Harden multiplayer session terminal handling

src/link/Net.lua

@@ -207,7 +207,7 @@ function Net:send(msg)
   end
   if self.peerEnd then -- loopback: re-encode through json like the wire
     local decoded = Json.decode(Json.encode(msg))
-    if decoded and not self.peerEnd.closed then
+    if decoded ~= nil and not self.peerEnd.closed then
       table.insert(self.peerEnd.inbox, decoded)
     end
     return
@@ -256,13 +256,12 @@ end
 
 function Net:handleTCPLine(line)
   local msg = Json.decode(line)
-  if not msg then
+  if msg == nil then
     Logger.warn("link: bad relay message %q", line:sub(1, 60))
     return
   end
-  if not handleGenericRelayControl(self, msg) then
-    table.insert(self.inbox, msg)
-  end
+  if type(msg) == "table" and handleGenericRelayControl(self, msg) then return end
+  table.insert(self.inbox, msg)
 end
 
 -- pulls every complete "\n"-terminated line out of rxBuf (leaving a
@@ -352,7 +351,7 @@ function Net:update()
       end
     elseif event.type == "receive" then
       local msg = Json.decode(event.data)
-      if msg then
+      if msg ~= nil then
         table.insert(self.inbox, msg)
       else
         Logger.warn("link: bad message %q", tostring(event.data):sub(1, 60))

src/link/Session.lua

@@ -48,13 +48,43 @@ function Session:_refreshStatus()
     self._status = self.paired and "paired" or "connecting"
     self.closed = false
     self.error = nil
+    return
   end
+  if #self._inbox > 0 then
+    self._status = "draining"
+    self.closed = false
+    self.error = nil
+    return
+  end
+  self._status = self._terminal.status
+  self.closed = true
+  self.error = self._terminal.status == "failed"
+    and (self._terminal.detail or self._terminal.reason) or nil
+end
+
+function Session:_latchTerminal(status, reason, detail)
+  if self._terminal then return false end
+  self._terminal = { status = status, reason = reason, detail = detail }
+  self:_refreshStatus()
+  return true
+end
+
+function Session:_closeTransport()
+  if self._transportCloseCalled then return true end
+  self._transportCloseCalled = true
+  local ok, detail = pcall(self._transport.close, self._transport)
+  return ok, ok and nil or tostring(detail)
 end
 
 function Session:getRole() return self._role end
 function Session:getKind() return self._kind end
 function Session:getStatus() return self._status end
-function Session:getFailure() return nil, nil end
+function Session:getFailure()
+  if not self._terminal or self._terminal.status ~= "failed" then
+    return nil, nil
+  end
+  return self._terminal.reason, self._terminal.detail
+end
 function Session:hasPending() return #self._inbox > 0 end
 
 function Session:send(message)
@@ -63,13 +93,62 @@ function Session:send(message)
 end
 
 function Session:update()
-  if self._terminal then return end
-  self._transport:update()
-  self:_syncMetadata()
-  local messages = self._transport:poll()
-  for _, message in ipairs(messages) do
-    self._inbox[#self._inbox + 1] = message
+  if self._terminal then
+    self:_refreshStatus()
+    return
   end
+
+  local failureReason, failureDetail
+  local updateOk, updateDetail = pcall(self._transport.update, self._transport)
+  self:_syncMetadata()
+  if not updateOk then
+    failureReason, failureDetail = "transport_error", tostring(updateDetail)
+  elseif self._transport.error then
+    failureReason = "transport_error"
+    failureDetail = tostring(self._transport.error)
+  end
+
+  local pollOk, messages = pcall(self._transport.poll, self._transport)
+  if not pollOk then
+    if not failureReason then
+      failureReason, failureDetail = "transport_error", tostring(messages)
+    end
+  elseif type(messages) ~= "table" then
+    if not failureReason then
+      failureReason, failureDetail = "transport_error",
+        "transport poll returned non-table"
+    end
+  else
+    for index = 1, #messages do
+      local message = messages[index]
+      if type(message) ~= "table" or type(message.type) ~= "string" then
+        if not failureReason then
+          failureReason = "protocol_error"
+          failureDetail = ("message %d must be a table with string type")
+            :format(index)
+        end
+        break
+      end
+      self._inbox[#self._inbox + 1] = message
+    end
+  end
+
+  self:_syncMetadata()
+  if failureReason then
+    self:_latchTerminal("failed", failureReason, failureDetail)
+    self:_closeTransport()
+  elseif self._transport.closed then
+    local closeOk, closeDetail = self:_closeTransport()
+    if closeOk then
+      self:_latchTerminal("closed")
+    else
+      self:_latchTerminal("failed", "transport_error", closeDetail)
+    end
+  end
+  self:_refreshStatus()
+end
+
+local function finishRead(self)
   self:_refreshStatus()
 end
 
@@ -77,7 +156,9 @@ function Session:take(messageType)
   assert(type(messageType) == "string", "Session.take requires a message type")
   for index, message in ipairs(self._inbox) do
     if message.type == messageType then
-      return table.remove(self._inbox, index)
+      local found = table.remove(self._inbox, index)
+      finishRead(self)
+      return found
     end
   end
   return nil
@@ -85,19 +166,33 @@ end
 
 function Session:pollOne()
   if #self._inbox == 0 then return nil end
-  return table.remove(self._inbox, 1)
+  local message = table.remove(self._inbox, 1)
+  finishRead(self)
+  return message
 end
 
 function Session:poll()
   local messages = self._inbox
   self._inbox = {}
+  finishRead(self)
   return messages
 end
 
 function Session:close()
-  if self._transportCloseCalled then return end
-  self._transportCloseCalled = true
-  self._transport:close()
+  if self._status == "closed" or self._status == "failed" then return end
+  if self._terminal then
+    self:_closeTransport()
+    self:_refreshStatus()
+    return
+  end
+  local ok, detail = self:_closeTransport()
+  if ok then
+    self:_latchTerminal("closed")
+  else
+    self:_latchTerminal("failed", "transport_error", detail)
+  end
+  self:_syncMetadata()
+  self:_refreshStatus()
 end
 
 return Session