[RFC] corrupted msgpack streams are printed to screen and/or saved

nvim/msgpack_rpc_stream.lua

@@ -11,6 +11,31 @@ local Tabpage = {}
 Tabpage.__index = Tabpage
 function Tabpage.new(id) return setmetatable({id=id}, Tabpage) end
 
+local function hexdump(str)
+  local len = string.len(str)
+  local dump = ""
+  local hex = ""
+  local asc = ""
+
+  for i = 1, len do
+    if 1 == i % 8 then
+      dump = dump .. hex .. asc .. "\n"
+      hex = string.format("%04x: ", i - 1)
+      asc = ""
+    end
+
+    local ord = string.byte(str, i)
+    hex = hex .. string.format("%02x ", ord)
+    if ord >= 32 and ord <= 126 then
+      asc = asc .. string.char(ord)
+    else
+      asc = asc .. "."
+    end
+  end
+
+  return dump .. hex .. string.rep("   ", 8 - len % 8) .. asc
+end
+
 local Response = {}
 Response.__index = Response
 
@@ -39,6 +64,7 @@ MsgpackRpcStream.__index = MsgpackRpcStream
 function MsgpackRpcStream.new(stream)
   return setmetatable({
     _stream = stream,
+    _previous_chunk = nil,
     _pack = mpack.Packer({
       ext = {
         [Buffer] = function(o) return 0, mpack.pack(o.id) end,
@@ -76,20 +102,38 @@ function MsgpackRpcStream:read_start(request_cb, notification_cb, eof_cb)
     if not data then
       return eof_cb()
     end
-    local type, id_or_cb
+    local status, type_, id_or_cb
     local pos = 1
     local len = #data
     while pos <= len do
-      type, id_or_cb, method_or_error, args_or_result, pos =
-        self._session:receive(data, pos)
-      if type == 'request' or type == 'notification' then
-        if type == 'request' then
+      -- grab a copy of pos since pcall() will set it to nil on error
+      local oldpos = pos
+      status, type_, id_or_cb, method_or_error, args_or_result, pos = pcall(
+            self._session.receive, self._session, data, pos)
+      if not status then
+        -- write the full blob of bad data to a specific file
+        local outfile = io.open('./msgpack-invalid-data', 'w')
+        outfile:write(data)
+        outfile:close()
+
+        -- build a printable representation of the bad part of the string
+        local printable = hexdump(data:sub(oldpos, oldpos + 8 * 10))
+
+        print(string.format("Error deserialising msgpack data stream at pos %d:\n%s\n",
+              oldpos, printable))
+        print(string.format("... occurred after %s", self._previous_chunk))
+        error(type_)
+      end
+      if type_ == 'request' or type_ == 'notification' then
+        self._previous_chunk = string.format('%s<%s>', type_, method_or_error)
+        if type_ == 'request' then
           request_cb(method_or_error, args_or_result, Response.new(self,
                                                                    id_or_cb))
         else
           notification_cb(method_or_error, args_or_result)
         end
-      elseif type == 'response' then
+      elseif type_ == 'response' then
+        self._previous_chunk = string.format('response<%s>', type(args_or_result))
         if method_or_error == mpack.NIL then
           method_or_error = nil
         else