[backend/federation] Handle incoming ASFlag activities (ISH-116)

Iceshrimp.Backend/Core/Database/DatabaseContext.cs

@@ -16,7 +16,7 @@ namespace Iceshrimp.Backend.Core.Database;
 public class DatabaseContext(DbContextOptions<DatabaseContext> options)
 	: DbContext(options), IDataProtectionKeyContext
 {
-	public virtual DbSet<AbuseUserReport>      AbuseUserReports      { get; init; } = null!;
+	public virtual DbSet<Report>               Reports               { get; init; } = null!;
 	public virtual DbSet<Announcement>         Announcements         { get; init; } = null!;
 	public virtual DbSet<AnnouncementRead>     AnnouncementReads     { get; init; } = null!;
 	public virtual DbSet<Antenna>              Antennas              { get; init; } = null!;

Iceshrimp.Backend/Core/Database/Migrations/DatabaseContextModelSnapshot.cs

@@ -36,84 +36,6 @@ namespace Iceshrimp.Backend.Core.Database.Migrations
             NpgsqlModelBuilderExtensions.HasPostgresExtension(modelBuilder, "pg_trgm");
             NpgsqlModelBuilderExtensions.UseIdentityByDefaultColumns(modelBuilder);
 
-            modelBuilder.Entity("Iceshrimp.Backend.Core.Database.Tables.AbuseUserReport", b =>
-                {
-                    b.Property<string>("Id")
-                        .HasMaxLength(32)
-                        .HasColumnType("character varying(32)")
-                        .HasColumnName("id");
-
-                    b.Property<string>("AssigneeId")
-                        .HasMaxLength(32)
-                        .HasColumnType("character varying(32)")
-                        .HasColumnName("assigneeId");
-
-                    b.Property<string>("Comment")
-                        .IsRequired()
-                        .HasMaxLength(2048)
-                        .HasColumnType("character varying(2048)")
-                        .HasColumnName("comment");
-
-                    b.Property<DateTime>("CreatedAt")
-                        .HasColumnType("timestamp with time zone")
-                        .HasColumnName("createdAt")
-                        .HasComment("The created date of the AbuseUserReport.");
-
-                    b.Property<bool>("Forwarded")
-                        .ValueGeneratedOnAdd()
-                        .HasColumnType("boolean")
-                        .HasDefaultValue(false)
-                        .HasColumnName("forwarded");
-
-                    b.Property<string>("ReporterHost")
-                        .HasMaxLength(512)
-                        .HasColumnType("character varying(512)")
-                        .HasColumnName("reporterHost")
-                        .HasComment("[Denormalized]");
-
-                    b.Property<string>("ReporterId")
-                        .IsRequired()
-                        .HasMaxLength(32)
-                        .HasColumnType("character varying(32)")
-                        .HasColumnName("reporterId");
-
-                    b.Property<bool>("Resolved")
-                        .ValueGeneratedOnAdd()
-                        .HasColumnType("boolean")
-                        .HasDefaultValue(false)
-                        .HasColumnName("resolved");
-
-                    b.Property<string>("TargetUserHost")
-                        .HasMaxLength(512)
-                        .HasColumnType("character varying(512)")
-                        .HasColumnName("targetUserHost")
-                        .HasComment("[Denormalized]");
-
-                    b.Property<string>("TargetUserId")
-                        .IsRequired()
-                        .HasMaxLength(32)
-                        .HasColumnType("character varying(32)")
-                        .HasColumnName("targetUserId");
-
-                    b.HasKey("Id");
-
-                    b.HasIndex("AssigneeId");
-
-                    b.HasIndex("CreatedAt");
-
-                    b.HasIndex("ReporterHost");
-
-                    b.HasIndex("ReporterId");
-
-                    b.HasIndex("Resolved");
-
-                    b.HasIndex("TargetUserHost");
-
-                    b.HasIndex("TargetUserId");
-
-                    b.ToTable("abuse_user_report");
-                });
-
             modelBuilder.Entity("Iceshrimp.Backend.Core.Database.Tables.AllowedInstance", b =>
                 {
                     b.Property<string>("Host")
@@ -3870,6 +3792,84 @@ namespace Iceshrimp.Backend.Core.Database.Migrations
                     b.ToTable("renote_muting");
                 });
 
+            modelBuilder.Entity("Iceshrimp.Backend.Core.Database.Tables.Report", b =>
+                {
+                    b.Property<string>("Id")
+                        .HasMaxLength(32)
+                        .HasColumnType("character varying(32)")
+                        .HasColumnName("id");
+
+                    b.Property<string>("AssigneeId")
+                        .HasMaxLength(32)
+                        .HasColumnType("character varying(32)")
+                        .HasColumnName("assigneeId");
+
+                    b.Property<string>("Comment")
+                        .IsRequired()
+                        .HasMaxLength(2048)
+                        .HasColumnType("character varying(2048)")
+                        .HasColumnName("comment");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("timestamp with time zone")
+                        .HasColumnName("createdAt")
+                        .HasComment("The created date of the Report.");
+
+                    b.Property<bool>("Forwarded")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("boolean")
+                        .HasDefaultValue(false)
+                        .HasColumnName("forwarded");
+
+                    b.Property<string>("ReporterHost")
+                        .HasMaxLength(512)
+                        .HasColumnType("character varying(512)")
+                        .HasColumnName("reporterHost")
+                        .HasComment("[Denormalized]");
+
+                    b.Property<string>("ReporterId")
+                        .IsRequired()
+                        .HasMaxLength(32)
+                        .HasColumnType("character varying(32)")
+                        .HasColumnName("reporterId");
+
+                    b.Property<bool>("Resolved")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("boolean")
+                        .HasDefaultValue(false)
+                        .HasColumnName("resolved");
+
+                    b.Property<string>("TargetUserHost")
+                        .HasMaxLength(512)
+                        .HasColumnType("character varying(512)")
+                        .HasColumnName("targetUserHost")
+                        .HasComment("[Denormalized]");
+
+                    b.Property<string>("TargetUserId")
+                        .IsRequired()
+                        .HasMaxLength(32)
+                        .HasColumnType("character varying(32)")
+                        .HasColumnName("targetUserId");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("AssigneeId");
+
+                    b.HasIndex("CreatedAt");
+
+                    b.HasIndex("ReporterHost");
+
+                    b.HasIndex("ReporterId");
+
+                    b.HasIndex("Resolved");
+
+                    b.HasIndex("TargetUserHost");
+
+                    b.HasIndex("TargetUserId");
+
+                    b.ToTable("report");
+                });
+
             modelBuilder.Entity("Iceshrimp.Backend.Core.Database.Tables.Rule", b =>
                 {
                     b.Property<string>("Id")
@@ -4922,30 +4922,19 @@ namespace Iceshrimp.Backend.Core.Database.Migrations
                     b.ToTable("data_protection_keys", (string)null);
                 });
 
-            modelBuilder.Entity("Iceshrimp.Backend.Core.Database.Tables.AbuseUserReport", b =>
+            modelBuilder.Entity("reported_note", b =>
                 {
-                    b.HasOne("Iceshrimp.Backend.Core.Database.Tables.User", "Assignee")
+                    b.Property<string>("note_id")
-                        .WithMany("AbuseUserReportAssignees")
+                        .HasColumnType("character varying(32)");
-                        .HasForeignKey("AssigneeId")
-                        .OnDelete(DeleteBehavior.SetNull);
 
-                    b.HasOne("Iceshrimp.Backend.Core.Database.Tables.User", "Reporter")
+                    b.Property<string>("report_id")
-                        .WithMany("AbuseUserReportReporters")
+                        .HasColumnType("character varying(32)");
-                        .HasForeignKey("ReporterId")
-                        .OnDelete(DeleteBehavior.Cascade)
-                        .IsRequired();
 
-                    b.HasOne("Iceshrimp.Backend.Core.Database.Tables.User", "TargetUser")
+                    b.HasKey("note_id", "report_id");
-                        .WithMany("AbuseUserReportTargetUsers")
-                        .HasForeignKey("TargetUserId")
-                        .OnDelete(DeleteBehavior.Cascade)
-                        .IsRequired();
 
-                    b.Navigation("Assignee");
+                    b.HasIndex("report_id");
 
-                    b.Navigation("Reporter");
+                    b.ToTable("reported_note");
-
-                    b.Navigation("TargetUser");
                 });
 
             modelBuilder.Entity("Iceshrimp.Backend.Core.Database.Tables.AnnouncementRead", b =>
@@ -5720,6 +5709,32 @@ namespace Iceshrimp.Backend.Core.Database.Migrations
                     b.Navigation("Muter");
                 });
 
+            modelBuilder.Entity("Iceshrimp.Backend.Core.Database.Tables.Report", b =>
+                {
+                    b.HasOne("Iceshrimp.Backend.Core.Database.Tables.User", "Assignee")
+                        .WithMany("AbuseUserReportAssignees")
+                        .HasForeignKey("AssigneeId")
+                        .OnDelete(DeleteBehavior.SetNull);
+
+                    b.HasOne("Iceshrimp.Backend.Core.Database.Tables.User", "Reporter")
+                        .WithMany("AbuseUserReportReporters")
+                        .HasForeignKey("ReporterId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.HasOne("Iceshrimp.Backend.Core.Database.Tables.User", "TargetUser")
+                        .WithMany("AbuseUserReportTargetUsers")
+                        .HasForeignKey("TargetUserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("Assignee");
+
+                    b.Navigation("Reporter");
+
+                    b.Navigation("TargetUser");
+                });
+
             modelBuilder.Entity("Iceshrimp.Backend.Core.Database.Tables.Session", b =>
                 {
                     b.HasOne("Iceshrimp.Backend.Core.Database.Tables.User", "User")
@@ -5930,6 +5945,21 @@ namespace Iceshrimp.Backend.Core.Database.Migrations
                     b.Navigation("User");
                 });
 
+            modelBuilder.Entity("reported_note", b =>
+                {
+                    b.HasOne("Iceshrimp.Backend.Core.Database.Tables.Note", null)
+                        .WithMany()
+                        .HasForeignKey("note_id")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.HasOne("Iceshrimp.Backend.Core.Database.Tables.Report", null)
+                        .WithMany()
+                        .HasForeignKey("report_id")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
             modelBuilder.Entity("Iceshrimp.Backend.Core.Database.Tables.Announcement", b =>
                 {
                     b.Navigation("AnnouncementReads");

Iceshrimp.Backend/Core/Database/Migrations/v2025.1-beta6/20250310231413_RefactorReportsSchema.cs

@@ -0,0 +1,242 @@
+using System;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Iceshrimp.Backend.Core.Database.Migrations
+{
+    /// <inheritdoc />
+    [DbContext(typeof(DatabaseContext))]
+    [Migration("20250310231413_RefactorReportsSchema")]
+    public partial class RefactorReportsSchema : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropForeignKey(
+                name: "FK_abuse_user_report_user_assigneeId",
+                table: "abuse_user_report");
+
+            migrationBuilder.DropForeignKey(
+                name: "FK_abuse_user_report_user_reporterId",
+                table: "abuse_user_report");
+
+            migrationBuilder.DropForeignKey(
+                name: "FK_abuse_user_report_user_targetUserId",
+                table: "abuse_user_report");
+
+            migrationBuilder.DropPrimaryKey(
+                name: "PK_abuse_user_report",
+                table: "abuse_user_report");
+
+            migrationBuilder.RenameTable(
+                name: "abuse_user_report",
+                newName: "report");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_abuse_user_report_targetUserId",
+                table: "report",
+                newName: "IX_report_targetUserId");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_abuse_user_report_targetUserHost",
+                table: "report",
+                newName: "IX_report_targetUserHost");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_abuse_user_report_resolved",
+                table: "report",
+                newName: "IX_report_resolved");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_abuse_user_report_reporterId",
+                table: "report",
+                newName: "IX_report_reporterId");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_abuse_user_report_reporterHost",
+                table: "report",
+                newName: "IX_report_reporterHost");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_abuse_user_report_createdAt",
+                table: "report",
+                newName: "IX_report_createdAt");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_abuse_user_report_assigneeId",
+                table: "report",
+                newName: "IX_report_assigneeId");
+
+            migrationBuilder.AlterColumn<DateTime>(
+                name: "createdAt",
+                table: "report",
+                type: "timestamp with time zone",
+                nullable: false,
+                comment: "The created date of the Report.",
+                oldClrType: typeof(DateTime),
+                oldType: "timestamp with time zone",
+                oldComment: "The created date of the AbuseUserReport.");
+
+            migrationBuilder.AddPrimaryKey(
+                name: "PK_report",
+                table: "report",
+                column: "id");
+
+            migrationBuilder.CreateTable(
+                name: "reported_note",
+                columns: table => new
+                {
+                    note_id = table.Column<string>(type: "character varying(32)", nullable: false),
+                    report_id = table.Column<string>(type: "character varying(32)", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_reported_note", x => new { x.note_id, x.report_id });
+                    table.ForeignKey(
+                        name: "FK_reported_note_note_note_id",
+                        column: x => x.note_id,
+                        principalTable: "note",
+                        principalColumn: "id",
+                        onDelete: ReferentialAction.Cascade);
+                    table.ForeignKey(
+                        name: "FK_reported_note_report_report_id",
+                        column: x => x.report_id,
+                        principalTable: "report",
+                        principalColumn: "id",
+                        onDelete: ReferentialAction.Cascade);
+                });
+
+            migrationBuilder.CreateIndex(
+                name: "IX_reported_note_report_id",
+                table: "reported_note",
+                column: "report_id");
+
+            migrationBuilder.AddForeignKey(
+                name: "FK_report_user_assigneeId",
+                table: "report",
+                column: "assigneeId",
+                principalTable: "user",
+                principalColumn: "id",
+                onDelete: ReferentialAction.SetNull);
+
+            migrationBuilder.AddForeignKey(
+                name: "FK_report_user_reporterId",
+                table: "report",
+                column: "reporterId",
+                principalTable: "user",
+                principalColumn: "id",
+                onDelete: ReferentialAction.Cascade);
+
+            migrationBuilder.AddForeignKey(
+                name: "FK_report_user_targetUserId",
+                table: "report",
+                column: "targetUserId",
+                principalTable: "user",
+                principalColumn: "id",
+                onDelete: ReferentialAction.Cascade);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropForeignKey(
+                name: "FK_report_user_assigneeId",
+                table: "report");
+
+            migrationBuilder.DropForeignKey(
+                name: "FK_report_user_reporterId",
+                table: "report");
+
+            migrationBuilder.DropForeignKey(
+                name: "FK_report_user_targetUserId",
+                table: "report");
+
+            migrationBuilder.DropTable(
+                name: "reported_note");
+
+            migrationBuilder.DropPrimaryKey(
+                name: "PK_report",
+                table: "report");
+
+            migrationBuilder.RenameTable(
+                name: "report",
+                newName: "abuse_user_report");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_report_targetUserId",
+                table: "abuse_user_report",
+                newName: "IX_abuse_user_report_targetUserId");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_report_targetUserHost",
+                table: "abuse_user_report",
+                newName: "IX_abuse_user_report_targetUserHost");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_report_resolved",
+                table: "abuse_user_report",
+                newName: "IX_abuse_user_report_resolved");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_report_reporterId",
+                table: "abuse_user_report",
+                newName: "IX_abuse_user_report_reporterId");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_report_reporterHost",
+                table: "abuse_user_report",
+                newName: "IX_abuse_user_report_reporterHost");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_report_createdAt",
+                table: "abuse_user_report",
+                newName: "IX_abuse_user_report_createdAt");
+
+            migrationBuilder.RenameIndex(
+                name: "IX_report_assigneeId",
+                table: "abuse_user_report",
+                newName: "IX_abuse_user_report_assigneeId");
+
+            migrationBuilder.AlterColumn<DateTime>(
+                name: "createdAt",
+                table: "abuse_user_report",
+                type: "timestamp with time zone",
+                nullable: false,
+                comment: "The created date of the AbuseUserReport.",
+                oldClrType: typeof(DateTime),
+                oldType: "timestamp with time zone",
+                oldComment: "The created date of the Report.");
+
+            migrationBuilder.AddPrimaryKey(
+                name: "PK_abuse_user_report",
+                table: "abuse_user_report",
+                column: "id");
+
+            migrationBuilder.AddForeignKey(
+                name: "FK_abuse_user_report_user_assigneeId",
+                table: "abuse_user_report",
+                column: "assigneeId",
+                principalTable: "user",
+                principalColumn: "id",
+                onDelete: ReferentialAction.SetNull);
+
+            migrationBuilder.AddForeignKey(
+                name: "FK_abuse_user_report_user_reporterId",
+                table: "abuse_user_report",
+                column: "reporterId",
+                principalTable: "user",
+                principalColumn: "id",
+                onDelete: ReferentialAction.Cascade);
+
+            migrationBuilder.AddForeignKey(
+                name: "FK_abuse_user_report_user_targetUserId",
+                table: "abuse_user_report",
+                column: "targetUserId",
+                principalTable: "user",
+                principalColumn: "id",
+                onDelete: ReferentialAction.Cascade);
+        }
+    }
+}

Iceshrimp.Backend/Core/Database/Tables/Report.cs

@@ -1,18 +1,19 @@
 using System.ComponentModel.DataAnnotations;
 using System.ComponentModel.DataAnnotations.Schema;
+using Iceshrimp.EntityFrameworkCore.Extensions;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Metadata.Builders;
 
 namespace Iceshrimp.Backend.Core.Database.Tables;
 
-[Table("abuse_user_report")]
+[Table("report")]
 [Index(nameof(ReporterId))]
 [Index(nameof(Resolved))]
 [Index(nameof(TargetUserHost))]
 [Index(nameof(TargetUserId))]
 [Index(nameof(CreatedAt))]
 [Index(nameof(ReporterHost))]
-public class AbuseUserReport
+public class Report
 {
 	[Key]
 	[Column("id")]
@@ -20,7 +21,7 @@ public class AbuseUserReport
 	public string Id { get; set; } = null!;
 
 	/// <summary>
-	///     The created date of the AbuseUserReport.
+	///     The created date of the Report.
 	/// </summary>
 	[Column("createdAt")]
 	public DateTime CreatedAt { get; set; }
@@ -71,11 +72,13 @@ public class AbuseUserReport
 	[InverseProperty(nameof(User.AbuseUserReportTargetUsers))]
 	public virtual User TargetUser { get; set; } = null!;
 
-	private class EntityTypeConfiguration : IEntityTypeConfiguration<AbuseUserReport>
+	public virtual ICollection<Note> Notes { get; set; } = new List<Note>();
+
+	private class EntityTypeConfiguration : IEntityTypeConfiguration<Report>
 	{
-		public void Configure(EntityTypeBuilder<AbuseUserReport> entity)
+		public void Configure(EntityTypeBuilder<Report> entity)
 		{
-			entity.Property(e => e.CreatedAt).HasComment("The created date of the AbuseUserReport.");
+			entity.Property(e => e.CreatedAt).HasComment("The created date of the Report.");
 			entity.Property(e => e.Forwarded).HasDefaultValue(false);
 			entity.Property(e => e.ReporterHost).HasComment("[Denormalized]");
 			entity.Property(e => e.Resolved).HasDefaultValue(false);
@@ -92,6 +95,10 @@ public class AbuseUserReport
 			entity.HasOne(d => d.TargetUser)
 			      .WithMany(p => p.AbuseUserReportTargetUsers)
 			      .OnDelete(DeleteBehavior.Cascade);
+
+			entity.HasMany(p => p.Notes)
+			      .WithMany()
+			      .UsingEntity("reported_note", "report_id", "note_id", DeleteBehavior.Cascade);
 		}
 	}
 }

Iceshrimp.Backend/Core/Database/Tables/User.cs

@@ -260,14 +260,14 @@ public class User : IIdentifiable
 
 	[Column("splitDomainResolved")] public bool SplitDomainResolved { get; set; }
 
-	[InverseProperty(nameof(AbuseUserReport.Assignee))]
+	[InverseProperty(nameof(Report.Assignee))]
-	public virtual ICollection<AbuseUserReport> AbuseUserReportAssignees { get; set; } = new List<AbuseUserReport>();
+	public virtual ICollection<Report> AbuseUserReportAssignees { get; set; } = new List<Report>();
 
-	[InverseProperty(nameof(AbuseUserReport.Reporter))]
+	[InverseProperty(nameof(Report.Reporter))]
-	public virtual ICollection<AbuseUserReport> AbuseUserReportReporters { get; set; } = new List<AbuseUserReport>();
+	public virtual ICollection<Report> AbuseUserReportReporters { get; set; } = new List<Report>();
 
-	[InverseProperty(nameof(AbuseUserReport.TargetUser))]
+	[InverseProperty(nameof(Report.TargetUser))]
-	public virtual ICollection<AbuseUserReport> AbuseUserReportTargetUsers { get; set; } = new List<AbuseUserReport>();
+	public virtual ICollection<Report> AbuseUserReportTargetUsers { get; set; } = new List<Report>();
 
 	[InverseProperty(nameof(AnnouncementRead.User))]
 	public virtual ICollection<AnnouncementRead> AnnouncementReads { get; set; } = new List<AnnouncementRead>();

Iceshrimp.Backend/Core/Federation/ActivityPub/ActivityHandlerService.cs

@@ -86,6 +86,7 @@ public class ActivityHandlerService(
 			ASUndo undo         => HandleUndoAsync(undo, resolvedActor),
 			ASUnfollow unfollow => HandleUnfollowAsync(unfollow, resolvedActor),
 			ASUpdate update     => HandleUpdateAsync(update, resolvedActor),
+			ASFlag flag         => HandleFlagAsync(flag, resolvedActor),
 
 			// Separated for readability
 			_ => throw GracefulException.UnprocessableEntity($"Activity type {activity.Type} is unknown")
@@ -527,6 +528,50 @@ public class ActivityHandlerService(
 		await userSvc.MoveRelationshipsAsync(source, target, sourceUri, targetUri);
 	}
 
+	private async Task HandleFlagAsync(ASFlag flag, User resolvedActor)
+	{
+		if (resolvedActor.IsLocalUser)
+			throw GracefulException.UnprocessableEntity("Refusing to process locally originating report via AP");
+		if (flag.Object is not { Length: > 0 })
+			throw GracefulException.UnprocessableEntity("ASFlag activity does not reference any objects");
+
+		var candidates = flag.Object.Take(25)
+		                     .Select(p => p.Id)
+		                     .NotNull()
+		                     .Where(p => p.StartsWith($"https://{config.Value.WebDomain}/users/")
+		                                 || p.StartsWith($"https://{config.Value.WebDomain}/notes/"))
+		                     .Select(p => p[$"https://{config.Value.WebDomain}/notes/".Length..])
+		                     .ToArray();
+
+		var userMatch = await db.Users.FirstOrDefaultAsync(p => p.IsLocalUser && candidates.Contains(p.Id));
+		var noteMatches = await db.Notes.Where(p => p.UserHost == null && candidates.Contains(p.Id))
+		                          .Include(note => note.User)
+		                          .ToListAsync();
+
+		if (userMatch == null && noteMatches.Count == 0)
+			throw GracefulException.UnprocessableEntity("ASFlag activity object resolution yielded zero results");
+
+		userMatch ??= noteMatches[0].User;
+
+		if (noteMatches.Count != 0 && noteMatches.Any(p => p.User != userMatch))
+			throw GracefulException.UnprocessableEntity("Refusing to process ASFlag: note author mismatch");
+
+		var report = new Report
+		{
+			Id             = IdHelpers.GenerateSnowflakeId(),
+			CreatedAt      = DateTime.UtcNow,
+			TargetUser     = userMatch,
+			TargetUserHost = userMatch.Host,
+			Reporter       = resolvedActor,
+			ReporterHost   = resolvedActor.Host,
+			Notes          = noteMatches,
+			Comment        = flag.Content ?? ""
+		};
+
+		db.Add(report);
+		await db.SaveChangesAsync();
+	}
+
 	private async Task UnfollowAsync(ASActor followeeActor, User follower)
 	{
 		//TODO: send reject? or do we not want to copy that part of the old ap core

Iceshrimp.Backend/Core/Federation/ActivityPub/ActivityRenderer.cs

@@ -239,4 +239,20 @@ public class ActivityRenderer(
 		PublishedAt = bite.CreatedAt,
 		To          = userRenderer.RenderLite(fallbackTo)
 	};
+
+	public ASFlag RenderFlag(User actor, IEnumerable<Note> notes, string comment) => new()
+	{
+		Id      = GenerateActivityId(),
+		Actor   = userRenderer.RenderLite(actor),
+		Object  = notes.Select(noteRenderer.RenderLite).ToArray<ASObject>(),
+		Content = comment
+	};
+
+	public ASFlag RenderFlag(User actor, User user, string comment) => new()
+	{
+		Id      = GenerateActivityId(),
+		Actor   = userRenderer.RenderLite(actor),
+		Object  = [userRenderer.RenderLite(user)],
+		Content = comment
+	};
 }

Iceshrimp.Backend/Core/Federation/ActivityStreams/Types/ASActivity.cs

@@ -35,6 +35,7 @@ public class ASActivity : ASObjectWithId
 		public const string Like     = $"{Ns}#Like";
 		public const string Block    = $"{Ns}#Block";
 		public const string Move     = $"{Ns}#Move";
+		public const string Flag     = $"{Ns}#Flag";
 
 		// Extensions
 		public const string Bite       = "https://ns.mia.jetzt/as#Bite";
@@ -42,6 +43,23 @@ public class ASActivity : ASObjectWithId
 	}
 }
 
+public class ASActivityWithObjectArray : ASActivity
+{
+	private ASObject[]? _object;
+
+	[J($"{Constants.ActivityStreamsNs}#object")]
+	[JC(typeof(ASObjectArrayConverter))]
+	public new ASObject[]? Object
+	{
+		get => _object;
+		set
+		{
+			_object     = value;
+			base.Object = value?.FirstOrDefault();
+		}
+	}
+}
+
 public class ASCreate : ASActivity
 {
 	public ASCreate() => Type = Types.Create;
@@ -128,6 +146,15 @@ public class ASBlock : ASActivity
 	public ASBlock() => Type = Types.Block;
 }
 
+public class ASFlag : ASActivityWithObjectArray
+{
+	public ASFlag() => Type = Types.Flag;
+
+	[J($"{Constants.ActivityStreamsNs}#content")]
+	[JC(typeof(VC))]
+	public string? Content { get; set; }
+}
+
 public class ASLike : ASActivity
 {
 	public ASLike() => Type = Types.Like;

Iceshrimp.Backend/Core/Federation/ActivityStreams/Types/ASObject.cs

@@ -1,4 +1,5 @@
 using Iceshrimp.Backend.Core.Configuration;
+using Iceshrimp.Backend.Core.Extensions;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
 using J = Newtonsoft.Json.JsonPropertyAttribute;
@@ -54,6 +55,7 @@ public class ASObject : ASObjectBase
 						ASActivity.Types.EmojiReact        => token.ToObject<ASEmojiReact>(),
 						ASActivity.Types.Block             => token.ToObject<ASBlock>(),
 						ASActivity.Types.Move              => token.ToObject<ASMove>(),
+						ASActivity.Types.Flag              => token.ToObject<ASFlag>(),
 						_                                  => token.ToObject<ASObject>()
 					};
 				case JTokenType.Array:
@@ -131,3 +133,40 @@ internal sealed class ASObjectConverter : JsonConverter
 		throw new NotImplementedException();
 	}
 }
+
+internal sealed class ASObjectArrayConverter : JsonConverter
+{
+	public override bool CanWrite => false;
+
+	public override bool CanConvert(Type objectType)
+	{
+		return true;
+	}
+
+	public override object? ReadJson(
+		JsonReader reader, Type objectType, object? existingValue,
+		JsonSerializer serializer
+	)
+	{
+		if (reader.TokenType == JsonToken.StartArray)
+		{
+			var obj = JArray.Load(reader);
+			var arr = obj.Select(ASObject.Deserialize).NotNull().ToArray();
+			return arr.Length > 0 ? arr : null;
+		}
+
+		if (reader.TokenType == JsonToken.StartObject)
+		{
+			var obj          = JObject.Load(reader);
+			var deserialized = ASObject.Deserialize(obj);
+			return deserialized != null ? new[]{ deserialized } : null;
+		}
+
+		throw new Exception("this shouldn't happen");
+	}
+
+	public override void WriteJson(JsonWriter writer, object? value, JsonSerializer serializer)
+	{
+		throw new NotImplementedException();
+	}
+}

Iceshrimp.Backend/Iceshrimp.Backend.csproj

@@ -28,7 +28,7 @@
         <PackageReference Include="EntityFrameworkCore.Projectables" Version="4.0.0" />
         <PackageReference Include="FlexLabs.EntityFrameworkCore.Upsert" Version="8.1.2" />
         <PackageReference Include="Iceshrimp.Assets.Fonts" Version="1.0.0" />
-        <PackageReference Include="Iceshrimp.EntityFrameworkCore.Extensions" Version="1.0.1" />
+        <PackageReference Include="Iceshrimp.EntityFrameworkCore.Extensions" Version="1.0.2" />
         <PackageReference Include="Iceshrimp.ObjectStorage.S3" Version="0.34.3" />
         <PackageReference Include="Isopoh.Cryptography.Argon2" Version="2.0.0" />
         <PackageReference Include="JetBrains.Annotations" Version="2024.3.0" />