fix: HTTP request smuggling via Transfer-Encoding token whitespace

Closes https://github.com/dart-lang/sdk/pull/63250

GitOrigin-RevId: 7c6b7bf7d033dd31dc23a7cc3a30b3dc4db41d16
Change-Id: I573328660bbef7ec9cd829ec376fcee894a6bc34
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/498420
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Slava Egorov <vegorov@google.com>

sdk/lib/_http/http_parser.dart

@@ -1112,20 +1112,31 @@ class _HttpParser extends Stream<_HttpIncoming> {
     value.length = length;
   }
 
+  static bool _isOWS(int c) {
+    return c == _CharCode.SP || c == _CharCode.HT;
+  }
+
   static List<String> _tokenizeFieldValue(String headerValue) {
+    int length = headerValue.length;
     List<String> tokens = <String>[];
+    // First non-OWS character of the token. Note that headerValue is already
+    // trimmed from start and end so we don't need to skip characters at start.
     int start = 0;
-    int index = 0;
-    while (index < headerValue.length) {
-      if (headerValue[index] == ",") {
-        tokens.add(headerValue.substring(start, index));
-        start = index + 1;
-      } else if (headerValue[index] == " " || headerValue[index] == "\t") {
+    while (start < length) {
+      int end = start + 1;
+      while (end < length && headerValue.codeUnitAt(end) != _CharCode.COMMA) {
+        end++;
+      }
+      int comma = end;
+      while (start < end && _isOWS(headerValue.codeUnitAt(end - 1))) {
+        end--;
+      }
+      tokens.add(headerValue.substring(start, end));
+      start = comma + 1;
+      while (start < length && _isOWS(headerValue.codeUnitAt(start))) {
         start++;
       }
-      index++;
     }
-    tokens.add(headerValue.substring(start, index));
     return tokens;
   }
 

tests/standalone/io/http_parser_test.dart

@@ -718,6 +718,27 @@ Content-Length: 38\r
 GET /admin HTTP/1.1\r\nHost: backend\r\n\r\n""";
     _testParseInvalidRequest(request);
 
+    // RFC 7230 section 3.2.6 forbids SP/HT inside a token. With the tokenizer
+    // treating "x chunked" as a single token (not "chunked"), the request has
+    // a Transfer-Encoding header whose final coding is not chunked, so it
+    // MUST be rejected (RFC 7230 section 3.3.3 rule 3) rather than falling
+    // back to Content-Length.
+    request = """
+POST /test HTTP/1.1\r
+Content-Length: 10\r
+Transfer-Encoding: x chunked\r
+\r
+0123456789""";
+    _testParseInvalidRequest(request);
+
+    request = """
+POST /test HTTP/1.1\r
+Content-Length: 10\r
+Transfer-Encoding: x\tchunked\r
+\r
+0123456789""";
+    _testParseInvalidRequest(request);
+
     // Content-Length and "Transfer-Encoding: chunked" are specified.
     request = """
 POST /test HTTP/1.1\r