1 files changed, 68 insertions, 18 deletions

diff --git a/src/9p_io.zig b/src/9p_io.zig
index 6f05e3ab..78ff5d59 100644
--- a/src/9p_io.zig
+++ b/src/9p_io.zig
@@ -1947,14 +1947,8 @@ pub const Client = struct {
         }
     };
 
-    fn transact(
-        s: *Session,
-        names: []const []const u8,
-        out: *std.Io.Writer.Allocating,
-        remote: *RemoteError,
-        write_bytes: ?[]const u8,
-        read_limit: usize,
-    ) !void {
+    /// Version, attach and a walk to `names`: the fid there and its qid.
+    fn walkTo(s: *Session, names: []const []const u8, remote: *RemoteError) !struct { fid: u32, qid: ninep.Qid } {
         _ = try s.ask(.{ .version = .{} }, remote);
         if (s.cl.msize == 0) return Error.Botch;
 
@@ -1978,6 +1972,20 @@ pub const Client = struct {
             next = if (next == 1) 2 else 1;
             i += n;
         }
+        return .{ .fid = cur, .qid = here };
+    }
+
+    fn transact(
+        s: *Session,
+        names: []const []const u8,
+        out: *std.Io.Writer.Allocating,
+        remote: *RemoteError,
+        write_bytes: ?[]const u8,
+        read_limit: usize,
+    ) !void {
+        const at = try walkTo(s, names, remote);
+        const cur = at.fid;
+        const here = at.qid;
         defer s.dropNoWait(cur);
 
         const directory = here.type & ninep.qtdir != 0;
@@ -2036,15 +2044,20 @@ pub const Client = struct {
         read_limit: usize,
     ) ![]u8 {
         if (comptime !supported) return Error.Dial;
+        const s = try startSession(gpa, sock, display_path);
+        defer endSession(gpa, s);
+        var out: std.Io.Writer.Allocating = .init(gpa);
+        errdefer out.deinit();
+        try transact(s, names, &out, remote, write_bytes, read_limit);
+        return out.toOwnedSlice();
+    }
+
+    /// A connected session whose requests have the usual deadline.
+    fn startSession(gpa: std.mem.Allocator, sock: Dial, display_path: []const u8) !*Session {
         const deadline = nowMs() +| budget_ms;
         const s = try gpa.create(Session);
         s.* = .{ .fd = -1, .deadline = deadline, .display_path = display_path };
-        defer {
-            if (quic_enabled and s.quic != null) {
-                s.quic.?.deinit();
-            } else if (s.fd >= 0) _ = libc.close(s.fd);
-            gpa.destroy(s);
-        }
+        errdefer endSession(gpa, s);
         if (sock == .quic) {
             if (comptime quic_enabled) {
                 s.quic = quic.Connection.dial(sock.quic) catch return Error.Dial;
@@ -2052,11 +2065,48 @@ pub const Client = struct {
             } else return Error.QuicUnavailable;
         } else s.fd = try connect(sock, deadline);
         s.cl = .init(.{ .in = &s.in, .out = &s.out });
+        return s;
+    }
 
-        var out: std.Io.Writer.Allocating = .init(gpa);
-        errdefer out.deinit();
-        try transact(s, names, &out, remote, write_bytes, read_limit);
-        return out.toOwnedSlice();
+    fn endSession(gpa: std.mem.Allocator, s: *Session) void {
+        if (quic_enabled and s.quic != null) {
+            s.quic.?.deinit();
+        } else if (s.fd >= 0) _ = libc.close(s.fd);
+        gpa.destroy(s);
+    }
+
+    /// Opens `path` on one connection and writes `first` to it (/log's
+    /// `follow new`), all with the usual deadline; then, once `ready(ctx)`
+    /// has said it is not done already, reads it with no deadline, a read at
+    /// a time, until `record(ctx, bytes)` says done. An end of file or a
+    /// dropped connection is Hangup. What `pardes --wait` blocks on.
+    pub fn follow(
+        gpa: std.mem.Allocator,
+        dial: []const u8,
+        path: []const u8,
+        first: []const u8,
+        ctx: anytype,
+        comptime ready: fn (@TypeOf(ctx)) bool,
+        comptime record: fn (@TypeOf(ctx), []const u8) bool,
+    ) !void {
+        if (comptime !supported) return error.Unsupported;
+        var names: [max_depth][]const u8 = undefined;
+        const n = try elements(path, &names);
+        var sock_buf: [sun_path_len]u8 = undefined;
+        const sock = try resolve(&sock_buf, dial);
+        var remote: RemoteError = .{};
+        const s = try startSession(gpa, sock, path);
+        defer endSession(gpa, s);
+        const fid = (try walkTo(s, names[0..n], &remote)).fid;
+        _ = try s.ask(.{ .open = .{ .fid = fid, .mode = ninep.ordwr } }, &remote);
+        _ = try s.ask(.{ .write = .{ .fid = fid, .offset = 0, .data = first } }, &remote);
+        if (ready(ctx)) return;
+        s.deadline = std.math.maxInt(i64);
+        while (true) {
+            const data = (try s.ask(.{ .read = .{ .fid = fid, .offset = 0, .count = s.cl.maxRead() } }, &remote)).read;
+            if (data.len == 0) return Error.Hangup;
+            if (record(ctx, data)) return;
+        }
     }
 
     fn connect(sock: Dial, deadline: i64) Error!c_int {