Update the DockerfileComponentDetector to enable nullability and use the updated utilities to reduce code duplication.

Author: jpinz

src/Microsoft.ComponentDetection.Detectors/dockerfile/DockerfileComponentDetector.cs

@@ -1,11 +1,9 @@
-#nullable disable
+#nullable enable
 namespace Microsoft.ComponentDetection.Detectors.Dockerfile;
 
 using System;
 using System.Collections.Generic;
 using System.IO;
-using System.Linq;
-using System.Text.RegularExpressions;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.ComponentDetection.Common;
@@ -36,7 +34,7 @@ public DockerfileComponentDetector(
 
     public override string Id { get; } = "DockerReference";
 
-    public override IEnumerable<string> Categories => [Enum.GetName(typeof(DetectorClass), DetectorClass.DockerReference)];
+    public override IEnumerable<string> Categories => [nameof(DetectorClass.DockerReference)];
 
     public override IList<string> SearchPatterns { get; } = ["dockerfile", "dockerfile.*", "*.dockerfile"];
 
@@ -84,12 +82,12 @@ private Task ParseDockerFileAsync(string fileContents, string fileLocation, ISin
         return Task.CompletedTask;
     }
 
-    private DockerReference ProcessDockerfileConstruct(DockerfileConstruct construct, char escapeChar, Dictionary<string, string> stageNameMap)
+    private DockerReference? ProcessDockerfileConstruct(DockerfileConstruct construct, char escapeChar, Dictionary<string, string> stageNameMap)
     {
         try
         {
             var instructionKeyword = construct.Type;
-            DockerReference baseImage = null;
+            DockerReference? baseImage = null;
             if (instructionKeyword == ConstructType.Instruction)
             {
                 var constructType = construct.GetType().Name;
@@ -115,10 +113,9 @@ private DockerReference ProcessDockerfileConstruct(DockerfileConstruct construct
         }
     }
 
-    private DockerReference ParseFromInstruction(DockerfileConstruct construct, char escapeChar, Dictionary<string, string> stageNameMap)
+    private DockerReference? ParseFromInstruction(DockerfileConstruct construct, char escapeChar, Dictionary<string, string> stageNameMap)
     {
-        var tokens = construct.Tokens.ToArray();
-        var resolvedFromStatement = construct.ResolveVariables(escapeChar).TrimEnd();
+        var resolvedFromStatement = construct.ResolveVariables(escapeChar)?.TrimEnd();
         var fromInstruction = (FromInstruction)construct;
         var reference = fromInstruction.ImageName;
         if (string.IsNullOrWhiteSpace(resolvedFromStatement) || string.IsNullOrEmpty(reference))
@@ -143,25 +140,15 @@ private DockerReference ParseFromInstruction(DockerfileConstruct construct, char
 
         if (!string.IsNullOrEmpty(stageNameReference))
         {
-            if (this.HasUnresolvedVariables(stageNameReference))
-            {
-                return null;
-            }
-
-            return DockerReferenceUtility.ParseFamiliarName(stageNameReference);
-        }
-
-        if (this.HasUnresolvedVariables(reference))
-        {
-            return null;
+            return DockerReferenceUtility.TryParseImageReference(stageNameReference);
         }
 
-        return DockerReferenceUtility.ParseFamiliarName(reference);
+        return DockerReferenceUtility.TryParseImageReference(reference);
     }
 
-    private DockerReference ParseCopyInstruction(DockerfileConstruct construct, char escapeChar, Dictionary<string, string> stageNameMap)
+    private DockerReference? ParseCopyInstruction(DockerfileConstruct construct, char escapeChar, Dictionary<string, string> stageNameMap)
     {
-        var resolvedCopyStatement = construct.ResolveVariables(escapeChar).TrimEnd();
+        var resolvedCopyStatement = construct.ResolveVariables(escapeChar)?.TrimEnd();
         var copyInstruction = (CopyInstruction)construct;
         var reference = copyInstruction.FromStageName;
         if (string.IsNullOrWhiteSpace(resolvedCopyStatement) || string.IsNullOrWhiteSpace(reference))
@@ -172,26 +159,9 @@ private DockerReference ParseCopyInstruction(DockerfileConstruct construct, char
         stageNameMap.TryGetValue(reference, out var stageNameReference);
         if (!string.IsNullOrEmpty(stageNameReference))
         {
-            if (this.HasUnresolvedVariables(stageNameReference))
-            {
-                return null;
-            }
-            else
-            {
-                return DockerReferenceUtility.ParseFamiliarName(stageNameReference);
-            }
+            return DockerReferenceUtility.TryParseImageReference(stageNameReference);
         }
 
-        if (this.HasUnresolvedVariables(reference))
-        {
-            return null;
-        }
-
-        return DockerReferenceUtility.ParseFamiliarName(reference);
-    }
-
-    private bool HasUnresolvedVariables(string reference)
-    {
-        return new Regex("[${}]").IsMatch(reference);
+        return DockerReferenceUtility.TryParseImageReference(reference);
     }
 }