Always obeys BalsaFrame::invalid_chars_level_ when parsing header fields.

The usage of HttpValidationPolicy::disallow_invalid_header_characters_in_response() in BalsaFrame is redundant: the only place it is set to true is in Envoy, which also sets InvalidCharsLevel::kError for responses.

Protected by no functional change; not protected.

PiperOrigin-RevId: 655623266

quiche/balsa/balsa_frame.cc

diff --git a/quiche/balsa/balsa_frame.cc b/quiche/balsa/balsa_frame.cc
index d88e0e9..75fc510 100644
--- a/quiche/balsa/balsa_frame.cc
+++ b/quiche/balsa/balsa_frame.cc
@@ -675,13 +675,10 @@
   QUICHE_DCHECK(!lines.empty());
   QUICHE_DVLOG(1) << "******@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@**********\n";
 
-  if (is_request() ||
-      http_validation_policy().disallow_invalid_header_characters_in_response) {
-    if (invalid_chars_error_enabled() &&
-        CheckHeaderLinesForInvalidChars(lines, headers)) {
-      HandleError(BalsaFrameEnums::INVALID_HEADER_CHARACTER);
-      return;
-    }
+  if (invalid_chars_error_enabled() &&
+      CheckHeaderLinesForInvalidChars(lines, headers)) {
+    HandleError(BalsaFrameEnums::INVALID_HEADER_CHARACTER);
+    return;
   }
 
   // There is no need to attempt to process headers (resp. trailers)

quiche/balsa/balsa_frame_test.cc

diff --git a/quiche/balsa/balsa_frame_test.cc b/quiche/balsa/balsa_frame_test.cc
index 6a048a9..0d98476 100644
--- a/quiche/balsa/balsa_frame_test.cc
+++ b/quiche/balsa/balsa_frame_test.cc
@@ -3999,7 +3999,7 @@
 
 TEST_F(HTTPBalsaFrameTest, InvalidCharsInResponseHeaderAllowed) {
   balsa_frame_.set_is_request(false);
-  balsa_frame_.set_invalid_chars_level(BalsaFrame::InvalidCharsLevel::kError);
+  balsa_frame_.set_invalid_chars_level(BalsaFrame::InvalidCharsLevel::kOff);
 
   const absl::string_view headers =
       "HTTP/1.1 200 OK\r\n"
@@ -4017,10 +4017,6 @@
   balsa_frame_.set_is_request(false);
   balsa_frame_.set_invalid_chars_level(BalsaFrame::InvalidCharsLevel::kError);
 
-  HttpValidationPolicy http_validation_policy;
-  http_validation_policy.disallow_invalid_header_characters_in_response = true;
-  balsa_frame_.set_http_validation_policy(http_validation_policy);
-
   const absl::string_view headers =
       "HTTP/1.1 200 OK\r\n"
       "Content-Length: 5\r\n"

quiche/balsa/http_validation_policy.h

diff --git a/quiche/balsa/http_validation_policy.h b/quiche/balsa/http_validation_policy.h
index e26f2f2..33cdf7b 100644
--- a/quiche/balsa/http_validation_policy.h
+++ b/quiche/balsa/http_validation_policy.h
@@ -49,6 +49,7 @@
   // the character '"'.
   bool disallow_double_quote_in_header_name = false;
 
+  // TODO(b/314138604): remove this field once upstream Envoy stops using it
   // If true, then signal an INVALID_HEADER_CHARACTER warning or error, or
   // neither, depending on InvalidCharsLevel, if a response header contains an
   // invalid character. Invalid characters are always disallowed according to