make HasVSIHandler test externally registered handlers

godal.cpp

@@ -1770,17 +1770,26 @@ namespace cpl
 
 } // namespace cpl
 
-void VSIInstallGoHandler(cctx *ctx, const char *pszPrefix, size_t bufferSize, size_t cacheSize)
+bool VSIHasGoHandler(const char *pszPrefix)
 {
-    godalWrap(ctx);
     CSLConstList papszPrefix = VSIFileManager::GetPrefixes();
     for( size_t i = 0; papszPrefix && papszPrefix[i]; ++i ) {
         if(strcmp(papszPrefix[i],pszPrefix)==0) {
-            CPLError(CE_Failure, CPLE_AppDefined, "handler already registered on prefix");
-            godalUnwrap();
-            return;
+            return true;
         }
     }
+    return false;
+}
+
+void VSIInstallGoHandler(cctx *ctx, const char *pszPrefix, size_t bufferSize, size_t cacheSize)
+{
+    bool alreadyExists = VSIHasGoHandler(pszPrefix);
+    godalWrap(ctx);
+    if (alreadyExists) {
+        CPLError(CE_Failure, CPLE_AppDefined, "handler already registered on prefix");
+        godalUnwrap();
+        return;
+    }
     VSIFilesystemHandler *poHandler = new cpl::VSIGoFilesystemHandler(bufferSize, cacheSize);
     const std::string sPrefix(pszPrefix);
     VSIFileManager::InstallHandler(sPrefix, poHandler);

godal.go

@@ -3900,7 +3900,7 @@ func RegisterVSIHandler(prefix string, handler KeySizerReaderAt, opts ...VSIHand
 
 // HasVSIHandler returns true if a VSIHandler is registered for this prefix
 func HasVSIHandler(prefix string) bool {
-	return handlers != nil && handlers[prefix].KeySizerReaderAt != nil
+	return bool(C.VSIHasGoHandler(C.CString(prefix)))
 }
 
 // BuildVRT runs the GDALBuildVRT function and creates a VRT dataset from a list of datasets

godal.h

@@ -130,6 +130,7 @@ extern "C" {
 	void godalStartTransaction(cctx *ctx, GDALDatasetH ds, int bForce);
 	void godalDatasetRollbackTransaction(cctx *ctx, GDALDatasetH ds);
 	void godalCommitTransaction(cctx *ctx, GDALDatasetH ds);
+	bool VSIHasGoHandler(const char *pszPrefix);
 	void VSIInstallGoHandler(cctx *ctx, const char *pszPrefix, size_t bufferSize, size_t cacheSize);
 
 	void godalGetColorTable(GDALRasterBandH bnd, GDALPaletteInterp *interp, int *nEntries, short **entries);

godal_test.go

@@ -3459,6 +3459,7 @@ func (mvp mvpHandler) ReadAtMulti(k string, buf [][]byte, off []int64) ([]int, e
 	}
 	return b.(KeyMultiReader).ReadAtMulti(k, buf, off)
 }
+
 func TestHasVSIHandler(t *testing.T) { // stripPrefix false
 	assert.False(t, HasVSIHandler("unregistered_prefix://"))
 
@@ -3467,11 +3468,6 @@ func TestHasVSIHandler(t *testing.T) { // stripPrefix false
 	assert.NoError(t, err)
 	assert.True(t, HasVSIHandler("registered_prefix://"))
 
-	// nil handler
-	err = RegisterVSIHandler("nil_prefix://", nil)
-	assert.NoError(t, err)
-	assert.False(t, HasVSIHandler("nil_prefix://"))
-
 	// unregistered_prefix
 	assert.False(t, HasVSIHandler("unregistered_prefix://"))
 }