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Entry  04 Jun 2025, Mark Grimes, Bug Report, Memory leak in mhttpd binary RPC code 
    Reply  04 Jun 2025, Konstantin Olchanski, Bug Report, Memory leak in mhttpd binary RPC code 
       Reply  07 Jun 2025, Mark Grimes, Bug Report, Memory leak in mhttpd binary RPC code msysmon-mu3ebe-20250601-042124-20250606-122124.png
Message ID: 3049     Entry time: 04 Jun 2025     Reply to this: 3050
Author: Mark Grimes 
Topic: Bug Report 
Subject: Memory leak in mhttpd binary RPC code 
Hi,
During an evening of running we noticed that memory usage of mhttpd grew to close to 100Gb. We think we've traced this to the following issue when making RPC calls.

  • The brpc method allocates memory for the response at src/mjsonrpc.cxx#lines-3449.
  • It then makes the call at src/mjsonrpc.cxx#lines-3460, which may set `buf_length` to zero if the response was empty.
  • It then uses `MJsonNode::MakeArrayBuffer` to pass ownership of the memory to an `MJsonNode`, providing `buf_length` as the size.
  • When the `MJsonNode` is destructed at mjson.cxx#lines-657, it only calls `free` on the buffer if the size is greater than zero.

Hence, mhttpd will leak at least 1024 bytes for every binary RPC call that returns an empty response.
I tried to submit a pull request to fix this but I don't have permission to push to https://bitbucket.org/tmidas/mjson.git. Could somebody take a look?

Thanks,

Mark.
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