Can a TCP/IP Socket send less than the bytes requested via write

ghz 8months ago ⋅ 55 views

Can a TCP/IP Socket send less than the bytes requested via write()/send()?

From my basic knowledge, I'd expect a socket representing a TCP/IP connection to guarantee delivery of the requested data. So, is there ever a case that the return value of send() or write() would be less than the number of bytes requested ?

Answers

Yes, it's possible for the return value of send() or write() to be less than the number of bytes requested, especially when dealing with TCP/IP sockets. This situation is known as a partial write.

Several factors can cause a partial write:

  1. Buffer Space: The underlying socket send buffer might be full. If the socket send buffer is smaller than the data being sent, the operating system may accept only part of the data, leaving the rest in the application's send buffer for later transmission. In this case, send() or write() returns the number of bytes actually written to the buffer.

  2. Non-blocking Mode: If the socket is set to non-blocking mode and the requested write would block (i.e., it cannot be completed immediately), the operation may write only part of the data and return the number of bytes written. This allows the application to handle other tasks while waiting for the socket to become writable again.

  3. Signal Interruption: The write operation might be interrupted by a signal, such as a SIGPIPE signal in Unix-like systems. This signal can occur if the remote end of the connection closes unexpectedly, and attempting to write to it would result in a broken pipe error. In this case, the send() or write() call may return a value less than the requested number of bytes.

  4. Error Conditions: Various error conditions, such as network congestion, connection resets, or socket errors, can also cause a partial write. In such cases, the send() or write() call may return an error code, and the number of bytes written may be less than requested.

To handle partial writes correctly, it's important to check the return value of send() or write() and handle any remaining data appropriately. This might involve retrying the write operation for the remaining data, adjusting buffer sizes, or handling errors gracefully. Additionally, using non-blocking I/O and implementing proper error handling can help mitigate issues related to partial writes.

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