[system.net.http] The backslash character may be used as a single-character quoting mechanism within quoted-string. Fixes #39569

2 files changed, 20 insertions, 0 deletions

diff --git a/mcs/class/System.Net.Http/System.Net.Http.Headers/Lexer.cs b/mcs/class/System.Net.Http/System.Net.Http.Headers/Lexer.cs
index 694bf6e56e6..71df86877c6 100644
--- a/mcs/class/System.Net.Http/System.Net.Http.Headers/Lexer.cs
+++ b/mcs/class/System.Net.Http/System.Net.Http.Headers/Lexer.cs
@@ -313,6 +313,20 @@ namespace System.Net.Http.Headers
 					start = pos - 1;
 					while (pos < s.Length) {
 						ch = s [pos++];
+
+						//
+						// The backslash character ("\") MAY be used as a single-character
+   						// quoting mechanism only within quoted-string
+						//
+						if (ch == '\\') {
+							if (pos + 1 < s.Length) {
+								++pos;
+								continue;
+							}
+
+							break;
+						}
+
 						if (ch == '"') {
 							ttype = Token.Type.QuotedString;
 							break;
diff --git a/mcs/class/System.Net.Http/Test/System.Net.Http.Headers/EntityTagHeaderValueTest.cs b/mcs/class/System.Net.Http/Test/System.Net.Http.Headers/EntityTagHeaderValueTest.cs
index 78c267072bf..5099ce42551 100644
--- a/mcs/class/System.Net.Http/Test/System.Net.Http.Headers/EntityTagHeaderValueTest.cs
+++ b/mcs/class/System.Net.Http/Test/System.Net.Http.Headers/EntityTagHeaderValueTest.cs
@@ -74,6 +74,12 @@ namespace MonoTests.System.Net.Http.Headers
 			Assert.AreEqual ("\"mm\"", res.Tag, "#11");
 			Assert.IsTrue (res.IsWeak, "#12");
 			Assert.AreEqual ("W/\"mm\"", res.ToString (), "#13");
+
+
+			res = EntityTagHeaderValue.Parse ("\"\\\"123\\\"\"");
+			Assert.AreEqual ("\"\\\"123\\\"\"", res.Tag, "#21");
+			Assert.IsFalse (res.IsWeak, "#22");
+			Assert.AreEqual ("\"\\\"123\\\"\"", res.ToString (), "#23");
 		}
 
 		[Test]