From d1345074584118aa7c56e6dde171502300b89ad7 Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Tue, 4 Aug 2026 16:09:22 +0900
Subject: [PATCH] Limit the number of informational responses per request

A peer that keeps sending 1xx responses keeps the client in the read
loop of transport_request indefinitely, since the per-response header
limit resets for each response. Cap the count at 100, the same value
CPython's http.client uses.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---
 lib/net/http.rb            |  6 ++++++
 lib/net/http/response.rb   |  4 ++++
 test/net/http/test_http.rb | 39 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/lib/net/http.rb b/lib/net/http.rb
index 6c43e62..4254cd9 100644
--- a/lib/net/http.rb
+++ b/lib/net/http.rb
@@ -2497,11 +2497,17 @@ def transport_request(req)
             # still read the received response.
           end
 
+          informational_count = 0
           begin
             res = HTTPResponse.read_new(@socket)
             res.decode_content = req.decode_content
             res.body_encoding = @response_body_encoding
             res.ignore_eof = @ignore_eof
+            if res.kind_of?(HTTPInformation)
+              informational_count += 1
+              raise Net::HTTPBadResponse, 'too many informational responses' if
+                informational_count > HTTPResponse::MAX_INFORMATIONAL_RESPONSES
+            end
           end while res.kind_of?(HTTPInformation)
 
           res.uri = req.uri
diff --git a/lib/net/http/response.rb b/lib/net/http/response.rb
index 0b5b326..31b35f9 100644
--- a/lib/net/http/response.rb
+++ b/lib/net/http/response.rb
@@ -136,6 +136,10 @@ class Net::HTTPResponse
   # The maximum total size in bytes of the response header.
   MAX_RESPONSE_HEADER_LENGTH = 1024 * 1024 # 1 MiB
 
+  # The maximum number of informational (1xx) responses accepted before the
+  # final response.
+  MAX_INFORMATIONAL_RESPONSES = 100
+
   class << self
     # true if the response has a body.
     def body_permitted?
diff --git a/test/net/http/test_http.rb b/test/net/http/test_http.rb
index e5028d4..bbce847 100644
--- a/test/net/http/test_http.rb
+++ b/test/net/http/test_http.rb
@@ -1171,6 +1171,45 @@ def test_info
   end
 end
 
+class TestNetHTTPInformationalResponses < Test::Unit::TestCase
+  CONFIG = {
+    'host' => '127.0.0.1',
+    'proxy_host' => nil,
+    'proxy_port' => nil,
+  }
+
+  include TestNetHTTPUtils
+
+  def logfile
+    @debug = StringIO.new('')
+  end
+
+  def mount_proc(count)
+    @server.mount('/info', proc {|req, res|
+      socket = req.instance_variable_get(:@socket)
+      count.times { socket << "HTTP/1.1 100 Continue\r\n\r\n" }
+      res.body = 'BODY'
+    })
+  end
+
+  def test_informational_responses
+    mount_proc 3
+    start {|http|
+      res = http.get('/info')
+      assert_equal('BODY', res.body)
+    }
+  end
+
+  def test_too_many_informational_responses
+    mount_proc Net::HTTPResponse::MAX_INFORMATIONAL_RESPONSES + 1
+    start {|http|
+      assert_raise(Net::HTTPBadResponse) {
+        http.get('/info')
+      }
+    }
+  end
+end
+
 class TestNetHTTPKeepAlive < Test::Unit::TestCase
   CONFIG = {
     'host' => '127.0.0.1',