Support embedded READMEs (loic-sharma#670)

NuGet's official embedded READMEs declares the README using the [`readme`](https://docs.microsoft.com/en-us/nuget/reference/nuspec#readme) metadata in the package's .nuspec.

Author: loic-sharma

src/BaGet.Core/Extensions/PackageArchiveReaderExtensions.cs

@@ -13,18 +13,8 @@ namespace BaGet.Core
 
     public static class PackageArchiveReaderExtensions
     {
-        private static readonly string[] OrderedReadmeFileNames = new[]
-        {
-            "readme.md",
-            "readme.txt",
-        };
-
-        private static readonly HashSet<string> ReadmeFileNames = new HashSet<string>(
-            OrderedReadmeFileNames,
-            StringComparer.OrdinalIgnoreCase);
-
         public static bool HasReadme(this PackageArchiveReader package)
-            => package.GetFiles().Any(ReadmeFileNames.Contains);
+            => !string.IsNullOrEmpty(package.NuspecReader.GetReadme());
 
         public static bool HasEmbeddedIcon(this PackageArchiveReader package)
             => !string.IsNullOrEmpty(package.NuspecReader.GetIcon());
@@ -33,19 +23,13 @@ public async static Task<Stream> GetReadmeAsync(
             this PackageArchiveReader package,
             CancellationToken cancellationToken)
         {
-            var packageFiles = package.GetFiles();
-
-            foreach (var readmeFileName in OrderedReadmeFileNames)
+            var readmePath = package.NuspecReader.GetReadme();
+            if (readmePath == null)
             {
-                var readmePath = packageFiles.FirstOrDefault(f => f.Equals(readmeFileName, StringComparison.OrdinalIgnoreCase));
-
-                if (readmePath != null)
-                {
-                    return await package.GetStreamAsync(readmePath, cancellationToken);
-                }
+                throw new InvalidOperationException("Package does not have a readme!");
             }
 
-            throw new InvalidOperationException("Package does not have a readme!");
+            return await package.GetStreamAsync(readmePath, cancellationToken);
         }
 
         public async static Task<Stream> GetIconAsync(

src/Directory.Build.props

@@ -40,7 +40,7 @@
     <MicrosoftAspNetCorePackageVersion>3.1.1</MicrosoftAspNetCorePackageVersion>
     <MicrosoftEntityFrameworkCorePackageVersion>3.1.1</MicrosoftEntityFrameworkCorePackageVersion>
     <MicrosoftExtensionsPackageVersion>3.1.1</MicrosoftExtensionsPackageVersion>
-    <NuGetPackageVersion>5.4.0</NuGetPackageVersion>
+    <NuGetPackageVersion>5.10.0</NuGetPackageVersion>
   </PropertyGroup>
 
   <ItemGroup Condition="'$(DOTNET_RUNNING_IN_CONTAINER)' == ''">

tests/BaGet.Tests/ApiIntegrationTests.cs

@@ -274,7 +274,7 @@ public async Task PackageMetadataReturnsOk()
             ""authors"": ""Test author"",
             ""dependencyGroups"": [
               {
-                ""targetFramework"": ""net50"",
+                ""targetFramework"": ""net5.0"",
                 ""dependencies"": []
               }
             ],

tests/Directory.Build.props

@@ -14,7 +14,7 @@
   <PropertyGroup>
     <MicrosoftAspNetCorePackageVersion>3.1.1</MicrosoftAspNetCorePackageVersion>
     <NewtonsoftJsonPackageVersion>12.0.2</NewtonsoftJsonPackageVersion>
-    <NuGetPackageVersion>5.4.0</NuGetPackageVersion>
+    <NuGetPackageVersion>5.10.0</NuGetPackageVersion>
     <XUnitPackageVersion>2.4.1</XUnitPackageVersion>
   </PropertyGroup>