我有一个应用程序，软件定义的无线电，它在一个端口上广播 UDP 数据包，告诉听众已经设置了什么频率和解调模式（除其他外）。
我编写了一个演示 python 客户端（下面的代码），它监听端口，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。
我遇到的问题/问题是：Python 应用程序必须在无线电应用程序之前启动，或者它声称在绑定期间端口已在使用中（ERRNO 47），我不明白为什么。广播应用程序正在广播 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。
所以这是 Python 代码（由于堆栈溢出的“make-it-code”缩进非常愚蠢，缩进有点混乱，但我向你保证没关系）：
#!/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'
作为参考，这是发送 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);
}
}
播送：
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
}