当应用程序进入后台时，在 iOS 设备的 Flutter 应用程序上发布请求失败

Question

I am requesting a post call from my flutter application.

 try {
      String token = await getToken();
      Map<String, String> headers = {
        'Content-Type': 'application/json',
        'Authorization': token
      };
      response = await http
          .post(encodedUri, headers: headersAuth ?? headers, body: requestBody)
          .timeout(const Duration(seconds: timeout));
    } on SocketException {
      Log.logError('Socket Error while calling post API');
      throw FetchDataException('No Internet Connection');
    } catch (e, s) { 
      throw FetchDataException('Error while calling post call');
    }

User has the option to put the application in background after doing this call. While doing that call I am getting error like this from dart IOClient

Error: Bad file descriptor

The stack trace is following

#0      IOClient.send (package:http/src/io_client.dart:66)
<asynchronous suspension>
#1      BaseClient._sendUnstreamed (package:http/src/base_client.dart:93)
<asynchronous suspension>
#2      _withClient (package:http/http.dart:164)
<asynchronous suspension>
#3      Future.timeout.<anonymous closure> (dart:async/future_impl.dart:870)
<asynchronous suspension>
#4      ApiService.post (package:fdgv2/services/api_service.dart:121)
<asynchronous suspension>

This is happening only for release build not in debug build. On xcode console following more errors are thrown.

2022-08-02 15:53:35.039710+0530 Runner[8357:850399] [connection] nw_read_request_report [C14] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.041675+0530 Runner[8357:850399] [connection] nw_read_request_report [C14] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.044130+0530 Runner[8357:850403] flutter: Info: 8/2/2022 3:53 PM - Formulas ran on reading launch
2022-08-02 15:53:35.048650+0530 Runner[8357:850399] [connection] nw_read_request_report [C1] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.051303+0530 Runner[8357:850399] [connection] nw_read_request_report [C1] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.055034+0530 Runner[8357:850399] [connection] nw_read_request_report [C3] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.056821+0530 Runner[8357:850403] flutter: Cancel succeeded for Operation: 7f32f82e-526b-43c3-97cf-3ace22894c40
2022-08-02 15:53:35.057394+0530 Runner[8357:850399] [connection] nw_read_request_report [C3] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.058136+0530 Runner[8357:850403] flutter: Cancel succeeded for Operation: db013087-d948-45ce-a43e-374b0d9ae0c3
2022-08-02 15:53:35.063756+0530 Runner[8357:850399] [connection] nw_read_request_report [C18] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.064509+0530 Runner[8357:850399] [connection] nw_read_request_report [C18] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.066183+0530 Runner[8357:850399] [connection] nw_read_request_report [C18] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.071824+0530 Runner[8357:850399] [connection] nw_read_request_report [C11] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.077681+0530 Runner[8357:850399] [connection] nw_read_request_report [C11] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.080873+0530 Runner[8357:850399] [connection] nw_read_request_report [C8] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.081923+0530 Runner[8357:850399] [connection] nw_read_request_report [C8] Receive failed with error "Socket is not connected"
2022-08-02 15:53:35.085330+0530 Runner[8357:850399] [connection] nw_read_request_report [C17] Receive failed with error "Software caused connection abort"
2022-08-02 15:53:35.086249+0530 Runner[8357:850399] [connection] nw_read_request_report [C13] Receive failed with error "Software caused connection abort"
2022-08-02 15:53:35.088127+0530 Runner[8357:850399] [] nw_flow_service_writes Failing write request <nw_write_request> [57: Socket is not connected]
2022-08-02 15:53:35.144915+0530 Runner[8357:850399] [connection] nw_write_request_report [C18] Send failed with error "Socket is not connected"
2022-08-02 15:53:35.199598+0530 Runner[8357:850399] Connection 18: write error 1:57
2022-08-02 15:53:35.208024+0530 Runner[8357:850399] [quic] quic_send_frames_for_key_state_block_invoke [C14.1.1:2] [-c95faba0f1ce339c] unable to request outbound data
2022-08-02 15:53:35.226047+0530 Runner[8357:850399] [quic] quic_send_frames_for_key_state_block_invoke [C1.1.1:2] [-c5ccd1eb1de55d67] unable to request outbound data
2022-08-02 15:53:35.263606+0530 Runner[8357:850399] [quic] quic_send_frames_for_key_state_block_invoke [C3.1.1:2] [-1e6494b1e41a8c90] unable to request outbound data
2022-08-02 15:53:35.266920+0530 Runner[8357:850399] [quic] quic_send_frames_for_key_state_block_invoke [C18.1.1:2] [-3326233f689377a5] unable to request outbound data
2022-08-02 15:53:35.267424+0530 Runner[8357:850399] [quic] quic_send_frames_for_key_state_block_invoke [C18.1.1:2] [-3326233f689377a5] unable to request outbound data
2022-08-02 15:53:35.293100+0530 Runner[8357:850399] [quic] quic_send_frames_for_key_state_block_invoke [C11.1.1:2] [-726354f32e176e2e] unable to request outbound data
2022-08-02 15:53:35.330543+0530 Runner[8357:850399] [quic] quic_send_frames_for_key_state_block_invoke [C8.1.1:2] [-886b86481a89ccec] unable to request outbound data
2022-08-02 15:53:35.341767+0530 Runner[8357:850399] Task <D40EAFA0-D987-4A96-9076-CFD41D41C68A>.<2> HTTP load failed, 1150/0 bytes (error code: -1005 [1:57])
2022-08-02 15:53:35.347143+0530 Runner[8357:850399] Connection 18: received failure notification
2022-08-02 15:53:35.354038+0530 Runner[8357:850399] [connection] nw_endpoint_handler_unregister_context [C18.1.1 34.107.204.85:443 failed channel-flow (satisfied (Path is satisfied), viable, interface: en0, ipv4, ipv6, dns)] Cannot unregister after flow table is released
2022-08-02 15:53:35.354133+0530 Runner[8357:850415] Task <D40EAFA0-D987-4A96-9076-CFD41D41C68A>.<2> finished with error [-1005] Error Domain=NSURLErrorDomain Code=-1005 "The network connection was lost." UserInfo={_kCFStreamErrorCodeKey=57, NSUnderlyingError=0x280111f50 {Error Domain=kCFErrorDomainCFNetwork Code=-1005 "(null)" UserInfo={NSErrorPeerAddressKey=<CFData 0x282d578e0 [0x1f475c1b8]>{length = 16, capacity = 16, bytes = 0x100201bb226bcc550000000000000000}, _kCFStreamErrorCodeKey=57, _kCFStreamErrorDomainKey=1}}, _NSURLErrorFailingURLSessionTaskErrorKey=LocalDataTask <D40EAFA0-D987-4A96-9076-CFD41D41C68A>.<2>, _NSURLErrorRelatedURLSessionTaskErrorKey=(
    "LocalDataTask <D40EAFA0-D987-4A96-9076-CFD41D41C68A>.<2>"
), NSLocalizedDescription=The network connection was lost., NSErrorFailingURLStringKey=https://data.pendo.io/v2/devices/analyticsData, NSErrorFailingURLKey=https://data.pendo.io/v2/devices/analyticsData, _kCFStreamErrorDomainKey=1}
2022-08-02 15:53:41.320830+0530 Runner[8357:850403] flutter: Info: 8/2/2022 3:53 PM - App on inactive mode by user
2022-08-02 15:53:41.321376+0530 Runner[8357:850403] flutter: Info: 8/2/2022 3:53 PM - Closing current reading
2022-08-02 15:53:41.326543+0530 Runner[8357:850403] flutter: Info: 8/2/2022 3:53 PM - Current Reading closed
2022-08-02 15:53:41.329393+0530 Runner[8357:850403] flutter: Info: 8/2/2022 3:53 PM - Initialized formula and carry forward manager
2022-08-02 15:53:41.330445+0530 Runner[8357:850403] flutter: Info: 8/2/2022 3:53 PM - Reading updated with data for 2022-08-01
2022-08-02 15:53:41.330958+0530 Runner[8357:850403] flutter: Info: 8/2/2022 3:53 PM - Attribute View Model updated with data from Attribute Presenter Model
2022-08-02 15:53:41.340179+0530 Runner[8357:850403] flutter: Info: 8/2/2022 3:53 PM - Formulas ran on reading launch
2022-08-02 15:53:41.340451+0530 Runner[8357:850403] flutter: called dismiss
2022-08-02 15:53:41.341208+0530 Runner[8357:850403] flutter: Error: 8/2/2022 3:53 PM - Error while calling Post API https://api-fdg-qa.joynai.net/mobile/api/rpc/readingdata/interpolate 
Error: Bad file descriptor 

Strangely enough, if do a get call and put the iOS device in background it is still getting successful. But for post call I am getting this error. Can any one please help me with this?

Answer 1

As you might know, connections between clients and servers are usually kept alive up to x amount of time. What Bad file descriptor means is that your device thinks the connection is still alive and it's trying to perform a call within a connection which at some point in time was closed.

I am no expert, but my guess is that when the app is put in background all connections get closed. This doesn't necessarily mean you can't perform any call with the app in background.

Long story short, this might be a race-condition issue: your app is trying to perform a call with a broken state (Thinking a connection is still in used). Try to delay the call by X amount of milliseconds, this will allow the app to understand that your last connection closed and it will need to open a new one to perform that specific call.