add client_max_body_size config directive

Since Rainbows! is supported when exposed directly to the
Internet, administrators may want to limit the amount of data a
user may upload in a single request body to prevent a
denial-of-service via disk space exhaustion.

This amount may be specified in bytes, the default limit being
1024*1024 bytes (1 megabyte).  To override this default, a user
may specify `client_max_body_size' in the Rainbows! block
of their server config file:

  Rainbows! do
    client_max_body_size 10 * 1024 * 1024
  end

Clients that exceed the limit will get a "413 Request Entity Too
Large" response if the request body is too large and the
connection will close.

For chunked requests, we have no choice but to interrupt during
the client upload since we have no prior knowledge of the
request body size.

1 files changed, 90 insertions, 0 deletions

diff --git a/lib/rainbows/max_body.rb b/lib/rainbows/max_body.rb
new file mode 100644
index 0000000..7450b2a
--- /dev/null
+++ b/lib/rainbows/max_body.rb
@@ -0,0 +1,90 @@
+# -*- encoding: binary -*-
+module Rainbows
+
+# middleware used to enforce client_max_body_size for TeeInput users,
+# there is no need to configure this middleware manually, it will
+# automatically be configured for you based on the client_max_body_size
+# setting
+class MaxBody < Struct.new(:app)
+
+  # this is meant to be included in Unicorn::TeeInput (and derived
+  # classes) to limit body sizes
+  module Limit
+    Util = Unicorn::Util
+
+    def initialize(socket, req, parser, buf)
+      self.len = parser.content_length
+
+      max = Rainbows.max_bytes # never nil, see MaxBody.setup
+      if len && len > max
+        socket.write(Const::ERROR_413_RESPONSE)
+        socket.close
+        raise IOError, "Content-Length too big: #{len} > #{max}", []
+      end
+
+      self.req = req
+      self.parser = parser
+      self.buf = buf
+      self.socket = socket
+      self.buf2 = ""
+      if buf.size > 0
+        parser.filter_body(buf2, buf) and finalize_input
+        buf2.size > max and raise IOError, "chunked request body too big", []
+      end
+      self.tmp = len && len < Const::MAX_BODY ? StringIO.new("") : Util.tmpio
+      if buf2.size > 0
+        tmp.write(buf2)
+        tmp.seek(0)
+        max -= buf2.size
+      end
+      @max_body = max
+    end
+
+    def tee(length, dst)
+      rv = _tee(length, dst)
+      if rv && ((@max_body -= rv.size) < 0)
+        $stderr.puts "#@max_body  TOO SMALL"
+        # make HttpParser#keepalive? => false to force an immediate disconnect
+        # after we write
+        parser.reset
+        throw :rainbows_EFBIG
+      end
+      rv
+    end
+
+  end
+
+  # this is called after forking, so it won't ever affect the master
+  # if it's reconfigured
+  def self.setup
+    Rainbows.max_bytes or return
+    case G.server.use
+    when :Rev, :EventMachine, :NeverBlock
+      return
+    when :Revactor
+      Rainbows::Revactor::TeeInput
+    else
+      Unicorn::TeeInput
+    end.class_eval do
+      alias _tee tee # can't use super here :<
+      remove_method :tee
+      remove_method :initialize if G.server.use != :Revactor # FIXME CODE SMELL
+      include Limit
+    end
+
+    # force ourselves to the outermost middleware layer
+    G.server.app = MaxBody.new(G.server.app)
+  end
+
+  # Rack response returned when there's an error
+  def err(env)
+    [ 413, [ %w(Content-Length 0), %w(Content-Type text/plain) ], [] ]
+  end
+
+  # our main Rack middleware endpoint
+  def call(env)
+    catch(:rainbows_EFBIG) { app.call(env) } || err(env)
+  end
+
+end # class
+end # module