VSI-AXPVMS-PAHO C-V0103-0-1-RELNOTE.PDF

This document introduces the Paho-C MQTT client API for OpenVMS Alpha and Integrity, a port of the Paho-C 1.3.0 distribution.

Key features and purpose:

• MQTT is a lightweight publish-subscribe protocol over TCP/IP, ideal for applications requiring a small code footprint, low power usage, and efficient data distribution (e.g., sensors, home automation, mobile apps).
• The OpenVMS port includes all original functionality, offering both synchronous (blocking) and asynchronous (non-blocking, callback-based using POSIX threads) APIs.
• It crucially includes built-in SSL/TLS support, statically linked with OpenSSL 1.1.1b, for secure communication.

Installation and Usage:

• The client is distributed as an OpenVMS PCSI kit, installed using PRODUCT INSTALL PAHO_C.
• Post-installation requires modifying SYSTARTUP_VMS.COM to define system-wide logical names for the Paho-C libraries, which come in variants for synchronous/asynchronous APIs and with/without TLS/SSL support.
• System requirements include OpenVMS 8.4-1H1+, a VSI/HPE/MultiNet TCP/IP stack, and a VSI C V7.4-001+ compiler. Developers should have OpenVMS development knowledge.
• Sample applications are provided to aid learning, and it's recommended to consult the Eclipse Foundation Paho documentation.
• While applications generally don't require special privileges, a high BYTLM is suggested, and specific privileges are needed for using ports below 1024.

Future Development:

• Future releases are planned to include OpenVMS-specific functionality and abstraction layers to simplify usage from languages other than C, such as COBOL, FORTRAN, and BASIC.