Add strong and weak ETag comparisons

Author: JunTaoLuo

src/Microsoft.Net.Http.Headers/EntityTagHeaderValue.cs

@@ -93,6 +93,15 @@ public override string ToString()
             return _tag;
         }
 
+        /// <summary>
+        /// Check against another <see cref="EntityTagHeaderValue"/> for equality.
+        /// This equality check should not be used to determine if two values match under the RFC specifications (https://tools.ietf.org/html/rfc7232#section-2.3.2).
+        /// </summary>
+        /// <param name="obj">The other value to check against for equality.</param>
+        /// <returns>
+        /// <c>true</c> if the strength and tag of the two values match,
+        /// <c>false</c> if the other value is null, is not an <see cref="EntityTagHeaderValue"/>, or if there is a mismatch of strength or tag between the two values.
+        /// </returns>
         public override bool Equals(object obj)
         {
             var other = obj as EntityTagHeaderValue;
@@ -103,7 +112,7 @@ public override bool Equals(object obj)
             }
 
             // Since the tag is a quoted-string we treat it case-sensitive.
-            return ((_isWeak == other._isWeak) && (string.CompareOrdinal(_tag, other._tag) == 0));
+            return _isWeak == other._isWeak && string.Equals(_tag, other._tag, StringComparison.Ordinal);
         }
 
         public override int GetHashCode()
@@ -112,6 +121,32 @@ public override int GetHashCode()
             return _tag.GetHashCode() ^ _isWeak.GetHashCode();
         }
 
+        /// <summary>
+        /// Compares against another <see cref="EntityTagHeaderValue"/> to see if they match under the RFC specifications (https://tools.ietf.org/html/rfc7232#section-2.3.2).
+        /// </summary>
+        /// <param name="other">The other <see cref="EntityTagHeaderValue"/> to compare against.</param>
+        /// <param name="useStrongComparison"><c>true</c> to use a strong comparison, <c>false</c> to use a weak comparison</param>
+        /// <returns>
+        /// <c>true</c> if the <see cref="EntityTagHeaderValue"/> match for the given comparison type,
+        /// <c>false</c> if the other value is null or the comparison failed.
+        /// </returns>
+        public bool Compare(EntityTagHeaderValue other, bool useStrongComparison)
+        {
+            if (other == null)
+            {
+                return false;
+            }
+
+            if (useStrongComparison)
+            {
+                return !IsWeak && !other.IsWeak && string.Equals(Tag, other.Tag, StringComparison.Ordinal);
+            }
+            else
+            {
+                return string.Equals(Tag, other.Tag, StringComparison.Ordinal);
+            }
+        }
+
         public static EntityTagHeaderValue Parse(string input)
         {
             var index = 0;

test/Microsoft.Net.Http.Headers.Tests/EntityTagHeaderValueTest.cs

@@ -99,6 +99,97 @@ public void Equals_UseSameAndDifferentETags_EqualOrNotEqualNoExceptions()
             Assert.True(etag1.Equals(etag5), "tag vs. tag..");
         }
 
+        [Fact]
+        public void Compare_WithNull_ReturnsFalse()
+        {
+            Assert.False(EntityTagHeaderValue.Any.Compare(null, useStrongComparison: true));
+            Assert.False(EntityTagHeaderValue.Any.Compare(null, useStrongComparison: false));
+        }
+
+        public static TheoryData<EntityTagHeaderValue, EntityTagHeaderValue> NotEquivalentUnderStrongComparison
+        {
+            get
+            {
+                return new TheoryData<EntityTagHeaderValue, EntityTagHeaderValue>
+                {
+                    { new EntityTagHeaderValue("\"tag\""), new EntityTagHeaderValue("\"TAG\"") },
+                    { new EntityTagHeaderValue("\"tag\"", true), new EntityTagHeaderValue("\"tag\"", true) },
+                    { new EntityTagHeaderValue("\"tag\""), new EntityTagHeaderValue("\"tag\"", true) },
+                    { new EntityTagHeaderValue("\"tag\""), new EntityTagHeaderValue("\"tag1\"") },
+                    { new EntityTagHeaderValue("\"tag\""), EntityTagHeaderValue.Any },
+                };
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(NotEquivalentUnderStrongComparison))]
+        public void CompareUsingStrongComparison_NonEquivalentPairs_ReturnFalse(EntityTagHeaderValue left, EntityTagHeaderValue right)
+        {
+            Assert.False(left.Compare(right, useStrongComparison: true));
+            Assert.False(right.Compare(left, useStrongComparison: true));
+        }
+
+        public static TheoryData<EntityTagHeaderValue, EntityTagHeaderValue> EquivalentUnderStrongComparison
+        {
+            get
+            {
+                return new TheoryData<EntityTagHeaderValue, EntityTagHeaderValue>
+                {
+                    { new EntityTagHeaderValue("\"tag\""), new EntityTagHeaderValue("\"tag\"") },
+                };
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(EquivalentUnderStrongComparison))]
+        public void CompareUsingStrongComparison_EquivalentPairs_ReturnTrue(EntityTagHeaderValue left, EntityTagHeaderValue right)
+        {
+            Assert.True(left.Compare(right, useStrongComparison: true));
+            Assert.True(right.Compare(left, useStrongComparison: true));
+        }
+
+        public static TheoryData<EntityTagHeaderValue, EntityTagHeaderValue> NotEquivalentUnderWeakComparison
+        {
+            get
+            {
+                return new TheoryData<EntityTagHeaderValue, EntityTagHeaderValue>
+                {
+                    { new EntityTagHeaderValue("\"tag\""), new EntityTagHeaderValue("\"TAG\"") },
+                    { new EntityTagHeaderValue("\"tag\""), new EntityTagHeaderValue("\"tag1\"") },
+                    { new EntityTagHeaderValue("\"tag\""), EntityTagHeaderValue.Any },
+                };
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(NotEquivalentUnderWeakComparison))]
+        public void CompareUsingWeakComparison_NonEquivalentPairs_ReturnFalse(EntityTagHeaderValue left, EntityTagHeaderValue right)
+        {
+            Assert.False(left.Compare(right, useStrongComparison: false));
+            Assert.False(right.Compare(left, useStrongComparison: false));
+        }
+
+        public static TheoryData<EntityTagHeaderValue, EntityTagHeaderValue> EquivalentUnderWeakComparison
+        {
+            get
+            {
+                return new TheoryData<EntityTagHeaderValue, EntityTagHeaderValue>
+                {
+                    { new EntityTagHeaderValue("\"tag\""), new EntityTagHeaderValue("\"tag\"") },
+                    { new EntityTagHeaderValue("\"tag\"", true), new EntityTagHeaderValue("\"tag\"", true) },
+                    { new EntityTagHeaderValue("\"tag\""), new EntityTagHeaderValue("\"tag\"", true) },
+                };
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(EquivalentUnderWeakComparison))]
+        public void CompareUsingWeakComparison_EquivalentPairs_ReturnTrue(EntityTagHeaderValue left, EntityTagHeaderValue right)
+        {
+            Assert.True(left.Compare(right, useStrongComparison: false));
+            Assert.True(right.Compare(left, useStrongComparison: false));
+        }
+
         [Fact]
         public void Parse_SetOfValidValueStrings_ParsedCorrectly()
         {