hackney:send_body does not accept functions anymore

[tomekowal]

Hi!

Thanks for the update to 2.x!

I have a question that is not covered by the migration guide.

According to the guide, in the streaming body scenario :hackney.send_body should not require any changes in the code https://hexdocs.pm/hackney/2.0.1/migration.html#streaming-request

However, up until 1.25, this function accepted function without any arguments that evaluated either to {:ok, body} | {:error, error} https://github.com/benoitc/hackney/blob/1.25.0/src/hackney_request.erl#L190

Is this something that was removed on purpose and should be part of the migration guide or is it an omission and should be added back?

[benoitc]

this has been fixed in latest version normally. Sorry for that. also 3.0.1 have a unified api which also simplify streaming.

To stream a body: https://hexdocs.pm/hackney/migration.html#streaming-request-body

[tomekowal]

No need to apologise! Thank you for the great library and quick response!

[tomekowal]

Hi! I might have been too quick closing the issue. Sorry for that.

I tried today 3.0.2 with the code I was using in 1.25.0

{:ok, conn_pid} = :hackney.request(:post, "http://localhost:5080/post", [], :stream, [])
:hackney.send_body(conn_pid, fn -> {:error, :fake_error} end)

and I got:

2026-02-15 11:15:20.800 [error] :gen_statem #PID<0.317.0> terminating
** (FunctionClauseError) no function clause matching in :hackney_conn.encode_chunk/1
    (hackney 3.0.2) /Users/tomaszkowal/bluecodecom/tesla/deps/hackney/src/hackney_conn.erl:1699: :hackney_conn.encode_chunk(#Function<43.81571850/0 in :erl_eval.expr/6>)
    (hackney 3.0.2) /Users/tomaszkowal/bluecodecom/tesla/deps/hackney/src/hackney_conn.erl:1044: :hackney_conn.streaming_body/3
    (stdlib 6.2.2) gen_statem.erl:3735: :gen_statem.loop_state_callback/11
    (stdlib 6.2.2) proc_lib.erl:329: :proc_lib.init_p_do_apply/3
Queue: [{{:call, {#PID<0.315.0>, #Reference<0.3974103028.3972792321.181559>}}, {:send_body_chunk, #Function<43.81571850/0 in :erl_eval.expr/6>}}]
Postponed: []
State: {:streaming_body, {:conn_data, #PID<0.315.0>, #Reference<0.3974103028.3972792321.181203>, ~c"localhost", 5080, "localhost:5080", :hackney_tcp, #Port<0.8>, "", 8000, :infinity, 2000, [], [], :undefined, false, #PID<0.316.0>, :undefined, :undefined, "POST", "/post", :undefined, :undefined, :undefined, :undefined, :undefined, :undefined, false, :undefined, :undefined, false, false, false, :http1, :undefined, %{}, false, :undefined, %{}, :undefined, false}}
Callback mode: :state_functions, state_enter: true
Client #PID<0.315.0> is alive

    (stdlib 6.2.2) gen.erl:241: :gen.do_call/4
    (stdlib 6.2.2) gen_statem.erl:3250: :gen_statem.call/3
    (elixir 1.19.5) src/elixir.erl:371: :elixir.eval_external_handler/3
    (stdlib 6.2.2) erl_eval.erl:919: :erl_eval.do_apply/7
    (elixir 1.19.5) src/elixir.erl:349: :elixir.eval_forms/4
    (elixir 1.19.5) lib/module/parallel_checker.ex:155: Module.ParallelChecker.verify/1
    (iex 1.19.5) lib/iex/evaluator.ex:344: IEx.Evaluator.eval_and_inspect/3
    (iex 1.19.5) lib/iex/evaluator.ex:316: IEx.Evaluator.safe_eval_and_inspect/3
** (exit) exited in: :gen_statem.call(#PID<0.317.0>, {:send_body_chunk, #Function<43.81571850/0 in :erl_eval.expr/6>}, :infinity)
    ** (EXIT) an exception was raised:
        ** (FunctionClauseError) no function clause matching in :hackney_conn.encode_chunk/1
            (hackney 3.0.2) /Users/tomaszkowal/bluecodecom/tesla/deps/hackney/src/hackney_conn.erl:1699: :hackney_conn.encode_chunk(#Function<43.81571850/0 in :erl_eval.expr/6>)
            (hackney 3.0.2) /Users/tomaszkowal/bluecodecom/tesla/deps/hackney/src/hackney_conn.erl:1044: :hackney_conn.streaming_body/3
            (stdlib 6.2.2) gen_statem.erl:3735: :gen_statem.loop_state_callback/11
            (stdlib 6.2.2) proc_lib.erl:329: :proc_lib.init_p_do_apply/3
    (stdlib 6.2.2) gen.erl:247: :gen.do_call/4
    (stdlib 6.2.2) gen_statem.erl:3250: :gen_statem.call/3
    iex:3: (file)

in 1.25.0 there was this clause when streaming body
https://github.com/benoitc/hackney/blob/1.25.0/src/hackney_request.erl#L190

and in master it is stil unhandled
https://github.com/benoitc/hackney/blob/master/src/hackney_conn.erl#L1699