Implement devices datasource (#34)

This commit implements the `tailscale_devices` data source and allows for
a `name_prefix` argument to filter the list of devices.

Closes #32

Signed-off-by: David Bond <[email protected]>

docs/data-sources/devices.md

@@ -0,0 +1,31 @@
+---
+page_title: "devices Data Source - terraform-provider-tailscale"
+subcategory: ""
+description: |-
+"The devices data source describes a list of devices in a tailnet.
+---
+
+# Data Source `devices`
+
+The devices data source describes a list of devices in a tailnet.
+
+## Example Usage
+
+```terraform
+data "tailscale_devices" "sample_devices" {
+  name_prefix = "example-"
+}
+
+```
+
+## Argument Reference
+
+- `name_prefix` - (Optional) Filters the returned list of devices to those whose name have this prefix.
+
+## Attributes Reference
+
+The following attributes are exported.
+
+- `devices` - The list of devices returned from the Tailscale API. Each element contains the following:
+  - `id` - The unique identifier of the device
+  - `name` - The name of the device

tailscale/data_source_devices.go

@@ -0,0 +1,72 @@
+package tailscale
+
+import (
+	"context"
+	"strings"
+
+	"github.com/davidsbond/terraform-provider-tailscale/internal/tailscale"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/diag"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
+)
+
+func dataSourceDevices() *schema.Resource {
+	return &schema.Resource{
+		Description: "The devices data source describes a list of devices in a tailnet",
+		ReadContext: dataSourceDevicesRead,
+		Schema: map[string]*schema.Schema{
+			"name_prefix": {
+				Optional:    true,
+				Type:        schema.TypeString,
+				Description: "Filters the device list to elements whose name has the provided prefix",
+			},
+			"devices": {
+				Computed:    true,
+				Type:        schema.TypeList,
+				Description: "The list of devices in the tailnet",
+				Elem: &schema.Resource{
+					Schema: map[string]*schema.Schema{
+						"name": {
+							Type:        schema.TypeString,
+							Description: "The name of the device",
+							Computed:    true,
+						},
+						"id": {
+							Type:        schema.TypeString,
+							Description: "The unique identifier of the device",
+							Computed:    true,
+						},
+					},
+				},
+			},
+		},
+	}
+}
+
+func dataSourceDevicesRead(ctx context.Context, d *schema.ResourceData, m interface{}) diag.Diagnostics {
+	client := m.(*tailscale.Client)
+
+	devices, err := client.Devices(ctx)
+	if err != nil {
+		return diagnosticsError(err, "Failed to fetch devices")
+	}
+
+	namePrefix, _ := d.Get("name_prefix").(string)
+	deviceMaps := make([]map[string]interface{}, 0)
+	for _, device := range devices {
+		if namePrefix != "" && !strings.HasPrefix(device.Name, namePrefix) {
+			continue
+		}
+
+		deviceMaps = append(deviceMaps, map[string]interface{}{
+			"name": device.Name,
+			"id":   device.ID,
+		})
+	}
+
+	if err = d.Set("devices", deviceMaps); err != nil {
+		return diag.FromErr(err)
+	}
+
+	d.SetId(createUUID())
+	return nil
+}

tailscale/provider.go

@@ -36,7 +36,8 @@ func Provider() *schema.Provider {
 			"tailscale_device_subnet_routes": resourceDeviceSubnetRoutes(),
 		},
 		DataSourcesMap: map[string]*schema.Resource{
-			"tailscale_device": dataSourceDevice(),
+			"tailscale_device":  dataSourceDevice(),
+			"tailscale_devices": dataSourceDevices(),
 		},
 	}
 }

tailscale/resource_device_subnet_routes_test.go

@@ -12,7 +12,7 @@ const testDeviceSubnetRoutes = `
 	}
 	
 	resource "tailscale_device_subnet_routes" "test_subnet_routes" {
-		device_id = tailscale_device.test_device.id,
+		device_id = data.tailscale_device.test_device.id,
 		routes = [
 			"10.0.1.0/24", 
 			"1.2.0.0/16",