protect against mem leag in case of failures sending requests to ffi thread

ffi/ffi_context.nim

@@ -60,18 +60,23 @@ proc sendRequestToFFIThread*(
   ## Sending the request
   let sentOk = ctx.reqChannel.trySend(ffiRequest)
   if not sentOk:
+    deleteRequest(ffiRequest)
     return err("Couldn't send a request to the ffi thread")
 
   let fireSyncRes = ctx.reqSignal.fireSync()
   if fireSyncRes.isErr():
+    deleteRequest(ffiRequest)
     return err("failed fireSync: " & $fireSyncRes.error)
 
   if fireSyncRes.get() == false:
+    deleteRequest(ffiRequest)
     return err("Couldn't fireSync in time")
 
   ## wait until the FFI working thread properly received the request
   let res = ctx.reqReceivedSignal.waitSync(timeout)
   if res.isErr():
+    ## Do not free ffiRequest here: the FFI thread was already signaled and
+    ## will process (and free) it.
     return err("Couldn't receive reqReceivedSignal signal")
 
   ## Notice that in case of "ok", the deallocShared(req) is performed by the FFI Thread in the

ffi/ffi_thread_request.nim

@@ -6,11 +6,16 @@ import std/[json, macros], results, tables
 import chronos, chronos/threadsync
 import ./ffi_types, ./internal/ffi_macro, ./alloc
 
+type FFIDestroyContentProc* = proc(content: pointer) {.nimcall.}
+
 type FFIThreadRequest* = object
   callback: FFICallBack
   userData: pointer
   reqId*: cstring
   reqContent*: pointer
+  deleteReqContent*: FFIDestroyContentProc
+    ## Called by sendRequestToFFIThread on failure to free reqContent when
+    ## the FFI thread will never process (and thus never free) this request.
 
 proc init*(
     T: typedesc[FFIThreadRequest],
@@ -26,7 +31,9 @@ proc init*(
   ret[].reqContent = reqContent
   return ret
 
-proc deleteRequest(request: ptr FFIThreadRequest) =
+proc deleteRequest*(request: ptr FFIThreadRequest) =
+  if not request[].deleteReqContent.isNil():
+    request[].deleteReqContent(request[].reqContent)
   deallocShared(request[].reqId)
   deallocShared(request)
 

ffi/internal/ffi_macro.nim

@@ -164,6 +164,9 @@ proc buildFfiNewReqProc(reqTypeName, body: NimNode): NimNode =
       let typeStr = $T
       var ret =
         FFIThreadRequest.init(callback, userData, typeStr.cstring, `reqObjIdent`)
+      proc destroyContent(content: pointer) {.nimcall.} =
+        ffiDeleteReq(cast[ptr `reqTypeName`](content))
+      ret[].deleteReqContent = destroyContent
       return ret
   )