tomnomnom/gron · error

error reading multiline input: %s: %s

Error message

error reading multiline input: %s: %s

What it means

gronStream reads one JSON object per line. If the underlying bufio.Scanner reports an I/O error while reading (sc.Err() != nil), the failure is wrapped as "error reading multiline input: %s: %s" with exit code exitFormStatements. The second %s carries the scanner error (e.g. token too long, read failure).

Source

Thrown at main.go:328

		for _, s := range ss {
			if opts&optJSON > 0 {
				s, err = s.jsonify()
				if err != nil {
					goto out
				}

			}
			fmt.Fprintln(w, conv(s))
		}
	}
	if err = sc.Err(); err != nil {
		errstr = "error reading multiline input: %s"
	}

out:
	if err != nil {
		return exitFormStatements, fmt.Errorf(errstr+": %s", err)
	}
	return exitOK, nil

}

// ungron is the reverse of gron. Given assignment statements as input,
// it returns JSON. The only option is optMonochrome
func ungron(r io.Reader, w io.Writer, opts int) (int, error) {
	scanner := bufio.NewScanner(r)
	var maker statementmaker

	// Allow larger internal buffer of the scanner (min: 64KiB ~ max: 1MiB)
	scanner.Buffer(make([]byte, 64*1024), 1024*1024)

	if opts&optJSON > 0 {
		maker = statementFromJSONSpec
	} else {
		maker = statementFromStringMaker

View on GitHub (pinned to 88a6234ea2)

Solutions

1. Split or compact overly long lines so each is under the 1MiB scanner limit
2. Check that the input source (file, pipe, socket) is healthy and not closing mid-read
3. Retry the streaming read if the upstream producer was interrupted
4. Fall back to plain `gron` (single document mode) if the data is one large JSON document rather than NDJSON

Example fix

// before
$ gron -s < huge_line.json   // bufio.Scanner: token too long

// after
$ jq -c . huge.json | split -l 1 --filter='gron' // or increase/max-lines under 1MiB per line

// pre-check line sizes before streaming
sc := bufio.NewScanner(r)
for sc.Scan() {
	if len(sc.Bytes()) > 1024*1024 { /* split or reject line */ }
}

code, err := gronStream(input, output, opts)
if err != nil {
	if strings.HasPrefix(err.Error(), "error reading multiline input:") {
		// retry stream or fall back to single-document gron
	}
	return err
}

When it happens

Trigger: Reading `gron --stream` input from a broken pipe, a file that disappears mid-read, a failing pipe/fifo, or input lines exceeding the scanner's 1MiB buffer (bufio.ErrTooLong).

Common situations: Streaming from a tail -f or socket that errors mid-stream; huge single-line JSON documents over 1MB in a line-oriented stream; disk/network I/O faults while reading stdin.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

• failed to read input statements
• non-assignment statement
• invalid JSON layout
• invalid statement
• statement has no value

AI-assisted analysis of tomnomnom/gron@88a6234ea2 (2026-09-06). Data as JSON: /api/errors/6bb860cabb1f1ab2. Report an issue: GitHub.