Treat buffer size as usize

`usize` is made exactly for this (e.g.: the size of a buffer), and
signatures are a bit more idiomatic.

These changes also try to cast the u32 to a usize as soon as we read it,
and will panic if there is an issue (whereas using `as usize` may result
in silent conversion errors on uncommon architectures.

src/main.rs

@@ -3,6 +3,7 @@ extern crate nix;
 #[cfg(windows)]
 extern crate named_pipe;
 
+use std::convert::TryInto;
 use std::io::{self, Read, Write};
 use std::thread;
 use byteorder::{ByteOrder, NativeEndian, WriteBytesExt};
@@ -11,23 +12,23 @@ mod proxy_socket;
 
 use proxy_socket::ProxySocket;
 
-const BUFFER_SIZE: u32 = 1024 ^ 2;	 // 1024 ^ 2 is the maximum
+const BUFFER_SIZE: usize = 1024 ^ 2;	 // 1024 ^ 2 is the maximum
 
-fn valid_length(length: u32) -> bool {
-    return length > 0 && length <= BUFFER_SIZE;
+fn valid_length(length: usize) -> bool {
+    length > 0 && length <= BUFFER_SIZE
 }
 
-fn read_header() -> u32 {
+fn read_header() -> usize {
     let stdin = io::stdin();
     let mut buf = vec![0; 4];
     let mut handle = stdin.lock();
 
     handle.read_exact(&mut buf).unwrap();
-    NativeEndian::read_u32(&buf)
+    NativeEndian::read_u32(&buf).try_into().unwrap()
 }
 
-fn read_body<T: Read + Write>(length: u32, socket: &mut ProxySocket<T>) {
-    let mut buffer = vec![0; length as usize];
+fn read_body<T: Read + Write>(length: usize, socket: &mut ProxySocket<T>) {
+    let mut buffer = vec![0; length];
     let stdin = io::stdin();
     let mut handle = stdin.lock();
 
@@ -39,7 +40,7 @@ fn read_body<T: Read + Write>(length: u32, socket: &mut ProxySocket<T>) {
 }
 
 fn read_response<T: Read>(socket: &mut ProxySocket<T>) {
-    let mut buf = vec![0; BUFFER_SIZE as usize];
+    let mut buf = vec![0; BUFFER_SIZE];
     if let Ok(len) = socket.read(&mut buf) {
         write_response(&buf[0..len]);
     }

src/proxy_socket.rs

@@ -32,7 +32,7 @@ impl<W: Write> Write for ProxySocket<W> {
 }
 
 #[cfg(windows)]
-pub fn connect(buffer_size: u32) -> io::Result<ProxySocket<PipeClient>> {
+pub fn connect(buffer_size: usize) -> io::Result<ProxySocket<PipeClient>> {
     let username = env::var("USERNAME").unwrap();
     let pipe_name = format!("\\\\.\\pipe\\keepassxc\\{}\\org.keepassxc.KeePassXC.BrowserServer", username);
     let client = PipeClient::connect(pipe_name)?;
@@ -40,7 +40,7 @@ pub fn connect(buffer_size: u32) -> io::Result<ProxySocket<PipeClient>> {
 }
 
 #[cfg(not(windows))]
-pub fn connect(buffer_size: u32) -> io::Result<ProxySocket<UnixStream>> {
+pub fn connect(buffer_size: usize) -> io::Result<ProxySocket<UnixStream>> {
     use std::time::Duration;
 
     let socket_name = "org.keepassxc.KeePassXC.BrowserServer";
@@ -50,8 +50,8 @@ pub fn connect(buffer_size: u32) -> io::Result<ProxySocket<UnixStream>> {
         format!("/tmp/{}", socket_name)
     };
     let s = UnixStream::connect(socket)?;
-    socket::setsockopt(s.as_raw_fd(), SndBuf, &(buffer_size as usize)).expect("setsockopt for SndBuf failed");
-    socket::setsockopt(s.as_raw_fd(), RcvBuf, &(buffer_size as usize)).expect("setsockopt for RcvBuf failed");
+    socket::setsockopt(s.as_raw_fd(), SndBuf, &buffer_size).expect("setsockopt for SndBuf failed");
+    socket::setsockopt(s.as_raw_fd(), RcvBuf, &buffer_size).expect("setsockopt for RcvBuf failed");
     let timeout: Option<Duration> = Some(Duration::from_secs(1));
     s.set_read_timeout(timeout)?;
     Ok(ProxySocket { inner: s })