Add logjet export as a sharedlib

Cargo.toml

@@ -5,8 +5,8 @@ edition = "2024"
 license = "Apache-2.0"
 
 [workspace]
-members = [".", "logjetd", "demo", "ljx"]
-default-members = [".", "logjetd", "demo", "ljx"]
+members = [".", "logjetd", "demo", "ljx", "liblogjet"]
+default-members = [".", "logjetd", "demo", "ljx", "liblogjet"]
 
 [profile.release]
 lto = true

README.md

@@ -154,6 +154,7 @@ fn replay_batches() -> Result<(), Box<dyn std::error::Error>> {
 ## Notes
 
 - Examples for standalone usage live in [examples](./examples).
+- C and C++ shared-library usage lives in [doc/c-cpp-integration.md](./doc/c-cpp-integration.md).
 - The reader is sequential by design.
 - Compression is per block, not per file.
 - The payload bytes are opaque to `logjet`.

demo/README.md

@@ -35,6 +35,8 @@ It also contains scenario demos under subdirectories:
   - one replay client stalls while another keeps flowing
 - [`replay-handoff`](./replay-handoff)
   - a late replay client drains retained backlog and then continues live on the same connection
+- [`cpp-shared-lib`](./cpp-shared-lib)
+  - a C++ process loads `liblogjet.so`, sends OTLP logs into `ljd`, and opens the result in `ljx view`
 - [`file-replay`](./file-replay)
   - replay stored `.logjet` files into a collector
 - [`file-tooling`](./file-tooling)

demo/cpp-shared-lib/README.md

@@ -0,0 +1,46 @@
+# C++ Shared Library Demo
+
+This demo shows one C++ process loading a Rust shared library and sending OTLP
+logs into `ljd` over gRPC.
+
+The path is:
+
+`C++ appliance -> liblogjet.so -> OTLP/gRPC -> ljd -> .logjet file -> ljx view`
+
+## Build First
+
+From the project root:
+
+```bash
+cargo build -p ljd -p ljx -p liblogjet
+```
+
+You also need `g++` available locally because the demo compiles the C++
+example on demand.
+
+## Run
+
+From this directory:
+
+```bash
+./run-demo.sh
+```
+
+## What It Does
+
+The script:
+
+1. builds the example C++ logger
+2. starts file-backed `ljd` on `127.0.0.1:4317`
+3. loads `liblogjet.so` through `dlopen`
+4. sends 25 OTLP log records from C++ by default
+5. opens `ljx view` on the resulting `./logs/cpp-demo.logjet`
+
+## Notes
+
+- the library now supports both OTLP/HTTP and OTLP/gRPC constructors
+- this demo specifically uses OTLP/gRPC
+- the FFI API is intentionally small: endpoint, service name, timestamp, severity, message body, and string attributes
+- those key/value pairs become OTLP `LogRecord.attributes`, which is the standard OTel metadata field for log records
+- if the appliance already has JSON metadata, the better long-term shape is to flatten that JSON into separate attributes where possible; a raw JSON blob can still be sent as one string attribute when needed
+- the demo uses a local symlink named `liblogjet.so` that points at Cargo's built shared object