objective c - Exception `-[NSConcreteFileHandle readDataOfLength:]: Bad file descriptor` when running a NSUserUnixTask -

i'm using nsuserunixtask run unsandboxed nstask on sandboxed app. however, code hangs on calls [nsfilehandle readdatatoendoffile]. if remove calls works perfectly. if replace [nsfilehandle readdatatoendoffile] [nsfilehandle availabledata] hangs well.

here code:

nsuserunixtask* unixtask = [[nsuserunixtask alloc] initwithurl: [nsurl fileurlwithpath: path] error: nil];  // create error file handle nsfilehandle* errorfh = [nsfilehandle filehandlewithstandarderror]; [unixtask setstandarderror: errorfh];  // create output file handle nsfilehandle* outputfh = [nsfilehandle filehandlewithstandardoutput]; [unixtask setstandardoutput: outputfh];  // run task termination handler [unixtask executewitharguments: nil completionhandler: ^(nserror* error2) {      // save output     nsstring* output = [[nsstring alloc] initwithdata: [outputfh readdatatoendoffile] encoding: nsutf8stringencoding];     if ([output length]) { // <-- execution never reaches line when block called         nslog(@"%@", output);     }      // read error 1     nsstring* error1 = [[nsstring alloc] initwithdata: [errorfh readdatatoendoffile] encoding: nsutf8stringencoding];     if ([error1 length]) {         nslog(@"%@", error1);     }      // read error 2     if (error2) {         nslog(@"%@", error2);     } }]; 

nothing logged on xcode's console, if open console.app see line:

warning: exception caught during decoding of received reply message 'executescript:interpreter:arguments:standardinput:standardoutput:standarderror::', dropping incoming message , calling failure block.  exception: *** -[nsconcretefilehandle readdataoflength:]: bad file descriptor 

hmmm, how can solve this? before had app sandboxed used nspipe in conjunction nstask , worked, nsuserunixtask requires use of nsfilehandle instead , reckon problem because i'm not using correctly. still have no idea i'm doing wrong.

it seems me have use nspipe read stderr , stdout nsuserunixtask in same way done nstask.

i have tested "/bin/ls" task , produced expected output:

nspipe *outpipe = [nspipe pipe]; nspipe *errpipe = [nspipe pipe]; nsstring *path = @"/bin/ls"; nsuserunixtask *unixtask = [[nsuserunixtask alloc] initwithurl: [nsurl fileurlwithpath: path] error: nil]; [unixtask setstandardoutput:[outpipe filehandleforwriting]]; [unixtask setstandarderror:[errpipe filehandleforwriting]]; [unixtask executewitharguments:nil completionhandler:^(nserror *error) {     nsstring *output = [[nsstring alloc] initwithdata: [[outpipe filehandleforreading] readdatatoendoffile] encoding: nsutf8stringencoding];     nslog(@"stdout: %@", output);      nsstring *error1 = [[nsstring alloc] initwithdata: [[errpipe filehandleforreading] readdatatoendoffile] encoding: nsutf8stringencoding];     nslog(@"stderr: %@", error1); }];