feat: add BVK exchange library

protocol.md

@@ -0,0 +1,63 @@
+# BVK Exchange Protocol
+
+Based on `Протокол_обмена_медиакомплекса_и_БВК.pdf`.
+
+## Role
+
+- BVK is the HTTP client.
+- Media complex is the HTTP server.
+- Default address from the document: `172.16.16.2:13280`.
+
+## Set Content
+
+```text
+GET /set-content?route=<R>&str=<S>&tpl_name=<T>
+```
+
+Parameters are URL-encoded.
+
+| Parameter | Meaning |
+| --- | --- |
+| `route` | Route number, 1 to 3 characters |
+| `str` | Ticker/running text |
+| `tpl_name` | Media content template name |
+
+Current library defaults:
+
+| Field | Default limit |
+| --- | ---: |
+| `route` | 3 characters |
+| `str` | 200 characters |
+| `tpl_name` | 200 characters |
+
+The exact text/template limits must be confirmed with the integrator because the
+PDF text layer is ambiguous for the original value.
+
+## Get Content
+
+```text
+GET /get-content
+```
+
+Response:
+
+```json
+{
+  "route": "<R>",
+  "str": "<S>",
+  "tpl_name": "<T>"
+}
+```
+
+Mila keeps `updated_at` internally, but the HTTP response is strict and exposes
+only the fields defined by the protocol.
+
+## Status Codes
+
+| Code | Meaning |
+| ---: | --- |
+| 200 | OK |
+| 400 | Bad request / validation error |
+| 404 | Path not found |
+| 500 | Internal server error |
+| 503 | State is not ready or dependency unavailable |