Ensuring all the data gets received through UDP socket in Python -
possibly related questions seem close don't describe issue understand it:
- reading data udp socket
- python udp socket semi-randomly failing receive
- python raw socket listening udp packets; half of packets received
problem
long file sent line line doesn't go way through udp on loopback.
long story
i have long file consisting of lines , breaks identical program on udp locally. let me emphasize the program sending packets on udp (there no choice here), , cannot feasibly modified process ack requests etc. while sending.
it looks (this tail):
stimulustime 56398 signal(0,2) -79.5457 signal(0,4) -81.7426 signal(0,6) -83.9978 signal(0,9) -63.3755 signal(0,11) -15.6045 signal(0,13) 31.1299 signal(0,16) 75.7539 signal(0,18) 98.301 signal(0,20) 98.301 signal(0,22) 48.4546 signal(0,25) 3.73159 signal(0,27) -49.9798 signal(0,29) -77.8449 signal(1,0) -22.0332 signal(1,2) -60.6384 signal(1,4) -98.0858 signal(1,6) -86.4579 signal(1,9) -68.9173 signal(1,11) -31.5552 signal(1,13) 35.2906 signal(1,16) 77.0686 signal(1,18) 96.3836 signal(1,20) 95.7246 signal(1,23) 25.6074 signal(1,25) -20.2101 signal(1,27) -60.2933 signal(1,29) -83.8169 signal(2,0) -31.8826 signal(2,2) -53.5045 signal(2,4) -89.9895 signal(2,7) -84.4503 signal(2,9) -59.7016 signal(2,11) -12.8569 signal(2,13) 28.857 signal(2,15) 58.0577 signal(2,18) 96.4222 signal(2,20) 79.783 signal(2,22) 58.6463 signal(2,25) -3.24883 signal(2,27) -45.5 signal(2,29) -88.8937 signal(3,0) -18.6625 signal(3,2) -53.3978 signal(1,16) 58.784 signal(1,17) 44.7782 signal(1,18) 6.247 signal(1,19) -12.0855 signal(1,20) -33.7644 signal(1,21) -49.4406 signal(1,22) -67.5791 signal(1,23) -92.0336 signal(1,24) -93.9841 end i wrote code takes file , sends line @ time on udp locally, , code receives , parses based on data type.
sender:
import socket import sys # sends udp test data piped in stdin listener. # ex: cat sampleoutput.txt | python testsender.py udp_ip = "127.0.0.1" udp_port = 5000 print "udp target ip:", udp_ip print "udp target port:", udp_port sock = socket.socket(socket.af_inet, # internet socket.sock_dgram) # udp # send stdin if len(sys.argv) < 2: while true: line = sys.stdin.readline() if line: sock.sendto(line, (udp_ip, udp_port)) else: break # file arg else: myfile = open(str(sys.argv[1]), "r") while true: line = myfile.readline() if line: sock.sendto(line, (udp_ip, udp_port)) else: break sock.close() listener:
import socket array import array udp_ip = "127.0.0.1" udp_port = 5000 sock = socket.socket(socket.af_inet, # internet socket.sock_dgram) # udp sock.bind((udp_ip, udp_port)) while true: data, addr = sock.recvfrom(1024) # buffer size arg print data # write file later testing # file = open("testdummy.txt", "a") # file.write(data) if data == "end\n": break i able use above listener produce test file original program, should work. unfortunately, fails around 500 lines of payload, tested tail -n 500 testdummy.txt | python testsender.py, although it's random. specifically, listener not receive of sent lines before sender exits, leaving hanging, waiting "end\n" string.
as understand it, socket in blocking mode--how can prevent occurring?
my first advice you, don't use udp if want transfer files sequence of lines preserved, use tcp if don't want code alot. reasons are;
- udp unreliable protocol, in sense packet sent not guaranteed received recipient.
- udp doesn't guarantee sequence of packets being received, because udp packets may go recipient via several routes (hops between computers). latter sent packets can take short route , reach recipient before former sent packets. ("end\n" packet can come before other packets)
tcp on other hand reliable , sequence of packets received guaranteed. ideal file transfer.
but don't worry file sharing applications bear share, bit torrents make use of udp there additional coding have do.
- you need implement acknowledgement protocol, in need have unique id each packet send recipient , when packet received recipient should send acknowledgement packet sender id saying packet received.
- if in case packet got lost , didn't reach recipient (no acknowledgement recipient) must resend packet again (and again) until acknowledgement.
- you can control order not sending next packet until acknowledgement previous one.
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