sftp.NewClient returns an error "packet too long"

[chrplr]

In the following code, sftp.newclient() returns an error "packet too long". This is not simply a connection issue as I can open a ssh connection and use run to display execute a command on the remote server. Below, I have pasted code from dlv showing that the error arises from github.com/pkg/sftp.recvPacket() at line 272.

Passing the option sftp.MaxPacketChecked(1024) or not, has no effect.

I suspect it must be a silly problem in my code, not pkg/sftp, but I do not see the bug.

package main

import (
    "fmt"
    "log"
    "bytes"
    "github.com/pkg/sftp"
    "golang.org/x/crypto/ssh"
    "os"
)

type Params struct  {
    server string
    login string
    passwd string
}

var param = Params{"xxxx", "yyyy", "zzzz"}

func main() {

    config := &ssh.ClientConfig{
        User: param.login,
        Auth: []ssh.AuthMethod{
            ssh.Password(param.passwd),
        },
        HostKeyCallback: ssh.InsecureIgnoreHostKey(),
    }

    client, err := ssh.Dial("tcp", param.server, config)
    if err != nil {
        log.Fatalf("ssh.dial %s", err)
    }
    defer client.Close()

    session, err := client.NewSession()
    if err != nil {
        log.Fatalf("client.Newsession %s", err)
    }
    defer session.Close()

    var buff bytes.Buffer
    session.Stdout = &buff
    if err := session.Run("ls -la"); err != nil {
        log.Fatalf("session.Run %s", err)
    }
    fmt.Println(buff.String())

    sftp, err := sftp.NewClient(client, sftp.MaxPacketChecked(1024))
    if err != nil {
        log.Fatalf("sftp.newclient %s",err)
    }
    defer sftp.Close()

    srcPath := "AAAAAA"
    dstPath := "BBBBBB"

    // Open the source file
    srcFile, err := os.Open(srcPath)
    if err != nil {
        fmt.Println("open src ", err)
    }
    defer srcFile.Close()

    // Create the destination file
    dstFile, err := sftp.Create(dstPath)
    if err != nil {
        fmt.Println("sftp.Create ", err)
    }
    defer dstFile.Close()

    // write to file
    if _, err := dstFile.ReadFrom(srcFile); err != nil {
        fmt.Println("transf")
        fmt.Println(err)
    }

}

---

github.com/pkg/sftp.recvPacket() /home/cp983411/go/pkg/mod/github.com/pkg/sftp@v1.13.5/packet.go:272 (PC: 0x65512d) 267: } 268: if , err := io.ReadFull(r, b[:4]); err != nil { 269: return 0, nil, err 270: } 271: length, := unmarshalUint32(b) => 272: if length > maxMsgLength { 273: debug("recv packet %d bytes too long", length) 274: return 0, nil, errLongPacket 275: } 276: if length == 0 { 277: debug("recv packet of 0 bytes too short") (dlv) p b []uint8 len: 4, cap: 4, [32,95,95,95] (dlv) p length 543121247

[puellanivis]

Likely, what is happening is that the remote service is has so many extensions, that it oversteps the builtin 256 kibibyte maximum packet size of the packet reader.

[chrplr]

Thanks!

I did not configure sftp manually (I only installed opensshserver under linux ubuntu 20.04)

But I did something I should have tried before, that is, connect from the command line, and the issue is already there (see below). So it is indeed a problem with the configuration of the sftp server. Sorry for opening this issue. I close it. HAve a nice day.

PS: explanation => https://www.pcwdld.com/troubleshooting-received-message-too-long (The starter bash files need to be quiet to not interfere with the SFTP (or SCP2) protocol.). The problem was solved by adding [[ $- == *i* ]] || return on the first line of ~/.bashrc

> sftp localhost
The authenticity of host 'localhost (127.0.0.1)' can't be established.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added 'localhost' (ECDSA) to the list of known hosts.
xxxxxx@localhost's password: 
Received message too long 543121247