Ignore non-package folders in package cache

Firely.Fhir.Packages.Tests/DiskPackageCacheTests.cs

@@ -0,0 +1,50 @@
+using FluentAssertions;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System.IO;
+using System.Linq;
+
+namespace Firely.Fhir.Packages.Tests
+{
+    [TestClass]
+    public class DiskPackageCacheTests
+    {
+        [TestMethod]
+        public void TestIgnoreInvalidPackageFolder()
+        {
+
+            //Create new packageCache folder:
+            //  --testcache
+            //  ---- validpackage#1.0.0
+            //  ---- invalidpackage
+            //  ---- #invalidpackage
+            //  ---- invalidpackage#
+
+            string root = "testCache";
+            string validPackage = "validpackage#2.0.0";
+            string invalidPackage1 = "invalidpackage";
+            string invalidPackage2 = "#invalidpackage";
+            string invalidPackage3 = "invalidpackage#";
+            string invalidPackage4 = "invalidpackage#2.0.0#invalid";
+
+
+            Directory.CreateDirectory(root);
+            Directory.CreateDirectory($"{root}/{validPackage}");
+            Directory.CreateDirectory($"{root}/{invalidPackage1}");
+            Directory.CreateDirectory($"{root}/{invalidPackage2}");
+            Directory.CreateDirectory($"{root}/{invalidPackage3}");
+            Directory.CreateDirectory($"{root}/{invalidPackage4}");
+
+            //Test
+            var packageCache = new DiskPackageCache(root);
+            var packages = packageCache.GetPackageReferences().Result;
+            packages.Should().OnlyContain(x => x.Name == validPackage.Split('#', System.StringSplitOptions.None).First());
+
+
+            //Cleanup
+            Directory.Delete(root, true);
+
+
+        }
+
+    }
+}

Firely.Fhir.Packages/Disk/DiskPackageCache.cs

@@ -13,6 +13,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 
 namespace Firely.Fhir.Packages
@@ -106,13 +107,22 @@ public Task<IEnumerable<PackageReference>> GetPackageReferences()
             {
                 var name = Disk.GetFolderName(folder);
 
-                var reference = parseFoldernameToReference(name);
-                references.Add(reference);
+                if (isValidPackageFolder(name))
+                {
+                    var reference = parseFoldernameToReference(name);
+                    references.Add(reference);
+                }
             }
 
             return Task.FromResult(references.AsEnumerable());
         }
 
+        //check whether the folder name has contains a single # sign which is not at the beginning or the end.
+        string pattern = @"^[^#]+#[^#]+$";
+
+        private bool isValidPackageFolder(string folderName) => Regex.IsMatch(folderName, pattern);
+
+
         private static PackageReference parseFoldernameToReference(string foldername)
         {
             var idx = foldername.IndexOf('#');