Issue #13396 has been updated by naruse (Yui NARUSE).


I just noticed that just use write_nonblock can solve this ticket:

```diff
diff --git a/lib/net/protocol.rb b/lib/net/protocol.rb
index 7ec636b384..2a806caeb6 100644
--- a/lib/net/protocol.rb
+++ b/lib/net/protocol.rb
@@ -77,6 +77,12 @@ class OpenTimeout            < Timeout::Error; end
 
   class ReadTimeout            < Timeout::Error; end
 
+  ##
+  # WriteTimeout, a subclass of Timeout::Error, is raised if a chunk of the
+  # response cannot be read within the read_timeout.
+
+  class WriteTimeout            < Timeout::Error; end
+
 
   class BufferedIO   #:nodoc: internal use only
     def initialize(io, read_timeout: 60, continue_timeout: nil, debug_output: nil)
@@ -237,9 +243,32 @@ def writing
 
     def write0(*strs)
       @debug_output << strs.map(&:dump).join if @debug_output
-      len = @io.write(*strs)
-      @written_bytes += len
-      len
+      case len = @io.write_nonblock(*strs, exception: false)
+      when Integer
+        orig_len = len
+        strs.each_with_index do |str, i|
+          len -= str.bytesize
+          if len == 0
+            if strs.size == i+1
+              @written_bytes += orig_len
+              return orig_len
+            else
+              strs = strs[i+1..] # rest
+              break
+            end
+          elsif len < 0
+            strs = strs[i..] # str and rest
+            strs[0] = str[len, -len]
+            break
+          else # len > 0
+            # next
+          end
+        end
+        # continue looping
+      when :wait_writable
+        @io.to_io.wait_writable(@write_timeout) or raise Net::ReadTimeout
+        # continue looping
+      end while true
     end
 
     #
```

----------------------------------------
Feature #13396: Net::HTTP has no write timeout
https://bugs.ruby-lang.org/issues/13396#change-72348

* Author: byroot (Jean Boussier)
* Status: Assigned
* Priority: Normal
* Assignee: naruse (Yui NARUSE)
* Target version: 
----------------------------------------
When sending a large request to an unresponsive server, `Net::HTTP` can hang pretty much forever.

```ruby
# server.rb
require 'socket'

server = TCPServer.new('localhost', 2345)
loop do
  socket = server.accept
end

```

```ruby
# client.rb
require 'net/http'

connection = Net::HTTP.new('localhost', 2345)
connection.open_timeout = 1
connection.read_timeout = 3
connection.start

post = Net::HTTP::Post.new('/')
body = (('a' * 1023) + "\n") * 5_000
post.body = body

puts "Sending #{body.bytesize} bytes"
connection.request(post)
```

The above code will hang forever on all system I tested it on (OSX / Linux 3.19).

The issue only trigger once the request body is above a certain threshold. That threshold depends on the system, I assume it's due to the system's TCP settings, but a request over 4MB will trigger the issue consistently.

I assume it happens when the request is bigger than the socket buffer. 

It's stuck on the following path:

```
/net/protocol.rb:211:in `write': Interrupt
/net/protocol.rb:211:in `write0'
/net/protocol.rb:185:in `block in write'
/net/protocol.rb:202:in `writing'
/net/protocol.rb:184:in `write'
/net/http/generic_request.rb:188:in `send_request_with_body'
/net/http/generic_request.rb:121:in `exec'
/net/http.rb:1435:in `block in transport_request'
/net/http.rb:1434:in `catch'
/net/http.rb:1434:in `transport_request'
/net/http.rb:1407:in `request'
```

I tried setting `setsockopt(Socket::SOL_SOCKET, Socket::SO_SNDTIMEO, ...)` on the client socket, but without success. However adding a `Timeout.timeout` call around `req.exec` did work.



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