terminal: DCS handler, XTGETTCAP parsing

src/terminal/Parser.zig

@@ -127,8 +127,8 @@ pub const Action = union(enum) {
     };
 
     pub const DCS = struct {
-        intermediates: []u8,
-        params: []u16,
+        intermediates: []const u8 = "",
+        params: []const u16 = &.{},
         final: u8,
     };
 

src/terminal/dcs.zig

@@ -0,0 +1,218 @@
+const std = @import("std");
+const assert = std.debug.assert;
+const Allocator = std.mem.Allocator;
+const terminal = @import("main.zig");
+const DCS = terminal.DCS;
+
+const log = std.log.scoped(.terminal_dcs);
+
+/// DCS command handler. This should be hooked into a terminal.Stream handler.
+/// The hook/put/unhook functions are meant to be called from the
+/// terminal.stream dcsHook, dcsPut, and dcsUnhook functions, respectively.
+pub const Handler = struct {
+    state: State = .{ .inactive = {} },
+
+    /// Maximum bytes any DCS command can take. This is to prevent
+    /// malicious input from causing us to allocate too much memory.
+    /// This is arbitrarily set to 1MB today, increase if needed.
+    max_bytes: usize = 1024 * 1024,
+
+    pub fn deinit(self: *Handler) void {
+        self.discard();
+    }
+
+    pub fn hook(self: *Handler, alloc: Allocator, dcs: DCS) void {
+        assert(self.state == .inactive);
+        self.state = if (tryHook(alloc, dcs)) |state_| state: {
+            if (state_) |state| break :state state else {
+                log.info("unknown DCS hook: {}", .{dcs});
+                break :state .{ .ignore = {} };
+            }
+        } else |err| state: {
+            log.info(
+                "error initializing DCS hook, will ignore hook err={}",
+                .{err},
+            );
+            break :state .{ .ignore = {} };
+        };
+    }
+
+    fn tryHook(alloc: Allocator, dcs: DCS) !?State {
+        return switch (dcs.intermediates.len) {
+            1 => switch (dcs.intermediates[0]) {
+                '+' => switch (dcs.final) {
+                    // XTGETTCAP
+                    // https://github.com/mitchellh/ghostty/issues/517
+                    'q' => .{
+                        .xtgettcap = try std.ArrayList(u8).initCapacity(
+                            alloc,
+                            128, // Arbitrary choice
+                        ),
+                    },
+
+                    else => null,
+                },
+
+                else => null,
+            },
+
+            else => null,
+        };
+    }
+
+    pub fn put(self: *Handler, byte: u8) void {
+        self.tryPut(byte) catch |err| {
+            // On error we just discard our state and ignore the rest
+            log.info("error putting byte into DCS handler err={}", .{err});
+            self.discard();
+            self.state = .{ .ignore = {} };
+        };
+    }
+
+    fn tryPut(self: *Handler, byte: u8) !void {
+        switch (self.state) {
+            .inactive,
+            .ignore,
+            => {},
+
+            .xtgettcap => |*list| {
+                if (list.items.len >= self.max_bytes) {
+                    return error.OutOfMemory;
+                }
+
+                try list.append(byte);
+            },
+        }
+    }
+
+    pub fn unhook(self: *Handler) ?Command {
+        defer self.state = .{ .inactive = {} };
+        return switch (self.state) {
+            .inactive,
+            .ignore,
+            => null,
+
+            .xtgettcap => |list| .{ .xtgettcap = .{ .data = list } },
+        };
+    }
+
+    fn discard(self: *Handler) void {
+        switch (self.state) {
+            .inactive,
+            .ignore,
+            => {},
+
+            .xtgettcap => |*list| list.deinit(),
+        }
+
+        self.state = .{ .inactive = {} };
+    }
+};
+
+pub const Command = union(enum) {
+    /// XTGETTCAP
+    xtgettcap: XTGETTCAP,
+
+    pub fn deinit(self: Command) void {
+        switch (self) {
+            .xtgettcap => |*v| {
+                v.data.deinit();
+            },
+        }
+    }
+
+    pub const XTGETTCAP = struct {
+        data: std.ArrayList(u8),
+
+        // Note: do not reset this. The next function mutates data so it is
+        // unsafe to reset this and reiterate.
+        i: usize = 0,
+
+        /// Returns the next terminfo key being requested and null
+        /// when there are no more keys.
+        pub fn next(self: *XTGETTCAP) ?[]const u8 {
+            if (self.i >= self.data.items.len) return null;
+
+            var rem = self.data.items[self.i..];
+            const idx = std.mem.indexOf(u8, rem, ";") orelse rem.len;
+
+            // Note that if we're at the end, idx + 1 is len + 1 so we're over
+            // the end but that's okay because our check above is >= so we'll
+            // never read.
+            self.i += idx + 1;
+
+            // HEX decode in-place so we don't have to allocate. If invalid
+            // hex is given then we just return null and stop processing.
+            return std.fmt.hexToBytes(rem, rem[0..idx]) catch null;
+        }
+    };
+};
+
+const State = union(enum) {
+    /// We're not in a DCS state at the moment.
+    inactive: void,
+
+    /// We're hooked, but its an unknown DCS command or one that went
+    /// invalid due to some bad input, so we're ignoring the rest.
+    ignore: void,
+
+    // XTGETTCAP
+    xtgettcap: std.ArrayList(u8),
+};
+
+test "unknown DCS command" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var h: Handler = .{};
+    defer h.deinit();
+    h.hook(alloc, .{ .final = 'A' });
+    try testing.expect(h.state == .ignore);
+    try testing.expect(h.unhook() == null);
+    try testing.expect(h.state == .inactive);
+}
+
+test "XTGETTCAP command" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var h: Handler = .{};
+    defer h.deinit();
+    h.hook(alloc, .{ .intermediates = "+", .final = 'q' });
+    for ("536D756C78") |byte| h.put(byte);
+    var cmd = h.unhook().?;
+    defer cmd.deinit();
+    try testing.expect(cmd == .xtgettcap);
+    try testing.expectEqualStrings("Smulx", cmd.xtgettcap.next().?);
+    try testing.expect(cmd.xtgettcap.next() == null);
+}
+
+test "XTGETTCAP command multiple keys" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var h: Handler = .{};
+    defer h.deinit();
+    h.hook(alloc, .{ .intermediates = "+", .final = 'q' });
+    for ("536D756C78;536D756C78") |byte| h.put(byte);
+    var cmd = h.unhook().?;
+    defer cmd.deinit();
+    try testing.expect(cmd == .xtgettcap);
+    try testing.expectEqualStrings("Smulx", cmd.xtgettcap.next().?);
+    try testing.expectEqualStrings("Smulx", cmd.xtgettcap.next().?);
+    try testing.expect(cmd.xtgettcap.next() == null);
+}
+
+test "XTGETTCAP command invalid data" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var h: Handler = .{};
+    defer h.deinit();
+    h.hook(alloc, .{ .intermediates = "+", .final = 'q' });
+    for ("who;536D756C78") |byte| h.put(byte);
+    var cmd = h.unhook().?;
+    defer cmd.deinit();
+    try testing.expect(cmd == .xtgettcap);
+    try testing.expect(cmd.xtgettcap.next() == null);
+}

src/terminal/main.zig

@@ -6,6 +6,7 @@ const ansi = @import("ansi.zig");
 const csi = @import("csi.zig");
 const sgr = @import("sgr.zig");
 pub const apc = @import("apc.zig");
+pub const dcs = @import("dcs.zig");
 pub const osc = @import("osc.zig");
 pub const point = @import("point.zig");
 pub const color = @import("color.zig");
@@ -16,6 +17,8 @@ pub const parse_table = @import("parse_table.zig");
 pub const Charset = charsets.Charset;
 pub const CharsetSlot = charsets.Slots;
 pub const CharsetActiveSlot = charsets.ActiveSlot;
+pub const CSI = Parser.Action.CSI;
+pub const DCS = Parser.Action.DCS;
 pub const MouseShape = @import("mouse_shape.zig").MouseShape;
 pub const Terminal = @import("Terminal.zig");
 pub const Parser = @import("Parser.zig");

src/terminal/stream.zig

@@ -64,7 +64,9 @@ pub fn Stream(comptime Handler: type) type {
                     .csi_dispatch => |csi_action| try self.csiDispatch(csi_action),
                     .esc_dispatch => |esc| try self.escDispatch(esc),
                     .osc_dispatch => |cmd| try self.oscDispatch(cmd),
-                    .dcs_hook => |dcs| log.warn("unhandled DCS hook: {}", .{dcs}),
+                    .dcs_hook => |dcs| if (@hasDecl(T, "dcsHook")) {
+                        try self.handler.dcsHook(dcs);
+                    } else log.warn("unimplemented DCS hook", .{}),
                     .dcs_put => |code| log.warn("unhandled DCS put: {x}", .{code}),
                     .dcs_unhook => log.warn("unhandled DCS unhook", .{}),
                     .apc_start => if (@hasDecl(T, "apcStart")) {

src/termio/Exec.zig

@@ -1199,6 +1199,11 @@ const StreamHandler = struct {
         };
     }
 
+    pub fn dcsHook(self: *StreamHandler, dcs: terminal.DCS) !void {
+        _ = self;
+        log.warn("DCS HOOK: {}", .{dcs});
+    }
+
     pub fn apcStart(self: *StreamHandler) !void {
         self.apc.start();
     }