wasm

wasm (WASI Preview 1)

Minimal example of building libfossil for a generic WASI Preview 1 wasm target. The produced .wasm binary is not tied to any specific runtime and is intended to run under wasmtime, wazero, or any other WASI P1 host.

Driver choice

The default modernc.org/sqlite driver pulls in syscalls (pthread, signal, stdio, sys/types, unistd, ...) that have no Go files under GOOS=wasip1, so _ "github.com/danmestas/libfossil/db/driver/modernc" will not compile for wasip1. This example blank-imports the ncruces driver instead:

_ "github.com/danmestas/libfossil/db/driver/ncruces"

ncruces/go-sqlite3 ships SQLite itself as WebAssembly and is the supported driver for wasip1 and browser (js) builds.

Build

From the repo root:

GOOS=wasip1 GOARCH=wasm go build -o libfossil-demo.wasm ./examples/wasm/

The output is a generic WASI P1 module (~22 MiB) with no runtime-specific imports.

Run

wasmtime

wasmtime requires an explicit --dir map so the guest can see a writable directory. The simplest form maps the current host directory to the guest root:

wasmtime run --dir=.::/ libfossil-demo.wasm

--dir=. alone works in newer wasmtime releases but some versions require the explicit HOST::GUEST form shown above.

wazero (CLI)

wazero run -mount .:/ libfossil-demo.wasm

What the example demonstrates

• Registering the ncruces driver via a blank import.
• libfossil.Create to create a fresh .fossil file in the mapped directory.
• libfossil.Open to re-open it.
• repo.Config("project-code") to read a config row.
• repo.Commit to write one file.
• repo.Timeline and repo.ListFiles to read back the commit.

Runtime limitations under WASI

WASI P1 does not expose POSIX / OFD / BSD file locking, which SQLite relies on for concurrency control. libfossil detects GOOS=wasip1 at compile time and switches to a WAL-free, exclusive-locking pragma profile (see db/config_wasm.go), but some combinations of host runtime and SQLite VFS still surface I/O errors when PRAGMA journal_mode is set through the DSN. If you hit sqlite3: invalid _pragma: sqlite3: disk I/O error under your runtime, the issue is in the SQLite VFS glue, not in this example — the build itself is a clean WASI P1 artifact and loads fine under wasmtime / wazero.

The example is designed for single-process, single-connection usage, which is the supported mode for libfossil on WASI.