Index: lib/net/http/header.rb
===================================================================
--- lib/net/http/header.rb	(revision 41241)
+++ lib/net/http/header.rb	(working copy)
@@ -258,6 +258,11 @@ module Net::HTTPHeader
 
   # Returns an Integer object which represents the HTTP Content-Length:
   # header field, or +nil+ if that field was not provided.
+  #
+  # For a response that has a gzip or deflate Content-Encoding the
+  # Content-Length will be updated with the decoded length after the body has
+  # been read.
+  #
   def content_length
     return nil unless key?('Content-Length')
     len = self['Content-Length'].slice(/\d+/) or
Index: lib/net/http/response.rb
===================================================================
--- lib/net/http/response.rb	(revision 41241)
+++ lib/net/http/response.rb	(working copy)
@@ -190,6 +190,9 @@ class Net::HTTPResponse
   #     end
   #   }
   #
+  # If the response has a gzip or deflate Content-Encoding the Content-Length
+  # will be updated with the decoded length after the body has been read.
+  #
   def read_body(dest = nil, &block)
     if @read
       raise IOError, "#{self.class}\#read_body called twice" if dest or block
@@ -222,6 +225,9 @@ class Net::HTTPResponse
   #     p res.body.object_id   # 538149362
   #   }
   #
+  # If the response has a gzip or deflate Content-Encoding the Content-Length
+  # will be updated with the decoded length after the body has been read.
+  #
   def body
     read_body()
   end
@@ -260,6 +266,7 @@ class Net::HTTPResponse
         yield inflate_body_io
       ensure
         inflate_body_io.finish
+        self['content-length'] = inflate_body_io.decoded_length
       end
     when 'none', 'identity' then
       self.delete 'content-encoding'
@@ -342,10 +349,16 @@ class Net::HTTPResponse
   class Inflater # :nodoc:
 
     ##
+    # Length of the decoded response body in bytes
+
+    attr_reader :decoded_length
+
+    ##
     # Creates a new Inflater wrapping +socket+
 
     def initialize socket
       @socket = socket
+      @decoded_length = 0
       # zlib with automatic gzip detection
       @inflate = Zlib::Inflate.new(32 + Zlib::MAX_WBITS)
     end
@@ -367,6 +380,7 @@ class Net::HTTPResponse
       block = proc do |compressed_chunk|
         @inflate.inflate(compressed_chunk) do |chunk|
           dest << chunk
+          @decoded_length += chunk.bytesize
         end
       end
 
Index: test/net/http/test_httpresponse.rb
===================================================================
--- test/net/http/test_httpresponse.rb	(revision 41241)
+++ test/net/http/test_httpresponse.rb	(working copy)
@@ -96,9 +96,11 @@ EOS
 
     if Net::HTTP::HAVE_ZLIB
       assert_equal nil, res['content-encoding']
+      assert_equal '5', res['content-length'], "Bug #8182"
       assert_equal 'hello', body
     else
       assert_equal 'deflate', res['content-encoding']
+      assert_equal '13', res['content-length'], "Bug #8182"
       assert_equal "x\x9C\xCBH\xCD\xC9\xC9\a\x00\x06,\x02\x15", body
     end
   end