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      1 # gRPC Server Backward Compatibility Issues and Workarounds Management
      2 
      3 ## Introduction
      4 This document lists the workarounds implemented on gRPC servers for record and reference when users need to enable a certain workaround.
      5 
      6 ## Workaround List
      7 
      8 ### Cronet Compression
      9 
     10 **Workaround ID:** WORKAROUND\_ID\_CRONET\_COMPRESSION
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     12 **Date added:** May 06, 2017
     13 
     14 **Status:** Implemented in C core and C++
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     16 **Issue:** Before version v1.3.0-dev, gRPC iOS client's Cronet transport did not implement compression. However the clients still claim to support compression. As a result, a client fails to parse received message when the message is compressed.
     17 The problem above was resolved in gRPC v1.3.0-dev. For backward compatibility, a server must forcingly disable compression for gRPC clients of version lower than or equal to v1.3.0-dev.
     18 
     19 **Workaround Description:** Implemented as a server channel filter in C core.  The filter identifies the version of peer client with incoming `user-agent` header of each call. If the client's gRPC version is lower that or equal to v1.3.x, a flag GRPC_WRITE_NO_COMPRESS is marked for all send_message ops which prevents compression of the messages to be sent out.
     20