module/apmsql: fuzz signature logic

And fix existing fuzz tests.

gofuzz.go

@@ -20,6 +20,7 @@ import (
 	"github.com/elastic/apm-agent-go/stacktrace"
 	"github.com/elastic/apm-server/processor"
 	error_processor "github.com/elastic/apm-server/processor/error"
+	metric_processor "github.com/elastic/apm-server/processor/metric"
 	transaction_processor "github.com/elastic/apm-server/processor/transaction"
 )
 
@@ -129,9 +130,6 @@ func Fuzz(data []byte) int {
 			return 0
 		}
 		for _, s := range t.Spans {
-			if s == nil {
-				continue
-			}
 			span := tx.StartSpan(s.Name, s.Type, nil)
 			span.Timestamp = tx.Timestamp.Add(time.Duration(s.Start * float64(time.Millisecond)))
 			if s.Context != nil && s.Context.Database != nil {
@@ -232,6 +230,13 @@ func (t *gofuzzTransport) SendErrors(ctx context.Context, payload *model.ErrorsP
 	return nil
 }
 
+func (t *gofuzzTransport) SendMetrics(ctx context.Context, payload *model.MetricsPayload) error {
+	t.writer.Reset()
+	payload.MarshalFastJSON(&t.writer)
+	t.process(metric_processor.NewProcessor())
+	return nil
+}
+
 func (t *gofuzzTransport) SendTransactions(ctx context.Context, payload *model.TransactionsPayload) error {
 	t.writer.Reset()
 	payload.MarshalFastJSON(&t.writer)

model/gofuzz.go

@@ -13,11 +13,11 @@ import (
 
 func Fuzz(data []byte) int {
 	type Payload struct {
-		Service      *Service       `json:"service"`
-		Process      *Process       `json:"process,omitempty"`
-		System       *System        `json:"system,omitempty"`
-		Errors       []*Error       `json:"errors"`
-		Transactions []*Transaction `json:"transactions"`
+		Service      *Service      `json:"service"`
+		Process      *Process      `json:"process,omitempty"`
+		System       *System       `json:"system,omitempty"`
+		Errors       []*Error      `json:"errors"`
+		Transactions []Transaction `json:"transactions"`
 	}
 
 	var payload Payload

module/apmsql/gofuzz_signature.go

@@ -0,0 +1,30 @@
+// +build gofuzz
+
+package apmsql
+
+import "strings"
+
+func Fuzz(data []byte) int {
+	sql := string(data)
+	sig := genericQuerySignature(sql)
+	if sig == "" {
+		return -1
+	}
+	prefixes := [...]string{
+		"CALL ",
+		"DELETE FROM ",
+		"INSERT INTO ",
+		"REPLACE INTO ",
+		"SELECT FROM ",
+		"UPDATE ",
+	}
+	for _, p := range prefixes {
+		if strings.HasPrefix(sig, p) {
+			// Give priority to input that is parsed
+			// successfully, and doesn't just result
+			// in the fallback.
+			return 1
+		}
+	}
+	return 0
+}