ssl - erlang socket send timeout never happens -


i implementing tcp server in erlang talks mobile phone clients. mobile phones offline lot, server must able detect it. hence want server send messages clients timeout, when timeout happens connection closed , client marked offline.

i used listen option on server:

[{certfile, "cert.pem"},     {keyfile, "key.pem"},  {reuseaddr, true},     {active, false},  {send_timeout, 10000}]

after set connection between server , mobile phone, switch phone airplane mode(which shuts down wireless signals), , ssl:send on server. send function happliy returned ok if packet transmitted.

what have done wrong?

did set {send_timeout_close, true} parameter on socket inet? if not, socket won't closed, return timeout error. there risk ssl swallows error , it.

some other points:

  • remember check return value of ssl:send , ssl:receive options error. important know send went well.

    ok = ssl:send(sock, data),

  • the underlying tcp/ip stack might accept data send_timeout set, won't able send other endpoint down. knowledge of closed port first arrives later on, when stack realizes never got ack.

  • there raw entry type sockets, defined in inet. allows set os-specific socket options. may possible coerce os being more aggressive @ detecting loss of connection.

  • another option cue on ssl:recv/3 call timeout signifies loss of device, regardless of socket status. has advantage of detecting application trouble in other end not progress along determined path. have processing further requests anyway.

  • the mobile phone client can act. if send's message on ssl , receive never arrives (due airplane mode) - knows wrong. server may not know however.

  • tcp/ip provides reliable, connection-oriented stream protocol. not guard against sudden disconnects. important protocol must handle disconnect problem itself. important if protocol has kind of confirmation or acknowledgement.


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