Mount dials: a relative socket path is a bad dial address, a socket path not there says no such socket (ENOENT), and the hint says tcp! takes a numeric address

`Mount peer rel/x.sock` dialled relative to wherever the editor ran;
`Mount peer unix!/nonexistent` said `dial failed: no answer` (EIO); and
the hint offered `tcp!host!port` where only a numeric address is taken.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/9p_io.zig b/src/9p_io.zig
index e199dea9..dd755f82 100644
--- a/src/9p_io.zig
+++ b/src/9p_io.zig
@@ -1427,6 +1427,7 @@ test "TCP addresses are numeric and normalize mapped IPv4" {
     try testing.expectError(error.BadDial, Client.validateDial("unix!work"));
     try testing.expectError(error.BadDial, Client.validateDial("nowhere!x"));
     try Client.validateDial("/tmp/odd!name.sock");
+    try testing.expectError(error.BadDial, Client.validateDial("rel/dir.sock"));
     try testing.expectError(error.BadDial, Client.validateDial("unix!"));
     try testing.expectError(error.BadDial, Client.validateDial("unix!/tmp/a\x00b"));
     try testing.expectError(error.BadDial, Client.validateDial("tcp!localhost!5640"));
@@ -2086,6 +2087,9 @@ pub const Client = struct {
         const path = if (explicit_unix) dial[5..] else dial;
         if (explicit_unix and !std.mem.startsWith(u8, path, "/")) return error.BadDial;
         if (std.mem.indexOfScalar(u8, path, '/') != null) {
+            // A socket's path is absolute: a relative one would mean wherever
+            // the editor happens to run.
+            if (path[0] != '/') return error.BadDial;
             if (std.mem.indexOfScalar(u8, path, 0) != null) return error.BadDial;
             return .{ .unix = std.fmt.bufPrintSentinel(buf, "{s}", .{path}, 0) catch return error.BadDial };
         }