---
title: SSLWriteFunc
framework: security
role: symbol
role_heading: Type Alias
path: security/sslwritefunc
---

# SSLWriteFunc

A pointer to a customized write function that secure transport calls to write data to the connection.

## Declaration

```swift
typealias SSLWriteFunc = (SSLConnectionRef, UnsafeRawPointer, UnsafeMutablePointer<Int>) -> OSStatus
```

## Parameters

- `connection`: The SSL session connection reference.
- `data`: A pointer to the data to write to the connection.You must allocate this memory before calling this function.
- `dataLength`: Before calling, an integer representing the length of the data in bytes. On return, this is the number of bytes actually transferred.

## Mentioned in

Using the Secure Socket Layer for Network Communication

## Return Value

Return Value A result code. See Secure Transport Result Codes.

## Discussion

Discussion Before using the secure transport API, you must write the functions SSLReadFunc and SSLWriteFunc and provide them to the library by calling the SSLSetIOFuncs(_:_:_:) function. You may configure the underlying connection to operate in a non-blocking manner. In that case, a write operation may well return errSSLWouldBlock, indicating less data than requested was transferred and nothing is wrong except that the requested I/O hasn’t completed. This result is returned to the caller from the functions SSLRead(_:_:_:_:), SSLWrite(_:_:_:_:), or SSLHandshake(_:).