Karl Fleischmann
Software Engineer at Open-Xchange
Leipzig, Saxony, Germany
Summary
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Rockstar🎓
Top SchoolKarl Fleischmann is a software engineer with a decade of experience building and stabilizing backend and systems software, currently at Open-Xchange in Leipzig. He has a strong systems background demonstrated by contributions to high-profile projects like the Dovecot mail server and the ckb-next Linux RGB driver, where he focused on authentication, IMAP internals, signal safety, and race-condition fixes. Karl moves between roles comfortably—from game programming to lead developer—and brings practical production-first thinking, including writing unit tests and removing risky or unnecessary functionality to improve maintainability. He holds an MSc in Computer Science from Universität Rostock and maintains his code history on sourcehut, reflecting a preference for minimal, sustainable tooling and long-lived, well-tested solutions.
10 years of coding experience
6 years of employment as a software developer
Master of Science - MS Computer Science, Master of Science - MS Computer Science at Universität Rostock
Stackoverflow
118reputation
9kreached
5answers
0questions
Github Skills (28)
debugging10
debug10
system-programming10
imap10
authentication10
user-authentication10
usb10
c1110
linux-kernel10
c1710
kernel10
device-driver10
signal-handling9
unit-testing9
multithreading9
Programming languages (11)
Github contributions (5)
ckb-next/ckb-next
Jan 2018 - Sep 2019
RGB Driver for Linux
Role in this project:
Back-end Developer & Systems Engineer
Back-end Developer & Systems EngineerContributions:3 reviews, 20 commits, 6 PRs in 1 year 7 months
Contributions summary:Karl primarily focused on improving the stability and maintainability of the ckb-next project, an RGB driver for Linux. Their contributions included refactoring the codebase by removing unnecessary functionality, such as the daemon-restart feature, and implementing a safer signal-handling mechanism. They also addressed potential race conditions and fixed a segfault on macOS. Furthermore, the user added support for the K63_WL keyboard, extending the driver's compatibility.
linuxrgblogitech
dovecot/core
Dec 2021 - Jan 2023
Dovecot mail server
Role in this project:Back-end Developer
Back-end DeveloperContributions:175 commits in 1 year 1 month
Contributions summary:Karl's contributions focused on enhancements and bug fixes within the Dovecot mail server. The commits demonstrate a deep understanding of the system's internal workings, particularly concerning authentication, IMAP commands, and storage mechanisms. The user implemented improvements to handle authentication flows, fix issues with the program client execution, and correct code related to handling IMAP commands and various mail storage operations. The user also wrote unit tests for mail parsing and program client execution.
imap-clientmailsmtpsendmailwebmail
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