add debugging protocol description draft

doc/specs/debugging_protocol.md

@@ -0,0 +1,153 @@
+# VC-DBG protocol v1
+
+## Notes
+
+- '?' in name means that the attribute is optional.
+
+## Connecting
+
+### Step 1
+
+Connection initiating with binary header exchange:
+
+```
+'v' 'c' '-' 'd' 'b' 'g' NUL XX
+76  63  2D  64  62  67  00  XX
+```
+
+XX - protocol version number
+
+Client sends header to the server. Then server responds.
+Server closes connection after sending header if it mismatches.
+
+### Step 2
+
+Client sends 'connect' command.
+
+## Messages
+
+Message is:
+- 32 bit little-endian unsigned integer - number of encoded message bytes.
+- message itself (UTF-8 encoded json).
+
+## Client-to-server
+
+### Establishing connection
+
+```json
+{
+    "type": "connect",
+    "?disconnect-action": "resume|detach|terminate"
+}
+```
+
+Configuring connection. Disconnect-action is action that debugged instance must perform on debugging client connection closed/refused.
+
+- `resume` - Resume from pause mode and start listening for client.
+- `detach` - Resume from pause mode and stop server.
+- `terminate` - Stop the debugged application.
+
+
+### Specific action signals.
+
+```json
+{
+    "type": "pause|resume|terminate|detach"
+}
+```
+
+### Breakpoints management
+
+```json
+{
+    "type": "set-breakpoint|remove-breakpoint",
+    "source": "entry_point:path",
+    "line": 1
+}
+```
+
+### Local value details request
+
+```json
+{
+    "type": "get-value",
+    "frame": 0,
+    "local": 1,
+    "path": ["path", "to", 1, "value"]
+}
+```
+
+- `frame` - Call stack frame index (indexing from most recent call)
+- `local` - Local variable index (based on `paused` event stack trace)
+- `path` - Requsted value path segments. Example: `['a', 'b', 5]` is `local_variable.a.b[5]`
+
+Responds with:
+
+```json
+{
+    "type": "value",
+    "frame": 0,
+    "local": 1,
+    "path": ["path", "to", 1, "value"],
+    "value": "value itself"
+}
+```
+
+Example: actual value is table: 
+```lua
+{a=5, b="test", 2={}}
+```
+
+Then `value` is:
+```json
+{
+    "a": {
+        "type": "number",
+        "short": "5"
+    },
+    "b": {
+        "type": "string",
+        "short": "test"
+    },
+    "1": {
+        "type": "table",
+        "short": "{...}"
+    }
+}
+```
+
+## Server-to-client
+
+### Response signals
+
+```json
+{
+    "type": "success|resumed"
+}
+```
+
+### Pause event
+
+```json
+{
+    "type": "paused",
+    "?reason": "breakpoint|exception|step",
+    "?message": "...",
+    "?stack": [
+        {
+            "?function": "function name",
+            "source": "source name",
+            "what": "what",
+            "line": 1,
+            "locals": [
+                "name": {
+                    "type": "local type",
+                    "index": 1,
+                    "short": "short value",
+                    "size": 0
+                }
+            ]
+        }
+    ]
+}
+```