redis: function stats unexpected %s engine map length

Error message

redis: function stats unexpected %s engine map length

What it means

Thrown by FunctionStatsCmd.readEngines (command.go:7027) when each engine's value map is not exactly 2 entries (libraries_count and functions_count). The parser uses ReadFixedMapLen(2), so any other length aborts.

Source

Thrown at command.go:7027

}

func (cmd *FunctionStatsCmd) readEngines(rd *proto.Reader) ([]Engine, error) {
	n, err := rd.ReadMapLen()
	if err != nil {
		return nil, err
	}

	engines := make([]Engine, 0, n)
	for i := 0; i < n; i++ {
		engine := Engine{}
		engine.Language, err = rd.ReadString()
		if err != nil {
			return nil, err
		}

		err = rd.ReadFixedMapLen(2)
		if err != nil {
			return nil, fmt.Errorf("redis: function stats unexpected %s engine map length", engine.Language)
		}

		for i := 0; i < 2; i++ {
			key, err := rd.ReadString()
			if err != nil {
				return nil, err
			}
			switch key {
			case "libraries_count":
				engine.LibrariesCount, err = rd.ReadInt()
			case "functions_count":
				engine.FunctionsCount, err = rd.ReadInt()
			default:
				// Unknown field: drain its value so the reader stays aligned
				// with the rest of the reply.
				err = rd.DiscardNext()
			}
			if err != nil {

View on GitHub (pinned to 36d97525cd)

Solutions

Upgrade go-redis to a release supporting the new engine-stat fields (or that drains extra fields).
Pin Redis to a compatible version.
Confirm with `FUNCTION STATS` what keys each engine map contains.

Defensive patterns

Strategy: validation

Validate before calling

// redis-cli FUNCTION STATS  -> confirm each engine map has exactly libraries_count + functions_count.

Try / catch

stats, err := client.FunctionStats(ctx).Result()
if err != nil {
    // upgrade go-redis for new engine-stat fields; degrade
    stats = redis.FunctionStats{}
}

Prevention

Pin Redis to a version your go-redis supports, or upgrade go-redis first.
Treat engine stats as best-effort.

When it happens

Trigger: client.FunctionStats(ctx) when an engine map under 'engines' has a length other than 2 — e.g. a newer Redis added a third engine-stat field, or a fork/proxy returned a different shape.

Common situations: Forward-compat drift: newer Redis adding per-engine statistics; Redis fork with a different engines shape.

Related errors

AI-assisted analysis of go-redis/redis@36d97525cd (2026-08-06). Data as JSON: /data/errors/e100ce458f48289d.json. Report an issue: GitHub.