apache/beam · error

empty file glob provided

Error message

empty file glob provided

What it means

This panic is thrown by filesystem.ValidateScheme when the path (or file glob) passed to a filesystem-backed Beam I/O operation is an empty or whitespace-only string. Before dispatching to a registered filesystem implementation, Beam extracts the scheme from the path and validates it; an empty string has no scheme, so the library fails fast. It is a programmer error, not a runtime condition.

Solutions

1. Ensure the file path/glob variable is non-empty before calling Read/Write/MatchFiles, e.g. fail early on flags with a default
2. Trim and check user-supplied paths: strings.TrimSpace(path) == ""
3. Provide a sensible default glob in your pipeline flag parsing
4. Log the variable source (flag/env/config) that produced the empty string

Example fix

// before
filesystem.MatchFiles(ctx, scope, inputGlob)
// after
if strings.TrimSpace(inputGlob) == "" {
    log.Fatalf("--input file glob must be provided")
}
filesystem.MatchFiles(ctx, scope, inputGlob)

func requireNonEmptyGlob(path string) error {
    if strings.TrimSpace(path) == "" {
        return fmt.Errorf("file glob must be non-empty")
    }
    return nil
}

defer func() { if r := recover(); r != nil { log.Fatalf("filesystem: %v", r) } }()

When it happens

Trigger: Calling beam/filesystem functions like filesystem.Read, Write, MatchFiles, MatchContinuously, TestFilesystem, or ReadWithFilename with a "" or " " path, typically because a variable holding the file pattern was never set or an option/flag was left empty.

Common situations: Pipeline options or flags like --input not provided and defaulting to empty string; a templated glob built from an empty prefix; config file missing the file pattern key.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• errorForMissingScheme(scheme, path)
• AfterProcessingTime trigger set without a delay or…
• At least one subtrigger required for composite triggers.
• attempted to add namespace to missing coder id
• attempted to add namespace to missing windowing strategy id

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/327ecf33a870e05d. Report an issue: GitHub.

Appendix: source

Thrown at sdks/go/pkg/beam/io/filesystem/filesystem.go:129

}

// Renamer is an interface for renaming or moving files in the filesystem.
type Renamer interface {
	Rename(ctx context.Context, oldpath, newpath string) error
}

func getScheme(path string) string {
	if index := strings.Index(path, "://"); index > 0 {
		return path[:index]
	}
	return "default"
}

// ValidateScheme panics if the given path's scheme does not have a
// corresponding file system registered.
func ValidateScheme(path string) {
	if strings.TrimSpace(path) == "" {
		panic("empty file glob provided")
	}
	scheme := getScheme(path)
	if _, ok := registry[scheme]; !ok {
		panic(errorForMissingScheme(scheme, path))
	}
}

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