我有一个应用程序，软件定义的 radio ，它在一个端口上广播 UDP 数据包，告诉听众设置了什么频率和解调模式(以及其他信息。)

我已经编写了一个演示 python 客户端(下面的代码)来监听端口，并将适当数据包中的信息转储到控制台。

它们都在 OSX 10.6 Snow Leopard 下运行。他们在那里工作。

我的问题是:Python 应用程序必须在 radio 应用程序之前启动，或者它声称端口在绑定(bind)期间已被使用 (ERRNO 47)，我不明白为什么。广播应用正在广播 UDP；当然，我想容纳多个听众 - 这就是广播的想法，或者至少，我是这么想的。

这是 Python 代码(由于堆栈溢出的真正愚蠢的“make-it-code”缩进，缩进有点困惑，但我向你保证没问题):

#!/usr/bin/python
import select, socket 

# AA7AS - for SdrDx UDP broadcast

# this is a sample python script that captures the UDP messages
# that are coming from SdrDx. SdrDx tells you what frequency and
# mode it has been set to. This, in turn, would be used to tell
# another radio to tune to that frequency and mode.

# UDP packet from SdrDx is zero terminated, but receiving the
# packet makes it seem like the string contains zeros all the
# way out to the 1024th character. This function extracts a
# python string up to the point where it hits the first zero,
# then returns that string.
# -----------------------------------------------------------
def zeroterm(msg):
    counter = 0;
    for c in msg:
        if ord(c) != 0:
            counter += 1
    strn = msg[:counter]
    return strn

port = 58083        # port where we expect to get a msg
bufferSize = 1024   # room for message

# Create port to listen upon
# --------------------------
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
try:
    s.bind(('', port))
except:
    print 'failure to bind'
    s.close()
    raise
    s.setblocking(0)

# Listen for messages
# -------------------
looping = True

while looping:
try:
    result = select.select([s],[],[])
except: # you can kill the client here with control-c in its shell
    s.close()   # must close socket
    print 'Closing, exception encountered during select' # warn
    raise SystemExit    # and quit
msg = result[0][0].recv(bufferSize) # actually fetch the UDP data
msg = zeroterm(msg) # convert content into python string

# in next line, [] contain optional repeats
# message format is keyword:data[|keyword:data]
# where from 1...n keyword:data pairs may appear, up to 1024 bytes
# ----------------------------------------------------------------

try:
    msgs = msg.split('|')       # can be more than one message in packet
except: # failed to split
    msgs = []                   # on the other hand, can just be one. :)
    msgs.append(msg)            # so build array with that one.
for m in msgs:                  # now, for every message we have
    keyw,data = m.split(':')    # break into keyword and data
    print keyw + "-->" + data   # you'd do something with this
    if keyw == "closing":       # Our client terminates when SdrDx does
        looping = False         # loop stops

 s.close()                          # must close socket
print 'Normal termination'

作为引用，这里是发送 UDP 消息的 Qt 代码:

设置:

bcast = new QHostAddress("192.168.1.255");
if (bcast)
{
    udpSocketSend = new QUdpSocket(0);
    if (udpSocketSend)
    {
        udpSocketSend->bind(*bcast, txudp);
    }
}

广播:

if (udpSocketSend)
{
    QByteArray *datagram = new QByteArray(1024,0);  // datagram is full of zeroes
    strcpy(datagram->data(),msg);                   // except where text message is in it at beginning
    udpSocketSend->writeDatagram(*datagram, QHostAddress::Broadcast,txudp); // send
}

最佳答案

您正在尝试绑定(bind)同一个端口，两次。

您在发件人中绑定(bind)一次:

if (udpSocketSend)
{
    udpSocketSend->bind(*bcast, txudp);
}

然后在接收器处再次

s.bind(('', port))

因为它们在同一台机器上运行，所以你会收到一个错误。

除非您关心源端口是什么，否则您不需要对发送方执行 bind()，只需发送它，堆栈就会选择一个合适的传出源端口号。对于发送方，当您传输 UDP 数据报时，您指定了目的地 (udpSocketSend->writeDatagram(...))，而 bind 实际上确定了 <传出数据报的 em="">源。如果您不bind，没关系，堆栈会为您分配一个端口。

如果您确实关心源端口是什么，那么我建议您对传出源端口和传入目标端口使用不同的端口号。然后您就可以毫无问题地绑定(bind)发送方和接收方。

最后，可以选择设置 SO_REUSEADDR 套接字选项(无论您使用何种语言)。如果您想在同一台机器上运行多个客户端，这将是必要的，因为所有客户端都必须绑定(bind)到相同的地址。但是，我不确定这个套接字选项是否跨平台(*nix 工作正常)，我认为以上建议更好。

关于Python 和 UDP 监听，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/10887844/