Invoke-RestMethod cmdlet error if the response is neither JSON nor XML (#2862)

* This change fixes the Invoke-RestMethod cmdlet behavior if the input is neither xml nor json.
* test description
* fixed the failed tests
* removed some duplication
* refactoring: eliminated some double castings
* added JsonObject unit tests; enhanced JSON deserialization exception message
* refactored JsonObject.Tests.ps1
* entitled test cases
* formatting

src/Microsoft.PowerShell.Commands.Utility/commands/utility/WebCmdlet/ConvertFromJsonCommand.cs

@@ -92,12 +92,7 @@ namespace Microsoft.PowerShell.Commands
                         // The first input string does not represent a complete Json Syntax. 
                         // Hence consider the the entire input as a single Json content.
                     }
-#if CORECLR
-                    catch (Newtonsoft.Json.JsonSerializationException)
-                    {
-                        // we use another serializer for CORECLR implementation
-                    }
-#endif
+
                     if (successfullyConverted)
                     {
                         for (int index = 1; index < _inputObjectBuffer.Count; index++)

src/Microsoft.PowerShell.Commands.Utility/commands/utility/WebCmdlet/JsonObject.cs

@@ -44,20 +44,32 @@ namespace Microsoft.PowerShell.Commands
             }
             error = null;
 #if CORECLR
-            object obj = JsonConvert.DeserializeObject(input, new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.None, MaxDepth = 1024 });
-
-            // JObject is a IDictionary
-            if (obj is JObject)
+            object obj = null;
+            try
             {
+                obj = JsonConvert.DeserializeObject(input, new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.None, MaxDepth = 1024 });
+
+                // JObject is a IDictionary
                 var dictionary = obj as JObject;
-                obj = PopulateFromJDictionary(dictionary, out error);
+                if (dictionary != null)
+                {
+                    obj = PopulateFromJDictionary(dictionary, out error);
+                }
+                else
+                {
+                    // JArray is a collection
+                    var list = obj as JArray;
+                    if (list != null)
+                    {
+                        obj = PopulateFromJArray(list, out error);
+                    }
+                }
             }
-
-            // JArray is a collection
-            else if (obj is JArray)
+            catch (JsonException je)
             {
-                var list = obj as JArray;
-                obj = PopulateFromJArray(list, out error);
+                var msg = string.Format(CultureInfo.CurrentCulture, WebCmdletStrings.JsonDeserializationFailed, je.Message);
+                // the same as JavaScriptSerializer does
+                throw new ArgumentException(msg, je);
             }
 #else
             //In ConvertTo-Json, to serialize an object with a given depth, we set the RecursionLimit to depth + 2, see JavaScriptSerializer constructor in ConvertToJsonCommand.cs.

src/Microsoft.PowerShell.Commands.Utility/resources/WebCmdletStrings.resx

@@ -207,4 +207,7 @@
   <data name="ReachedMaximumDepthAllowed" xml:space="preserve">
     <value>The maximum depth allowed for serialization is {0}.</value>
   </data>
+  <data name="JsonDeserializationFailed" xml:space="preserve">
+    <value>Conversion from JSON failed with error: {0}</value>
+  </data>
 </root>

test/powershell/Modules/Microsoft.PowerShell.Utility/JsonObject.Tests.ps1

@@ -0,0 +1,46 @@
+Describe 'Unit tests for JsonObject' -tags "CI" {
+
+    function ShouldThrow
+    {
+        param (
+            [Parameter(ValueFromPipeline = $true)]
+            $InputObject,
+            [Parameter(Position = 0)]
+            $ExpectedException
+        )
+
+        try
+        {
+            & $InputObject
+            throw "Should throw exception"
+        }
+        catch
+        {
+            $_.FullyQualifiedErrorId | should be $ExpectedException
+        }
+    }
+
+    $validStrings = @(
+        @{ name = "empty"; str = "" }
+        @{ name = "spaces"; str = "  " }
+        @{ name = "object"; str = "{a:1}" }
+    )
+
+    It 'no error for valid string - <name>' -TestCase $validStrings {
+        param ($str)
+        $errRecord = $null
+        [Microsoft.PowerShell.Commands.JsonObject]::ConvertFromJson($str, [ref]$errRecord)
+        $errRecord | Should BeNullOrEmpty
+    }
+
+    $invalidStrings = @(
+        @{ name = "plain text"; str = "plaintext" }
+        @{ name = "part"; str = '{"a" :' }
+    )
+
+    It 'throw ArgumentException for invalid string - <name>' -TestCase $invalidStrings  {
+        param ($str)
+        $errRecord = $null
+        { [Microsoft.PowerShell.Commands.JsonObject]::ConvertFromJson($str, [ref]$errRecord) } | ShouldThrow 'ArgumentException'
+    }
+}

test/powershell/Modules/Microsoft.PowerShell.Utility/WebCmdlets.Tests.ps1

@@ -635,4 +635,11 @@ Describe "Invoke-RestMethod tests" -Tags "Feature" {
         $result = ExecuteWebCommand -command $command
         $result.Error | Should BeNullOrEmpty
     }
+
+    It "Invoke-RestMethod supports request that returns plain text response." {
+
+        $command = "Invoke-RestMethod -Uri 'http://httpbin.org/encoding/utf8'"
+        $result = ExecuteWebCommand -command $command
+        $result.Error | Should BeNullOrEmpty
+    }
 }