Controller info endpoint and API integration examples (#75)

* Controller API: introduce controller's information endpoint

* Prevent generation of empty events after channel closure

* Allow events to be buffered in the events channel

* Controller API: introduce controller's information endpoint[1]

* IntegrationGuide.md: a couple of Python and Golang examples

* Rephrase a sentence

Co-authored-by: Fedor Korotkov <fedor.korotkov@gmail.com>

---------

Co-authored-by: Fedor Korotkov <fedor.korotkov@gmail.com>

IntegrationGuide.md

@@ -6,6 +6,179 @@ You can run `orchard dev` locally and navigate to http://127.0.0.1:6120/v1/ for
 
 ![](docs/orchard-api-documentation-browser.png)
 
+## Using the API
+
+Below you'll find examples of using Orchard API via vanilla Python's request library and Golang package that Orchard CLI build on top of.
+
+### Authentication
+
+When running in non-development mode, Orchard API expects a [basic access authentication](https://en.wikipedia.org/wiki/Basic_access_authentication) to be provided for each API call.
+
+Below you'll find two snippets that retrieve controller's information and output its version:
+
+**Python**
+
+```python
+import requests
+from requests.auth import HTTPBasicAuth
+
+
+def main():
+  # Authentication
+  basic_auth = HTTPBasicAuth("service account name", "service account token")
+
+  response = requests.get("http://127.0.0.1:6120/v1/info", auth=basic_auth)
+
+  print(response.json()["version"])
+
+
+if __name__ == '__main__':
+  main()
+```
+
+**Golang**
+
+```go
+package main
+
+import (
+  "context"
+  "fmt"
+  "github.com/cirruslabs/orchard/pkg/client"
+  "log"
+)
+
+func main() {
+  client, err := client.New()
+  if err != nil {
+    log.Fatalf("failed to initialize Orchard API client: %v", err)
+  }
+
+  controllerInfo, err := client.Controller().Info(context.Background())
+  if err != nil {
+    log.Fatalf("failed to retrieve controller's information: %v", err)
+  }
+
+  fmt.Println(controllerInfo.Version)
+}
+```
+
+Note that we don't provide any credentials for Golang's version of the snippet: this is because Orchard's Golang API client (`github.com/cirruslabs/orchard/pkg/client`) has the ability to read the current's user Orchard context automatically.
+
+### Creating a VM
+
+A more intricate example would be spinning off a VM with a startup script that outputs date, reading its logs and removing it from the controller:
+
+**Python**
+
+```python
+import time
+import uuid
+
+import requests
+from requests.auth import HTTPBasicAuth
+
+
+def main():
+  vm_name = str(uuid.uuid4())
+
+  basic_auth = HTTPBasicAuth("service account name", "service account token")
+
+  # Create VM
+  response = requests.post("http://127.0.0.1:6120/v1/vms", auth=basic_auth, json={
+    "name": vm_name,
+    "image": "ghcr.io/cirruslabs/macos-ventura-base:latest",
+    "cpu": 4,
+    "memory": 4096,
+    "startup_script": {
+      "script_content": "date",
+    }
+  })
+  response.raise_for_status()
+
+  # Retrieve VM's logs
+  while True:
+    response = requests.get(f"http://127.0.0.1:6120/v1/vms/{vm_name}/events", auth=basic_auth)
+    response.raise_for_status()
+
+    result = response.json()
+
+    if isinstance(result, list) and len(result) != 0:
+      print(result[0]["payload"])
+      break
+
+    time.sleep(1)
+
+  # Delete VM
+  response = requests.delete(f"http://127.0.0.1:6120/v1/vms/{vm_name}", auth=basic_auth)
+  response.raise_for_status()
+
+
+if __name__ == '__main__':
+  main()
+```
+
+**Golang**
+
+```go
+package main
+
+import (
+  "context"
+  "fmt"
+  "github.com/cirruslabs/orchard/pkg/client"
+  v1 "github.com/cirruslabs/orchard/pkg/resource/v1"
+  "github.com/google/uuid"
+  "log"
+  "time"
+)
+
+func main() {
+  vmName := uuid.New().String()
+
+  client, err := client.New()
+  if err != nil {
+    log.Fatalf("failed to initialize Orchard API client: %v", err)
+  }
+
+  // Create VM
+  err = client.VMs().Create(context.Background(), &v1.VM{
+    Meta: v1.Meta{
+      Name: vmName,
+    },
+    Image:  "ghcr.io/cirruslabs/macos-ventura-base:latest",
+    CPU:    4,
+    Memory: 4096,
+    StartupScript: &v1.VMScript{
+      ScriptContent: "date",
+    },
+  })
+  if err != nil {
+    log.Fatalf("failed to create VM: %v")
+  }
+
+  // Retrieve VM's logs
+  for {
+    vmLogs, err := client.VMs().Logs(context.Background(), vmName)
+    if err != nil {
+      log.Fatalf("failed to retrieve VM logs")
+    }
+
+    if len(vmLogs) != 0 {
+      fmt.Println(vmLogs[0])
+      break
+    }
+
+    time.Sleep(time.Second)
+  }
+
+  // Delete VM
+  if err := client.VMs().Delete(context.Background(), vmName); err != nil {
+    log.Fatalf("failed to delete VM: %v", err)
+  }
+}
+```
+
 ## Resource management
 
 Some resources, such as `Worker` and `VM`, have a `resource` field which is a dictionary that maps between resource names and their amounts (amount requested or amount provided, depending on the resource) and is useful for scheduling.