Added path checks to AssemlyLoading, Binary and SVMLight Loader APIs

Author: mstfbl

src/Microsoft.ML.Core/ComponentModel/AssemblyLoadingUtils.cs

@@ -31,6 +31,10 @@ public static void LoadAndRegister(IHostEnvironment env, string[] assemblies)
                     {
                         // REVIEW: Will LoadFrom ever return null?
                         Contracts.CheckNonEmpty(path, nameof(path));
+                        if (!File.Exists(path))
+                        {
+                            throw Contracts.ExceptParam(nameof(path), "File does not exist at path: {0}", path);
+                        }
                         var assem = LoadAssembly(env, path);
                         if (assem != null)
                             continue;

src/Microsoft.ML.Data/DataLoadSave/Binary/BinaryLoaderSaverCatalog.cs

@@ -47,6 +47,10 @@ public static IDataView LoadFromBinary(this DataOperationsCatalog catalog, IMult
         public static IDataView LoadFromBinary(this DataOperationsCatalog catalog, string path)
         {
             Contracts.CheckNonEmpty(path, nameof(path));
+            if (!File.Exists(path))
+            {
+                throw Contracts.ExceptParam(nameof(path), "File does not exist at path: {0}", path);
+            }
 
             var env = catalog.GetEnvironment();
 

src/Microsoft.ML.Transforms/SvmLight/SvmLightLoaderSaverCatalog.cs

@@ -65,6 +65,10 @@ public static IDataView LoadFromSvmLightFile(this DataOperationsCatalog catalog,
             bool zeroBased = false)
         {
             Contracts.CheckNonEmpty(path, nameof(path));
+            if (!File.Exists(path))
+            {
+                throw Contracts.ExceptParam(nameof(path), "File does not exist at path: {0}", path);
+            }
 
             var file = new MultiFileSource(path);
             var loader = catalog.CreateSvmLightLoader(numberOfRows, inputSize, zeroBased, file);
@@ -83,6 +87,10 @@ public static IDataView LoadFromSvmLightFileWithFeatureNames(this DataOperations
             long? numberOfRows = null)
         {
             Contracts.CheckNonEmpty(path, nameof(path));
+            if (!File.Exists(path))
+            {
+                throw Contracts.ExceptParam(nameof(path), "File does not exist at path: {0}", path);
+            }
 
             var file = new MultiFileSource(path);
             var loader = catalog.CreateSvmLightLoaderWithFeatureNames(numberOfRows, file);