java - 如何在我的 FTP 服务器中实现对 EPSV (ALL) 命令的 react ？

Question

我正在尝试通过 Wi-Fi 在本地网络上用 Java 设置 FTP 服务器。我一直在处理 EPSV ALL 命令。作为客户，我在 iPhone 上使用 VLC 播放器。当我尝试播放 .mp4 文件时，它正在向服务器发送 EPSV ALL 。服务器响应这一行:

"229 Entering Extended Passive Mode (|||" + freeDataPort + "|)"

服务器在freeDataPort上创建serverSocket，监听收入连接，但没有任何反应。

我尝试通过连接到 FileZilla 服务器来打开电影 - 它有效。另外我不明白为什么客户端在此命令(EPSV)之后尝试建立第二个连接(请求用户并再次传递的连接)，而PASV命令创建数据连接并执行简单的数据传输，例如对 LIST 的响应，在第一个处理中处理。

这是我使用的 EPSV 处理程序:

private void handleEpsv() {
    sendMsgToClient("229 Entering Extended Passive Mode (|||" + freeDataPort + "|)");
    try {
        dataSocket = new ServerSocket(freeDataPort);
        System.out.println("waiting for connect... port: " + freeDataPort);
        dataConnection = dataSocket.accept();
        dataOutWriter = new PrintWriter(dataConnection.getOutputStream(), true);
    } catch (IOException e)
    {
        debugOutput("Could not create data connection.");
        e.printStackTrace();
    }
}

上次的结果是:

FTP Server started listening on port 21
{/192.168.0.105=INITIALThread-0    Threads in data list: 0}
New connection received. Worker was created.
from INITIAL THREAD
Thread-0 - send to client:    220 Welcome to the FTP-Server

USER a from INITIAL THREAD
Thread-0 - send to client:    331 User name okay, need password

PASS a from INITIAL THREAD
Thread-0 - send to client:    230 User logged in successfully

SYST from INITIAL THREAD
Thread-0 - send to client:    215 UNIX Type: L8

PWD from INITIAL THREAD
Thread-0 - send to client:    257 "/"

TYPE I from INITIAL THREAD
Thread-0 - send to client:    200 OK

CWD // from INITIAL THREAD
Thread-0 - send to client:    250 CWD successful. / is current directory

PASV from INITIAL THREAD
Thread-0 - send to client:    227 Entering Passive Mode (192,168,0,199,7,232)

waiting for connect... port: 2024
Data connection - Passive Mode - established
LIST from INITIAL THREAD
Thread-0 - send to client:    125 Opening ASCII mode data connection for file list.

from INITIAL THREAD
Thread-0 - send to client:    226 Transfer complete.

{/192.168.0.105=INITIALThread-0    Threads in data list: 1}
New connection received. Worker was created.

Thread-1 - send to client:    220 Welcome to the FTP-Server

FEAT 
Thread-1 - send to client:    211-Features:


Thread-1 - send to client:    MDTM


Thread-1 - send to client:    REST STREAM


Thread-1 - send to client:    SIZE


Thread-1 - send to client:    MLST type*;size*;modify*;


Thread-1 - send to client:    MLSD


Thread-1 - send to client:    UTF8


Thread-1 - send to client:    CLNT


Thread-1 - send to client:    MFMT


Thread-1 - send to client:    EPSV


Thread-1 - send to client:    EPRT


Thread-1 - send to client:    211 END

USER a 
Thread-1 - send to client:    331 User name okay, need password

PASS a 
Thread-1 - send to client:    230 User logged in successfully

EPSV ALL 
Thread-1 - send to client:    229 Entering Extended Passive Mode (|||2025|)

used by Thread-1 Thread DATA type
waiting for connect... port: 2025

Answer 1

EPSV ALL 不是 EPSV。 EPSV ALL 具有特殊含义。客户端使用它来指示它将仅使用 EPSV，而不是 PASV、PORT 或 EPRT >。您应该只回复类似 200 OK 的内容。您应该阅读RFC 2428 .

实际上我从来没有见过任何FTP客户端使用这个命令。大多数服务器会忽略它或错误地处理它。 VLC 无法与您的服务器通信的原因可能是，除了响应不正确之外，您还阻止了控制连接以等待传入的数据传输。 VLC 正在发送更多命令，并在等待服务器响应时超时(因此它可能会通过打开新连接来重试)。

这是 VLC 连接到 FileZilla FTP 服务器的记录。请注意，FileZilla 也会通过响应 229 Entering Extended Passive Mode 来错误地处理 EPSV ALL。但它不会阻塞控制连接并正确处理以下命令(包括后面的EPSV)。

230 Logged on
EPSV ALL
229 Entering Extended Passive Mode (|||65079|)
TYPE I
200 Type set to I
SIZE video.avi
213 119035510
EPSV
229 Entering Extended Passive Mode (|||63465|)
TYPE I
200 Type set to I
RETR video.avi
150 Opening data channel for file download from server of "/video.avi"
...

<小时/>

实际上，即使命令是普通的 EPSV，您也不应该阻止控制连接，因为客户端将发送更多命令，特别是 RETR(或 STOR、LIST、MLSD...)。