Asking a smart question

/by apr/

Among the many helpful jPOS developers in our community, @marklsalter stands out for his professional, accurate, and detailed answers, but he has his standards when it comes to how you ask questions. You need to ask a smart question. jPOS has Mark (and Victor, and Andy, and Dave, and Matias, and Chhil, and Barzi, and, and, and), but if you go to any other open source community asking for free advice, you’ll find another Mark, or worst than that, you’ll find no Mark and your question will just get ignored and you won’t even know why.

This is what you should expect as a response if you don’t do your homework and ask a smart question (from a recent reply in jpos-users, in this case, related to a vague question about to the Transaction Manager – could have been anything else).

Please always start by asking a smart question.

Please read this now :-

Yes, the whole things, go on, treat yourself, it will take 5-10 minutes and save us both hours going forward.

Preparing to ask a smart question should cause you to read the available documentation, to understand it and enable you to make sure you include all the relevant details needed for another remote person to help you, but should also make sure you have understood the documentation and how it applies to your need.

I can honestly say that on this opening post that I could see that it was going to be another thread that would drag on – without you …

  1. Apparently making any effort to understand what you have done incorrectly or “misunderstood”.
  2. Trying first to understand how and why your set-up is broken
  3. Referring to the documentation on the life cycle of the TransactionManager and it’s given participants – which perhaps surprisingly, works perfectly when users follow the few simple rules and grasp what it does for you.

By the way, I understand that a TM configuration might not be obvious straight away, but often the best things are worth the effort. I still refer to the documentation again and again (and again).

I will include some comment below to, in the hope that you read it and take the time next time to ask a smart question.

Remember as you read through that I am not taking the piss out of you, but trying to highlight why this is a terrible opening question and how you can (hopefully) help yourself next time.

jPOS-EE Crypto Service

In many jPOS systems, we secure sensitive data using ANS X9.24 DUKPT as described in the Encrypting sensitive data post. The approach served us well, but now we believe we have a better one, using PKI and AES-256.

The cryptoservice module uses AES-256 to encrypt sensitive data, such as primary account numbers and protects the encryption key using PGP.

At start-up time, and at regular intervals, the crypto service generates a new AES-256 key, encrypts it using PGP using one or more recipient ids, and stores the resulting encrypted message in the sysconfig table, using the “key.” prefix, and a unique key UUID, i.e.:

id: key.f55fe6ec-ed9e-47a1-a0fe-c63dcbf128cb
Version: BCPG v1.56



The key is used to encrypt subsequent data for a given period of time (defaults to one day) until a new key is automatically generated.

Here is a sample usage:

private void encryptCardData (TLCapture tl, Card card)      <1>
   throws Exception {
     Map<String,String> m = new HashMap<>();
     m.put ("P", card.getPan());
     m.put ("E", card.getExp());
     SecureData sd = getCryptoService().aesEncrypt(         <2>
     tl.setKid(sd.getId());                                 <3>
     tl.setSecureData(sd.getEncoded());                     <4>
  • <1> TLCapture in this example is a general purpose capture table.
  • <2> getCryptoService() just locates the CryptoService using the NameRegistrar
  • <3> kid stands for Key ID, we store the key UUID here
  • <4> secureData is a general purpose blob

The crypto service can be configured using a QBean descriptor like this:

<crypto-service class='org.jpos.crypto.CryptoService' logger='Q2'>
    <property name="custodian" value='' />               <1>
    <property name="pubkeyring" value='cfg/' />            <2>
    <property name="privkeyring" value='cfg/keyring.priv' />          <3>
    <property name="lazy" value="false" />                            <4>
    <property name="keylength" value="256" />                         <5>
    <property name="duration" value="86400000" />                     <6>
  • <1> custodian PGP id, there can be many custodian entries.
  • <2> path to the public keyring.
  • <3> path to the password-protected private keyring.
  • <4> if lazy=true, a key is generated the first time we call aesEncrypt, otherwise, a new one is created at service start.
  • <5> key length defaults to 256. Can be reduced if AES-256 is not supported by the JVM due to export restrictions.
  • <6> key duration

This allows jPOS nodes to encrypt data securely without storing the encryption key to disk.

NOTE: The transient encryption key is still in memory, so core dumps and swap should be
disabled at the operating system level. This approach is still more secure
than obfuscating encryption keys.

Decryption — that can of course run in a different node, at a different time — requires
access to the private keyring, with its optional password. Said password can be entered
manually, obtained from a remote service or HSM, etc. and it’s a two step process.

First the key has to be loaded into memory, using the loadKey method. Once the key
is loaded, the aesDecrypt can be called.

These are the method’s signatures:

public void loadKey (String jobId, String keyId, char[] password) throws Exception;
public byte[] aesDecrypt (String jobId, String keyId, byte[] encoded) throws Exception;

Here keyId, password, and encoded cryptogram don’t require too much explanation, but jobId does and here is the rationale. We could have a one-shot aesDecrypt method accepting the private key password, but decrypting the AES-256 key using PGP is an expensive operation. In situations where you have extract a daily file, probably encrypted by just a handful keys, you don’t want to decrypt the key on every aesDecrypt call. We don’t want to expose the key to the caller either, so the CryptoService keeps it in a private field. In order to do that, loadKey caches the key (until it’s unloaded), so it’s cheap to call loadKey followed by aesDecrypt, after the first call where the key is actually decrypted, subsequent calls will be pretty fast.

In order to protect different clients from accessing keys loaded by other ones, we use a jobId that can be something as simple as a UUID or any nonce, only known to the caller. That jobId can then be used to unload those keys, using the unloadKey and unloadAll methods:

public boolean unloadKey (String jobId, String keyId);
public void unloadAll(String jobId);

There’s also a no-args unloadAll() that unloads all keys, and should be used with care.

NOTE: In order to simplify development and testing, and eventually to troubleshoot problems, we’ve also created a couple of CLI commands: aesencrypt and aesdecrypt.

TIP: If you’re accessing the CLI using the command line q2 --cli, remember that the default deployDir is deploy-cli instead of deploy. You need a copy (or symlink) of 25_cryptoservice.xml in that directory. If you ssh to a running Q2 to reach the CLI, then you can ignore this tip.

For up-to-date information about this CryptoService module, please see the jPOS-EE guide.


There’s a new handy org.jpos.transaction.TxnId class in the jPOS-EE txn module that can be used to generate transaction ids in multi-node systems.

The id is composed of:

  • 1-digit century
  • 2-digits year
  • 3-digits day of year
  • 5-digits second of day
  • 3-digits node id
  • 5-digits transaction id

A typical ID long value would look like this: 173000702600000001, and the toString() method would show as 017-300-07026-000-00001 and the toRrn() method would return 1bbfmplq9la9.

TxnId also has a handy toRrn() method that can be used to create (and parse) 12-characters strings suitable to be used as retrieval reference numbers.

TxnId can be used instead of UUIDs. It puts less pressure in the database index and provides chronological order.

NOTE: The last two groups, node-id and transaction-id are supposed to be unique. transaction-id is easy to get from the transaction manager and node-id is a tricky one, user has to ensure each node has a unique node-id to avoid collisions.

Sample usage:

TxnId txnId = TxnId.create(, 0, id);

jPOS 2.1.0 has been released

jPOS 2.1.0 has been released, new development version is now 2.1.1-SNAPSHOT

Please see the ChangeLog.

Remember we are using Semantic Versioning so the change from 2.0.10 to 2.1.0 means a full rebuild has to be done in your applications. Some of the most notable changes are:

  • TransactionContext is now backed by a Map<String,Object> instead of the old Map<Object,Object> so that needs review
  • Some methods that used to throw ISOException are not throwing it anymore

Other than those two minor changes, jPOS 2.1.0 has a large number of improvements, including TransactionManager metrics, new org.jpos.rc package, bug fixes and improved TransactionManager capacity.

jPOS-EE 2.2.4 has been released as well, new development versions are jPOS 2.1.0-SNAPSHOT and jPOS-EE 2.2.5-SNAPSHOT.

See Resources Page for details.

Tutorial – Writing a gateway the jPOS way

I get to see dozens of third party jPOS gateway implementations just using 5% of jPOS capabilities.

People download jPOS just to use the ISO-8583 packing/unpacking and sometimes they don’t even get to use the channels, multiplexers, servers, transaction manager. I see developers trying to stay away from Q2 probably because they don’t know it, but it’s quite simple to use.

So I wrote a little tutorial, that walks you through the process of installing jPOS and writing a production grade gateway capable of processing thousands of transactions per second.

The tutorial has two parts, first you get it running (takes about 5 minutes), then the second part explains why that very simple configuration works.

The second part has plenty of links to the jPOS programmer’s guide documentation (freely available), while it’s just a couple pages, understanding it and following the links may take some more time and may raise some questions that we’ll be happy to answer.

Investor’s Dilemma : How do I Handle Unlicensed Copies of AGPL Software in a Portfolio Company

Every once in a while we receive a request from an investor or private equity firm who, in the process of conducting due-diligence on an existing or established potential portfolio company, encounters an unlicensed copy of jPOS. Often the company has released a commercial product which incorporates this unlicensed software. Investors want to know, how should we proceed and what are the responsibilities of the company vis-à-vis the license and source code?

The easiest and first answer is of course, the company should purchase a license and not rely on pirated software to conduct their business. The more subtle question is what does it imply when a start-up is willing to pirate software which is intended to be reasonably priced and positioned to benefit the authors and the overall Fintech software community as a whole?

Isn’t it risky to partner with a company that disregards good business practices, either because of bad faith or negligence?

If it were me, I’d invest somewhere else!

jPOS-EE BinLog module

jPOS-EE has a new binlog module, a general purpose binary log that can be used as a reliable event store.

The jPOS BinLog has the following features:

  • multiple readers and writers can be used from the same JVM
  • multiple readers and writers can be used from different JVMs

Here is a sample Writer:

File dir = new File("/tmp/binlog");
try (BinLogWriter bl = new BinLogWriter(dir)) {
    bl.add( ... ); // byte array
    bl.add( ... ); // byte array
    bl.add( ... ); // byte array

and a sample Reader:

File dir = new File("/tmp/binlog");
try (BinLogReader bl = new BinLogReader(dir)) {
    while (bl.hasNext()) {
        byte[] b =;
        // do something with the byte[]

The BinLogReader implements an Iterator<BinLog.Entry>. Each BinLog.Entry has two main methods:

  • BinLog.Rer ref()
  • byte[] get()

While iterating over a BinLog, it might make sense to persistently store its BinLog.Ref in order to be able to restart the iterator at a given point if required (this is useful if using the BinLog to implement a Store and Forward.

The BinLogReader has two constructors:

  • BinLogReader(File dir)
  • BinLogReader(File dir, BinLog.Ref ref)

the latter can be used to restart the iterator at a given reference point obtained from a previous run.

In addition to the standard hasNext() method required by the Iterator implementation, BinLogReader also has a hasNext(long millis) method that waits a given number of milliseconds once it reaches the end of the log, attempting to wait for a new entry to be available.

The goal behind the BinLog implementation is to have a future proof file format easy to read from any language, 10 years down the road. We found that the Mastercard simple IPM file format, that’s basically a two-byte message length followed by the message itself was suitable for that. The payload on each record can be ISO-8583 (like Mastercard), JSON, FSDMsg based, Protocol buffers or whatever format the user choose.

But that format isn’t crash proof. If a system crashes while a record is being written to disk, the file can get easily corrupted. So we picked some ideas from Square’s tape project that implements a highly crash proof on-disk persistent circular queue using a very small header. Tape is great and we encourage you to consider it instead of this binlog for some use cases, but we didn’t want a circular queue, we wanted a place to securely store events for audit or store and forward purposes, and we also wanted to be able to access the same binlog from multiple JVMs with access to the same file-system, so we had to write our own.

The on-disk file format looks like this:

256 bytes Header
... Data
... Data

Header format (256 bytes):
4 bytes header length
2 bytes version
2 bytes Status (00=open, 01=closed)
8 bytes Last element position
4 bytes this log number
4 bytes next log number
232 bytes reserved

4 bytes Data length
...     Data

Each record has a length prefix (four bytes in network byte order) followed by its data. The header has a fixed length of 256 bytes but we found useful to make it look like a regular record too by providing its length at the very beginning. An implementation in any language reading a jPOS binlog can just be programmed to skip the first record.

At any given time (usually at end of day), a process can request a cut-over by calling the BinLogWriter.cutover() method in that case, all writers and readers will close the current file and move to the next one (Readers can choose to not-follow to the next file, for example while producing daily extracts).

In order to achieve file crash resilience, each write does the following:

  • Lock the file
  • Write the record’s length and data
  • Sync to disc
  • Write the last element position to the header
  • Sync to disc
  • Unlock the file

In an MBP with SDRAM we’ve managed to achieve approximately 6000 writes per second. On an iMac with regular disk the numbers go down to approximately 1500 writes per second for regular ISO-8583 message lengths (500..1000 bytes per record).

Due to the fact that the header is small enough to fit in an operating system block, the second write where we place the last element position happens to be atomic. While this works OK for readers and writers reading the file from different JVMs, that’s not the case for readers and writers running on the same JVM, even if they use a different file descriptor to open the file, the operating system stack has early access to the header that under high concurrency can lead to garbage values, that’s the reason the code synchronizes on a mutex object at specific places.

Supporting CLI commands

The binlog CLI command is a subsystem that currently have two commands:

  • monitor (to visually monitor a binlog)
  • cutover (to force a cutover)
  • exit (builtin command)

binlog accepts a parameter with the binlog’s path, i.e: binlog /tmp/binlog

So a cutover can be triggered from cron using the following command:

q2 --command="binlog /tmp/binlog; cutover; exit; shutdown --force"

jPOS 2.0.10 has been released

jPOS 2.0.10 has been released, new development version is now 2.1.0-SNAPSHOT

This release upgrades JLine to 3.0.0, adds new CLI commands and subsystems, upgrades Gradle to 3.1.0, allows license to be read from external file and removes double-logging in PADChannel. The main reason for this small release is to flush small enhancements before we make some bigger changes to the TransactionManager with improved audit logging (those are already available in 2.1.0-SNAPSHOT). It also updates the copyright year to 2017 and changes the copyright owner to the new entity jPOS Software SRL.

Starting with this release we’ll move to semantic versioning, so next release is going to be 2.1.0 and requires a full clean build of your projects in order to make sure some of the API changes don’t break your system.

see ChangeLog for details.

Q2 User Interface (aka ‘QI’)

I’m happy to share some new stuff we have in jPOS-EE that we call “QI” (short for Q2 UI).

TL;DR: go to using user admin and password test in order to see what I’m talking about. If you like it, keep reading, otherwise please ignore this message.

QI uses the Vaadin framework that we found very useful for our company’s web development and graphics design skillset (basically no skills). It allows us to create nice reusable web/mobile-friendly applications from Java in a highly modular way.

If you monitor @jposcommits you might have noticed a few new jPOS-EE components, like:

  • qi-core
  • qi-eeuser
  • qi-sysconfig

(see jPOS-EE/modules)

The main goal of the project is to have a bunch of reusable little QI modules (for instance, qi-minigl is coming) that you can use to put together very easily to administrate your jPOS application.

As the rest of the Q2 system, it uses an XML configuration file that gives you a top level control of your particular application, including centralised role-based permissions to access the different parts of the system.

<xml-config name="QI" logger="Q2">
    <title>jPOS QI</title>
        <menu name="System" icon="COG" style="icon-cog" action="system" />
        <menu name="Accounting"  action="accounting" />

    <sidebar id="info">
        <section name="Info"/>
        <option name="Info" action="info"/>

    <sidebar id="system">
        <section name="System"/>
        <option name="Info" action="info"/>
        <option name="Log" action="log"/>
        <option name="Exception log" action="exceptions"/>
        <option name="Users" action="users"/>
        <option name="Roles" action="roles"/>
        <option name="Permissions" action="permissions"/>
        <option name="SysConfig" action="sysconfig"/>
        <option name="Audit Log" action="syslog"/>
        <option name="Revision History" action="revision_history"/>

There you can see the top level menu that triggers two different sidebars. When we hit for example ‘Log’ it brings us to the ‘log’ action that is defined like this:

<view route="log" class="org.jpos.qi.system.LogListenerView" perm="sysadmin" sidebar="system" >
    <property name="name" value="logger.Q2.buffered"/>
    <property name="entityName" value="log"/>

If you hit the ‘info’ action, you get a tabbed pane, the tabbed pane is defined like this:

<view route="info" class="org.jpos.qi.views.TabView" perm="login" sidebar="system">
    <view caption="About" class="org.jpos.qi.system.AboutView" perm="login"/>
    <view caption="Memory" route="memory" 
        class="org.jpos.qi.system.MemoryUsageView" perm="login"/>
    <view caption="Sysmon" route="sysmon" 
        class="org.jpos.qi.system.ObjectView" perm="sysadmin" repeat="1000"
     <object class="org.jpos.util.SystemMonitor"/>
    <view caption="Uptime" route="uptime" class="org.jpos.qi.system.ProcessView" perm="sysadmin" repeat="1000"
    <view caption="Date" route="date" class="org.jpos.qi.system.ObjectView" 
        perm="login" repeat="1000"
      <object class="java.util.Date"/>

I suggest you take a look at how a simple view is implemented, for example the About view:

public class AboutView extends VerticalLayout implements View {
    public AboutView() {
        Label html = new Label(Q2.getVersionString());
    public void enter(ViewChangeListener.ViewChangeEvent event) { }

Some others like ObjectView or ProcessView are interesting, ObjectView can view any object and refresh it regularly, that’s how the ‘Date’ tab is implemented with a very simple XML configuration:

 <view caption="Date" route="date" class="org.jpos.qi.system.ObjectView" 
        perm="login" repeat="1000"
     <object class="java.util.Date"/>

The ObjectView implementation is very simple (see code here) but behind the scenes QI uses web sockets (courtesy of a pre-configured Atmosphere setup) to refresh it.

If you go see the log and you telnet to on port 9000 (that has an open XMLChannel with an auto-responder) you can see how smooth it is.

If you like this stuff you can clone the qitest project that demonstrate how to use QI in your own application.

Your feedback and contributions are greatly appreciated. If you really want to use this stuff, we’ll be happy to walk you through the setup and help with questions for undocumented features (we’ll be adding documentation to the jPOS-EE manual as time permits). The easiest way to do that is here on the list, or better yet, in the jPOS Slack (we are usually around from 1600 to 2000 GMT – see to get an invite)