
- SetCredential
- SetPathSpecificOption

Changed the C# `utf8_path` typemap to use the built-in UTF-8 encoding marshaller.

Author: Mbucari

swig/csharp/CMakeLists.txt

@@ -701,6 +701,16 @@ if (BUILD_TESTING)
       SYSTEM_DEPENDS
       OSGeo.GDAL)
 
+    gdal_build_csharp_sample(
+      OUTPUT
+      GDALTestUtf8.exe
+      SOURCE
+      ${CMAKE_CURRENT_SOURCE_DIR}/apps/GDALTestUtf8.cs
+      DEPENDS
+      gdal_csharp
+      SYSTEM_DEPENDS
+      OSGeo.GDAL)
+
     gdal_build_csharp_sample(
       OUTPUT
       OGRLayerAlg.exe
@@ -766,6 +776,7 @@ if (BUILD_TESTING)
               OSGeo.GDAL.Samples.GDALOverviews
               OSGeo.GDAL.Samples.GDALCreateCopy
               OSGeo.GDAL.Samples.GDALGetHistogram
+              OSGeo.GDAL.Samples.GDALTestUtf8
               OSGeo.GDAL.Samples.GDALTest
               OSGeo.GDAL.Samples.OGRLayerAlg
               OSGeo.GDAL.Samples.GDALWarp
@@ -863,4 +874,9 @@ if (BUILD_TESTING)
       WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
       COMMAND ${CSHARP_INTERPRETER} GetCRSInfo/GetCRSInfo${_ex} "EPSG" 20)
     set_property(TEST csharp_getcrsinfo PROPERTY ENVIRONMENT "${TEST_ENV}")
+    add_test(
+      NAME csharp_testutf8
+      WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+      COMMAND ${CSHARP_INTERPRETER} GDALTestUtf8/GDALTestUtf8${_ex})
+    set_property(TEST csharp_testutf8 PROPERTY ENVIRONMENT "${TEST_ENV}")
 endif()

swig/csharp/apps/GDALTestUtf8.cs

@@ -0,0 +1,51 @@
+using System;
+using OSGeo.GDAL;
+
+namespace testapp
+{
+    class GdalTestUtf8
+    {
+        const string ConfigKey = "UNICODE_STRING";
+        const string UnicodeString = "Ĥĕļĺō Ŵŏŕľď";
+
+        public static void Main()
+        {
+            Console.OutputEncoding = System.Text.Encoding.UTF8;
+            RunTest("ConfigOption", Gdal.GetConfigOption, Gdal.SetConfigOption);
+            RunTest("ThreadLocalConfigOption", Gdal.GetThreadLocalConfigOption, Gdal.SetThreadLocalConfigOption);
+            RunTest("ThreadLocalConfigOption", (k, d) => Gdal.GetPathSpecificOption("/", k, d), (k, v) => Gdal.SetPathSpecificOption("/", k, v));
+            RunTest("Credential", (k, d) => Gdal.GetCredential("/", k, d), (k, v) => Gdal.SetCredential("/", k, v));
+        }
+
+        private static void RunTest(string name, Func<string, string, string> getter, Action<string, string> setter)
+        {
+            Console.WriteLine($"Testing {name}");
+            Console.WriteLine($"  Setting and getting Unicode string");
+            setter(ConfigKey, UnicodeString);
+            var configValue = getter(ConfigKey, null);
+            AssertEqual(UnicodeString, configValue, name);
+
+            Console.WriteLine($"  Setting null value");
+            setter(ConfigKey, null);
+            configValue = getter(ConfigKey, null);
+            AssertEqual(null, configValue, name);
+
+            Console.WriteLine($"  Getting unset key with Unicode default value");
+            configValue = getter(ConfigKey, UnicodeString);
+            AssertEqual(UnicodeString, configValue, name);
+        }
+
+        private static void AssertEqual(string expected, string actual, string funcName)
+        {
+            if (expected == actual)
+            {
+                Console.WriteLine($"    {funcName} returned the expected value: '{expected ?? "NULL"}'");
+            }
+            else
+            {
+                throw new Exception($"Expected '{expected}' but {funcName} returned '{actual ?? "NULL"}'");
+            }
+        }
+    }
+}
+

swig/include/cpl.i

@@ -470,6 +470,10 @@ void VSICloseDir(VSIDIR* dir);
 
 #endif
 
+/* Utf-8 string marshalling for C# */
+#if defined(SWIGCSHARP)
+%apply (const char *utf8_or_null) { (const char* pszValue), (const char* pszDefault) };
+#endif
 %apply Pointer NONNULL {const char * pszKey};
 void CPLSetConfigOption( const char * pszKey, const char * pszValue );
 void CPLSetThreadLocalConfigOption( const char * pszKey, const char * pszValue );
@@ -532,6 +536,9 @@ const char *wrapper_VSIGetPathSpecificOption( const char* pszPathPrefix, const c
 
 %clear const char * pszPathPrefix;
 %clear const char * pszKey;
+#if defined(SWIGCSHARP)
+%clear (const char* pszValue), (const char* pszDefault);
+#endif
 
 
 %inline {

swig/include/csharp/typemaps_csharp.i

@@ -477,20 +477,21 @@ CSHARP_OBJECT_ARRAYS_PINNED(GDALRasterBandShadow, Band)
 %apply (int inout[ANY]) {int *pList};
 
 /*
- * Typemap for const char *utf8_path.
+ * Typemap for const char *utf8_path and utf8_or_null.
  */
-%typemap(csin) (const char *utf8_path)  "$module.StringToUtf8Bytes($csinput)"
-%typemap(imtype, out="IntPtr") (const char *utf8_path) "byte[]"
-%typemap(out) (const char *utf8_path) %{ $result = $1; %}
-%typemap(csout, excode=SWIGEXCODE) (const char *utf8_path) {
-        /* %typemap(csout) (const char *utf8_path) */
-        IntPtr cPtr = $imcall;
-        string ret = $module.Utf8BytesToString(cPtr);
-        $excode
-        return ret;
-}
-
-%apply ( const char *utf8_path ) { const char* GetFieldAsString };
+%typemap(imtype,
+  inattributes="[MarshalAs(UnmanagedType.LPUTF8Str)]",
+  outattributes="[return: MarshalAs(UnmanagedType.LPUTF8Str)]")
+    (const char *utf8_path), (const char *utf8_or_null = NULL) "string"
+
+%apply ( const char *utf8_path ) {
+    const char* GetFieldAsString,
+    const char* wrapper_CPLGetConfigOption,
+    const char* wrapper_CPLGetGlobalConfigOption,
+    const char* wrapper_CPLGetThreadLocalConfigOption,
+    const char* wrapper_VSIGetCredential,
+    const char* wrapper_VSIGetPathSpecificOption
+};
 
 /*
  * Typemap for double *defaultval.