Host Simulator

Overview

The Host Simulator in ISO8583Studio acts as a payment host simulator for development and testing. It accepts incoming connections from POS terminals, ATMs, or other financial clients and returns configurable responses based on matching rules. This eliminates the need for a real host environment during development and QA testing.

Quick Start Guide

Follow these steps to get a basic host simulator up and running:

1. Create a new simulator — From the Home screen, navigate to Simulator → Host Simulator and create a new configuration.
2. Choose a Gateway Type — Select Server to accept incoming connections, Client to connect outward, or Proxy to bridge two sides.
3. Configure Transmission Settings — Set the IP address, port, connection type (TCP/IP or REST), and message length type.
4. Add Transaction Rules — In the Settings tab, add transactions with MTI, processing code, and the ISO8583 response fields you want to return.
5. Configure the ISO8583 Template — Ensure the template matches your message specification (field formats, lengths, encoding).
6. Start the Simulator — Open the Host Handler tab and click Start. The simulator will begin accepting connections and responding to requests.

Gateway Types

The host simulator supports three gateway modes, each suited to different testing scenarios:

Gateway Configuration

The Gateway Type tab provides the core configuration for your simulator instance.

Basic Settings

Response Delay

Control how quickly the simulator responds to incoming requests. Useful for simulating real-world network conditions.

Performance Settings

• Max Concurrent Transactions — Limit the number of simultaneous transactions the simulator will process.
• Detailed Logging — Enable verbose logging for debugging purposes.

Transmission Settings

Configure how the simulator communicates over the network. Settings differ based on your gateway type.

Incoming Connection (Server / Proxy)

Configure the listener that accepts incoming connections:

• IP Address — Bind address (e.g. 0.0.0.0 for all interfaces, or a specific IP).
• Port — TCP port to listen on.
• Message Length Type — How message boundaries are determined.
• Max Concurrent Connections — Limit on simultaneous client connections.
• Timeout — Connection idle timeout in seconds.

Outgoing Connection (Client / Proxy)

Configure the connection to the destination host:

• Target Address — Hostname or IP of the target.
• Target Port — Port to connect to.
• Terminate on Error — Whether to close the connection on errors.

Message Length Types

Connection Types

The simulator supports multiple connection protocols for maximum flexibility:

Message Formats

The simulator can handle multiple message encoding formats for both source and destination.

ISO8583 Formats

REST Message Formats

When using REST connections, the following content types are supported:

• JSON — Application/json content type
• XML — Application/xml content type
• HEX — Hex-encoded message body
• BASE64 — Base64-encoded message body
• BINARY — Raw binary body
• FORM_DATA — Multipart form data

Format Mapping

For non-binary formats (JSON, XML, PlainText), use the Format Mapping Config in the ISO8583 Template tab to map ISO8583 fields to JSON keys, XML elements, or delimited fields.

Log Settings

Configure how the simulator logs transactions and connections.

Host Handler

The Host Handler is the main runtime interface for controlling and monitoring the simulator.

Controls

• Start / Stop — Launch or shut down the simulator server.
• Hold Message — When enabled, the simulator will not auto-respond. Responses are sent only when you manually click "Send" or after a configurable delay. Useful for inspecting requests before responding.

Live View

The Host Handler provides real-time visibility into all traffic:

• Formatted View — Parsed ISO8583 fields shown in a readable table.
• Raw Hex View — Full hexadecimal dump of the message bytes.
• Request / Response Split — Side-by-side view of incoming request and outgoing response.

Transaction Rules

Transaction rules define how the simulator matches incoming requests and what responses to return. Configure these in the Settings tab.

Rule Structure

Each transaction rule consists of:

Matching Logic

When a request arrives, the simulator evaluates rules in order:

1. Parse the incoming message to extract MTI and processing code (Field 3).
2. Compare against each configured transaction rule.
3. The first matching rule wins and its response fields are used to build the response.

Example Rule

MTI:            0200
Processing Code: 000000
Description:    Purchase Transaction

Response Fields:
  Field 39 (Response Code):     00
  Field 38 (Auth Code):         [RAND]
  Field 11 (System Trace):      [SV]
  Field 37 (RRN):               [SV]
  Field 12 (Local Time):        [TIME]
  Field 13 (Local Date):        [TIME]

Dynamic Placeholders

Use placeholders in response field values to generate dynamic content at runtime instead of static values.

REST API Matching

When using REST connections, the simulator provides advanced request matching beyond MTI/processing code.

Match Criteria

• Path — Match the URL path exactly or use * as a wildcard.
• HTTP Method — Match by GET, POST, PUT, DELETE, etc.
• Query Parameters — Match by URL query parameters.
• Headers — Match by HTTP request headers.
• Body Fields — Match by fields in the request body (JSON/XML).

Match Operators

Each matcher supports these comparison operators:

Response Mapping

For REST responses, use Response Mapping to define which fields appear in the response body and headers:

• targetKey — JSON/XML key in the response body.
• value — Static value or placeholder ([SV], [TIME], [RAND]).
• targetHeader — Set a response HTTP header instead of a body field.

ISO8583 Template

The ISO8583 Template tab defines the message specification used for parsing and building messages.

Template Configuration

• Bit Definitions — Define each ISO8583 field (bit number, name, format, length, encoding).
• Message Format — Select the encoding format: ByteArray, JSON, XML, HEX, or PlainText.
• Format Mapping — Map ISO8583 fields to JSON keys, XML elements, or text delimiters for non-binary formats.
• TPDU / Header — Configure transaction protocol data unit and message header settings.

Unsolicited Messages

Unsolicited messages are messages sent outside the normal request-response flow, typically for network management, notifications, or terminal updates.

Send Message (Client / Proxy)

Craft and send outbound unsolicited messages to connected hosts. Available in Client and Proxy modes. Use the message builder to construct ISO8583 messages with specific fields and send them on demand.

Receive Unsolicited (Server / Proxy)

In Server and Proxy modes, incoming unsolicited messages from clients are displayed in the Unsolicited Message tab. Messages are parsed using the active ISO8583 template.

Security Options

The simulator supports several security features for testing encrypted and authenticated connections.

Cipher Types

Cipher Modes

ECB, CBC, CFB, OFB, and CTS modes are available for block cipher operations.

Authentication

• None — No authentication required.
• Single Password — One shared password for all clients.
• Client Password — Per-client authentication credentials.

SSL/TLS

Enable SSL for both the server listener and REST API client connections for encrypted transport.

Tabs Reference

The runtime simulator screen has different tabs available depending on the gateway type.