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Sula: A Gemini protocol server written in Scryer Prolog
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Illustration only Photo by Samuel Ramos on Unsplash
A Gemini protocol server called Sula has been implemented in Scryer Prolog, requiring a patched version of the Prolog system to handle TLS, non-blocking I/O, and graceful shutdown.
For engineers, Sula demonstrates that a logic programming language can serve a modern internet protocol, but the need for a custom Scryer Prolog fork with native stream copying, non-blocking socket acceptance, and rustls integration means adoption carries a maintenance burden. The server's current limitations, no client certificates, no CGI, no rate limiting, make it a proof of concept rather than a production-ready Gemini capsule. Anyone considering it must weigh the novelty of Prolog-based server logic against the cost of tracking a patched runtime and the absence of features expected in a Gemini server.
Written by elseif from the cluster below · every claim links back to a sourceThe three things worth knowing
Sula is a Gemini protocol server written entirely in Scryer Prolog, launched via a polyglot script that detects the Prolog interpreter.
It depends on a patched Scryer Prolog that adds native binary streaming, non-blocking socket polling, and rustls-based TLS with optional client certificate support.
The server currently lacks planned features such as CGI scripts, rate limiting, virtual hosting, and file logging, limiting its use to simple static Gemini sites.
THE READ
What elseif makes of it.
Sula introduces a Gemini server implemented in Scryer Prolog, a language not commonly used for network services. The author chose Prolog for its declarative nature, using DCGs for parsing configuration, MIME types, and Gemini URIs. However, this choice imposes a dependency on a specific patched version of Scryer Prolog, which includes modifications to the runtime for streaming binary data without heap materialization, non-blocking socket acceptance, and TLS via rustls. These patches are not part of the main Scryer Prolog distribution, so engineers must build and maintain a custom fork.
The server's architecture separates concerns into small Prolog modules: config.pl for CLI parsing, cert.pl for certificate handling, mime.pl for MIME type mapping, and request.pl for reading Gemini requests. Binary responses are streamed directly from file to TLS socket using a native copy_stream/2 builtin, avoiding Prolog heap overhead. This design shows attention to performance, but the reliance on a patched runtime means that any upstream changes to Scryer Prolog could break compatibility. The startup also shells out to openssl to verify the certificate's CN, adding an external dependency.
Sula currently supports only a subset of the Gemini protocol: it serves static files with MIME type negotiation, handles TLS handshake failures gracefully, and shuts down cleanly on SIGINT. Missing features include client certificates, CGI scripts, rate limiting, virtual hosting, and file logging, all listed as planned. For a working engineer, this means Sula is suitable only for simple personal capsules or testing. The lack of rate limiting and virtual hosting makes it unsuitable for multi-tenant or public-facing services without additional infrastructure.
The project's documentation emphasizes the patched Scryer Prolog requirements and the need for openssl on PATH. The build process involves cloning a specific branch and running cargo install. This level of setup friction is typical for experimental software but may deter engineers looking for a drop-in Gemini server. The planned features suggest the author intends to mature the project, but as of now, the server's value lies in demonstrating Prolog's viability for network programming rather than providing a robust production tool.
Written by elseif from the cluster below · checked for specifics the sources never containedTHE CLUSTER