From 39b78a8cf967679018fe8e1da6e684155da4d684 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C4=90=E1=BB=97=20Tr=E1=BB=8Dng=20H=E1=BA=A3i?=
 <41283691+hainenber@users.noreply.github.com>
Date: Tue, 21 Nov 2023 01:59:55 +0700
Subject: [PATCH] feat(module/git): allow module.git use cached content when
 failed to fetch (#5712)

Signed-off-by: hainenber <dotronghai96@gmail.com>
---
 CHANGELOG.md                             |  2 ++
 component/module/git/git.go              | 18 +++++++++++++--
 component/module/git/internal/vcs/git.go | 28 +++++++++++++++---------
 3 files changed, 36 insertions(+), 12 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 15df9feae598..d71aeae69605 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -110,6 +110,8 @@ v0.38.0-rc.0 (2023-11-16)
 
 - Updated windows exporter to use prometheus-community/windows_exporter commit 1836cd1. (@mattdurham)
 
+- Allow agent to start with `module.git` config if cached before. (@hainenber)
+
 ### Bugfixes
 
 - Set exit code 1 on grafana-agentctl non-runnable command. (@fgouteroux)
diff --git a/component/module/git/git.go b/component/module/git/git.go
index 42ac468477de..6a211fdc8843 100644
--- a/component/module/git/git.go
+++ b/component/module/git/git.go
@@ -3,6 +3,7 @@ package git
 
 import (
 	"context"
+	"errors"
 	"path/filepath"
 	"reflect"
 	"sync"
@@ -91,8 +92,15 @@ func New(o component.Options, args Arguments) (*Component, error) {
 		argsChanged: make(chan struct{}, 1),
 	}
 
+	// Only acknowledge the error from Update if it's not a
+	// vcs.UpdateFailedError; vcs.UpdateFailedError means that the Git repo
+	// exists but we were just unable to update it.
 	if err := c.Update(args); err != nil {
-		return nil, err
+		if errors.As(err, &vcs.UpdateFailedError{}) {
+			level.Error(c.log).Log("msg", "failed to update repository", "err", err)
+		} else {
+			return nil, err
+		}
 	}
 	return c, nil
 }
@@ -193,10 +201,16 @@ func (c *Component) Update(args component.Arguments) (err error) {
 	}
 
 	// Create or update the repo field.
+	// Failure to update repository makes the module loader temporarily use cached contents on disk
 	if c.repo == nil || !reflect.DeepEqual(repoOpts, c.repoOpts) {
 		r, err := vcs.NewGitRepo(context.Background(), repoPath, repoOpts)
 		if err != nil {
-			return err
+			if errors.As(err, &vcs.UpdateFailedError{}) {
+				level.Error(c.log).Log("msg", "failed to update repository", "err", err)
+				c.updateHealth(err)
+			} else {
+				return err
+			}
 		}
 		c.repo = r
 		c.repoOpts = repoOpts
diff --git a/component/module/git/internal/vcs/git.go b/component/module/git/internal/vcs/git.go
index 8209190b90da..dece43c10b2f 100644
--- a/component/module/git/internal/vcs/git.go
+++ b/component/module/git/internal/vcs/git.go
@@ -58,16 +58,24 @@ func NewGitRepo(ctx context.Context, storagePath string, opts GitRepoOptions) (*
 	}
 
 	// Fetch the latest contents. This may be a no-op if we just did a clone.
-	err = repo.FetchContext(ctx, &git.FetchOptions{
+	fetchRepoErr := repo.FetchContext(ctx, &git.FetchOptions{
 		RemoteName: "origin",
 		Force:      true,
 		Auth:       opts.Auth.Convert(),
 	})
-	if err != nil && !errors.Is(err, git.NoErrAlreadyUpToDate) {
-		return nil, UpdateFailedError{
-			Repository: opts.Repository,
-			Inner:      err,
+	if fetchRepoErr != nil && !errors.Is(fetchRepoErr, git.NoErrAlreadyUpToDate) {
+		workTree, err := repo.Worktree()
+		if err != nil {
+			return nil, err
 		}
+		return &GitRepo{
+				opts:     opts,
+				repo:     repo,
+				workTree: workTree,
+			}, UpdateFailedError{
+				Repository: opts.Repository,
+				Inner:      fetchRepoErr,
+			}
 	}
 
 	// Finally, hard reset to our requested revision.
@@ -92,7 +100,7 @@ func NewGitRepo(ctx context.Context, storagePath string, opts GitRepoOptions) (*
 		opts:     opts,
 		repo:     repo,
 		workTree: workTree,
-	}, nil
+	}, err
 }
 
 func isRepoCloned(dir string) bool {
@@ -103,15 +111,16 @@ func isRepoCloned(dir string) bool {
 // Update updates the repository by fetching new content and re-checking out to
 // latest version of Revision.
 func (repo *GitRepo) Update(ctx context.Context) error {
-	err := repo.repo.FetchContext(ctx, &git.FetchOptions{
+	var err error
+	fetchRepoErr := repo.repo.FetchContext(ctx, &git.FetchOptions{
 		RemoteName: "origin",
 		Force:      true,
 		Auth:       repo.opts.Auth.Convert(),
 	})
-	if err != nil && !errors.Is(err, git.NoErrAlreadyUpToDate) {
+	if fetchRepoErr != nil && !errors.Is(fetchRepoErr, git.NoErrAlreadyUpToDate) {
 		return UpdateFailedError{
 			Repository: repo.opts.Repository,
-			Inner:      err,
+			Inner:      fetchRepoErr,
 		}
 	}
 
@@ -120,7 +129,6 @@ func (repo *GitRepo) Update(ctx context.Context) error {
 	if err != nil {
 		return InvalidRevisionError{Revision: repo.opts.Revision}
 	}
-
 	err = repo.workTree.Reset(&git.ResetOptions{
 		Commit: hash,
 		Mode:   git.HardReset,