Make the archives created on Unix have the read permissions by default

src/libraries/Common/src/System/IO/Compression/ZipArchiveEntryConstants.Unix.cs

@@ -0,0 +1,23 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.IO.Compression
+{
+    internal static partial class ZipArchiveEntryConstants
+    {
+        /// <summary>
+        /// The default external file attributes are used to support zip archives on multiple platforms.
+        /// </summary>
+        internal const UnixFileMode DefaultFileEntryPermissions = UnixFileMode.UserRead | UnixFileMode.UserWrite
+                                                            | UnixFileMode.GroupRead
+                                                            | UnixFileMode.OtherRead;
+
+        /// <summary>
+        /// The default external directory attributes are used to support zip archives on multiple platforms.
+        /// Directories on Unix require the execute permissions to get into them.
+        /// </summary>
+        internal const UnixFileMode DefaultDirectoryEntryPermissions = UnixFileMode.UserRead | UnixFileMode.UserWrite | UnixFileMode.UserExecute
+                                                               | UnixFileMode.GroupRead | UnixFileMode.GroupExecute
+                                                               | UnixFileMode.OtherRead | UnixFileMode.OtherExecute;
+    }
+}

src/libraries/Common/src/System/IO/Compression/ZipArchiveEntryConstants.Windows.cs

@@ -0,0 +1,20 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.IO.Compression
+{
+    internal static partial class ZipArchiveEntryConstants
+    {
+        /// <summary>
+        /// The default external file attributes are used to support zip archives on multiple platforms.
+        /// Since Windows doesn't use file permissions, there's no default value needed.
+        /// </summary>
+        internal const UnixFileMode DefaultFileEntryPermissions = UnixFileMode.None;
+
+        /// <summary>
+        /// The default external directory attributes are used to support zip archives on multiple platforms.
+        /// Since Windows doesn't use file permissions, there's no default value needed.
+        /// </summary>
+        internal const UnixFileMode DefaultDirectoryEntryPermissions = UnixFileMode.None;
+    }
+}

src/libraries/System.IO.Compression.ZipFile/src/System.IO.Compression.ZipFile.csproj

@@ -25,6 +25,7 @@
   <ItemGroup Condition="'$(TargetPlatformIdentifier)' == ''">
     <Compile Include="System\IO\Compression\ZipFileExtensions.ZipArchive.Create.Unix.cs" />
     <Compile Include="System\IO\Compression\ZipFileExtensions.ZipArchiveEntry.Extract.Unix.cs" />
+    <Compile Include="$(CommonPath)System\IO\Compression\ZipArchiveEntryConstants.Unix.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.IOErrors.cs"
              Link="Common\Interop\Unix\Interop.IOErrors.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.Libraries.cs"

src/libraries/System.IO.Compression.ZipFile/src/System/IO/Compression/ZipFileExtensions.ZipArchive.Create.Unix.cs

@@ -1,16 +1,27 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
+
+using static System.IO.Compression.ZipArchiveEntryConstants;
+
 namespace System.IO.Compression
 {
     public static partial class ZipFileExtensions
     {
         static partial void SetExternalAttributes(FileStream fs, ZipArchiveEntry entry)
         {
+            Debug.Assert(!OperatingSystem.IsWindows());
+
+            // SetExternalAttributes is only used to overwrite the default values when reading on the unix systems
+            // This assert ensures that nothing else sets values different to the default before
+            // overwriting it with the data read from the files
+            Debug.Assert(entry.ExternalAttributes == ((uint)DefaultFileEntryPermissions << 16));
+
             Interop.Sys.FileStatus status;
             Interop.CheckIo(Interop.Sys.FStat(fs.SafeFileHandle, out status), fs.Name);
 
-            entry.ExternalAttributes |= status.Mode << 16;
+            entry.ExternalAttributes = status.Mode << 16;
         }
     }
 }

src/libraries/System.IO.Compression/src/System.IO.Compression.csproj

@@ -45,12 +45,14 @@
   <!-- Windows specific files -->
   <ItemGroup Condition="'$(TargetPlatformIdentifier)' == 'windows'">
     <Compile Include="System\IO\Compression\ZipArchiveEntry.Windows.cs" />
+    <Compile Include="$(CommonPath)System\IO\Compression\ZipArchiveEntryConstants.Windows.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.Libraries.cs"
              Link="Common\Interop\Windows\Interop.Libraries.cs" />
   </ItemGroup>
   <!-- Unix specific files -->
   <ItemGroup Condition="'$(TargetPlatformIdentifier)' == 'Unix' or '$(TargetPlatformIdentifier)' == 'Browser'">
     <Compile Include="System\IO\Compression\ZipArchiveEntry.Unix.cs" />
+    <Compile Include="$(CommonPath)System\IO\Compression\ZipArchiveEntryConstants.Unix.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.Libraries.cs"
              Link="Common\Interop\Unix\Interop.Libraries.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.PathConf.cs"

src/libraries/System.IO.Compression/src/System/IO/Compression/ZipArchiveEntry.cs

@@ -9,6 +9,8 @@
 using System.Threading;
 using System.Threading.Tasks;
 
+using static System.IO.Compression.ZipArchiveEntryConstants;
+
 namespace System.IO.Compression
 {
     // The disposable fields that this class owns get disposed when the ZipArchive it belongs to gets disposed
@@ -115,7 +117,11 @@ internal ZipArchiveEntry(ZipArchive archive, string entryName)
 
             _compressedSize = 0; // we don't know these yet
             _uncompressedSize = 0;
-            _externalFileAttr = 0;
+            UnixFileMode defaultEntryPermissions = entryName.EndsWith(Path.DirectorySeparatorChar) || entryName.EndsWith(Path.AltDirectorySeparatorChar)
+                                        ? DefaultDirectoryEntryPermissions
+                                        : DefaultFileEntryPermissions;
+            _externalFileAttr = (uint)(defaultEntryPermissions) << 16;
+
             _offsetOfLocalHeader = 0;
             _storedOffsetOfCompressedData = null;
             _crc32 = 0;

src/libraries/System.IO.Compression/tests/System.IO.Compression.Tests.csproj

@@ -41,6 +41,10 @@
     <Compile Include="$(CommonPath)System\Net\MultiArrayBuffer.cs" Link="ProductionCode\Common\System\Net\MultiArrayBuffer.cs" />
     <Compile Include="$(CommonPath)System\Net\StreamBuffer.cs" Link="ProductionCode\Common\System\Net\StreamBuffer.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetPlatformIdentifier)' == 'Unix' or '$(TargetPlatformIdentifier)' == 'Browser'">
+    <Compile Include="ZipArchive\zip_CreateTests.Unix.cs" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="$(CommonTestPath)StreamConformanceTests\StreamConformanceTests.csproj" />
   </ItemGroup>

src/libraries/System.IO.Compression/tests/ZipArchive/zip_CreateTests.Unix.cs

@@ -0,0 +1,22 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Threading.Tasks;
+using Xunit;
+
+namespace System.IO.Compression.Tests
+{
+    public partial class zip_CreateTests : ZipFileTestBase
+    {
+        [Theory]
+        [InlineData("folder/", 493 << 16)]
+        [InlineData("folder/file", 420 << 16)]
+        [InlineData("folder\\file", 420 << 16)]
+        public static void Verify_Default_Permissions_Are_Applied_For_Entries(string path, int permissions)
+        {
+            using var archive = new ZipArchive(new MemoryStream(), ZipArchiveMode.Create, false);
+            var newEntry = archive.CreateEntry(path);
+            Assert.Equal(newEntry.ExternalAttributes, permissions);
+        }
+    }
+}