fix: resolve clippy warnings

Reduce clippy warnings from54 to16 by fixing mechanical issues:

- collapsible_if: collapse nested if-let chains with let-chains
- clone_on_copy: remove unnecessary .clone() on Copy types
- manual_clamp: replace .max().min() with .clamp()
- unnecessary_cast: remove redundant type casts
- collapsible_else_if: flatten else-if chains
- contains_vs_iter_any: replace .iter().any() with .contains()
- unnecessary_closure: replace .or_else(|| x) with .or(x)
- useless_conversion: remove redundant .into() calls
- is_none_or: replace .map_or(true, ...) with .is_none_or(...)
- while_let_loop: convert loop with if-let-break to while-let

Remaining16 warnings are design-level issues (too_many_arguments,
await_holding_lock, type_complexity, new_ret_no_self) that require
architectural changes to fix.

src/proxy/client.rs

@@ -594,18 +594,18 @@ impl RunningClientHandler {
         peer_addr: SocketAddr,
         ip_tracker: &UserIpTracker,
     ) -> Result<()> {
-        if let Some(expiration) = config.access.user_expirations.get(user) {
-            if chrono::Utc::now() > *expiration {
-                return Err(ProxyError::UserExpired {
-                    user: user.to_string(),
-                });
-            }
+        if let Some(expiration) = config.access.user_expirations.get(user)
+            && chrono::Utc::now() > *expiration
+        {
+            return Err(ProxyError::UserExpired {
+                user: user.to_string(),
+            });
         }
 
         // IP limit check
         if let Err(reason) = ip_tracker.check_and_add(user, peer_addr.ip()).await {
             warn!(
-                user = %user, 
+                user = %user,
                 ip = %peer_addr.ip(),
                 reason = %reason,
                 "IP limit exceeded"
@@ -615,20 +615,20 @@ impl RunningClientHandler {
             });
         }
 
-        if let Some(limit) = config.access.user_max_tcp_conns.get(user) {
-            if stats.get_user_curr_connects(user) >= *limit as u64 {
-                return Err(ProxyError::ConnectionLimitExceeded {
-                    user: user.to_string(),
-                });
-            }
+        if let Some(limit) = config.access.user_max_tcp_conns.get(user)
+            && stats.get_user_curr_connects(user) >= *limit as u64
+        {
+            return Err(ProxyError::ConnectionLimitExceeded {
+                user: user.to_string(),
+            });
         }
 
-        if let Some(quota) = config.access.user_data_quota.get(user) {
-            if stats.get_user_total_octets(user) >= *quota {
-                return Err(ProxyError::DataQuotaExceeded {
-                    user: user.to_string(),
-                });
-            }
+        if let Some(quota) = config.access.user_data_quota.get(user)
+            && stats.get_user_total_octets(user) >= *quota
+        {
+            return Err(ProxyError::DataQuotaExceeded {
+                user: user.to_string(),
+            });
         }
 
         Ok(())

src/proxy/direct_relay.rs

@@ -118,10 +118,10 @@ fn get_dc_addr_static(dc_idx: i16, config: &ProxyConfig) -> Result<SocketAddr> {
     // Unknown DC requested by client without override: log and fall back.
     if !config.dc_overrides.contains_key(&dc_key) {
         warn!(dc_idx = dc_idx, "Requested non-standard DC with no override; falling back to default cluster");
-        if let Some(path) = &config.general.unknown_dc_log_path {
-            if let Ok(mut file) = OpenOptions::new().create(true).append(true).open(path) {
-                let _ = writeln!(file, "dc_idx={dc_idx}");
-            }
+        if let Some(path) = &config.general.unknown_dc_log_path
+            && let Ok(mut file) = OpenOptions::new().create(true).append(true).open(path)
+        {
+            let _ = writeln!(file, "dc_idx={dc_idx}");
         }
     }
 

src/proxy/masking.rs

@@ -19,12 +19,12 @@ const MASK_BUFFER_SIZE: usize = 8192;
 /// Detect client type based on initial data
 fn detect_client_type(data: &[u8]) -> &'static str {
     // Check for HTTP request
-    if data.len() > 4 {
-        if data.starts_with(b"GET ") || data.starts_with(b"POST") ||
+    if data.len() > 4
+        && (data.starts_with(b"GET ") || data.starts_with(b"POST") ||
            data.starts_with(b"HEAD") || data.starts_with(b"PUT ") ||
-           data.starts_with(b"DELETE") || data.starts_with(b"OPTIONS") {
-            return "HTTP";
-        }
+           data.starts_with(b"DELETE") || data.starts_with(b"OPTIONS"))
+    {
+        return "HTTP";
     }
 
     // Check for TLS ClientHello (0x16 = handshake, 0x03 0x01-0x03 = TLS version)

src/proxy/middle_relay.rs

@@ -393,13 +393,13 @@ where
         .unwrap_or_else(|e| Err(ProxyError::Proxy(format!("ME writer join error: {e}"))));
 
     // When client closes, but ME channel stopped as unregistered - it isnt error
-    if client_closed {
-        if matches!(
+    if client_closed
+        && matches!(
             writer_result,
             Err(ProxyError::Proxy(ref msg)) if msg == "ME connection lost"
-        ) {
-            writer_result = Ok(());
-        }
+        )
+    {
+        writer_result = Ok(());
     }
 
     let result = match (main_result, c2me_result, writer_result) {
@@ -549,7 +549,7 @@ where
 
     match proto_tag {
         ProtoTag::Abridged => {
-            if data.len() % 4 != 0 {
+            if !data.len().is_multiple_of(4) {
                 return Err(ProxyError::Proxy(format!(
                     "Abridged payload must be 4-byte aligned, got {}",
                     data.len()
@@ -567,7 +567,7 @@ where
                 frame_buf.push(first);
                 frame_buf.extend_from_slice(data);
                 client_writer
-                    .write_all(&frame_buf)
+                    .write_all(frame_buf)
                     .await
                     .map_err(ProxyError::Io)?;
             } else if len_words < (1 << 24) {
@@ -581,7 +581,7 @@ where
                 frame_buf.extend_from_slice(&[first, lw[0], lw[1], lw[2]]);
                 frame_buf.extend_from_slice(data);
                 client_writer
-                    .write_all(&frame_buf)
+                    .write_all(frame_buf)
                     .await
                     .map_err(ProxyError::Io)?;
             } else {
@@ -618,7 +618,7 @@ where
                 rng.fill(&mut frame_buf[start..]);
             }
             client_writer
-                .write_all(&frame_buf)
+                .write_all(frame_buf)
                 .await
                 .map_err(ProxyError::Io)?;
         }