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fix(ssh): unique sftp temp filename so concurrent uploads don't collide

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When two sessions on the same task launch back-to-back they both call
ensureAgentctlOnHost which streams to <remotePath>.tmp before renaming.
With a shared .tmp name the second uploader's rename errors with
"file does not exist" once the first uploader's rename consumed the temp
file. Give each uploader its own pid+random-suffix temp; uploaders write
identical sha256-keyed content, so the rename race is then safe.
This commit is contained in:
José Almeida
2026-05-18 02:33:57 +01:00
parent 628ceaabb5
commit c4e5f593b6
1 changed files with 11 additions and 3 deletions
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apps/backend/internal/agent/runtime/lifecycle/executor_ssh_operations.go
+11 -3
View File
@@ -228,6 +228,14 @@ func ensureAgentctlOnHost(ctx context.Context, client *ssh.Client, resolver *Age
// sftpUploadBytes writes data to remotePath via SFTP with the given mode.
// Intermediate directories must already exist.
//
// The temp filename includes a random suffix so two concurrent uploaders
// targeting the same remotePath don't collide: with a shared `.tmp` name
// the second rename would error with "file does not exist" once the first
// uploader's rename consumed the temp file. Each uploader writes to its
// own temp, then races on the rename — last-writer-wins is safe because
// callers always upload identical content (sha256-keyed binary) or
// content that doesn't matter if it loses the race (the sha256 sidecar).
func sftpUploadBytes(client *ssh.Client, remotePath string, data []byte, mode os.FileMode) error {
c, err := sftp.NewClient(client)
if err != nil {
@@ -235,9 +243,7 @@ func sftpUploadBytes(client *ssh.Client, remotePath string, data []byte, mode os
}
defer func() { _ = c.Close() }()
// Stream to a temp path then rename, so a half-uploaded file never appears
// as the final name (matters most for the agentctl binary).
tmp := remotePath + ".tmp"
tmp := fmt.Sprintf("%s.tmp.%d.%d", remotePath, os.Getpid(), mrand.Uint64())
f, err := c.Create(tmp)
if err != nil {
return fmt.Errorf("sftp: create %s: %w", tmp, err)
@@ -252,11 +258,13 @@ func sftpUploadBytes(client *ssh.Client, remotePath string, data []byte, mode os
return fmt.Errorf("sftp: close %s: %w", tmp, err)
}
if err := c.Chmod(tmp, mode); err != nil {
_ = c.Remove(tmp)
return fmt.Errorf("sftp: chmod %s: %w", tmp, err)
}
if err := c.PosixRename(tmp, remotePath); err != nil {
// Some servers don't support POSIX rename; fall back to a non-atomic rename.
if rerr := c.Rename(tmp, remotePath); rerr != nil {
_ = c.Remove(tmp)
return fmt.Errorf("sftp: rename %s -> %s: %w", tmp, remotePath, rerr)
}
}