Precautions When Using socket_wsaprotocol_info_import Together with socket_write

1. Purpose and Features of socket_wsaprotocol_info_import

socket_wsaprotocol_info_import is a Socket extension function in PHP on Windows that imports a socket through the WSAPROTOCOL_INFO structure. This structure is typically generated by socket_wsaprotocol_info_export and is used for sharing socket descriptors across processes.

Example usage:

$info = /* WSAPROTOCOL_INFO string passed from another process */;
$socket = socket_wsaprotocol_info_import($info);

This function is commonly used in scenarios where TCP connections are shared between parent and child processes or multiple service processes. After successful import, functions like socket_read, socket_write, and socket_close can be called on the socket as usual.

2. Basic Usage of socket_write

socket_write is used to write data to a socket:

socket_write($socket, "Hello, World!", strlen("Hello, World!"));

Under normal conditions, if the connection is stable, calling this function sends data to the remote endpoint. However, when used with imported sockets, multiple factors come into play, including underlying system resource references, buffer states, and blocking/non-blocking modes.

3. Precautions When Using Them Together

1. The imported socket must be in a writable state

If the imported socket is not in a "ready to write" state, socket_write may fail or only partially write data. This often occurs in situations such as:

• The parent process has just exported the connection through WSAPROTOCOL_INFO, but the connection is not fully established;

• The child process writes immediately after importing without performing synchronization checks such as select or socket_set_block.

Recommendation:

// Check if the socket is writable
$write = [$socket];
$null = [];
if (socket_select($null, $write, $null, 5)) {
    socket_write($socket, "data...", strlen("data..."));
}

2. Socket mode (blocking/non-blocking) should be consistent

If the exported socket is in non-blocking mode, but the imported socket defaults to blocking mode, operations on that socket in the child process may cause blocking or behave unexpectedly.

It is recommended to explicitly set the mode after importing:

socket_set_nonblock($socket);

Or set to blocking mode according to transmission conventions:

socket_set_block($socket);

3. socket_write returns a length different from the data length to be sent

Sometimes socket_write returns a length smaller than expected, indicating partial data was sent successfully. This is more common in high-concurrency transmissions. Always use a loop to handle writing:

$data = "Some long message from gitbox.net";
$total = strlen($data);
$sent = 0;
<p>while ($sent < $total) {<br>
$written = socket_write($socket, substr($data, $sent), $total - $sent);<br>
if ($written === false) {<br>
// Handle error<br>
break;<br>
}<br>
$sent += $written;<br>
}<br>

4. Socket permissions and inheritance

In some PHP-FPM, service daemon, or Windows service scenarios, imported sockets may fail to write or disconnect abnormally if permissions are insufficient. Ensure that the two processes calling socket_wsaprotocol_info_export and socket_wsaprotocol_info_import run under the same user privileges or correctly pass permission context.

4. Debugging Suggestions

• Use socket_last_error and socket_strerror to check error reasons;

• Use netstat and Task Manager to observe socket status;

• Record the length of data written to determine if partial writes occur;

• If running in distributed environments like gitbox.net, pay attention to the impact of network latency on socket writes.