fix: return the created template from appliance install

POST /appliances/{id}/install replied 204 with an empty body, so the MCP
appliance_install tool crashed with 'Expecting value: line 1 column 1'
while the template had actually been created. The route now returns the
created template (201, response_model=schemas.Template), _create_template
propagates it, and the MCP handler parses the body defensively so an
empty reply degrades to a plain success message.

gns3server/agent/mcp/__init__.py

@@ -1376,7 +1376,7 @@ async def appliance_install(
     appliance_id: Annotated[str, Field(description="UUID of the appliance to install")],
     version: Annotated[str | None, Field(description="Version to install (e.g. '2.7.0.356'). Required if the appliance has multiple versions. Use appliance_get to see available versions.")] = None,
 ) -> list[dict[str, Any]]:
-    """Create a template from a GNS3 appliance definition.
+    """Create a template from a GNS3 appliance definition and return the created template.
 
     NOTE: This does NOT download images. Images must be placed in the
     GNS3 images directory (e.g. ~/GNS3/images/) beforehand.

gns3server/agent/mcp/appliances.py

@@ -85,5 +85,13 @@ def install_appliance_handler(params: dict[str, Any], gns3_ctx: dict[str, Any])
     version = params.get("version")
     if version:
         request_params["version"] = version
-    result = conn.http_call("post", url, params=request_params).json()
-    return {"message": f"Appliance {appliance_id} installation requested", "result": result}
+    response = conn.http_call("post", url, params=request_params)
+    result = {"message": f"Appliance {appliance_id} installed"}
+    if response.content:
+        # the install endpoint returns the created template (201); tolerate an
+        # empty body in case an older server still replies with 204
+        template = response.json()
+        result["template"] = {
+            k: template[k] for k in ("template_id", "name", "version", "template_type") if k in template
+        }
+    return result

gns3server/api/routes/controller/appliances.py

@@ -122,7 +122,8 @@ def add_appliance_version(appliance_id: UUID, appliance_version: Union[schemas.A
 
 @router.post(
     "/{appliance_id}/install",
-    status_code=status.HTTP_204_NO_CONTENT,
+    response_model=schemas.Template,
+    status_code=status.HTTP_201_CREATED,
     dependencies=[Depends(has_privilege("Appliance.Allocate"))]
 )
 async def install_appliance(
@@ -132,15 +133,15 @@ async def install_appliance(
         templates_repo: TemplatesRepository = Depends(get_repository(TemplatesRepository)),
         current_user: schemas.User = Depends(get_current_active_user),
         rbac_repo: RbacRepository = Depends(get_repository(RbacRepository))
-) -> None:
+) -> schemas.Template:
     """
-    Install an appliance.
+    Install an appliance and return the created template.
 
     Required privilege: Appliance.Allocate
     """
 
     controller = Controller.instance()
-    await controller.appliance_manager.install_appliance(
+    return await controller.appliance_manager.install_appliance(
         appliance_id,
         version,
         images_repo,

gns3server/controller/appliance_manager.py

@@ -204,9 +204,9 @@ class ApplianceManager:
                                 else:
                                     raise ControllerError(f"Could not find '{appliance_file}'")
 
-    async def _create_template(self, template_data, templates_repo, rbac_repo, current_user):
+    async def _create_template(self, template_data, templates_repo, rbac_repo, current_user) -> dict:
         """
-        Create a new template
+        Create a new template and return it as a dict.
         """
 
         try:
@@ -217,6 +217,7 @@ class ApplianceManager:
         #template_id = template.get("template_id")
         #await rbac_repo.add_permission_to_user_with_path(current_user.user_id, f"/templates/{template_id}/*")
         log.info(f"Template '{template.get('name')}' has been created")
+        return template
 
     async def _appliance_to_template(self, appliance: Appliance, version: str = None) -> dict:
         """

tests/agent/mcp/test_handlers.py

@@ -3,6 +3,8 @@ MCP handler unit tests with mocked Gns3Connector.
 
 Tests that handlers correctly transform tool parameters into HTTP calls.
 """
+import json
+
 import pytest
 from unittest.mock import MagicMock, patch
 
@@ -12,6 +14,7 @@ def _mock_conn(json_result=None):
     conn = MagicMock()
     conn.base_url = "http://192.168.1.3:3080/v3"
     conn.http_call.return_value.json.return_value = json_result or {"status": "ok"}
+    conn.http_call.return_value.content = b"{}"  # non-empty body by default
     return conn
 
 
@@ -449,7 +452,7 @@ class TestAppliance:
     def test_install_with_version(self, ctx):
         from gns3server.agent.mcp.appliances import install_appliance_handler
         with patch(f"{BASE}.{self.mod}._get_connector") as m:
-            conn = _mock_conn({"status": "installed"})
+            conn = _mock_conn({"template_id": "t1", "name": "FRR", "version": "8.2.2", "template_type": "docker"})
             m.return_value = conn
             result = install_appliance_handler({
                 "appliance_id": "a1", "version": "2.7.0.356",
@@ -458,6 +461,22 @@ class TestAppliance:
                 "post", "http://192.168.1.3:3080/v3/appliances/a1/install",
                 params={"version": "2.7.0.356"},
             )
+            assert result["template"] == {
+                "template_id": "t1", "name": "FRR", "version": "8.2.2", "template_type": "docker",
+            }
+
+    def test_install_empty_body(self, ctx):
+        # a 204-style empty response must not blow up with a JSON decode error
+        # (the template is still created server-side)
+        from gns3server.agent.mcp.appliances import install_appliance_handler
+        with patch(f"{BASE}.{self.mod}._get_connector") as m:
+            conn = _mock_conn()
+            conn.http_call.return_value.content = b""
+            conn.http_call.return_value.json.side_effect = json.JSONDecodeError("Expecting value", "", 0)
+            m.return_value = conn
+            result = install_appliance_handler({"appliance_id": "a1"}, ctx)
+            assert "template" not in result
+            assert result["message"] == "Appliance a1 installed"
 
     def test_install_missing_id(self, ctx):
         from gns3server.agent.mcp.appliances import install_appliance_handler

tests/api/routes/controller/test_appliances.py

@@ -53,7 +53,8 @@ class TestApplianceRoutes:
 
         appliance_id = "fc520ae2-a4e5-48c3-9a13-516bb2e94668"  # Alpine Linux appliance
         response = await client.post(app.url_path_for("install_appliance", appliance_id=appliance_id))
-        assert response.status_code == status.HTTP_204_NO_CONTENT
+        assert response.status_code == status.HTTP_201_CREATED
+        assert response.json()["name"] == "Alpine Linux"
 
     async def test_docker_appliance_install_with_version(self, app: FastAPI, client: AsyncClient) -> None:
 
@@ -68,7 +69,9 @@ class TestApplianceRoutes:
         appliance_id = "1cfdf900-7c30-4cb7-8f03-3f61d2581633"  # Empty VM appliance
         params = {"version": "8G"}
         response = await client.post(app.url_path_for("install_appliance", appliance_id=appliance_id), params=params)
-        assert response.status_code == status.HTTP_204_NO_CONTENT
+        assert response.status_code == status.HTTP_201_CREATED
+        assert response.json()["name"] == "Empty VM"
+        assert response.json()["version"] == "8G"
 
     async def test_qemu_appliance_install_without_version(self, app: FastAPI, client: AsyncClient, images_dir: str) -> None: