---
title: "sendSynchronousRequest(_:returning:)"
framework: foundation
role: symbol
role_heading: Type Method
path: "foundation/nsurlconnection/sendsynchronousrequest(_:returning:)"
---

# sendSynchronousRequest(_:returning:)

Performs a synchronous load of the specified URL request.

## Declaration

```swift
class func sendSynchronousRequest(_ request: URLRequest, returning response: AutoreleasingUnsafeMutablePointer<URLResponse?>?) throws -> Data
```

## Parameters

- `request`: The URL request to load. The request object is deep-copied as part of the initialization process. Changes made to request after this method returns do not affect the request that is used for the loading process.
- `response`: Out parameter for the URL response returned by the server.

## Return Value

Return Value The downloaded data for the URL request. Returns nil if a connection could not be created or if the download fails.

## Discussion

Discussion A synchronous load is built on top of the asynchronous loading code made available by the class. The calling thread is blocked while the asynchronous loading system performs the URL load on a thread spawned specifically for this load request. No special threading or run loop configuration is necessary in the calling thread in order to perform a synchronous load. important: Because this call can potentially take several minutes to complete (particularly when using a cellular network in iOS), you should never call this function from the main thread of your application. Doing so may cause a 0x8badf00d exception with the main thread at mach_msg_trap. The solution is to migrate to URL loading using URLSession. If authentication is required in order to download the request, the required credentials must be specified as part of the URL. If authentication fails, or credentials are missing, the connection will attempt to continue without credentials. note: In Swift, this method returns a nonoptional result and is marked with the throws keyword to indicate that it throws an error in cases of failure. You call this method in a try expression and handle any errors in the catch clauses of a do statement, as described in Error Handling in The Swift Programming Language and About Imported Cocoa Error Parameters.