add query context with timeline

Also change the row column types to sql.NullString to handle cases where
null values were causing errors in row scanning.

cmd/themis-server/main.go

@@ -12,6 +12,7 @@ import (
 	"strconv"
 	"strings"
 	"syscall"
+	"time"
 
 	"github.com/bwmarrin/discordgo"
 	_ "github.com/mattn/go-sqlite3"
@@ -378,7 +379,9 @@ func main() {
 			}
 
 			q := i.ApplicationCommandData().Options[0].StringValue()
-			rows, err := roDB.Query(q)
+			deadlined, cancelDeadline := context.WithTimeout(ctx, 15*time.Second)
+			defer cancelDeadline()
+			rows, err := roDB.QueryContext(deadlined, q)
 			if err != nil {
 				log.Error().Err(err).Msg("failed to exec user-provided query")
 				return
@@ -389,7 +392,10 @@ func main() {
 				log.Error().Err(err).Msg("failed to format rows")
 			}
 
-			table := fmt.Sprintf("```\n%s\n```", fmtd[:min(len(fmtd), 1990)]) // TODO(wperron) find a better way to cutover
+			// 2000 is a magic number here, it's the character limit for a discord
+			// message, we're cutting slightly under that to allow the backticks
+			// for the monospaced block.
+			table := fmt.Sprintf("```\n%s\n```", fmtd[:min(len(fmtd), 1990)])
 
 			if err := s.InteractionRespond(i.Interaction, &discordgo.InteractionResponse{
 				Type: discordgo.InteractionResponseChannelMessageWithSource,
@@ -429,6 +435,7 @@ func main() {
 	}()
 
 	<-ctx.Done()
+	log.Info().Msg("context cancelled, exiting")
 
 	for _, c := range registeredCommands {
 		err = discord.ApplicationCommandDelete(appId, guildId, c.ID)

fmt.go

@@ -29,7 +29,7 @@ func FormatRows(rows *sql.Rows) (string, error) {
 	for rows.Next() {
 		row := make([]interface{}, len(cols))
 		for i := range row {
-			row[i] = new(string)
+			row[i] = new(sql.NullString)
 		}
 		if err := rows.Scan(row...); err != nil {
 			return "", fmt.Errorf("failed to scan next row: %w", err)
@@ -37,9 +37,9 @@ func FormatRows(rows *sql.Rows) (string, error) {
 
 		scanned = append(scanned, row) // keep track of row for later
 		for i, a := range row {
-			s := a.(*string)
-			if len(*s) > lengths[i] {
-				lengths[i] = len(*s)
+			s := a.(*sql.NullString)
+			if len(s.String) > lengths[i] {
+				lengths[i] = len(s.String)
 			}
 		}
 	}
@@ -62,7 +62,7 @@ func FormatRows(rows *sql.Rows) (string, error) {
 	for _, r := range scanned {
 		curr = curr[:0] // empty slice but preserve capacity
 		for i := range lengths {
-			s := r[i].(*string)
+			s := r[i].(*sql.NullString)
 			curr = append(curr, lengths[i], *s)
 		}
 		sb.WriteString(fmt.Sprintf(pattern, curr...))