From a1a0e268ba3f7da087efafe29accd0f2ab4a25ca Mon Sep 17 00:00:00 2001
From: Yingzi Zhang <164733623+LindseyZ1205@users.noreply.github.com>
Date: Wed, 30 Sep 2026 14:41:36 -0400
Subject: [PATCH] fix(cmd): keep SetArgs ExpireAt milliseconds (#4053)

SetArgs always sent ExpireAt as EXAT with Unix seconds, so any
millisecond part was silently dropped. Send PXAT with Unix milliseconds
when ExpireAt has millisecond precision, and keep EXAT otherwise.
---
 string_commands.go           |  9 ++++++--
 string_commands_unit_test.go | 41 ++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/string_commands.go b/string_commands.go
index 4600d91c..cbe8e0ac 100644
--- a/string_commands.go
+++ b/string_commands.go
@@ -516,7 +516,8 @@ type SetArgs struct {
 	MatchDigest uint64
 
 	// Zero `TTL` or `Expiration` means that the key has no expiration time.
-	TTL      time.Duration
+	TTL time.Duration
+	// ExpireAt is sent as EXAT, or as PXAT when it has millisecond precision.
 	ExpireAt time.Time
 
 	// When Get is true, the command returns the old value stored at key, or nil when key did not exist.
@@ -538,7 +539,11 @@ func (c cmdable) SetArgs(ctx context.Context, key string, value interface{}, a S
 	}
 
 	if !a.ExpireAt.IsZero() {
-		args = append(args, "exat", a.ExpireAt.Unix())
+		if a.ExpireAt.Nanosecond() >= int(time.Millisecond) {
+			args = append(args, "pxat", a.ExpireAt.UnixMilli())
+		} else {
+			args = append(args, "exat", a.ExpireAt.Unix())
+		}
 	}
 	if a.TTL > 0 {
 		if usePrecise(a.TTL) {
diff --git a/string_commands_unit_test.go b/string_commands_unit_test.go
index 21f7198e..93276309 100644
--- a/string_commands_unit_test.go
+++ b/string_commands_unit_test.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"reflect"
 	"testing"
+	"time"
 )
 
 // captureCmdable returns a cmdable that records the Cmder passed to it without
@@ -176,3 +177,43 @@ func TestIncrEXFloat_Args(t *testing.T) {
 		})
 	}
 }
+
+func TestSetArgs_ExpireAt(t *testing.T) {
+	tests := []struct {
+		name     string
+		expireAt time.Time
+		want     []interface{}
+	}{
+		{
+			name:     "whole_seconds",
+			expireAt: time.Unix(1700000000, 0),
+			want:     []interface{}{"set", "key", "value", "exat", int64(1700000000)},
+		},
+		{
+			name:     "sub_millisecond_is_truncated",
+			expireAt: time.Unix(1700000000, 500_000),
+			want:     []interface{}{"set", "key", "value", "exat", int64(1700000000)},
+		},
+		{
+			name:     "milliseconds",
+			expireAt: time.UnixMilli(1700000000123),
+			want:     []interface{}{"set", "key", "value", "pxat", int64(1700000000123)},
+		},
+		{
+			name:     "beyond_nanosecond_range",
+			expireAt: time.Date(2270, time.January, 2, 3, 4, 5, 123000000, time.UTC),
+			want:     []interface{}{"set", "key", "value", "pxat", int64(9467204645123)},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var cmd Cmder
+			c := captureCmdable(&cmd)
+			c.SetArgs(context.Background(), "key", "value", SetArgs{ExpireAt: tt.expireAt})
+			if got := cmd.Args(); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("args = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}