Allow for a personal token to be specified for self-updates (#5568)

* Allow for a personal token to be specified for self-updates

This change will allow for setting the $GITHUB_ACCESS_TOKEN environment variable with a Github personal access token, allowing e.g. for higher rate limits

* Refactor github request and add test

---------

Co-authored-by: Paulo Saraiva <pauloman@cern.ch>

changelog/unreleased/issue-3738

@@ -0,0 +1,8 @@
+Enhancement: Allow Github personal access token to be specified for `self-update`
+
+`restic self-update` previously only used unauthenticated GitHub API requests when checking for the latest release. This caused some users sharing IP addresses to hit the GitHub rate limit, resulting in a 403 Forbidden error and preventing updates.
+
+Restic still uses unauthenticated requests by default, but it now optionally supports authenticated GitHub API requests during `self-update`. Users can set the `$GITHUB_ACCESS_TOKEN` environment variable to use a [personal access token](https://github.com/settings/tokens) for this effect, avoiding update failures due to rate limiting.
+
+https://github.com/restic/restic/issues/3738
+https://github.com/restic/restic/pull/5568

doc/020_installation.rst

@@ -25,7 +25,12 @@ you can download and run without having to do additional installation work.
 
 Please see the :ref:`official_binaries` section below for various downloads.
 Official binaries can be updated in place by using the ``restic self-update``
-command.
+command. 
+
+The environment variable ``$GITHUB_ACCESS_TOKEN`` can be set to use a personal 
+access token when updating. This increases the rate limit through authenticated GitHub API 
+requests, and prevents update failures when many 
+unauthenticated requests have already been made from the same IP.
 
 Alpine Linux
 ============

internal/selfupdate/github.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"os"
 	"strings"
 	"time"
 
@@ -45,6 +46,23 @@ type githubError struct {
 	Message string
 }
 
+func newGitHubRequest(ctx context.Context, url, acceptHeader string) (*http.Request, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	// Set the Accept header to pin the API version
+	req.Header.Set("Accept", acceptHeader)
+
+	// Add Authorization header if token is available
+	if token := os.Getenv("GITHUB_ACCESS_TOKEN"); token != "" {
+		req.Header.Set("Authorization", "token "+token)
+	}
+
+	return req, nil
+}
+
 // GitHubLatestRelease uses the GitHub API to get information about the latest
 // release of a repository.
 func GitHubLatestRelease(ctx context.Context, owner, repo string) (Release, error) {
@@ -52,14 +70,11 @@ func GitHubLatestRelease(ctx context.Context, owner, repo string) (Release, erro
 	defer cancel()
 
 	url := fmt.Sprintf("https://api.github.com/repos/%s/%s/releases/latest", owner, repo)
-	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	req, err := newGitHubRequest(ctx, url, "application/vnd.github.v3+json")
 	if err != nil {
 		return Release{}, err
 	}
 
-	// pin API version 3
-	req.Header.Set("Accept", "application/vnd.github.v3+json")
-
 	res, err := http.DefaultClient.Do(req)
 	if err != nil {
 		return Release{}, err
@@ -111,14 +126,11 @@ func GitHubLatestRelease(ctx context.Context, owner, repo string) (Release, erro
 }
 
 func getGithubData(ctx context.Context, url string) ([]byte, error) {
-	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	req, err := newGitHubRequest(ctx, url, "application/octet-stream")
 	if err != nil {
 		return nil, err
 	}
 
-	// request binary data
-	req.Header.Set("Accept", "application/octet-stream")
-
 	res, err := http.DefaultClient.Do(req)
 	if err != nil {
 		return nil, err

internal/selfupdate/github_test.go

@@ -0,0 +1,37 @@
+package selfupdate
+
+import (
+	"context"
+	"net/http"
+	"testing"
+
+	rtest "github.com/restic/restic/internal/test"
+)
+
+func TestNewGitHubRequest(t *testing.T) {
+	ctx := context.Background()
+	url := "https://api.github.com/repos/restic/restic/releases/latest"
+	acceptHeader := "application/vnd.github.v3+json"
+
+	t.Run("With GITHUB_ACCESS_TOKEN", func(t *testing.T) {
+		expectedToken := "testtoken123"
+		t.Setenv("GITHUB_ACCESS_TOKEN", expectedToken)
+
+		req, err := newGitHubRequest(ctx, url, acceptHeader)
+		rtest.OK(t, err)
+
+		rtest.Assert(t, req.Method == http.MethodGet, "expected method %s, got %s", http.MethodGet, req.Method)
+		rtest.Assert(t, req.URL.String() == url, "expected URL %s, got %s", url, req.URL.String())
+		rtest.Assert(t, req.Header.Get("Accept") == acceptHeader, "expected Accept header %s, got %s", acceptHeader, req.Header.Get("Accept"))
+		rtest.Assert(t, req.Header.Get("Authorization") == "token "+expectedToken, "expected Authorization header 'token %s', got %s", expectedToken, req.Header.Get("Authorization"))
+	})
+
+	t.Run("Without GITHUB_ACCESS_TOKEN", func(t *testing.T) {
+		t.Setenv("GITHUB_ACCESS_TOKEN", "")
+
+		req, err := newGitHubRequest(ctx, url, acceptHeader)
+		rtest.OK(t, err)
+
+		rtest.Assert(t, req.Header.Get("Authorization") == "", "expected no Authorization header, got %s", req.Header.Get("Authorization"))
+	})
+}