taglogwriter (Rust)

A safe Rust interface to the C++ SQLite log writer. LogWriter wraps the tlw_* functions of tagcore_c. It encodes each message with prost and passes the bytes, so the database is exactly the one the C++ tools write. The protobuf types come from tagcore-rs. The Rust tag-dwnld is built on it. The architecture covers both crates and the library together.

Building

The crate links a library that CMake builds, through tagcore-c-sys, so cargo build alone is not enough:

cmake -DBUILD_TAGCORE_C=ON <build-dir>
cmake --build <build-dir> --target tagcore_c_static tagcore_c
export TAGCORE_C_LIB_DIR=<build-dir>/Release/lib
cargo build                          # macOS: libtagcore_c.a; Linux, Windows: shared
TAGCORE_C_LINK=dylib cargo build     # force the shared library

The link follows the platform's packaging (owner's decision, 2026-10-27). macOS links statically: each application is its own bundle, so a shared library would be copied into every one, and a static executable needs nothing at run time. Linux and Windows link the shared library: the tools share one install directory, so one copy serves them all. With the shared library, a binary finds it through an rpath. That rpath is set by tagcore-c-sys's build script for this crate's own examples and tests. For a dependent binary, its own package's build script sets it, from DEP_TAGCORE_C_LIB_DIR, which Cargo gives to direct dependents of tagcore-c-sys; see commandline-rs/build.rs. On Windows the DLL must sit beside the executable or on PATH.

Using it

LogWriter::create(path, config, replace), then write_header(&LogHeader), begin_log(), one write_log(&Ack) per page, and end_log(). write_log returns how many records the page consumed, which advances the index of the next page to request, and 0 at the end of the log. Only the writer can say either, since both depend on the tag type. set_debug() sets the C++ writer's logging, as -d does for the C++ tools. The rustdoc on src/lib.rs has the details.

Checking

examples/log-import.rs repeats tag-log-import through the wrapper, with the same calls in the same order:

cargo run --release --example log-import -- download.jsonl rust.db3
tag-log-import download.jsonl -o cpp.db3
cmp rust.db3 cpp.db3            # identical, given the same input path

The input path matters because both tools record it in the import_file info row.