Every EINVAL a write gets says why; DEL in an exec or look line is a control character

An empty name, a word written to log other than follow, a data, sel, dot
or dirty write to a pane with no text, a truncate other than to zero,
and a control character in a look line written through a held open were
refused with no words, logged as `Invalid argument`. Each says its reason
now; and DEL is refused in exec and look lines as in names.

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

1 files changed, 9 insertions, 6 deletions

diff --git a/src/ninep/pane.zig b/src/ninep/pane.zig
index 66b3728c..4c967fc5 100644
--- a/src/ninep/pane.zig
+++ b/src/ninep/pane.zig
@@ -481,8 +481,11 @@ fn writeTag(req: Req, pane: *Pane) Reply {
     return .{ .tag = req.tag, .written = @intCast(take) };
 }
 
+/// A write only text takes, to a pane with none: said, as every EINVAL is.
+pub const e_no_text = "invalid write: this pane has no text (a terminal, an image or a PDF)";
+
 fn writeData(p: *Pardes, req: Req, pane: *Pane) Reply {
-    if (fileOf(pane) == null) return Reply.fail(req.tag, E.INVAL);
+    if (fileOf(pane) == null) return tree.failText(req.tag, E.INVAL, e_no_text);
     const pf = &pane.fs;
     if (pf.addr_failed) return tree.failText(req.tag, E.INVAL, e_addr_failed);
     clampAddr(pf, bodyOf(pane).len);
@@ -501,7 +504,7 @@ fn writeData(p: *Pardes, req: Req, pane: *Pane) Reply {
 }
 
 fn writeSel(p: *Pardes, req: Req, pane: *Pane) Reply {
-    if (fileOf(pane) == null) return Reply.fail(req.tag, E.INVAL);
+    if (fileOf(pane) == null) return tree.failText(req.tag, E.INVAL, e_no_text);
     const d = dotOf(pane);
     const q0: usize = d.q0;
     const q1: usize = @max(q0, @as(usize, d.q1));
@@ -558,7 +561,7 @@ fn writeRange(req: Req, pane: *Pane, file: PaneFile) Reply {
         .limit => pf.limit = range,
         // Setting dot scrolls to it, which is the whole of acme's `show`.
         .dot => {
-            if (fileOf(pane) == null) return Reply.fail(req.tag, E.INVAL);
+            if (fileOf(pane) == null) return tree.failText(req.tag, E.INVAL, e_no_text);
             setDot(pane, range);
         },
         else => unreachable,
@@ -573,7 +576,7 @@ fn writeFlag(p: *Pardes, req: Req, pane: *Pane, file: PaneFile) Reply {
     const pf = &pane.fs;
     switch (file) {
         .dirty => {
-            const f = fileOf(pane) orelse return Reply.fail(req.tag, E.INVAL);
+            const f = fileOf(pane) orelse return tree.failText(req.tag, E.INVAL, e_no_text);
             f.saved_revision = if (on) f.revision -% 1 else f.revision;
         },
         // acme's nomark joins the writes after it into one undo step. The
@@ -616,7 +619,7 @@ fn nameFault(name: []const u8) ?[]const u8 {
 fn writeName(p: *Pardes, req: Req, id: usize, pane: *Pane) Reply {
     // One name: its newline ends it, as `echo` writes it, and it is one.
     const name = if (std.mem.endsWith(u8, req.data, "\n")) req.data[0 .. req.data.len - 1] else req.data;
-    if (name.len == 0) return Reply.fail(req.tag, E.INVAL);
+    if (name.len == 0) return tree.failText(req.tag, E.INVAL, e_name_char ++ ": an empty name");
     if (nameFault(name)) |why| return tree.failText(req.tag, E.INVAL, why);
     if (fileOf(pane) == null) return tree.failText(req.tag, E.PERM, if (pane.isTerminal())
         "rename not allowed: a terminal is named by its shell's directory; cd there, or Tty in another"
@@ -624,7 +627,7 @@ fn writeName(p: *Pardes, req: Req, id: usize, pane: *Pane) Reply {
         "rename not allowed: an image or PDF is named by the file it shows");
     const full = std.fs.path.resolvePosix(p.scratch.allocator(), &.{ pardes.Pardes.paneDir(pane), name }) catch
         return Reply.fail(req.tag, E.NOMEM);
-    if (!std.fs.path.isAbsolute(full) or full.len >= 4096) return Reply.fail(req.tag, E.INVAL);
+    if (!std.fs.path.isAbsolute(full) or full.len >= 4096) return tree.failText(req.tag, E.INVAL, "invalid file name: longer than a path may be");
     nameBuffer(p, id, full, false) catch |err| return Reply.fail(req.tag, switch (err) {
         error.OutOfMemory => E.NOMEM,
         else => E.INVAL,