Validate custom HTTP method names

akka-http-core/src/main/scala/akka/http/impl/model/parser/CommonRules.scala

@@ -6,11 +6,11 @@ package akka.http.impl.model.parser
 
 import scala.collection.immutable
 import scala.collection.immutable.TreeMap
-
 import akka.http.scaladsl.model._
 import akka.http.scaladsl.model.headers._
 import akka.parboiled2._
 import akka.parboiled2.support.hlist._
+import akka.util.ConstantFun
 
 private[parser] trait CommonRules { this: Parser with StringBuilding =>
   protected def maxCommentParsingDepth: Int
@@ -465,7 +465,7 @@ private[parser] trait CommonRules { this: Parser with StringBuilding =>
     token ~> { s =>
       HttpMethods.getForKey(s) match {
         case Some(m) => m
-        case None    => HttpMethod.custom(s)
+        case None    => HttpMethod(s, isSafe = false, isIdempotent = false, requestEntityAcceptance = RequestEntityAcceptance.Expected, ConstantFun.anyToTrue)
       }
     }
   }

akka-http-core/src/main/scala/akka/http/scaladsl/model/HttpMethod.scala

@@ -48,13 +48,21 @@ object HttpMethod {
   // the allowsEntity condition was used to determine what responses provided the Content-Length header, before #4213 was fixed
   private def oldContentLengthCondition(status: StatusCode) = status.allowsEntity
 
+  // See:
+  //  https://www.rfc-editor.org/rfc/rfc9112.html#name-method
+  //  https://www.rfc-editor.org/rfc/rfc9110.html#name-tokens
+  private val httpMethodNameRegex = "[a-zA-Z0-9!#$%&'*+.^_`|~-]+".r
+
+  private def validateHttpMethodName(name: String): Unit =
+    require(httpMethodNameRegex.matches(name), "invalid HTTP method name")
+
   /**
    * Create a custom method type.
    * @deprecated The created method will compute the presence of Content-Length headers based on deprecated logic (before issue #4213).
    */
   @Deprecated
   def custom(name: String, safe: Boolean, idempotent: Boolean, requestEntityAcceptance: RequestEntityAcceptance): HttpMethod = {
-    require(name.nonEmpty, "value must be non-empty")
+    validateHttpMethodName(name)
     require(!safe || idempotent, "An HTTP method cannot be safe without being idempotent")
     apply(name, safe, idempotent, requestEntityAcceptance, oldContentLengthCondition)
   }
@@ -63,7 +71,7 @@ object HttpMethod {
    * Create a custom method type.
    */
   def custom(name: String, safe: Boolean, idempotent: Boolean, requestEntityAcceptance: RequestEntityAcceptance, contentLengthAllowed: Boolean): HttpMethod = {
-    require(name.nonEmpty, "value must be non-empty")
+    validateHttpMethodName(name)
     require(!safe || idempotent, "An HTTP method cannot be safe without being idempotent")
     // use constant functions so custom HttpMethod instances are equal (case class equality) when built with the same parameters
     apply(name, safe, idempotent, requestEntityAcceptance, if (contentLengthAllowed) ConstantFun.anyToTrue else ConstantFun.anyToFalse)

akka-http-core/src/test/scala/akka/http/scaladsl/model/HttpMethodSpec.scala

@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2009-2024 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package akka.http.scaladsl.model
+
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.wordspec.AnyWordSpec
+
+class HttpMethodSpec extends AnyWordSpec with Matchers {
+  "HttpMethod.custom()" should {
+    "accept a valid name" in {
+      HttpMethod.custom("Yes.Thi$_is_1~'VAL|D`_me+h*d-^ame!#%&")
+    }
+    "validate that an invalid character is not present" in {
+      an[Exception] should be thrownBy HttpMethod.custom("INJECT /path HTTP/1.1\r\n")
+      an[Exception] should be thrownBy HttpMethod.custom("INJECT\r\n")
+      an[Exception] should be thrownBy HttpMethod.custom("INJECT ")
+    }
+  }
+}