AB#2299 License check in CLI during init (#366)

* license server interaction
* logic to read from license file
* print license information during init
Signed-off-by: Fabian Kammel <fk@edgeless.systems>
Co-authored-by: Moritz Eckert <m1gh7ym0@gmail.com>

internal/license/license.go

@@ -0,0 +1,91 @@
+package license
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/url"
+)
+
+const (
+	// CommunityLicense is used by everyone who has not bought an enterprise license.
+	CommunityLicense = "00000000-0000-0000-0000-000000000000"
+	// CommunityQuota is the vCPU quota allowed for community installations of Constellation.
+	CommunityQuota = 8
+	apiHost        = "license.confidential.cloud"
+	licensePath    = "api/v1/license"
+)
+
+type Action string
+
+const (
+	Init Action = "init"
+	test Action = "test"
+)
+
+// Client interacts with the ES license server.
+type Client struct {
+	httpClient *http.Client
+}
+
+// NewClient creates a new client to interact with ES license server.
+func NewClient() *Client {
+	return &Client{
+		httpClient: http.DefaultClient,
+	}
+}
+
+// CheckQuotaRequest is JSON request to license server to check quota for a given license and action.
+type CheckQuotaRequest struct {
+	Action  Action `json:"action"`
+	License string `json:"license"`
+}
+
+// CheckQuotaResponse is JSON response by license server.
+type CheckQuotaResponse struct {
+	Quota int `json:"quota"`
+}
+
+// CheckQuota for a given license and action, passed via CheckQuotaRequest.
+func (c *Client) CheckQuota(ctx context.Context, checkRequest CheckQuotaRequest) (CheckQuotaResponse, error) {
+	reqBody, err := json.Marshal(checkRequest)
+	if err != nil {
+		return CheckQuotaResponse{}, fmt.Errorf("unable to marshal input: %w", err)
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, licenseURL().String(), bytes.NewBuffer(reqBody))
+	if err != nil {
+		return CheckQuotaResponse{}, fmt.Errorf("unable to create request: %w", err)
+	}
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return CheckQuotaResponse{}, fmt.Errorf("unable to do request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return CheckQuotaResponse{}, fmt.Errorf("http error %d", resp.StatusCode)
+	}
+
+	responseContentType := resp.Header.Get("Content-Type")
+	if responseContentType != "application/json" {
+		return CheckQuotaResponse{}, fmt.Errorf("expected server JSON response but got '%s'", responseContentType)
+	}
+
+	var parsedResponse CheckQuotaResponse
+	err = json.NewDecoder(resp.Body).Decode(&parsedResponse)
+	if err != nil {
+		return CheckQuotaResponse{}, fmt.Errorf("unable to parse response: %w", err)
+	}
+
+	return parsedResponse, nil
+}
+
+func licenseURL() *url.URL {
+	return &url.URL{
+		Scheme: "https",
+		Host:   apiHost,
+		Path:   licensePath,
+	}
+}