Refactor zlib tests and fix typo:

close #1744

* Fixed typo in enum name
* Added missing zlib error enumerator
* Marked caveat in zlib impl to avoid future confusion
* Created Compressor/Decompressor abstractions in Beast.zlib tests
* Applied abstractions on Beast.zlib tests
* Workaround Travis-CI' 10min silence timeout
* Add test for Beast.zlib's need_dict error
* Avoid breaking user-code dependant on deprecated enumerator interface

Signed-off-by: AeroStun <24841307+AeroStun@users.noreply.github.com>

include/boost/beast/zlib/detail/deflate_stream.ipp

@@ -399,7 +399,7 @@ doWrite(z_params& zs, boost::optional<Flush> flush, error_code& ec)
         }
     }
     else if(zs.avail_in == 0 && (
-            old_flush && flush <= *old_flush
+            old_flush && flush <= *old_flush // Caution: depends on enum order
         ) && flush != Flush::finish)
     {
         /* Make sure there is something to do and avoid duplicate consecutive

include/boost/beast/zlib/error.hpp

@@ -66,6 +66,17 @@ enum class error
     */
     end_of_stream,
 
+    /** Preset dictionary required
+
+        This error indicates that a preset dictionary was not provided and is now
+        needed at this point.
+
+        This does not always indicate a failure condition.
+
+        @note This is the same as `Z_NEED_DICT` returned by ZLib.
+    */
+    need_dict,
+
     /** Invalid stream or parameters.
 
         This error is returned when invalid parameters are passed,
@@ -95,7 +106,10 @@ enum class error
     too_many_symbols,
 
     /// Invalid code lengths
-    invalid_code_lenths,
+    invalid_code_lengths,
+#ifndef BOOST_BEAST_NO_DEPRECATED
+    invalid_code_lenths = invalid_code_lengths,
+#endif
 
     /// Invalid bit length repeat
     invalid_bit_length_repeat,

include/boost/beast/zlib/impl/error.ipp

@@ -62,12 +62,13 @@ public:
         {
         case error::need_buffers: return "need buffers";
         case error::end_of_stream: return "unexpected end of deflate stream";
+        case error::need_dict: return "need dict";
         case error::stream_error: return "stream error";
 
         case error::invalid_block_type: return "invalid block type";
         case error::invalid_stored_length: return "invalid stored block length";
         case error::too_many_symbols: return "too many symbols";
-        case error::invalid_code_lenths: return "invalid code lengths";
+        case error::invalid_code_lengths: return "invalid code lengths";
         case error::invalid_bit_length_repeat: return "invalid bit length repeat";
         case error::missing_eob: return "missing end of block code";
         case error::invalid_literal_length: return "invalid literal/length code";