VSI-AXPVMS-PAHO C-V0103-0A-1-RELNOTES.PDF

This document introduces the Paho-C MQTT client API for OpenVMS Alpha and Integrity, based on the Paho-C 1.3.0 distribution.

Key Features and Purpose:

• MQTT Protocol: It's a fully-featured, lightweight publish-subscribe protocol over TCP/IP, suitable for remote connections, low bandwidth, small code footprints, and mobile applications (e.g., sensors, home automation, healthcare providers).
• API Variants: Offers both synchronous (blocking I/O) and asynchronous (non-blocking with callbacks, using POSIX threads on OpenVMS) APIs.
• Full Functionality: Includes all features of the open-source Paho-C release, notably comprehensive SSL/TLS support (statically linked with OpenSSL 1.1.1g).
• Bug Fix: This release specifically addresses a bug causing network write operation failures with high maxInflightMessages values.

System Requirements:

• OpenVMS 8.4-1H1 or later.
• VSI TCP/IP, HPE TCP/IP Services, or MultiNet TCP/IP stack.
• VSI C V7.4-001 or a comparable C compiler.

Installation and Usage:

• Distributed as an OpenVMS PCSI kit.
• Requires post-installation steps to add startup/shutdown commands to SYSTARTUP_VMS.COM to define system-wide logical names for development.
• Logical names are provided for different library configurations (synchronous/asynchronous, with/without TLS/SSL support).
• Sample applications are included, with notes on linking for TLS/SSL.
• Most applications do not require special privileges, but SYSPRV, BYPASS, or OPER are needed for applications using privileged ports (below 1024).

Future Development:

• Future releases may introduce OpenVMS-specific functionality and abstraction layers to simplify use from other languages like COBOL, FORTRAN, and BASIC.