feat: forward application OSC 52 clipboard writes through boo ui (#95)

Forward an application's own OSC 52 clipboard writes through boo ui to the real terminal, so a copy made inside a session reaches the user's clipboard over SSH. boo ui renders sessions from libghostty state and the view-canvas has no clipboard effect, so these writes were dropped; plain boo attach was already unaffected. Read requests are not forwarded. The scanner walks output in runs (indexOfScalar / appendSlice) and its unit tests are wired into main.zig's test block.

Author: kylecarbs

src/main.zig

@@ -1130,6 +1130,7 @@ test {
     _ = @import("pty.zig");
     _ = @import("altscreen.zig");
     _ = @import("oscquery.zig");
+    _ = @import("osc52.zig");
     _ = @import("window.zig");
     _ = @import("daemon.zig");
     _ = @import("client.zig");

src/osc52.zig

@@ -0,0 +1,286 @@
+//! Forwarding of application OSC 52 clipboard *writes* to the real
+//! terminal for `boo ui`.
+//!
+//! A `boo ui` view never passes session output through to the terminal
+//! raw. The focused session feeds a client-side libghostty terminal and
+//! the UI repaints the viewport from that terminal's state (see the
+//! header of `ui.zig`). libghostty-vt parses OSC 52 but exposes no
+//! clipboard effect, so an application that copies text itself (an
+//! editor's yank, a pager's mouse selection, anything emitting
+//! `ESC ] 52 ; c ; <base64> BEL`) has its clipboard write silently
+//! dropped instead of reaching the user's terminal. A plain `boo attach`
+//! does not have this problem: its output is written to the real
+//! terminal byte for byte, OSC 52 included.
+//!
+//! This scanner recovers the `boo ui` case. It watches the same
+//! passthrough bytes the view-canvas consumes and, on a complete OSC 52
+//! clipboard write, hands the verbatim sequence to a sink that writes it
+//! to the real terminal, exactly as the ui's own selection copy does
+//! (`copySelection` in `ui.zig`). The clipboard write then works over
+//! SSH and through nested multiplexers like any other OSC 52.
+//!
+//! Only writes are forwarded. A read request (`ESC ] 52 ; c ; ? ST`)
+//! asks the terminal to send the clipboard *back* to the application; a
+//! remote session must not be able to read the user's local clipboard,
+//! so a `?` payload is recognized and ignored. Sequences split across
+//! feeds are carried over to the next call.
+
+const std = @import("std");
+
+/// `ESC ] 5 2 ;`: the exact prefix of an OSC 52 sequence. The trailing
+/// `;` keeps neighbours such as OSC 520 from matching.
+const prefix = "\x1b]52;";
+
+/// Cap on a single buffered clipboard write. The payload is base64, so
+/// this still allows roughly 1.5 MiB of copied text. A larger write is
+/// dropped rather than buffered without bound: its tail is base64 plus a
+/// BEL or ST terminator, none of which can be mistaken for a new OSC 52
+/// prefix, so abandoning it to the ground state never produces a false
+/// match.
+const max_seq = 2 * 1024 * 1024;
+
+/// Incremental scanner over a session's output. It emits nothing of its
+/// own; it only recognizes OSC 52 clipboard writes and forwards them.
+/// Held candidate bytes persist across feeds so a write split over reads
+/// is still recognized.
+pub const Filter = struct {
+    /// Bytes of an in-progress candidate, starting at ESC. Empty in the
+    /// ground state.
+    buf: std.ArrayList(u8) = .empty,
+    /// The previous body byte was an ESC that may begin an ST terminator
+    /// (`ESC \`).
+    esc_pending: bool = false,
+
+    pub fn deinit(self: *Filter, alloc: std.mem.Allocator) void {
+        self.buf.deinit(alloc);
+    }
+
+    /// Scan `input`. On each complete OSC 52 clipboard write, call
+    /// `sink.clipboard(seq)` with the verbatim sequence bytes, terminator
+    /// included. `sink` is any value (or pointer) exposing that method.
+    pub fn feed(
+        self: *Filter,
+        alloc: std.mem.Allocator,
+        input: []const u8,
+        sink: anytype,
+    ) std.mem.Allocator.Error!void {
+        var i: usize = 0;
+        while (i < input.len) {
+            const byte = input[i];
+            var advance = true;
+
+            if (self.buf.items.len == 0) {
+                // Ground: only ESC can begin a candidate. Skip the run
+                // of non-ESC bytes to the next ESC in one vectorized pass.
+                if (byte != 0x1b) {
+                    const rel = std.mem.indexOfScalar(u8, input[i..], 0x1b) orelse input.len - i;
+                    i += rel;
+                    continue;
+                }
+                try self.buf.append(alloc, byte);
+            } else if (self.buf.items.len < prefix.len) {
+                // Matching the fixed prefix one byte at a time.
+                if (byte == prefix[self.buf.items.len]) {
+                    try self.buf.append(alloc, byte);
+                } else {
+                    // Not OSC 52 after all. Drop the candidate and
+                    // reconsider this byte from the ground state, so an
+                    // ESC that starts a fresh candidate is not lost.
+                    self.reset();
+                    advance = false;
+                }
+            } else if (self.esc_pending) {
+                self.esc_pending = false;
+                if (byte == '\\') {
+                    // ST terminator (`ESC \`) completes the sequence.
+                    try self.buf.append(alloc, byte);
+                    self.emit(sink);
+                    self.reset();
+                } else {
+                    // The ESC did not form ST: a malformed OSC. Abandon
+                    // it and reconsider this byte from the ground state.
+                    self.reset();
+                    advance = false;
+                }
+            } else if (byte == 0x07) {
+                // BEL terminator completes the sequence.
+                try self.buf.append(alloc, byte);
+                self.emit(sink);
+                self.reset();
+            } else {
+                // Body: base64 data up to a BEL or ST terminator. Neither
+                // terminator byte occurs in base64, so accumulate the
+                // whole run in one copy instead of byte by byte.
+                const rest = input[i..];
+                const run = std.mem.indexOfAny(u8, rest, &[_]u8{ 0x07, 0x1b }) orelse rest.len;
+                if (run == 0) {
+                    // The byte is ESC (BEL is handled above); it may open ST.
+                    try self.buf.append(alloc, byte);
+                    self.esc_pending = true;
+                } else if (self.buf.items.len + run > max_seq) {
+                    // Oversized: drop it. The skipped tail is base64 plus
+                    // a terminator, never a new OSC 52 prefix (see max_seq).
+                    self.reset();
+                    i += run;
+                    continue;
+                } else {
+                    try self.buf.appendSlice(alloc, rest[0..run]);
+                    i += run;
+                    continue;
+                }
+            }
+
+            if (advance) i += 1;
+        }
+    }
+
+    fn reset(self: *Filter) void {
+        self.buf.clearRetainingCapacity();
+        self.esc_pending = false;
+    }
+
+    /// Forward a completed candidate, unless it is a read request.
+    fn emit(self: *Filter, sink: anytype) void {
+        if (isWrite(self.buf.items)) sink.clipboard(self.buf.items);
+    }
+};
+
+/// Whether a complete OSC 52 sequence is a clipboard *write* (data to
+/// store) rather than a read request (`?`). The sequence is
+/// `ESC ] 52 ; <Pc> ; <Pd> <terminator>`; a read request's `<Pd>` is `?`.
+fn isWrite(seq: []const u8) bool {
+    if (seq.len < prefix.len) return false;
+    // After the prefix: `<Pc> ; <Pd> <terminator>`.
+    const rest = seq[prefix.len..];
+    const semi = std.mem.indexOfScalar(u8, rest, ';') orelse return false;
+    var pd = rest[semi + 1 ..];
+    // Strip the terminator (BEL, or the two-byte ST `ESC \`).
+    if (pd.len >= 1 and pd[pd.len - 1] == 0x07) {
+        pd = pd[0 .. pd.len - 1];
+    } else if (pd.len >= 2 and pd[pd.len - 2] == 0x1b and pd[pd.len - 1] == '\\') {
+        pd = pd[0 .. pd.len - 2];
+    }
+    // A read request is a literal `?`. Anything else (base64, or empty
+    // to clear the clipboard) is a write.
+    return !(pd.len > 0 and pd[0] == '?');
+}
+
+const Collector = struct {
+    alloc: std.mem.Allocator,
+    seqs: std.ArrayList([]u8) = .empty,
+
+    fn clipboard(self: *Collector, seq: []const u8) void {
+        const dup = self.alloc.dupe(u8, seq) catch return;
+        self.seqs.append(self.alloc, dup) catch self.alloc.free(dup);
+    }
+
+    fn deinit(self: *Collector) void {
+        for (self.seqs.items) |s| self.alloc.free(s);
+        self.seqs.deinit(self.alloc);
+    }
+};
+
+fn expectForwards(input: []const u8, expected: []const []const u8) !void {
+    const alloc = std.testing.allocator;
+    var f: Filter = .{};
+    defer f.deinit(alloc);
+    var c: Collector = .{ .alloc = alloc };
+    defer c.deinit();
+    try f.feed(alloc, input, &c);
+    try std.testing.expectEqual(expected.len, c.seqs.items.len);
+    for (expected, c.seqs.items) |want, got| {
+        try std.testing.expectEqualStrings(want, got);
+    }
+}
+
+test "clipboard write with BEL terminator is forwarded verbatim" {
+    try expectForwards(
+        "before\x1b]52;c;SGVsbG8=\x07after",
+        &.{"\x1b]52;c;SGVsbG8=\x07"},
+    );
+}
+
+test "clipboard write with ST terminator is forwarded verbatim" {
+    try expectForwards(
+        "\x1b]52;c;SGVsbG8=\x1b\\",
+        &.{"\x1b]52;c;SGVsbG8=\x1b\\"},
+    );
+}
+
+test "a read request is not forwarded" {
+    try expectForwards("\x1b]52;c;?\x07", &.{});
+}
+
+test "an empty payload (clear) is forwarded" {
+    try expectForwards("\x1b]52;c;\x07", &.{"\x1b]52;c;\x07"});
+}
+
+test "an empty Pc field is forwarded" {
+    try expectForwards("\x1b]52;;QQ==\x07", &.{"\x1b]52;;QQ==\x07"});
+}
+
+test "a write split across feeds is recognized" {
+    const alloc = std.testing.allocator;
+    var f: Filter = .{};
+    defer f.deinit(alloc);
+    var c: Collector = .{ .alloc = alloc };
+    defer c.deinit();
+    try f.feed(alloc, "x\x1b]52;c;SGVs", &c);
+    try std.testing.expectEqual(@as(usize, 0), c.seqs.items.len);
+    try f.feed(alloc, "bG8=\x07y", &c);
+    try std.testing.expectEqual(@as(usize, 1), c.seqs.items.len);
+    try std.testing.expectEqualStrings("\x1b]52;c;SGVsbG8=\x07", c.seqs.items[0]);
+}
+
+test "a read request split across feeds is still ignored" {
+    const alloc = std.testing.allocator;
+    var f: Filter = .{};
+    defer f.deinit(alloc);
+    var c: Collector = .{ .alloc = alloc };
+    defer c.deinit();
+    try f.feed(alloc, "\x1b]52;c;", &c);
+    try f.feed(alloc, "?\x07", &c);
+    try std.testing.expectEqual(@as(usize, 0), c.seqs.items.len);
+}
+
+test "back-to-back writes are both forwarded" {
+    try expectForwards(
+        "\x1b]52;c;QQ==\x07\x1b]52;p;Qg==\x1b\\",
+        &.{ "\x1b]52;c;QQ==\x07", "\x1b]52;p;Qg==\x1b\\" },
+    );
+}
+
+test "OSC 520 and other OSC sequences are not matched" {
+    try expectForwards("\x1b]520;c;QQ==\x07", &.{});
+    try expectForwards("\x1b]2;a title\x07", &.{});
+    try expectForwards("\x1b]11;rgb:1234/5678/9abc\x07", &.{});
+}
+
+test "plain text and CSI sequences pass without a match" {
+    try expectForwards("hello \x1b[2J\x1b[1;5H\x1b[31mworld", &.{});
+}
+
+test "a near-miss prefix then a real write still forwards the write" {
+    // ESC ] 5 3 aborts the candidate; the following real write matches.
+    try expectForwards(
+        "\x1b]53;c;QQ==\x07\x1b]52;c;Qg==\x07",
+        &.{"\x1b]52;c;Qg==\x07"},
+    );
+}
+
+test "a long under-cap payload is buffered and forwarded" {
+    const alloc = std.testing.allocator;
+    var input: std.ArrayList(u8) = .empty;
+    defer input.deinit(alloc);
+    try input.appendSlice(alloc, "\x1b]52;c;");
+    try input.appendSlice(alloc, "QQ==" ** 4096); // ~16 KiB of base64
+    try input.append(alloc, 0x07);
+
+    var f: Filter = .{};
+    defer f.deinit(alloc);
+    var c: Collector = .{ .alloc = alloc };
+    defer c.deinit();
+    try f.feed(alloc, input.items, &c);
+    try std.testing.expectEqual(@as(usize, 1), c.seqs.items.len);
+    try std.testing.expectEqualStrings(input.items, c.seqs.items[0]);
+}

src/ui.zig

@@ -25,6 +25,7 @@ const vt = @import("ghostty-vt");
 
 const client = @import("client.zig");
 const keys = @import("keys.zig");
+const osc52 = @import("osc52.zig");
 const paths = @import("paths.zig");
 const protocol = @import("protocol.zig");
 const ptypkg = @import("pty.zig");
@@ -668,6 +669,15 @@ pub const InputParser = struct {
 
 // -- Focused session view ----------------------------------------------------
 
+/// Sink for `osc52.Filter`: writes a forwarded clipboard sequence to
+/// the real terminal (fd 1), the same destination as the ui's own
+/// selection copy.
+const ClipboardSink = struct {
+    pub fn clipboard(_: ClipboardSink, seq: []const u8) void {
+        protocol.writeAll(1, seq) catch {};
+    }
+};
+
 /// The attach connection and local terminal state of the focused
 /// session. Heap-allocated and pinned: the stream handler keeps a
 /// pointer to `term`, and effects callbacks recover the View with
@@ -688,6 +698,10 @@ pub const View = struct {
     /// `.screen` messages. Decides whether a wheel over the viewport
     /// pages local scrollback or sends arrow keys.
     app_alt: bool = false,
+    /// Recovers application clipboard writes (OSC 52) from the output
+    /// stream so a copy inside the session reaches the real terminal
+    /// (see osc52.zig and feedOutput).
+    clip: osc52.Filter = .{},
 
     pub const State = enum { live, ended, stolen, lost };
     pub const Stream = vt.TerminalStream;
@@ -767,6 +781,7 @@ pub const View = struct {
         self.stream.deinit();
         self.term.deinit(self.alloc);
         self.decoder.deinit();
+        self.clip.deinit(self.alloc);
         self.alloc.destroy(self);
     }
 
@@ -826,6 +841,12 @@ pub const View = struct {
     }
 
     pub fn feedOutput(self: *View, bytes: []const u8) void {
+        // The view-canvas stream below parses OSC 52 but has no
+        // clipboard effect, so an application's own clipboard write
+        // would be dropped. Forward it to the real terminal first, the
+        // same path the ui's selection copy uses, so a copy inside a
+        // session reaches the user's clipboard over SSH.
+        self.clip.feed(self.alloc, bytes, ClipboardSink{}) catch {};
         self.stream.nextSlice(bytes);
     }
 

test/integration.zig

@@ -1624,6 +1624,34 @@ test "ui: dragging in the viewport selects text and copies it via osc 52" {
     try ui.waitFor("copied");
 }
 
+test "ui: an application's own OSC 52 clipboard write reaches the real terminal" {
+    const alloc = std.testing.allocator;
+    var h = try Harness.init(alloc);
+    defer h.deinit();
+
+    // boo ui renders sessions from terminal state rather than passing
+    // bytes through, and the view-canvas has no clipboard effect, so an
+    // application's own OSC 52 clipboard write is parsed and dropped
+    // unless the ui forwards it to the real terminal.
+    try h.startDetached("clip", &.{"sh"});
+
+    var ui = try PtyClient.spawn(&h, &.{"ui"}, 24, 100);
+    defer ui.deinit();
+    try ui.waitFor("clip");
+
+    // Confirm the session is focused and rendering before the copy.
+    try h.sendLine("clip", "printf 'CLIPREADY\\n'");
+    try ui.waitFor("CLIPREADY");
+    ui.clearOutput();
+
+    // The application copies "HELLO" to the clipboard via OSC 52. The
+    // sequence must reach the ui's real terminal verbatim. The echoed
+    // command line carries the literal text "\\033]52..." (a backslash,
+    // not a real ESC), so only the forwarded sequence matches the wait.
+    try h.sendLine("clip", "printf '\\033]52;c;SEVMTE8=\\007'");
+    try ui.waitFor("\x1b]52;c;SEVMTE8=\x07");
+}
+
 test "ui: mouse events forward natively when the application asks for them" {
     const alloc = std.testing.allocator;
     var h = try Harness.init(alloc);