fix(mods): harden streamed import cleanup

src/import/RomImporter.lua

@@ -388,8 +388,16 @@ local function openImportSource(path)
   -- read into one Lua string before validation.
   local native = io.open(path, "rb")
   if native then
-    local size = native:seek("end")
+    local size, sizeErr = native:seek("end")
-    if size then native:seek("set", 0) end
+    if size == nil or size == false then
+      native:close()
+      return nil, sizeErr or "could not determine source file size"
+    end
+    local reset, resetErr = native:seek("set", 0)
+    if reset == nil or reset == false then
+      native:close()
+      return nil, resetErr or "could not rewind source file"
+    end
     return {
       size = size,
       read = function(_, n) return native:read(n) end,
@@ -410,7 +418,6 @@ local function openImportSource(path)
   end
   return nil, "streaming source access is unavailable"
 end
-
 local function streamRequiredImport(manifest, importId, source)
   local RequiredImports = require("src.mods.RequiredImports")
   local spec = RequiredImports.spec(manifest, importId)
@@ -426,19 +433,31 @@ local function streamRequiredImport(manifest, importId, source)
   local CacheFs = require("src.import.CacheFs")
   local destination = RequiredImports.path(manifest, spec)
   local savedPrefix = CacheFs.prefix
-  CacheFs.prefix = ""
+  local output
-  CacheFs.remove(RequiredImports.receiptPath(manifest, spec))
+  local inputClosed, outputClosed = false, false
-  CacheFs.remove(destination)
+
-  local output, makeErr = CacheFs.openWrite(destination)
+  local function closeInput()
-  if not output then
+    if inputClosed then return end
-    CacheFs.prefix = savedPrefix
+    inputClosed = true
-    input:close()
+    pcall(function() input:close() end)
-    return nil, makeErr or "could not create imported file"
   end
 
-  local function cleanupDestination()
+  local function closeOutput()
+    if outputClosed or not output then return end
+    outputClosed = true
+    pcall(function() output:close() end)
+  end
+
+  local resultOk, resultDetail
+  CacheFs.prefix = ""
+  local ran, thrown = xpcall(function()
+    CacheFs.remove(RequiredImports.receiptPath(manifest, spec))
     CacheFs.remove(destination)
-    CacheFs.prefix = savedPrefix
+    local makeErr
+    output, makeErr = CacheFs.openWrite(destination)
+    if not output then
+      resultDetail = makeErr or "could not create imported file"
+      return
     end
 
     local MD5 = require("src.mods.StreamMD5")
@@ -450,34 +469,55 @@ local function streamRequiredImport(manifest, importId, source)
       md5:update(chunk)
       local wrote, writeErr = output:write(chunk)
       if wrote == false or wrote == nil then
-      input:close(); output:close(); cleanupDestination()
+        resultDetail = "could not copy import: "
-      return nil, "could not copy import: " .. tostring(writeErr or "write failed")
+.. tostring(writeErr or "write failed")
+        return
       end
       total = total + #chunk
       if #chunk < chunkBytes then break end
     end
-  input:close()
-  output:close()
 
+    closeInput()
+    closeOutput()
     if input.size and total ~= input.size then
-    cleanupDestination()
+      resultDetail = ("source read ended early (expected %d bytes, copied %d)")
-    return nil, ("source read ended early (expected %d bytes, copied %d)"):format(input.size, total)
+        :format(input.size, total)
+      return
     end
     local storedSizeErr = RequiredImports.sizeError(spec, total, true)
-  if storedSizeErr then cleanupDestination(); return nil, storedSizeErr end
+    if storedSizeErr then resultDetail = storedSizeErr; return end
     local digest = md5:final()
+
+    -- acceptStoredDigest uses the normal engine path/receipt rules, so
+    -- restore the caller's prefix before handing control to it.
     CacheFs.prefix = savedPrefix
     local accepted, detail = RequiredImports.acceptStoredDigest(
       manifest, importId, digest, love.filesystem)
-  if not accepted then
+    if not accepted then resultDetail = detail; return end
-    CacheFs.prefix = ""
+    resultOk, resultDetail = true, detail
-    CacheFs.remove(destination)
+  end, function(err)
-    CacheFs.prefix = savedPrefix
+    if debug and debug.traceback then
-    return nil, detail
+      return debug.traceback(tostring(err), 2)
     end
-  return true, detail
+    return tostring(err)
-end
+  end)
 
+  -- finally: resource handles and the process-global CacheFs prefix must
+  -- be restored even when a read/hash/write helper raises a Lua error.
+  closeInput()
+  closeOutput()
+  CacheFs.prefix = ""
+  if not ran or not resultOk then
+    pcall(function() CacheFs.remove(destination) end)
+  end
+  CacheFs.prefix = savedPrefix
+
+  if not ran then
+    return nil, "could not copy import: " .. tostring(thrown)
+  end
+  if not resultOk then return nil, resultDetail end
+  return true, resultDetail
+end
 local function readDroppedFile(file)
   local ok, openError = file:open("r")
   if not ok then return nil, openError end

src/mods/RequiredImports.lua

@@ -228,9 +228,21 @@ function RequiredImports.acceptStoredDigest(manifest, importId, digest, fs)
   if sizeErr then return nil, sizeErr end
   if love and fs == love.filesystem then
     local savedPrefix = CacheFs.prefix
+    local ok, prefixErr = xpcall(function()
       CacheFs.prefix = ""
       CacheFs.remove(removedMarker(manifest, spec))
       CacheFs.prefix = savedPrefix
+      -- writeReceipt has its own temporary CacheFs prefix switch. Keep it
+      -- inside this guard too so a write error cannot leak global state.
+      writeReceipt(manifest, spec, digest, info, fs)
+    end, function(err)
+      return tostring(err)
+    end)
+    CacheFs.prefix = savedPrefix
+    if not ok then
+      return nil, "could not finalize import receipt: " .. tostring(prefixErr)
+    end
+    return true, digest
   elseif fs and fs.remove then
     fs.remove(removedMarker(manifest, spec))
   end

tests/engine/required_import_streaming_test.lua

@@ -88,6 +88,74 @@ T.eq(love.filesystem.read("mods/stream_probe/baseroms/source.bin"), "abc",
 T.eq(importer.requiredImportNotice, nil, "successful stream leaves no import error")
 T.eq(importer._refreshed, true, "successful stream refreshes the mod list")
 
+local CacheFs = require("src.import.CacheFs")
+
+-- A thrown writer error must not leak the temporary empty CacheFs prefix.
+local workingNewFile = love.filesystem.newFile
+local workingPrefix = CacheFs.prefix
+CacheFs.prefix = "sentinel/"
+love.filesystem.newFile = function(path)
+  local file = workingNewFile(path)
+  if path == "mods/stream_probe/baseroms/source.bin" then
+    function file:write()
+      error("forced writer failure")
+    end
+  end
+  return file
+end
+importer.requiredImportNotice = nil
+RequiredImports.LARGE_WARN_BYTES = 2
+local failedWrite = importer:_importRequiredSource(
+  "stream_probe", "source", source, true)
+RequiredImports.LARGE_WARN_BYTES = oldWarn
+T.eq(failedWrite, nil, "thrown streaming writer error is contained")
+T.eq(CacheFs.prefix, "sentinel/",
+  "streaming writer error restores CacheFs.prefix")
+love.filesystem.newFile = workingNewFile
+CacheFs.prefix = workingPrefix
+
+-- acceptStoredDigest has its own prefix switch for marker/receipt I/O.
+-- Even an unexpected CacheFs failure must restore the caller's prefix.
+love.filesystem.write("mods/stream_probe/baseroms/source.bin", "abc")
+local workingRemove = CacheFs.remove
+CacheFs.prefix = "sentinel/"
+CacheFs.remove = function()
+  error("forced marker removal failure")
+end
+local accepted = RequiredImports.acceptStoredDigest(
+  manifest, "source", "900150983cd24fb0d6963f7d28e17f72", love.filesystem)
+T.eq(accepted, nil, "acceptStoredDigest contains CacheFs failure")
+T.eq(CacheFs.prefix, "sentinel/",
+  "acceptStoredDigest failure restores CacheFs.prefix")
+CacheFs.remove = workingRemove
+CacheFs.prefix = workingPrefix
+
+-- Native sources are rejected cleanly if seek-to-start fails after the
+-- size probe; never return a handle left sitting at EOF.
+local realIoOpen = io.open
+local fakeCloses = 0
+io.open = function(path, mode)
+  if path ~= source then return realIoOpen(path, mode) end
+  local calls = 0
+  return {
+    seek = function(_, whence)
+      calls = calls + 1
+      if whence == "end" then return 3 end
+      if whence == "set" then return nil, "forced rewind failure" end
+      return nil, "unexpected seek"
+    end,
+    close = function() fakeCloses = fakeCloses + 1 end,
+  }
+end
+importer.requiredImportNotice = nil
+RequiredImports.LARGE_WARN_BYTES = 2
+local failedSeek = importer:_importRequiredSource(
+  "stream_probe", "source", source, true)
+RequiredImports.LARGE_WARN_BYTES = oldWarn
+io.open = realIoOpen
+T.eq(failedSeek, nil, "failed native rewind rejects import source")
+T.ok(fakeCloses >= 2, "failed native rewind closes probed source handles")
+
 love.filesystem.remove("mods/stream_probe/baseroms/source.bin")
 love.filesystem.remove("mods/stream_probe/baseroms/source.iso")
 os.remove(source)