Kazuho Oku
Senior Principal Open Source Software Developer at Fastly
Tokyo, Japan
Summary
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Rockstar🎓
Top SchoolKazuho Oku is a Senior Principal Open Source Software Developer based in Tokyo with 16 years of experience building high-performance networking and systems software. He leads development on H2O, an optimized HTTP/1–3 server, and has deep expertise in TLS, QUIC/HTTP3 integration, and performance tuning for real-world deployments. A prolific open-source contributor, his low-level work spans lightweight language runtimes (mruby), tiny HTTP parsers, and robust C/C++ libraries like picojson and picohttpparser. His background includes building deployment systems, a cloud gaming engine, and language tooling (JSX) at scale, reflecting a blend of systems architecture and practical product shipping. Notably, he pairs protocol-level security improvements with pragmatic optimizations such as sendfile and QAT acceleration, demonstrating a rare combination of cryptographic awareness and systems performance engineering.
17 years of coding experience
20 years of employment as a software developer
University of Tokyo
Japanese, English
Stackoverflow
291reputation
9kreached
3answers
0questions
Github Skills (40)
json-parser10
json10
ss10
ssl10
lib10
c-language10
api-design10
http10
jsonp10
sslv310
data-serialization10
c1110
perl10
psgi10
ruby10
Programming languages (15)
Github contributions (5)
h2o/h2o
Jun 2014 - Jan 2023
H2O - the optimized HTTP/1, HTTP/2, HTTP/3 server
Role in this project:
Back-end Developer & Security Engineer
Back-end Developer & Security EngineerContributions:70 releases, 698 reviews, 7909 commits in 8 years 8 months
Contributions summary:Kazuho's commits focused on enhancing the security and functionality of the H2O HTTP server, specifically in the context of TLS 1.2 and HTTP/3. They implemented features such as moving TLS state to picotls after the handshake to optimize performance. The commits also added the necessary code to enable QUIC with a focus on improving security and stability of the underlying network traffic. Further improvements include enabling and testing QAT-based performance optimizations.
kazuho/picojson
Jul 2011 - Jan 2021
a header-file-only, JSON parser serializer in C++
Role in this project:Back-end Developer
Back-end DeveloperContributions:1 release, 148 commits, 27 PRs in 9 years 7 months
Contributions summary:Kazuho primarily contributed to the picojson library by enhancing its functionality and fixing bugs. They added missing inline keywords, modified the serialization process to correctly handle integral numbers, and implemented a SAX interface. Furthermore, the user updated the copyright information and introduced enhancements to the API related to streaming and handling of decimal points based on the locale settings. They also made changes to enhance stability and correctness.
cppjson-parserserializer
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