Bug 425734

fish:// doesn't work here either, but I can connect flawlessly with sftp...

Same KDE / Dolphin version? My system is a just installed Neon.

Can't reproduce. I've downloaded the latest neon user edition ISO and can access the sftp://demo@demo.wftpserver.com:2222 URI just fine. What's more the sftp error makes no sense. We explicitly disable compression but according to the output that was pasted it's enabled. https://invent.kde.org/network/kio-extras/-/blob/master/sftp/kio_sftp.cpp#L614

Maybe try to get a verbose log https://community.kde.org/Guidelines_and_HOWTOs/Debugging/Debugging_IOSlaves/Debugging_kio_sftp#Logging_with_libssh_debug_output

This is the log:

log_kio_sftp: *** Starting kio_sftp 
log_kio_sftp: pid =  8323
log_kio_sftp: debug =  10
log_kio_sftp: "demo" @ "demo.wftpserver.com" : 2222
log_kio_sftp: 
log_kio_sftp: list directory:  QUrl("sftp://demo@demo.wftpserver.com:2222")
log_kio_sftp: checking cache: info.username = "demo" , info.url = "sftp://demo@demo.wftpserver.com:2222"
log_kio_sftp: Creating the SSH session and setting options
log_kio_sftp: [ ssh_config_parse_file ] ( 3 )  ssh_config_parse_file: Reading configuration data from /home/pavila/.ssh/config
log_kio_sftp: [ ssh_config_parse_line ] ( 1 )  ssh_config_parse_line: Unsupported option: ServerAliveInterval, line: 2
log_kio_sftp: [ ssh_config_parse_line ] ( 1 )  ssh_config_parse_line: Unsupported option: AddKeysToAgent, line: 3
log_kio_sftp: [ ssh_config_parse_line ] ( 2 )  ssh_config_parse_line: Unapplicable option: ForwardX11, line: 5
log_kio_sftp: [ ssh_config_parse_file ] ( 3 )  ssh_config_parse_file: Reading configuration data from /etc/ssh/ssh_config
log_kio_sftp: [ ssh_config_parse_line ] ( 2 )  ssh_config_parse_line: Unapplicable option: SendEnv, line: 50
log_kio_sftp: [ ssh_config_parse_line ] ( 1 )  ssh_config_parse_line: Unsupported option: HashKnownHosts, line: 51
log_kio_sftp: Trying to connect to the SSH server
log_kio_sftp: username= "demo" , host= "demo.wftpserver.com" , port= 2222
log_kio_sftp: [ ssh_connect ] ( 2 )  ssh_connect: libssh 0.9.3 (c) 2003-2019 Aris Adamantiadis, Andreas Schneider and libssh contributors. Distributed under the LGPL, please refer to COPYING file for information about your rights, using threading threads_pthread
log_kio_sftp: [ ssh_socket_connect ] ( 2 )  ssh_socket_connect: Nonblocking connection socket: 7
log_kio_sftp: [ ssh_connect ] ( 2 )  ssh_connect: Socket connecting, now waiting for the callbacks to work
log_kio_sftp: [ ssh_connect ] ( 3 )  ssh_connect: Actual timeout : 30000
log_kio_sftp: *** Starting kio_sftp 
log_kio_sftp: pid =  8327
log_kio_sftp: debug =  10
log_kio_sftp: "demo" @ "demo.wftpserver.com" : 2222
log_kio_sftp: 
log_kio_sftp: file system free space of QUrl("sftp://demo@demo.wftpserver.com:2222")
log_kio_sftp: checking cache: info.username = "demo" , info.url = "sftp://demo@demo.wftpserver.com:2222"
log_kio_sftp: Creating the SSH session and setting options
log_kio_sftp: [ ssh_config_parse_file ] ( 3 )  ssh_config_parse_file: Reading configuration data from /home/pavila/.ssh/config
log_kio_sftp: [ ssh_config_parse_line ] ( 1 )  ssh_config_parse_line: Unsupported option: ServerAliveInterval, line: 2
log_kio_sftp: [ ssh_config_parse_line ] ( 1 )  ssh_config_parse_line: Unsupported option: AddKeysToAgent, line: 3
log_kio_sftp: [ ssh_config_parse_line ] ( 2 )  ssh_config_parse_line: Unapplicable option: ForwardX11, line: 5
log_kio_sftp: [ ssh_config_parse_file ] ( 3 )  ssh_config_parse_file: Reading configuration data from /etc/ssh/ssh_config
log_kio_sftp: [ ssh_config_parse_line ] ( 2 )  ssh_config_parse_line: Unapplicable option: SendEnv, line: 50
log_kio_sftp: [ ssh_config_parse_line ] ( 1 )  ssh_config_parse_line: Unsupported option: HashKnownHosts, line: 51
log_kio_sftp: Trying to connect to the SSH server
log_kio_sftp: username= "demo" , host= "demo.wftpserver.com" , port= 2222
log_kio_sftp: [ ssh_connect ] ( 2 )  ssh_connect: libssh 0.9.3 (c) 2003-2019 Aris Adamantiadis, Andreas Schneider and libssh contributors. Distributed under the LGPL, please refer to COPYING file for information about your rights, using threading threads_pthread
log_kio_sftp: [ ssh_socket_connect ] ( 2 )  ssh_socket_connect: Nonblocking connection socket: 7
log_kio_sftp: [ ssh_connect ] ( 2 )  ssh_connect: Socket connecting, now waiting for the callbacks to work
log_kio_sftp: [ ssh_connect ] ( 3 )  ssh_connect: Actual timeout : 30000
log_kio_sftp: [ ssh_socket_pollcallback ] ( 4 )  ssh_socket_pollcallback: Poll callback on socket 7 (POLLOUT ), out buffer 0
log_kio_sftp: [ ssh_socket_pollcallback ] ( 3 )  ssh_socket_pollcallback: Received POLLOUT in connecting state
log_kio_sftp: [ socket_callback_connected ] ( 1 )  socket_callback_connected: Socket connection callback: 1 (0)
log_kio_sftp: [ ssh_socket_pollcallback ] ( 4 )  ssh_socket_pollcallback: Poll callback on socket 7 (POLLOUT ), out buffer 0
log_kio_sftp: [ ssh_socket_unbuffered_write ] ( 3 )  ssh_socket_unbuffered_write: Enabling POLLOUT for socket
log_kio_sftp: [ ssh_socket_pollcallback ] ( 3 )  ssh_socket_pollcallback: Received POLLOUT in connecting state
log_kio_sftp: [ socket_callback_connected ] ( 1 )  socket_callback_connected: Socket connection callback: 1 (0)
log_kio_sftp: [ ssh_socket_pollcallback ] ( 4 )  ssh_socket_pollcallback: Poll callback on socket 7 (POLLOUT ), out buffer 0
log_kio_sftp: [ ssh_socket_unbuffered_write ] ( 3 )  ssh_socket_unbuffered_write: Enabling POLLOUT for socket
log_kio_sftp: [ ssh_socket_pollcallback ] ( 4 )  ssh_socket_pollcallback: Poll callback on socket 7 (POLLOUT ), out buffer 0
log_kio_sftp: [ ssh_socket_pollcallback ] ( 4 )  ssh_socket_pollcallback: Poll callback on socket 7 (POLLIN ), out buffer 0
log_kio_sftp: [ callback_receive_banner ] ( 3 )  callback_receive_banner: Received banner: SSH-2.0-WingFTPServer
log_kio_sftp: [ ssh_client_connection_callback ] ( 2 )  ssh_client_connection_callback: SSH server banner: SSH-2.0-WingFTPServer
log_kio_sftp: [ ssh_analyze_banner ] ( 2 )  ssh_analyze_banner: Analyzing banner: SSH-2.0-WingFTPServer
log_kio_sftp: [ ssh_socket_pollcallback ] ( 4 )  ssh_socket_pollcallback: Poll callback on socket 7 (POLLIN ), out buffer 0
log_kio_sftp: [ callback_receive_banner ] ( 3 )  callback_receive_banner: Received banner: SSH-2.0-WingFTPServer
log_kio_sftp: [ ssh_client_connection_callback ] ( 2 )  ssh_client_connection_callback: SSH server banner: SSH-2.0-WingFTPServer
log_kio_sftp: [ ssh_analyze_banner ] ( 2 )  ssh_analyze_banner: Analyzing banner: SSH-2.0-WingFTPServer
log_kio_sftp: [ ssh_client_select_hostkeys ] ( 3 )  ssh_client_select_hostkeys: Order of wanted host keys: "ssh-ed25519,ecdsa-sha2-nistp521,ecdsa-sha2-nistp384,ecdsa-sha2-nistp256,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ssh-dss"
log_kio_sftp: [ ssh_client_select_hostkeys ] ( 3 )  ssh_client_select_hostkeys: Order of wanted host keys: "ssh-ed25519,ecdsa-sha2-nistp521,ecdsa-sha2-nistp384,ecdsa-sha2-nistp256,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ssh-dss"
log_kio_sftp: [ ssh_known_hosts_read_entries ] ( 1 )  ssh_known_hosts_read_entries: Failed to open the known_hosts file '/etc/ssh/ssh_known_hosts': No existe el archivo o el directorio
log_kio_sftp: [ ssh_client_select_hostkeys ] ( 3 )  ssh_client_select_hostkeys: Algorithms found in known_hosts files: "ecdsa-sha2-nistp256"
log_kio_sftp: [ ssh_client_select_hostkeys ] ( 3 )  ssh_client_select_hostkeys: Changing host key method to "ecdsa-sha2-nistp256,ssh-ed25519,ecdsa-sha2-nistp521,ecdsa-sha2-nistp384,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ssh-dss"
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: kex algos: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group18-sha512,diffie-hellman-group16-sha512,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1,ext-info-c
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: server host key algo: ecdsa-sha2-nistp256,ssh-ed25519,ecdsa-sha2-nistp521,ecdsa-sha2-nistp384,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ssh-dss
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: encryption client->server: aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,3des-cbc
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: encryption server->client: aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,3des-cbc
log_kio_sftp: [ ssh_known_hosts_read_entries ] ( 1 )  ssh_known_hosts_read_entries: Failed to open the known_hosts file '/etc/ssh/ssh_known_hosts': No existe el archivo o el directorio
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: mac algo client->server: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
log_kio_sftp: [ ssh_client_select_hostkeys ] ( 3 )  ssh_client_select_hostkeys: Algorithms found in known_hosts files: "ecdsa-sha2-nistp256"
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: mac algo server->client: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: compression algo client->server: zlib@openssh.com,zlib
log_kio_sftp: [ ssh_client_select_hostkeys ] ( 3 )  ssh_client_select_hostkeys: Changing host key method to "ecdsa-sha2-nistp256,ssh-ed25519,ecdsa-sha2-nistp521,ecdsa-sha2-nistp384,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ssh-dss"
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: compression algo server->client: zlib@openssh.com,zlib
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: languages client->server: 
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: kex algos: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group18-sha512,diffie-hellman-group16-sha512,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1,ext-info-c
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: languages server->client: 
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: server host key algo: ecdsa-sha2-nistp256,ssh-ed25519,ecdsa-sha2-nistp521,ecdsa-sha2-nistp384,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ssh-dss
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: encryption client->server: aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,3des-cbc
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: encryption server->client: aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,3des-cbc
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: mac algo client->server: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: mac algo server->client: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: compression algo client->server: zlib@openssh.com,zlib
log_kio_sftp: [ ssh_socket_unbuffered_write ] ( 3 )  ssh_socket_unbuffered_write: Enabling POLLOUT for socket
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: compression algo server->client: zlib@openssh.com,zlib
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: languages client->server: 
log_kio_sftp: [ packet_send2 ] ( 3 )  packet_send2: packet: wrote [type=20, len=980, padding_size=10, comp=969, payload=969]
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: languages server->client: 
log_kio_sftp: [ ssh_send_kex ] ( 3 )  ssh_send_kex: SSH_MSG_KEXINIT sent
log_kio_sftp: [ ssh_packet_socket_callback ] ( 3 )  ssh_packet_socket_callback: packet: read type 20 [len=804,padding=8,comp=795,payload=795]
log_kio_sftp: [ ssh_packet_process ] ( 3 )  ssh_packet_process: Dispatching handler for packet type 20
log_kio_sftp: [ ssh_socket_unbuffered_write ] ( 3 )  ssh_socket_unbuffered_write: Enabling POLLOUT for socket
log_kio_sftp: [ packet_send2 ] ( 3 )  packet_send2: packet: wrote [type=20, len=980, padding_size=10, comp=969, payload=969]
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: kex algos: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
log_kio_sftp: [ ssh_send_kex ] ( 3 )  ssh_send_kex: SSH_MSG_KEXINIT sent
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: server host key algo: ecdsa-sha2-nistp256,rsa-sha2-512,rsa-sha2-256,ssh-rsa
log_kio_sftp: [ ssh_packet_socket_callback ] ( 3 )  ssh_packet_socket_callback: packet: read type 20 [len=804,padding=8,comp=795,payload=795]
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: encryption client->server: aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,3des-cbc,chacha20-poly1305@openssh.com
log_kio_sftp: [ ssh_packet_process ] ( 3 )  ssh_packet_process: Dispatching handler for packet type 20
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: encryption server->client: aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,3des-cbc,chacha20-poly1305@openssh.com
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: kex algos: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: mac algo client->server: hmac-sha2-256,hmac-sha2-512,hmac-sha1,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: server host key algo: ecdsa-sha2-nistp256,rsa-sha2-512,rsa-sha2-256,ssh-rsa
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: mac algo server->client: hmac-sha2-256,hmac-sha2-512,hmac-sha1,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: encryption client->server: aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,3des-cbc,chacha20-poly1305@openssh.com
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: compression algo client->server: none
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: encryption server->client: aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,3des-cbc,chacha20-poly1305@openssh.com
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: mac algo client->server: hmac-sha2-256,hmac-sha2-512,hmac-sha1,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: compression algo server->client: none
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: mac algo server->client: hmac-sha2-256,hmac-sha2-512,hmac-sha1,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: languages client->server: 
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: compression algo client->server: none
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: languages server->client: 
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: compression algo server->client: none
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: languages client->server: 
log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: languages server->client: 
log_kio_sftp: [ ssh_kex_select_methods ] ( 1 )  ssh_kex_select_methods: kex error : no match for method compression algo client->server: server [none], client [zlib@openssh.com,zlib]
log_kio_sftp: [ ssh_kex_select_methods ] ( 1 )  ssh_kex_select_methods: kex error : no match for method compression algo client->server: server [none], client [zlib@openssh.com,zlib]
log_kio_sftp: [ ssh_connect ] ( 3 )  ssh_connect: current state : 9
log_kio_sftp: 
log_kio_sftp: [ ssh_connect ] ( 3 )  ssh_connect: current state : 9
log_kio_sftp:

I'm fairly certain there is something in either your .ssh/config or etc/ssh/ssh_config that messes with things. I can't reproduce this on a pristine neon install.

It could very well be a bug in libssh though.

One of the instances says
> log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: compression algo client->server: none
> ...
> log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: compression algo server->client: none
> ...
> log_kio_sftp: [ ssh_kex_select_methods ] ( 1 )  ssh_kex_select_methods: kex error : no match for method compression algo client->server: server [none], client [zlib@openssh.com,zlib]

Neither end was taking about zlib, yet somehow the internal kex list contained zlib.... Which may be because irritatingly almost at the beginning there was a connection being made with compression:

> log_kio_sftp: [ ssh_list_kex ] ( 4 )  ssh_list_kex: compression algo client->server: zlib@openssh.com,zlib

I do not see that being the case when using a new neon installation. So my best guess is that something in your config prompted libssh to connect with compression enabled and later getting confused about the kex list because there was a connection with compression and then there was one without.

You're right: I've removed the "Compression yes" line in my .ssh/config file and worked. It's a bit weird because in my Linux Mint Cinnamon computer this line is enabled and works fine.

Anyway it's working right now.

Thanks a lot.

Could still be a bug in libssh mind you. I'm not sure why it'd make a connection before we've configured the session though, must be some internal magic.