reject empty readme file & fix error message for invalid extension (#8464)

* reject empty readme file & fix error message for invalid extension

Author: lyndaidaii

src/NuGetGallery/Services/PackageMetadataValidationService.cs

@@ -458,6 +458,16 @@ private async Task<PackageValidationResult> CheckReadmeMetadataAsync(PackageArch
             }
 
             var readmeFileEntry = nuGetPackage.GetEntry(readmeFilePath);
+
+            if (readmeFileEntry.Length == 0)
+            {
+                return PackageValidationResult.Invalid(
+                    string.Format(
+                        Strings.ReadmeErrorEmpty,
+                        Strings.UploadPackage_ReadmeFileType,
+                        readmeFilePath));
+            }
+
             if (readmeFileEntry.Length > MaxAllowedReadmeLengthForUploading)
             {
                 return PackageValidationResult.Invalid(

src/NuGetGallery/Strings.Designer.cs

@@ -1166,7 +1166,7 @@ The {1} Team</value>
     <value>The &lt;readme&gt; element is not currently supported.</value>
   </data>
   <data name="UploadPackage_InvalidReadmeFileExtension" xml:space="preserve">
-    <value>The readme file has an invalid extension '{0}'. Extension must be one of the following: {1}.</value>
+    <value>The readme file has an invalid extension '{0}'. The extension must be: '{1}'.</value>
     <comment>{0} is the readme file extension specified in the .nuspec, {1} is the list of allowed extensions</comment>
   </data>
   <data name="UploadPackage_ReadmeFileType" xml:space="preserve">
@@ -1215,4 +1215,7 @@ The {1} Team</value>
   <data name="UploadPackage_OwnerlessIdNamespaceConflictHtml" xml:space="preserve">
     <value>The package ID is reserved. You can upload your package with a different package ID. Reach out to &lt;a href="mailto:[email protected]"&gt;[email protected]&lt;/a&gt; if you have questions.</value>
   </data>
+  <data name="ReadmeErrorEmpty" xml:space="preserve">
+    <value>The readme file '{0}' cannot be empty.</value>
+  </data>
 </root>