apache/answer · error

failed to copy file contents from %s to %s: %w

Error message

failed to copy file contents from %s to %s: %w

What it means

Returned by the copy helper in internal/cli/build.go when io.Copy(dstFile, srcFile) fails after both files were opened. This means an I/O error occurred mid-transfer: a read failure on the source, a write failure on the destination (disk full, quota exceeded), or a close-time flush error. The wrapped error identifies which side failed.

Source

Thrown at internal/cli/build.go:550

		} else {
			// Open the source file
			srcFile, err := sourceFs.Open(srcPath)
			if err != nil {
				return fmt.Errorf("failed to open source file %s: %w", srcPath, err)
			}
			defer srcFile.Close()

			// Create the destination file
			dstFile, err := os.Create(dstPath)
			if err != nil {
				return fmt.Errorf("failed to create destination file %s: %w", dstPath, err)
			}
			defer dstFile.Close()

			// Copy the file contents
			_, err = io.Copy(dstFile, srcFile)
			if err != nil {
				return fmt.Errorf("failed to copy file contents from %s to %s: %w", srcPath, dstPath, err)
			}
		}

		return nil
	})

	return err
}

// format plugins dir name from dash to underline
func formatUIPluginsDirName(dirPath string) {
	entries, err := os.ReadDir(dirPath)
	if err != nil {
		fmt.Printf("read ui plugins dir failed: [%s] %s\n", dirPath, err)
		return
	}
	for _, entry := range entries {
		if !entry.IsDir() || !strings.Contains(entry.Name(), "-") {

View on GitHub (pinned to 3b9f137061)

Solutions

1. Check free disk space on the destination volume (df -h) — 'no space left on device' is the most common wrapped error
2. Re-run the operation; transient I/O errors on network mounts often resolve on retry
3. Check the source file's integrity/readability and the destination device health (dmesg for I/O errors)
4. If dstFile is buffered, ensure error handling also covers dstFile.Sync()/Close() results

// preflight: check free space on destination before copying
out, err := exec.Command("df", "-h", targetDir).Output()
if err != nil {
    log.Printf("could not check disk space: %v", err)
} else {
    fmt.Println(string(out))
}

for attempt := 0; attempt < 3; attempt++ {
    if err := copyFile(srcPath, dstPath); err == nil {
        break
    } else if attempt == 2 {
        return fmt.Errorf("copy from %s to %s failed after retries: %w", srcPath, dstPath, err)
    }
    time.Sleep(time.Duration(attempt+1) * time.Second)
}

When it happens

Trigger: Disk is full or quota exceeded while writing dstPath; source file shrinks or becomes unreadable during copy; I/O error on the underlying device; rare short-write/pipe errors on network-mounted filesystems.

Common situations: Docker/container image builds exhausting disk space; copying large embedded assets to a nearly-full volume; NFS/EFS mounts dropping mid-copy in CI environments.

Related errors

• failed to open source file %s: %w
• failed to create destination file %s: %w
• validate check exception
• base.request_format_error
• error.password.space_invalid

AI-assisted analysis of apache/answer@3b9f137061 (2026-09-05). Data as JSON: /api/errors/bf2de5bd63fd7824. Report an issue: GitHub.