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• SVN Server not responding

  - by Rob Forrest

  I've been bashing my head against a wall with this one all day and I would greatly appreciate a few more eyes on the problem at hand. We have an in-house SVN Server that contains all live and development code for our website. Our live server can connect to this and get updates from the repository. This was all working fine until we migrated the SVN Server from a physical machine to a vSphere VM. Now, for some reason that continues to fathom me, we can no longer connect to the SVN Server. The SVN Server runs CentOS 6.2, Apache and SVN 1.7.2. SELinux is well and trully disabled and the problem remains when iptables is stopped. Our production server does run an older version of CentOS and SVN but the same system worked previously so I don't think that this is the issue. Of note, if I have iptables enabled, using service iptables status, I can see a single packet coming in and being accepted but the production server simply hangs on any svn command. If I give up waiting and do a CTRL-C to break the process I get a "could not connect to server". To me it appears to be something to do with the SVN Server rejecting external connections but I have no idea how this would happen. Any thoughts on what I can try from here? Thanks, Rob Edit: Network topology Production server sits externally to our in-house SVN server. Our IPCop (?) firewall allows connections from it (and it alone) on port 80 and passes the connection to the SVN Server. The hardware is all pretty decent and I don't doubt that its doing its job correctly, especially as iptables is seeing the new connections. subversion.conf (in /etc/httpd/conf.d) LoadModule dav_svn_module modules/mod_dav_svn.so <Location /repos> DAV svn SVNPath /var/svn/repos <LimitExcept PROPFIND OPTIONS REPORT> AuthType Basic AuthName "SVN Server" AuthUserFile /var/svn/svn-auth Require valid-user </LimitExcept> </Location> ifconfig eth0 Link encap:Ethernet HWaddr 00:0C:29:5F:C8:3A inet addr:172.16.0.14 Bcast:172.16.0.255 Mask:255.255.255.0 inet6 addr: fe80::20c:29ff:fe5f:c83a/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:32317 errors:0 dropped:0 overruns:0 frame:0 TX packets:632 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:2544036 (2.4 MiB) TX bytes:143207 (139.8 KiB) netstat -lntp Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN 1484/mysqld tcp 0 0 0.0.0.0:111 0.0.0.0:* LISTEN 1135/rpcbind tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 1351/sshd tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN 1230/cupsd tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN 1575/master tcp 0 0 0.0.0.0:58401 0.0.0.0:* LISTEN 1153/rpc.statd tcp 0 0 0.0.0.0:5672 0.0.0.0:* LISTEN 1626/qpidd tcp 0 0 :::139 :::* LISTEN 1678/smbd tcp 0 0 :::111 :::* LISTEN 1135/rpcbind tcp 0 0 :::80 :::* LISTEN 1615/httpd tcp 0 0 :::22 :::* LISTEN 1351/sshd tcp 0 0 ::1:631 :::* LISTEN 1230/cupsd tcp 0 0 ::1:25 :::* LISTEN 1575/master tcp 0 0 :::445 :::* LISTEN 1678/smbd tcp 0 0 :::56799 :::* LISTEN 1153/rpc.statd iptables --list -v -n (when iptables is stopped) Chain INPUT (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination Chain FORWARD (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination iptables --list -v -n (when iptables is running, after one attempted svn connection) Chain INPUT (policy ACCEPT 68 packets, 6561 bytes) pkts bytes target prot opt in out source destination 19 1304 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED 0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 0 0 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0 0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22 1 60 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:80 0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:80 0 0 ACCEPT udp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:80 Chain FORWARD (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination Chain OUTPUT (policy ACCEPT 17 packets, 1612 bytes) pkts bytes target prot opt in out source destination tcpdump 17:08:18.455114 IP 'production server'.43255 > 'svn server'.local.http: Flags [S], seq 3200354543, win 5840, options [mss 1380,sackOK,TS val 2011458346 ecr 0,nop,wscale 7], length 0 17:08:18.455169 IP 'svn server'.local.http > 'production server'.43255: Flags [S.], seq 629885453, ack 3200354544, win 14480, options [mss 1460,sackOK,TS val 816478 ecr 2011449346,nop,wscale 7], length 0 17:08:19.655317 IP 'svn server'.local.http > 'production server'k.43255: Flags [S.], seq 629885453, ack 3200354544, win 14480, options [mss 1460,sackOK,TS val 817679 ecr 2011449346,nop,wscale 7], length 0

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• Is SYN flooding still a threat?

  - by Rob

  Well recently I've been reading about different Denial of Service methods. One method that kind of stuck out was SYN flooding. I'm a member of some not-so-nice forums, and someone was selling a python script that would DoS a server using SYN packets with a spoofed IP address. However, if you sent a SYN packet to a server, with a spoofed IP address, the target server would return the SYN/ACK packet to the host that was spoofed. In which case, wouldn't the spoofed host return an RST packet, thus negating the 75 second long-wait, and ultimately failing in its attempt to DoS the server?

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• Iptables Allow MYSQL server incoming requests

  - by thompatry

  I am trying to get my new MediaWiki server to allow connections to our MySql Server and right now I cannot get my iptables firewall set up right for this. The rule I am applying is the following iptables -A INPUT -p tcp -d 129.130.155.39 --dport 3306 -j ACCEPT # MySQL But my iptables log is still show that the connections can not be established and is being blocked/denied. Nov 21 09:48:39 hds-it kernel: Firewall Deny: [OUTPUT] IN= OUT=eth1 SRC=129.130.155.210 DST=129.130.155.39 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=29232 DF PROTO=TCP SPT=58862 DPT=3306 SEQ=914529531 ACK=0 WINDOW=14600 RES=0x00 SYN URGP=0 OPT (020405B40402080A03BCF2BC0000000001030307) When I turn off iptables, everything works as it should including editing the wiki database. What am I doing wrong with my rule.

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• Load balancing + NAT issue on BNT GBE 2-7 gear

  - by Clément Game

  Hi guys, I've got troubles configuring an Hardware load-Balancer with NAT functions. I have the following architecture: Internet === VIP (public) LB (private ip) ==== private addressed servers When a connection is initialised from the outside (internet) , the LB correctly forwards the SYN packet to one of the private servers. But when these servers want to reply with a SYN/ACK there is a problem. the initial SYN packet had as ip header : VIP = Private_server_Address But the private servers cannot reach VIP from their side (this is normal since it's nated), and then provide a correct reply. Have you guys any solution to correctly forward the packets to their correct destination ? Note: The load balancer, which is the default gw for the servers, also has a NAT rule for "masquerading" (actually more SNAT than real masquerading) Regards, Clément.

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• What can impact the throughput rate at tcp or Os level?

  - by Jimm

  I am facing a problem, where running the same application on different servers, yields unexpected performance results. For example, running the application on a particular faster server (faster cpu, more memory), with no load, yields slower performance than running on a less powerful server on the same network. I am suspecting that either OS or TCP is causing the slowness on the faster server. I cannot use IPerf , unless i modify it, because the "performance" in my application is defined as Component A sends a message to Component B. Component B sends an ACK to component A and ONLY then Component A would send the next message. So it is different from what IPerf does, which to my knowledge, simply tries to push as many messages as possible. Is there a tool that can look at OS and TCP configuration and suggest the cause of slowness?

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• Do TCP connections work differently within the same subnet?

  - by Dean

  I've encountered some network behaviour that confuses me while trying to get Java RMI working. I use netcat to connect to a local machine: [my_machine]$ nc -w 1 192.168.0.100 60000 && echo success success I try to do the same to my server: [my_machine]$ nc -w 1 my-servers-ip 60000 && echo success This doesn't work, unless I explicitly listen on the server socket: [amazon_ec2]$ nc -l 60000 [my_machine]$ nc -w 1 my-servers-ip 60000 && echo success success For the version that fails, the SYN packet receives a RST, ACK in response. I'm not too knowledgable about this stuff, at this point I only have wild theories such as the one in the question. Any ideas? Potentially useful details: Local Machine (192.168.0.100) - Macbook Remote Machine (Amazon EC2) - Amazon Linux AMI 2012.03 Security Group Settings: 22 (SSH) 0.0.0.0/0 1099 0.0.0.0/0 49152-65535 0.0.0.0/0 "iptables -L" shows no rules set

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• Is 50% download speed on a wireless G network normal?

  - by Bartlomiej Skwira

  I have a wired connection of about 36Mb/s, but my wireless speed is max at about 18-19Mb/s. I have a WRT54G-TM (T-Mobile, 802.11G) router with DD-WRT firmware - I've upgraded it to latest build. Done some settings changes: changed channel - 13 wireless network mode - G-only ACK Timing - 0 Fragmentation Threshold and RTS Threshold - 2304 Basic Rate - All Signal/Noise ratio: -46/-94, signal quality ~50-60%. Is this normal with G networks? Edit: The AP is located about 2 meters from laptop, no walls or metal objects, but its next to a TV. I've done a channel scan (had problems locating it, go to "Status - Wireless - Site survey" - lame naming) and everybody else is on channels 1 and 6. Switched to channel 11 but it didn't help. As for trasmit power I got best results with default 71mw. The antenna might be a factor, I'm using the default 2 antennas.

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• Host data transfer limit calculations and network protocol headers

  - by UpTheCreek

  OK, this might be a really stupid question, but... I'm building a web app that utilises websockets. There's fairly rapid messaging going on, so I've been taking a look at the network traffic with wireshark, to see if there's any way of reducing the amount of data we are sending over the wire, and hence costs. A typical message has approx 150 byte data payload, and according to wireshark the lower layer stuff takes up about: Ethernet: 14 bytes IP: 20 Bytes TCP: 20 Bytes My question is, are these network headers included in data transfer calculations? What about TCP ACK messages? (another 54 bytes according to wireshark) This may seem petty, but because we have so much messaging going on, and because the payload is a similar size to these headers, it's significant.

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• In Wireshark's Protocol Hierarchy Statistics screen, is the total byte count of a capture the sum of the Bytes column or just the top line (Frame)?

  - by Howiecamp

  Part 1 - I'm looking at Wireshark's Protocol Hierarchy Statistics screen (sample below), is the total byte count of the capture the sum of the Bytes column or just the top line (Frame)? I'm 99% that it's the latter because of protocol rollup but I wanted to conform. Part 2 - From Wireshark documentation on this screen, "Protocol layers can consist of packets that won't contain any higher layer protocol, so the sum of all higher layer packets may not sum up to the protocols packet count. Example: In the screenshot TCP has 85,83% but the sum of the subprotocols (HTTP, ...) is much less. This may be caused by TCP protocol overhead, e.g. TCP ACK packets won't be counted as packets of the higher layer)." Can you explain this?

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• Random TCP Resets

  - by allenwei

  We got randomly TCP "reset" error when we send request to remote server. Log from remote server Cisco TCP Connection Terminated,Nov 05 14:43:39 EST: %ASA-session-6-302014: Teardown TCP connection 640068283 for Outside:xxxx to xxxx duration 0:00:00 bytes 4160 TCP Reset-O One my local machine I saw when I use netstat 100703 connections reset due to unexpected data 324186 connections reset due to early user close I also use tcpdump to see what's wrong with it, I saw xxxx.https: Flags [R.], seq 290, ack 1369, win 136, options [nop,nop,TS val 2871790533 ecr 1897173283], length 0 The problem just happened today, we didn't change anything on our server. Anyone know what's wrong with it? Is it related to code we wrote send out request or related to linux configuration?

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• Why do I see different TCP behaviour between IIS and FTP server applications on Windows 2003?

  - by rupello

  I am comparing Wireshark traces of a 10MB file download file from: the FileZilla FTP server and IIS (using HTTP) on the same Windows 2003 server. The FTP download performs faster and the trace shows the server behaving as expected, sending more data to the client with every ACK received: Link to full-size image The HTTP server trace shows a more bursty pattern. The timing of the send bursts are sometimes unrelated to any ACKs received from the client (circled in red): Link to full-size image Anyone have a suggestion as to why IIS traffic is having like this? Update: We have tried modifying the http.sys registry settings (setting MaxBytesPerSend to 256k and MaxBufferedSendBytes to 64k as recommended). Changing MaxBytesPerSend does seem to improve performance by increasing the amount of in-flight data , but we still see the same bursty pattern.

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• BizTalk HL7 Receive Pipeline Exception

  - by Paul Petrov

  If you experience sequence of errors below with BizTalk HL7 MLLP receive ports you may need to request a hotfix from Microsoft. Knowledge base article number is 2454887 but it’s still not available on the KB site. The hotfix is recently released and you may need to open support ticket to get to it. It requires three other hotfixes installed: ·         970492 (DASM 3.7.502.2) ·         973909 (additional ACK codes) ·         981442 (Microsoft.solutions.btahl7.mllp.dll 3.7.509.2) If the exceptions below repeatedly appear in the event log you most likely would be helped by the hotfix: Fatal error encountered in 2XDasm. Exception information is Cannot access a disposed object. Object name: 'CEventingReadStream'. There was a failure executing the receive pipeline: "BTAHL72XPipelines.BTAHL72XReceivePipeline, BTAHL72XPipelines, Version=1.3.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" Source: "BTAHL7 2.X Disassembler" Receive Port: "ReceivePortName" URI: "IPAddress:portNumber" Reason: Cannot access a disposed object. Object name: 'CEventingReadStream'. The Messaging Engine received an error from transport adapter "MLLP" when notifying the adapter with the BatchComplete event. Reason "Object reference not set to an instance of an object." We’ve been through a lot of troubleshooting with Microsoft Product Support and they did a great job finding an issue and releasing a fix.

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• UFW blocking random packets on 443

  - by s2jcpete

  All, I have UFW setup to allow traffic on port 443. It works as expected, though I have a large amount of UFW Block log entries. To Action From -- ------ ---- 80 ALLOW Anywhere 443 ALLOW Anywhere 22222 ALLOW Anywhere 80 ALLOW Anywhere (v6) 443 ALLOW Anywhere (v6) 22222 ALLOW Anywhere (v6) However in my syslog file I see this: [UFW BLOCK] IN=eth0 OUT= MAC=XXX SRC=<foreignip> DST=<serverip> LEN=40 TOS=0x00 PREC=0x00 TTL=116 ID=22025 DF PROTO=TCP SPT=49622 DPT=443 WINDOW=0 RES=0x00 ACK RST URGP=0 About 30 or so seconds later pound (which I'm using for SSL decryption and port redirection) throws a connection timed out messsage. I'm assuming this is because UFW is blocking the packet. I'm at a loss as to an explination. Could the packet be malformed or something, is this normal? Edit - I have since changed the /etc/defaults/ufw and set ipv6=no, so the v6 rules are no longer in the mix. The server is still showing the block / connection timed out behavior though. The new ufw status output is: Status: active Logging: on (low) Default: deny (incoming), allow (outgoing) New profiles: skip To Action From -- ------ ---- 80 ALLOW IN Anywhere 443 ALLOW IN Anywhere 22222 ALLOW IN Anywhere

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• List all BPM Processes for a user

  - by kasriniv

  Hello, Happy to start contributing to this blog..  The title of the blog is probably deceptively simple and warrants an elaboration. Customized BPM workspaces/user interfaces are a fairly common requirement. One of our marquee customers in the online stock trading business, envisioned this user interaction for their BPM application: User logs in to the internal portal Use will have list of roles which he is granted as a drop down list Once user selects the role, a list of processes which user is part of appear. Logged in user can be part of any swimlane role of the process This can be a fairly common/reasonable user-UI interaction pattern. 1. and 2. are easily achievable and hence the subject matter of this blog is the requirement in 3. Objective: Given a username and a role, list all the BPM processes that the user is part of, in any swimlane of any process. Here is quick overview of the major steps/logic in the code: Intialize workflow/BPM  context as usual Get a handle on InstanceQueryService(getInstanceQueryService), InstanceManagementService,        ProcessMetadataService and ProcessModelService List all Processes for that bpmcontext (listProcessMetadataSumary) and get Granted roles to that user For each of the processes [method  getAccessibleProcesss(ProcessMetadataSummary, Set)]for each of the lanes in the process, check if the role granted to the user, matches the roleName for that swimlane. If so, add to output. Notes: The usual caveats apply including BPM APIs are subject to change.  JDeveloper method introspection is your better friend than API documentation :-)... (I am going to try upload the source code  and if it doesnt work, will follow this blog up with the corresponding source code.) Hope this helps.  Ack: Yogesh K, BPM Dev team.

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• How do I prevent TCP connection freezes over an OpenVPN network?

  - by Jason R

  New details added at the end of this question; it's possible that I'm zeroing in on the cause. I have a UDP OpenVPN-based VPN set up in tap mode (I need tap because I need the VPN to pass multicast packets, which doesn't seem to be possible with tun networks) with a handful of clients across the Internet. I've been experiencing frequent TCP connection freezes over the VPN. That is, I will establish a TCP connection (e.g. an SSH connection, but other protocols have similar issues), and at some point during the session, it seems that traffic will cease being transmitted over that TCP session. This seems to be related to points at which large data transfers occur, such as if I execute an ls command in an SSH session, or if I cat a long log file. Some Google searches turn up a number of answers like this previous one on Server Fault, indicating that the likely culprit is an MTU issue: that during periods of high traffic, the VPN is trying to send packets that get dropped somewhere in the pipes between the VPN endpoints. The above-linked answer suggests using the following OpenVPN configuration settings to mitigate the problem: fragment 1400 mssfix This should limit the MTU used on the VPN to 1400 bytes and fix the TCP maximum segment size to prevent the generation of any packets larger than that. This seems to mitigate the problem a bit, but I still frequently see the freezes. I've tried a number of sizes as arguments to the fragment directive: 1200, 1000, 576, all with similar results. I can't think of any strange network topology between the two ends that could trigger such a problem: the VPN server is running on a pfSense machine connected directly to the Internet, and my client is also connected directly to the Internet at another location. One other strange piece of the puzzle: if I run the tracepath utility, then that seems to band-aid the problem. A sample run looks like: [~]$ tracepath -n 192.168.100.91 1: 192.168.100.90 0.039ms pmtu 1500 1: 192.168.100.91 40.823ms reached 1: 192.168.100.91 19.846ms reached Resume: pmtu 1500 hops 1 back 64 The above run is between two clients on the VPN: I initiated the trace from 192.168.100.90 to the destination of 192.168.100.91. Both clients were configured with fragment 1200; mssfix; in an attempt to limit the MTU used on the link. The above results would seem to suggest that tracepath was able to detect a path MTU of 1500 bytes between the two clients. I would assume that it would be somewhat smaller due to the fragmentation settings specified in the OpenVPN configuration. I found that result somewhat strange. Even stranger, however: if I have a TCP connection in the stalled state (e.g. an SSH session with a directory listing that froze in the middle), then executing the tracepath command shown above causes the connection to start up again! I can't figure out any reasonable explanation for why this would be the case, but I feel like this might be pointing toward a solution to ultimately eradicate the problem. Does anyone have any recommendations for other things to try? Edit: I've come back and looked at this a bit further, and have found only more confounding information: I set the OpenVPN connection to fragment at 1400 bytes, as shown above. Then, I connected to the VPN from across the Internet and used Wireshark to look at the UDP packets that were sent to the VPN server while the stall occurred. None were greater than the specified 1400 byte count, so the fragmentation seems to be functioning properly. To verify that even a 1400-byte MTU would be sufficient, I pinged the VPN server using the following (Linux) command: ping <host> -s 1450 -M do This (I believe) sends a 1450-byte packet with fragmentation disabled (I at least verified that it didn't work if I set it to an obviously-too-large value like 1600 bytes). These seem to work just fine; I get replies back from the host with no issue. So, maybe this isn't an MTU issue at all. I'm just confused as to what else it might be! Edit 2: The rabbit hole just keeps getting deeper: I've now isolated the problem a bit more. It seems to be related to the exact OS that the VPN client uses. I have successfully duplicated the problem on at least three Ubuntu machines (versions 12.04 through 13.04). I can reliably duplicate an SSH connection freeze within a minute or so by just cat-ing a large log file. However, if I do the same test using a CentOS 6 machine as a client, then I don't see the problem! I've tested using the exact same OpenVPN client version as I was using on the Ubuntu machines. I can cat log files for hours without seeing the connection freeze. This seems to provide some insight as to the ultimate cause, but I'm just not sure what that insight is. I have examined the traffic over the VPN using Wireshark. I'm not a TCP expert, so I'm not sure what to make of the gory details, but the gist is that at some point, a UDP packet gets dropped due to the limited bandwidth of the Internet link, causing TCP retransmissions inside the VPN tunnel. On the CentOS client, these retransmissions occur properly and things move on happily. At some point with the Ubuntu clients, though, the remote end starts retransmitting the same TCP segment over and over (with the transmit delay increasing between each retransmission). The client sends what looks like a valid TCP ACK to each retransmission, but the remote end still continues to transmit the same TCP segment periodically. This extends ad infinitum and the connection stalls. My question here would be: Does anyone have any recommendations for how to troubleshoot and/or determine the root cause of the TCP issue? It's as if the remote end isn't accepting the ACK messages sent by the VPN client. One common difference between the CentOS node and the various Ubuntu releases is that Ubuntu has a much more recent Linux kernel version (from 3.2 in Ubuntu 12.04 to 3.8 in 13.04). A pointer to some new kernel bug maybe? I'm assuming that if that were so, then I wouldn't be the only one experiencing the problem; I don't think this seems like a particularly exotic setup.

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• paypal API in VB.net

  - by StealthRT

  Hey all, i have converted some C# PayPal API Code over to VB.net. I have added that code to a class within my project but i can not seem to access it: Imports System Imports com.paypal.sdk.services Imports com.paypal.sdk.profiles Imports com.paypal.sdk.util Namespace GenerateCodeNVP Public Class GetTransactionDetails Public Sub New() End Sub Public Function GetTransactionDetailsCode(ByVal transactionID As String) As String Dim caller As New NVPCallerServices() Dim profile As IAPIProfile = ProfileFactory.createSignatureAPIProfile() profile.APIUsername = "xxx" profile.APIPassword = "xxx" profile.APISignature = "xxx" profile.Environment = "sandbox" caller.APIProfile = profile Dim encoder As New NVPCodec() encoder("VERSION") = "51.0" encoder("METHOD") = "GetTransactionDetails" encoder("TRANSACTIONID") = transactionID Dim pStrrequestforNvp As String = encoder.Encode() Dim pStresponsenvp As String = caller.[Call](pStrrequestforNvp) Dim decoder As New NVPCodec() decoder.Decode(pStresponsenvp) Return decoder("ACK") End Function End Class End Namespace I am using this to access that class: Private Sub cmdGetTransDetail_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdGetTransDetail.Click Dim thereturn As String thereturn =GetTransactionDetailsCode("test51322") End Sub But it keeps telling me: Error 2 Name 'GetTransactionDetailsCode' is not declared. I'm new at calling classes in VB.net so any help would be great! :o) David

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• piping findstr's output

  - by Gauthier

  Windows command line, I want to search a file for all rows starting with: # NNN "<file>.inc" where NNN is a number and <file> any string. I want to use findstr, because I cannot require that the users of the script install ack. Here is the expression I came up with: >findstr /r /c:"^# [0-9][0-9]* \"[a-zA-Z0-9_]*.inc" all_pre.txt The file to search is all_pre.txt. So far so good. Now I want to pipe that to another command, say for example more. >findstr /r /c:"^# [0-9][0-9]* \"[a-zA-Z0-9]*.inc" all_pre.txt | more The result of this is the same output as the previous command, but with the file name as prefix for every row (all_pre.txt). Then comes: FINDSTR: cannot open | FINDSTR: cannot open more Why doesn't the pipe work? snip of the content of all_pre.txt # 1 "main.ss" # 7 "main.ss" # 11 "main.ss" # 52 "main.ss" # 1 "Build_flags.inc" # 7 "Build_flags.inc" # 11 "Build_flags.inc" # 20 "Build_flags.inc"

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• Multiple Socket Connections

  - by BSchlinker

  I need to write a server which accepts connections from multiple client machines, maintains track of connected clients and sends individual clients data as necessary. Sometimes, all clients may be contacted at once with the same message, other times, it may be one individual client or a group of clients. Since I need confirmation that the clients received the information and don't want to build an ACK structure for a UDP connection, I decided to use a TCP streaming method. However, I've been struggling to understand how to maintain multiple connections and keep them idle. I seem to have three options. Use a fork for each incoming connection to create a separate child process, use pthread_create to create an entire new thread for each process, or use select() to wait on all open socket IDs for a connection. Recommendations as to how to attack this? I've begun working with pthreads but since performance will likely not be an issue, multicore processing is not necessary and perhaps there is a simpler way.

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• fastest (low latency) method for Inter Process Communication between Java and C/C++

  - by Bastien

  Hello, I have a Java app, connecting through TCP socket to a "server" developed in C/C++. both app & server are running on the same machine, a Solaris box (but we're considering migrating to Linux eventually). type of data exchanged is simple messages (login, login ACK, then client asks for something, server replies). each message is around 300 bytes long. Currently we're using Sockets, and all is OK, however I'm looking for a faster way to exchange data (lower latency), using IPC methods. I've been researching the net and came up with references to the following technologies: - shared memory - pipes - queues but I couldn't find proper analysis of their respective performances, neither how to implement them in both JAVA and C/C++ (so that they can talk to each other), except maybe pipes that I could imagine how to do. can anyone comment about performances & feasibility of each method in this context ? any pointer / link to useful implementation information ? thanks for your help

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• Recommendation for serial communications in Access 2007

  - by bglenn

  I need to communicate with a bar code scanner connected over a serial port in Microsoft Access. In older versions of Access I was able to use a wrapper around MSCOMM32.ocx that no longer seems to work. I can't use wedge communication because I need to use ACK/NACK which is only supported through the RS232 interface and I need to send messages to the scanner, which is also only supported through the RS232 interface. Are there any controls in widespread use that support serial communication in Access 2007? EDIT: In case anyone comes across this, the newest version of MSCOMM32.ocx (I believe dated 3/09) still works fine as of this writing. It is older versions of MSCOMM32.ocx that do not work.

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• SYN flooding still a threat to servers?

  - by Rob

  Well recently I've been reading about different Denial of Service methods. One method that kind of stuck out was SYN flooding. I'm a member of some not-so-nice forums, and someone was selling a python script that would DoS a server using SYN packets with a spoofed IP address. However, if you sent a SYN packet to a server, with a spoofed IP address, the target server would return the SYN/ACK packet to the host that was spoofed. In which case, wouldn't the spoofed host return an RST packet, thus negating the 75 second long-wait, and ultimately failing in its attempt to DoS the server?

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• Using TCP Acks to measure latency to a server?

  - by Ted Graham

  I am trying to measure latency to a server that I don't control. This is in a colocated environment, so the latency is on the order of 500 us (.5 ms). I understand that Cisco gear frequently deprioritizes ICMP traffic, making ping times unreliable. Is there a way for me to tell if this is the case on the gear I am traversing? Can I use TCP acknowledgements to determine the minimum latency to the remote server? To do this, I would somehow need to force the remote server to send a TCP ack immediately on receiving my data.

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• Intelligent serial port mocks with Moq

  - by Padu Merloti

  I have to write a lot of code that deals with serial ports. Usually there will be a device connected at the other end of the wire and I usually create my own mocks to simulate their behavior. I'm starting to look at Moq to help with my unit tests. It's pretty simple to use it when you need just a stub, but I want to know if it is possible and if yes how do I create a mock for a hardware device that responds differently according to what I want to test. A simple example: One of the devices I interface with receives a command (move to position x), gives back an ACK message and goes to a "moving" state until it reaches the ordered position. I want to create a test where I send the move command and then keep querying state until it reaches the final position. I want to create two versions of the mock for two different tests, one where I expect the device to reach the final position successfully and the other where it will fail. Too much to ask?

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• How to gain greater control of network packets on Android

  - by mauvehead

  I'm looking to design an application that will require some deep control over IP packets. Looking over the reference guide on the developers site at Android I see very limited control over packets from java.net:SocketOptions and java.net:DatagramPacket. Specifically I'm looking to control the individual bits within the packet to set TCP Flags, SYN/ACK/RST, and so forth. Based on the docs I am assuming I cannot do this within the Java API provided by Android and I'm guessing I'll have to do it some other way? Anyone have any insight on this?

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• how to detect an escape sequence in a string

  - by mix

  Given a string named line whose raw version has this value: \rRAWSTRING how can I detect if it has the escape character \r? What I've tried is: if repr(line).startswith('\r'): blah... but it doesn't catch it. I also tried find, such as: if repr(line).find('\r') != -1: blah doesn't work either. What am I missing? thx! EDIT: thanks for all the replies and the corrections re terminolgy and sorry for the confusion. OK, if i do this print repr(line) then what it prints is: '\rSET ENABLE ACK\n' (including the single quotes). i have tried all the suggestions, including: line.startswith(r'\r') line.startswith('\\r') each of which returns False. also tried: line.find(r'\r') line.find('\\r') each of which returns -1

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