Connection blocks main thread

[Nihildum]

For some reasons the use of dartssh2 blocks the main thread of my flutter application. This happens when I connect to the server and when I run a simple command on the server e.g. cat file.txt which is very small (like 100 characters). I run my application with a debugger and stopped it during the hangs. For the connection it seems that the loading of the ssh key takes quite some time, for the cat I not that sure.

Since dart has just one thread und there are no async calls in between, the main application hangs. Is there something I can to to prevent the hangs?

Connect to the server:
F (bcrypt.dart:1242)
Blowfish.encipher (bcrypt.dart:1154)
Blowfish.expand0state (bcrypt.dart:1193)
bcrypt_hash (bcrypt.dart:1267)
bcrypt_pbkdf (bcrypt.dart:1343)
OpenSSHKeyPairs._decryptPrivateKeyBlob (ssh_key_pair.dart:213)
OpenSSHKeyPairs.getPrivateKeys (ssh_key_pair.dart:138)
SSHKeyPair.fromPem (ssh_key_pair.dart:24)
ServerConnection._connect (connection.dart:23)

Run command cat:
int.+ (integers.dart:8)
TweetNaCl._M_off (tweetnacl.dart:1184)
TweetNaCl._M (tweetnacl.dart:803)
TweetNaCl.crypto_scalarmult (tweetnacl.dart:1394)
TweetNaCl.crypto_scalarmult_base (tweetnacl.dart:1416)
_ScalarMult.scalseMultBase (kex_x25519.dart:63)
new SSHKexX25519 (kex_x25519.dart:18)
SSHTransport._handleMessageKexInit (ssh_transport.dart:714)
SSHTransport._handleMessage (ssh_transport.dart:637)
SSHTransport._processPackets (ssh_transport.dart:317)
SSHTransport._processVersionExchange (ssh_transport.dart:300)
SSHTransport._processData (ssh_transport.dart:257)
SSHTransport._onSocketData (ssh_transport.dart:237)
_rootRunUnary (zone.dart:1434)
_CustomZone.runUnary (zone.dart:1335)
_CustomZone.runUnaryGuarded (zone.dart:1244)
_BufferingStreamSubscription._sendData (stream_impl.dart:341)
_BufferingStreamSubscription._add (stream_impl.dart:271)
_SyncStreamControllerDispatch._sendData (stream_controller.dart:774)
_StreamController._add (stream_controller.dart:648)
_StreamController.add (stream_controller.dart:596)
_Socket._onData (socket_patch.dart:2314)
_rootRunUnary (zone.dart:1442)
_CustomZone.runUnary (zone.dart:1335)
_CustomZone.runUnaryGuarded (zone.dart:1244)
_BufferingStreamSubscription._sendData (stream_impl.dart:341)
_BufferingStreamSubscription._add (stream_impl.dart:271)
_SyncStreamControllerDispatch._sendData (stream_controller.dart:774)
_StreamController._add (stream_controller.dart:648)
_StreamController.add (stream_controller.dart:596)
new _RawSocket. (socket_patch.dart:1839)
_NativeSocket.issueReadEvent.issue (socket_patch.dart:1322)
_microtaskLoop (schedule_microtask.dart:40)
_startMicrotaskLoop (schedule_microtask.dart:49)

[Nihildum]

P.S.: My ssh key is an 4096 RSA key. With https://pub.dev/packages/ssh2 I did not had these problem, but there the release version of my App was not working properly.

[xtyxtyx]

The algorithm used in encrypted private keys is bcrypt, which is a password hashing algorithm and is slow by design. You can use the compute function to move the computation to other isolates, as described in README.

[Nihildum]

Thanks for the answer. Using the compute to load the key solver the issue with the connection.

What do you mean in "bcrypt, which is a password hashing algorithm and is slow by design" with "slow by design". Slow in order to take long or slow because it needs a lot of computations?

Nevertheless, the application still hangs on the cat of the file.

[vanlooverenkoen]

@Nihildum did you find a solution? I have the same issue with any interaction of the package

[Nihildum]

I switched technology in my project. The ssh connection to the server was used in first prototype. When I implemented a real server with protobuf, I no longer neded the dartssh2 package.

[vanlooverenkoen]

Unfortunately I don't have that option

[vanlooverenkoen]

@xtyxtyx I am just using username & onPasswordRequest. Is there a way to prevent the main thread from blocking? Or do you have an idea on how we can prevent this in general?