diff --git a/CLAUDE.md b/CLAUDE.md
index 17225d41..6d8b4fd9 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -102,12 +102,12 @@ A library `libshadowsocks-c` (legacy names `libshadowsocks-libev.*` are kept) is
 ### Source Organization (`src/`)
 
 **Shared by all binaries:**
-- `utils.c` - logging, system utilities, `ss_malloc`/`ss_free`
+- `utils.cpp` - logging, system utilities, `ss_malloc`/`ss_free`
 - `jconf.cpp` / `json.cpp` - JSON config file parsing
 - `netutils.cpp` - network address utilities
 - `cache.cpp` - uthash-based connection cache (UDP relay, AEAD-2022 tables)
-- `udprelay.c` - UDP relay implementation (shared, but uses `#ifdef MODULE_*` for per-binary behavior)
-- `ss_event.c` / `ss_event.h` - event loop API over libuv
+- `udprelay.cpp` - UDP relay implementation (shared, but uses `#ifdef MODULE_*` for per-binary behavior)
+- `ss_event.cpp` / `ss_event.h` - event loop API over libuv
 - `resolv.cpp` - asynchronous DNS via c-ares
 
 **Crypto layer** (behind a common `crypto_t` function-pointer interface):
diff --git a/CONTRIBUTION.md b/CONTRIBUTION.md
index 4f39d86d..082ed9e4 100644
--- a/CONTRIBUTION.md
+++ b/CONTRIBUTION.md
@@ -78,7 +78,7 @@ notices.
 Doxygen 1.9.4 or newer renders HTML and man pages directly from native source
 snippets. Each CLI parser has a `cli-options` snippet containing Doxygen
 `\snippet{doc}` references to its option descriptions. Shared descriptions live
-in `src/utils.c`; command-specific descriptions live beside the parser. The
+in `src/utils.cpp`; command-specific descriptions live beside the parser. The
 `ss-nat` script keeps its snippets in a quoted no-op heredoc so documentation
 cannot execute shell substitutions. Cipher tables are included directly with
 Doxygen code snippets.
diff --git a/cmake/EventLoop.cmake b/cmake/EventLoop.cmake
index f60dd303..9055c296 100644
--- a/cmake/EventLoop.cmake
+++ b/cmake/EventLoop.cmake
@@ -1,4 +1,4 @@
-add_library(ss_ev STATIC ${PROJECT_SOURCE_DIR}/src/ss_event.c)
+add_library(ss_ev STATIC ${PROJECT_SOURCE_DIR}/src/ss_event.cpp)
 target_include_directories(ss_ev PUBLIC ${PROJECT_SOURCE_DIR}/src)
 target_link_libraries(ss_ev PUBLIC ss_uv Threads::Threads ${SS_MATH_LIBRARY} ${CMAKE_DL_LIBS})
 if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
diff --git a/doc/ss-local.md b/doc/ss-local.md
index 2e6a0692..98c7bc20 100644
--- a/doc/ss-local.md
+++ b/doc/ss-local.md
@@ -21,7 +21,7 @@ For more information, check out shadowsocks-libev(8).
 
 Options include all supported platform variants; restrictions are noted below.
 
-\snippet{doc} local.c cli-options
+\snippet{doc} local.cpp cli-options
 
 \section ss_local_example EXAMPLE
 
diff --git a/doc/ss-manager.md b/doc/ss-manager.md
index a67d15cf..63b1dec7 100644
--- a/doc/ss-manager.md
+++ b/doc/ss-manager.md
@@ -24,7 +24,7 @@ section.
 
 Options include all supported platform variants; restrictions are noted below.
 
-\snippet{doc} manager.c cli-options
+\snippet{doc} manager.cpp cli-options
 
 \section ss_manager_protocol PROTOCOL
 
diff --git a/doc/ss-redir.md b/doc/ss-redir.md
index 008d89e6..ecb44f6e 100644
--- a/doc/ss-redir.md
+++ b/doc/ss-redir.md
@@ -23,7 +23,7 @@ For more information, check out shadowsocks-libev(8) and the following
 
 Options include all supported platform variants; restrictions are noted below.
 
-\snippet{doc} redir.c cli-options
+\snippet{doc} redir.cpp cli-options
 
 \section ss_redir_example EXAMPLE
 
diff --git a/doc/ss-server.md b/doc/ss-server.md
index e3eac576..0385837d 100644
--- a/doc/ss-server.md
+++ b/doc/ss-server.md
@@ -21,7 +21,7 @@ For more information, check out shadowsocks-libev(8).
 
 Options include all supported platform variants; restrictions are noted below.
 
-\snippet{doc} server.c cli-options
+\snippet{doc} server.cpp cli-options
 
 \section ss_server_example EXAMPLE
 
diff --git a/doc/ss-tunnel.md b/doc/ss-tunnel.md
index 67897e9b..a78aae93 100644
--- a/doc/ss-tunnel.md
+++ b/doc/ss-tunnel.md
@@ -22,7 +22,7 @@ For more information, check out shadowsocks-libev(8).
 
 Options include all supported platform variants; restrictions are noted below.
 
-\snippet{doc} tunnel.c cli-options
+\snippet{doc} tunnel.cpp cli-options
 
 \section ss_tunnel_example EXAMPLE
 
diff --git a/scripts/no_heap_baseline.txt b/scripts/no_heap_baseline.txt
index 7c7fe012..bc94968b 100644
--- a/scripts/no_heap_baseline.txt
+++ b/scripts/no_heap_baseline.txt
@@ -10,9 +10,17 @@ src/crypto.cpp 4
 src/ipset.cpp 3
 src/jconf.cpp 16
 src/json.cpp 2
+src/local.cpp 16
+src/manager.cpp 14
 src/plugin.cpp 3
 src/process.cpp 26
+src/redir.cpp 15
 src/resolv.cpp 6
 src/rule.cpp 2
+src/server.cpp 17
+src/ss_event.cpp 5
 src/ssurl.cpp 3
 src/stream.cpp 3
+src/tunnel.cpp 14
+src/udprelay.cpp 7
+src/utils.cpp 10
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 74ba2e00..566163ae 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -50,20 +50,20 @@ endif()
 
 set(SS_SHARED_SOURCES
         ppbloom.cpp
-        utils.c
+        utils.cpp
         jconf.cpp
         json.cpp
         netutils.cpp
         )
 if (MINGW)
-set(SS_SHARED_SOURCES ${SS_SHARED_SOURCES} winsock.c)
+set(SS_SHARED_SOURCES ${SS_SHARED_SOURCES} winsock.cpp)
 endif ()
 
 set(LIBSHADOWSOCKS_LIBEV_SOURCE
         ${SS_SHARED_SOURCES}
-        udprelay.c
+        udprelay.cpp
         cache.cpp
-        local.c
+        local.cpp
         resolv.cpp
         ssurl.cpp
         ${SS_CRYPTO_SOURCE}
@@ -78,19 +78,19 @@ set(SS_LOCAL_SOURCE
 
 set(SS_TUNNEL_SOURCE
         ${SS_SHARED_SOURCES}
-        udprelay.c
+        udprelay.cpp
         cache.cpp
-        tunnel.c
+        tunnel.cpp
         ${SS_CRYPTO_SOURCE}
         ${SS_PLUGIN_SOURCE}
         )
 
 set(SS_SERVER_SOURCE
         ${SS_SHARED_SOURCES}
-        udprelay.c
+        udprelay.cpp
         cache.cpp
         resolv.cpp
-        server.c
+        server.cpp
         ${SS_CRYPTO_SOURCE}
         ${SS_PLUGIN_SOURCE}
         ${SS_ACL_SOURCE}
@@ -98,14 +98,14 @@ set(SS_SERVER_SOURCE
 
 set(SS_MANAGER_SOURCE
         ${SS_SHARED_SOURCES}
-        manager.c
+        manager.cpp
         )
 
 set(SS_REDIR_SOURCE
         ${SS_SHARED_SOURCES}
-        udprelay.c
+        udprelay.cpp
         cache.cpp
-        redir.c
+        redir.cpp
         ${SS_CRYPTO_SOURCE}
         ${SS_PLUGIN_SOURCE}
         )
diff --git a/src/core/fixed_map.hpp b/src/core/fixed_map.hpp
index a821e313..bb34462e 100644
--- a/src/core/fixed_map.hpp
+++ b/src/core/fixed_map.hpp
@@ -3,7 +3,7 @@
 #define SS_CORE_FIXED_MAP_HPP
 
 // Fixed-capacity associative containers. Replace uthash (cache.cpp,
-// ss_event.c, manager.c) without any per-entry allocation.
+// ss_event.cpp, manager.cpp) without any per-entry allocation.
 //
 // FixedHashMap<K, V>
 //     Open addressing with linear probing and backward-shift deletion (no
diff --git a/src/local.c b/src/local.cpp
similarity index 97%
rename from src/local.c
rename to src/local.cpp
index c000c1c7..a20fa6b9 100644
--- a/src/local.c
+++ b/src/local.cpp
@@ -1,5 +1,5 @@
 /*
- * local.c - Setup a socks5 proxy through remote shadowsocks server
+ * local.cpp - Setup a socks5 proxy through remote shadowsocks server
  *
  * Copyright (C) 2013 - 2019, Max Lv <max.c.lv@gmail.com>
  *
@@ -1600,63 +1600,63 @@ Same behavior as `-S`; see that option for details. Short alias: `-S`.
 [cli_long_stat_path] */
 
 /* [cli-options]
-\snippet{doc} utils.c cli_short_f
-\snippet{doc} utils.c cli_short_s
-\snippet{doc} utils.c cli_short_p
-\snippet{doc} utils.c cli_short_l
-\snippet{doc} utils.c cli_short_k
-\snippet{doc} utils.c cli_short_t
-\snippet{doc} utils.c cli_short_m
-\snippet{doc} utils.c cli_short_i
-\snippet{doc} utils.c cli_short_c
-\snippet{doc} utils.c cli_short_b
-\snippet{doc} utils.c cli_short_a
-\snippet{doc} utils.c cli_short_n
-\snippet{doc} utils.c cli_short_S
-\snippet{doc} utils.c cli_short_h
-\snippet{doc} utils.c cli_short_u
-\snippet{doc} utils.c cli_short_U
-\snippet{doc} utils.c cli_short_v
-\snippet{doc} utils.c cli_short_V
-\snippet{doc} utils.c cli_short_6
-\snippet{doc} utils.c cli_short_A
-\snippet{doc} local.c cli_long_config
-\snippet{doc} local.c cli_long_cipher
-\snippet{doc} local.c cli_long_timeout
-\snippet{doc} local.c cli_long_user
-\snippet{doc} local.c cli_long_pid_file
-\snippet{doc} local.c cli_long_nofile
-\snippet{doc} local.c cli_long_udp
-\snippet{doc} local.c cli_long_udp_only
-\snippet{doc} local.c cli_long_ipv6_first
-\snippet{doc} local.c cli_long_verbose
-\snippet{doc} local.c cli_long_server
-\snippet{doc} local.c cli_long_server_port
-\snippet{doc} local.c cli_long_listen_address
-\snippet{doc} local.c cli_long_listen_port
-\snippet{doc} local.c cli_long_interface
-\snippet{doc} utils.c cli_long_version
-\snippet{doc} utils.c cli_long_tcp_only
-\snippet{doc} utils.c cli_long_ipv4_first
-\snippet{doc} local.c cli_long_vpn
-\snippet{doc} local.c cli_long_stat_path
-\snippet{doc} utils.c cli_long_reuse_port
-\snippet{doc} utils.c cli_long_tcp_incoming_sndbuf
-\snippet{doc} utils.c cli_long_tcp_incoming_rcvbuf
-\snippet{doc} utils.c cli_long_tcp_outgoing_sndbuf
-\snippet{doc} utils.c cli_long_tcp_outgoing_rcvbuf
-\snippet{doc} utils.c cli_long_fast_open
-\snippet{doc} utils.c cli_long_no_delay
-\snippet{doc} utils.c cli_long_acl
-\snippet{doc} utils.c cli_long_mtu
-\snippet{doc} utils.c cli_long_mptcp
-\snippet{doc} utils.c cli_long_plugin
-\snippet{doc} utils.c cli_long_plugin_opts
-\snippet{doc} utils.c cli_long_password
-\snippet{doc} utils.c cli_long_key
-\snippet{doc} utils.c cli_long_server_url
-\snippet{doc} utils.c cli_long_printable_salt
-\snippet{doc} utils.c cli_long_help
+\snippet{doc} utils.cpp cli_short_f
+\snippet{doc} utils.cpp cli_short_s
+\snippet{doc} utils.cpp cli_short_p
+\snippet{doc} utils.cpp cli_short_l
+\snippet{doc} utils.cpp cli_short_k
+\snippet{doc} utils.cpp cli_short_t
+\snippet{doc} utils.cpp cli_short_m
+\snippet{doc} utils.cpp cli_short_i
+\snippet{doc} utils.cpp cli_short_c
+\snippet{doc} utils.cpp cli_short_b
+\snippet{doc} utils.cpp cli_short_a
+\snippet{doc} utils.cpp cli_short_n
+\snippet{doc} utils.cpp cli_short_S
+\snippet{doc} utils.cpp cli_short_h
+\snippet{doc} utils.cpp cli_short_u
+\snippet{doc} utils.cpp cli_short_U
+\snippet{doc} utils.cpp cli_short_v
+\snippet{doc} utils.cpp cli_short_V
+\snippet{doc} utils.cpp cli_short_6
+\snippet{doc} utils.cpp cli_short_A
+\snippet{doc} local.cpp cli_long_config
+\snippet{doc} local.cpp cli_long_cipher
+\snippet{doc} local.cpp cli_long_timeout
+\snippet{doc} local.cpp cli_long_user
+\snippet{doc} local.cpp cli_long_pid_file
+\snippet{doc} local.cpp cli_long_nofile
+\snippet{doc} local.cpp cli_long_udp
+\snippet{doc} local.cpp cli_long_udp_only
+\snippet{doc} local.cpp cli_long_ipv6_first
+\snippet{doc} local.cpp cli_long_verbose
+\snippet{doc} local.cpp cli_long_server
+\snippet{doc} local.cpp cli_long_server_port
+\snippet{doc} local.cpp cli_long_listen_address
+\snippet{doc} local.cpp cli_long_listen_port
+\snippet{doc} local.cpp cli_long_interface
+\snippet{doc} utils.cpp cli_long_version
+\snippet{doc} utils.cpp cli_long_tcp_only
+\snippet{doc} utils.cpp cli_long_ipv4_first
+\snippet{doc} local.cpp cli_long_vpn
+\snippet{doc} local.cpp cli_long_stat_path
+\snippet{doc} utils.cpp cli_long_reuse_port
+\snippet{doc} utils.cpp cli_long_tcp_incoming_sndbuf
+\snippet{doc} utils.cpp cli_long_tcp_incoming_rcvbuf
+\snippet{doc} utils.cpp cli_long_tcp_outgoing_sndbuf
+\snippet{doc} utils.cpp cli_long_tcp_outgoing_rcvbuf
+\snippet{doc} utils.cpp cli_long_fast_open
+\snippet{doc} utils.cpp cli_long_no_delay
+\snippet{doc} utils.cpp cli_long_acl
+\snippet{doc} utils.cpp cli_long_mtu
+\snippet{doc} utils.cpp cli_long_mptcp
+\snippet{doc} utils.cpp cli_long_plugin
+\snippet{doc} utils.cpp cli_long_plugin_opts
+\snippet{doc} utils.cpp cli_long_password
+\snippet{doc} utils.cpp cli_long_key
+\snippet{doc} utils.cpp cli_long_server_url
+\snippet{doc} utils.cpp cli_long_printable_salt
+\snippet{doc} utils.cpp cli_long_help
 [cli-options] */
     static struct option long_options[] = {
         { "config", required_argument, NULL, 'c' },
diff --git a/src/manager.c b/src/manager.cpp
similarity index 96%
rename from src/manager.c
rename to src/manager.cpp
index f1af4fcb..7e9494ec 100644
--- a/src/manager.c
+++ b/src/manager.cpp
@@ -1,5 +1,5 @@
 /*
- * server.c - Provide shadowsocks service
+ * server.cpp - Provide shadowsocks service
  *
  * Copyright (C) 2013 - 2019, Max Lv <max.c.lv@gmail.com>
  *
@@ -1348,51 +1348,51 @@ Same behavior as `-d`; see that option for details. Short alias: `-d`.
 [cli_long_nameserver] */
 
 /* [cli-options]
-\snippet{doc} utils.c cli_short_f
-\snippet{doc} manager.c cli_short_s
-\snippet{doc} utils.c cli_short_k
-\snippet{doc} utils.c cli_short_t
-\snippet{doc} utils.c cli_short_m
-\snippet{doc} manager.c cli_short_c
-\snippet{doc} utils.c cli_short_i
-\snippet{doc} utils.c cli_short_d
-\snippet{doc} utils.c cli_short_a
-\snippet{doc} utils.c cli_short_n
-\snippet{doc} utils.c cli_short_D
-\snippet{doc} utils.c cli_short_6
-\snippet{doc} utils.c cli_short_h
-\snippet{doc} utils.c cli_short_u
-\snippet{doc} utils.c cli_short_U
-\snippet{doc} utils.c cli_short_v
-\snippet{doc} utils.c cli_short_A
-\snippet{doc} manager.c cli_long_config
-\snippet{doc} manager.c cli_long_cipher
-\snippet{doc} manager.c cli_long_timeout
-\snippet{doc} manager.c cli_long_user
-\snippet{doc} manager.c cli_long_pid_file
-\snippet{doc} manager.c cli_long_nofile
-\snippet{doc} manager.c cli_long_udp
-\snippet{doc} manager.c cli_long_udp_only
-\snippet{doc} manager.c cli_long_ipv6_first
-\snippet{doc} manager.c cli_long_verbose
-\snippet{doc} manager.c cli_long_listen_address
-\snippet{doc} manager.c cli_long_interface
-\snippet{doc} manager.c cli_long_nameserver
-\snippet{doc} utils.c cli_long_version
-\snippet{doc} utils.c cli_long_tcp_only
-\snippet{doc} utils.c cli_long_ipv4_first
-\snippet{doc} utils.c cli_long_fast_open
-\snippet{doc} utils.c cli_long_no_delay
-\snippet{doc} utils.c cli_long_reuse_port
-\snippet{doc} utils.c cli_long_acl
-\snippet{doc} utils.c cli_long_manager_address
-\snippet{doc} utils.c cli_long_executable
-\snippet{doc} utils.c cli_long_mtu
-\snippet{doc} utils.c cli_long_plugin
-\snippet{doc} utils.c cli_long_plugin_opts
-\snippet{doc} utils.c cli_long_password
-\snippet{doc} utils.c cli_long_workdir
-\snippet{doc} utils.c cli_long_help
+\snippet{doc} utils.cpp cli_short_f
+\snippet{doc} manager.cpp cli_short_s
+\snippet{doc} utils.cpp cli_short_k
+\snippet{doc} utils.cpp cli_short_t
+\snippet{doc} utils.cpp cli_short_m
+\snippet{doc} manager.cpp cli_short_c
+\snippet{doc} utils.cpp cli_short_i
+\snippet{doc} utils.cpp cli_short_d
+\snippet{doc} utils.cpp cli_short_a
+\snippet{doc} utils.cpp cli_short_n
+\snippet{doc} utils.cpp cli_short_D
+\snippet{doc} utils.cpp cli_short_6
+\snippet{doc} utils.cpp cli_short_h
+\snippet{doc} utils.cpp cli_short_u
+\snippet{doc} utils.cpp cli_short_U
+\snippet{doc} utils.cpp cli_short_v
+\snippet{doc} utils.cpp cli_short_A
+\snippet{doc} manager.cpp cli_long_config
+\snippet{doc} manager.cpp cli_long_cipher
+\snippet{doc} manager.cpp cli_long_timeout
+\snippet{doc} manager.cpp cli_long_user
+\snippet{doc} manager.cpp cli_long_pid_file
+\snippet{doc} manager.cpp cli_long_nofile
+\snippet{doc} manager.cpp cli_long_udp
+\snippet{doc} manager.cpp cli_long_udp_only
+\snippet{doc} manager.cpp cli_long_ipv6_first
+\snippet{doc} manager.cpp cli_long_verbose
+\snippet{doc} manager.cpp cli_long_listen_address
+\snippet{doc} manager.cpp cli_long_interface
+\snippet{doc} manager.cpp cli_long_nameserver
+\snippet{doc} utils.cpp cli_long_version
+\snippet{doc} utils.cpp cli_long_tcp_only
+\snippet{doc} utils.cpp cli_long_ipv4_first
+\snippet{doc} utils.cpp cli_long_fast_open
+\snippet{doc} utils.cpp cli_long_no_delay
+\snippet{doc} utils.cpp cli_long_reuse_port
+\snippet{doc} utils.cpp cli_long_acl
+\snippet{doc} utils.cpp cli_long_manager_address
+\snippet{doc} utils.cpp cli_long_executable
+\snippet{doc} utils.cpp cli_long_mtu
+\snippet{doc} utils.cpp cli_long_plugin
+\snippet{doc} utils.cpp cli_long_plugin_opts
+\snippet{doc} utils.cpp cli_long_password
+\snippet{doc} utils.cpp cli_long_workdir
+\snippet{doc} utils.cpp cli_long_help
 [cli-options] */
     static struct option long_options[] = {
         { "config", required_argument, NULL, 'c' },
diff --git a/src/redir.c b/src/redir.cpp
similarity index 95%
rename from src/redir.c
rename to src/redir.cpp
index dea814c6..60892412 100644
--- a/src/redir.c
+++ b/src/redir.cpp
@@ -1,5 +1,5 @@
 /*
- * redir.c - Provide a transparent TCP proxy through remote shadowsocks
+ * redir.cpp - Provide a transparent TCP proxy through remote shadowsocks
  *           server
  *
  * Copyright (C) 2013 - 2019, Max Lv <max.c.lv@gmail.com>
@@ -1003,56 +1003,56 @@ Same behavior as `-T`; see that option for details. Short alias: `-T`.
 [cli_long_tproxy] */
 
 /* [cli-options]
-\snippet{doc} utils.c cli_short_f
-\snippet{doc} utils.c cli_short_s
-\snippet{doc} utils.c cli_short_p
-\snippet{doc} utils.c cli_short_l
-\snippet{doc} utils.c cli_short_k
-\snippet{doc} utils.c cli_short_t
-\snippet{doc} utils.c cli_short_m
-\snippet{doc} utils.c cli_short_c
-\snippet{doc} utils.c cli_short_b
-\snippet{doc} utils.c cli_short_a
-\snippet{doc} utils.c cli_short_n
-\snippet{doc} utils.c cli_short_h
-\snippet{doc} redir.c cli_short_u
-\snippet{doc} utils.c cli_short_U
-\snippet{doc} utils.c cli_short_T
-\snippet{doc} utils.c cli_short_v
-\snippet{doc} utils.c cli_short_6
-\snippet{doc} utils.c cli_short_A
-\snippet{doc} redir.c cli_long_config
-\snippet{doc} redir.c cli_long_cipher
-\snippet{doc} redir.c cli_long_timeout
-\snippet{doc} redir.c cli_long_user
-\snippet{doc} redir.c cli_long_pid_file
-\snippet{doc} redir.c cli_long_nofile
-\snippet{doc} redir.c cli_long_udp
-\snippet{doc} redir.c cli_long_udp_only
-\snippet{doc} redir.c cli_long_ipv6_first
-\snippet{doc} redir.c cli_long_verbose
-\snippet{doc} redir.c cli_long_server
-\snippet{doc} redir.c cli_long_server_port
-\snippet{doc} redir.c cli_long_listen_address
-\snippet{doc} redir.c cli_long_listen_port
-\snippet{doc} redir.c cli_long_tproxy
-\snippet{doc} utils.c cli_long_version
-\snippet{doc} utils.c cli_long_tcp_only
-\snippet{doc} utils.c cli_long_ipv4_first
-\snippet{doc} utils.c cli_long_fast_open
-\snippet{doc} utils.c cli_long_mtu
-\snippet{doc} utils.c cli_long_mptcp
-\snippet{doc} utils.c cli_long_plugin
-\snippet{doc} utils.c cli_long_plugin_opts
-\snippet{doc} utils.c cli_long_reuse_port
-\snippet{doc} utils.c cli_long_tcp_incoming_sndbuf
-\snippet{doc} utils.c cli_long_tcp_incoming_rcvbuf
-\snippet{doc} utils.c cli_long_tcp_outgoing_sndbuf
-\snippet{doc} utils.c cli_long_tcp_outgoing_rcvbuf
-\snippet{doc} utils.c cli_long_no_delay
-\snippet{doc} utils.c cli_long_password
-\snippet{doc} utils.c cli_long_key
-\snippet{doc} utils.c cli_long_help
+\snippet{doc} utils.cpp cli_short_f
+\snippet{doc} utils.cpp cli_short_s
+\snippet{doc} utils.cpp cli_short_p
+\snippet{doc} utils.cpp cli_short_l
+\snippet{doc} utils.cpp cli_short_k
+\snippet{doc} utils.cpp cli_short_t
+\snippet{doc} utils.cpp cli_short_m
+\snippet{doc} utils.cpp cli_short_c
+\snippet{doc} utils.cpp cli_short_b
+\snippet{doc} utils.cpp cli_short_a
+\snippet{doc} utils.cpp cli_short_n
+\snippet{doc} utils.cpp cli_short_h
+\snippet{doc} redir.cpp cli_short_u
+\snippet{doc} utils.cpp cli_short_U
+\snippet{doc} utils.cpp cli_short_T
+\snippet{doc} utils.cpp cli_short_v
+\snippet{doc} utils.cpp cli_short_6
+\snippet{doc} utils.cpp cli_short_A
+\snippet{doc} redir.cpp cli_long_config
+\snippet{doc} redir.cpp cli_long_cipher
+\snippet{doc} redir.cpp cli_long_timeout
+\snippet{doc} redir.cpp cli_long_user
+\snippet{doc} redir.cpp cli_long_pid_file
+\snippet{doc} redir.cpp cli_long_nofile
+\snippet{doc} redir.cpp cli_long_udp
+\snippet{doc} redir.cpp cli_long_udp_only
+\snippet{doc} redir.cpp cli_long_ipv6_first
+\snippet{doc} redir.cpp cli_long_verbose
+\snippet{doc} redir.cpp cli_long_server
+\snippet{doc} redir.cpp cli_long_server_port
+\snippet{doc} redir.cpp cli_long_listen_address
+\snippet{doc} redir.cpp cli_long_listen_port
+\snippet{doc} redir.cpp cli_long_tproxy
+\snippet{doc} utils.cpp cli_long_version
+\snippet{doc} utils.cpp cli_long_tcp_only
+\snippet{doc} utils.cpp cli_long_ipv4_first
+\snippet{doc} utils.cpp cli_long_fast_open
+\snippet{doc} utils.cpp cli_long_mtu
+\snippet{doc} utils.cpp cli_long_mptcp
+\snippet{doc} utils.cpp cli_long_plugin
+\snippet{doc} utils.cpp cli_long_plugin_opts
+\snippet{doc} utils.cpp cli_long_reuse_port
+\snippet{doc} utils.cpp cli_long_tcp_incoming_sndbuf
+\snippet{doc} utils.cpp cli_long_tcp_incoming_rcvbuf
+\snippet{doc} utils.cpp cli_long_tcp_outgoing_sndbuf
+\snippet{doc} utils.cpp cli_long_tcp_outgoing_rcvbuf
+\snippet{doc} utils.cpp cli_long_no_delay
+\snippet{doc} utils.cpp cli_long_password
+\snippet{doc} utils.cpp cli_long_key
+\snippet{doc} utils.cpp cli_long_help
 [cli-options] */
     static struct option long_options[] = {
         { "config", required_argument, NULL, 'c' },
diff --git a/src/server.c b/src/server.cpp
similarity index 97%
rename from src/server.c
rename to src/server.cpp
index 0a2c9bf4..e12d97c8 100644
--- a/src/server.c
+++ b/src/server.cpp
@@ -1,5 +1,5 @@
 /*
- * server.c - Provide shadowsocks service
+ * server.cpp - Provide shadowsocks service
  *
  * Copyright (C) 2013 - 2019, Max Lv <max.c.lv@gmail.com>
  *
@@ -1929,59 +1929,59 @@ Same behavior as `-d`; see that option for details. Short alias: `-d`.
 [cli_long_nameserver] */
 
 /* [cli-options]
-\snippet{doc} utils.c cli_short_f
-\snippet{doc} server.c cli_short_s
-\snippet{doc} server.c cli_short_p
-\snippet{doc} utils.c cli_short_k
-\snippet{doc} utils.c cli_short_t
-\snippet{doc} utils.c cli_short_m
-\snippet{doc} server.c cli_short_b
-\snippet{doc} utils.c cli_short_c
-\snippet{doc} utils.c cli_short_i
-\snippet{doc} utils.c cli_short_d
-\snippet{doc} utils.c cli_short_a
-\snippet{doc} utils.c cli_short_n
-\snippet{doc} utils.c cli_short_h
-\snippet{doc} utils.c cli_short_u
-\snippet{doc} utils.c cli_short_U
-\snippet{doc} utils.c cli_short_v
-\snippet{doc} utils.c cli_short_6
-\snippet{doc} utils.c cli_short_A
-\snippet{doc} server.c cli_long_config
-\snippet{doc} server.c cli_long_cipher
-\snippet{doc} server.c cli_long_timeout
-\snippet{doc} server.c cli_long_user
-\snippet{doc} server.c cli_long_pid_file
-\snippet{doc} server.c cli_long_nofile
-\snippet{doc} server.c cli_long_udp
-\snippet{doc} server.c cli_long_udp_only
-\snippet{doc} server.c cli_long_ipv6_first
-\snippet{doc} server.c cli_long_verbose
-\snippet{doc} server.c cli_long_listen_address
-\snippet{doc} server.c cli_long_listen_port
-\snippet{doc} server.c cli_long_outbound_address
-\snippet{doc} server.c cli_long_interface
-\snippet{doc} server.c cli_long_nameserver
-\snippet{doc} utils.c cli_long_version
-\snippet{doc} utils.c cli_long_tcp_only
-\snippet{doc} utils.c cli_long_ipv4_first
-\snippet{doc} utils.c cli_long_fast_open
-\snippet{doc} utils.c cli_long_reuse_port
-\snippet{doc} utils.c cli_long_tcp_incoming_sndbuf
-\snippet{doc} utils.c cli_long_tcp_incoming_rcvbuf
-\snippet{doc} utils.c cli_long_tcp_outgoing_sndbuf
-\snippet{doc} utils.c cli_long_tcp_outgoing_rcvbuf
-\snippet{doc} utils.c cli_long_no_delay
-\snippet{doc} utils.c cli_long_acl
-\snippet{doc} utils.c cli_long_manager_address
-\snippet{doc} utils.c cli_long_mtu
-\snippet{doc} utils.c cli_long_help
-\snippet{doc} utils.c cli_long_plugin
-\snippet{doc} utils.c cli_long_plugin_opts
-\snippet{doc} utils.c cli_long_password
-\snippet{doc} utils.c cli_long_key
-\snippet{doc} utils.c cli_long_mptcp
-\snippet{doc} utils.c cli_long_nftables_sets
+\snippet{doc} utils.cpp cli_short_f
+\snippet{doc} server.cpp cli_short_s
+\snippet{doc} server.cpp cli_short_p
+\snippet{doc} utils.cpp cli_short_k
+\snippet{doc} utils.cpp cli_short_t
+\snippet{doc} utils.cpp cli_short_m
+\snippet{doc} server.cpp cli_short_b
+\snippet{doc} utils.cpp cli_short_c
+\snippet{doc} utils.cpp cli_short_i
+\snippet{doc} utils.cpp cli_short_d
+\snippet{doc} utils.cpp cli_short_a
+\snippet{doc} utils.cpp cli_short_n
+\snippet{doc} utils.cpp cli_short_h
+\snippet{doc} utils.cpp cli_short_u
+\snippet{doc} utils.cpp cli_short_U
+\snippet{doc} utils.cpp cli_short_v
+\snippet{doc} utils.cpp cli_short_6
+\snippet{doc} utils.cpp cli_short_A
+\snippet{doc} server.cpp cli_long_config
+\snippet{doc} server.cpp cli_long_cipher
+\snippet{doc} server.cpp cli_long_timeout
+\snippet{doc} server.cpp cli_long_user
+\snippet{doc} server.cpp cli_long_pid_file
+\snippet{doc} server.cpp cli_long_nofile
+\snippet{doc} server.cpp cli_long_udp
+\snippet{doc} server.cpp cli_long_udp_only
+\snippet{doc} server.cpp cli_long_ipv6_first
+\snippet{doc} server.cpp cli_long_verbose
+\snippet{doc} server.cpp cli_long_listen_address
+\snippet{doc} server.cpp cli_long_listen_port
+\snippet{doc} server.cpp cli_long_outbound_address
+\snippet{doc} server.cpp cli_long_interface
+\snippet{doc} server.cpp cli_long_nameserver
+\snippet{doc} utils.cpp cli_long_version
+\snippet{doc} utils.cpp cli_long_tcp_only
+\snippet{doc} utils.cpp cli_long_ipv4_first
+\snippet{doc} utils.cpp cli_long_fast_open
+\snippet{doc} utils.cpp cli_long_reuse_port
+\snippet{doc} utils.cpp cli_long_tcp_incoming_sndbuf
+\snippet{doc} utils.cpp cli_long_tcp_incoming_rcvbuf
+\snippet{doc} utils.cpp cli_long_tcp_outgoing_sndbuf
+\snippet{doc} utils.cpp cli_long_tcp_outgoing_rcvbuf
+\snippet{doc} utils.cpp cli_long_no_delay
+\snippet{doc} utils.cpp cli_long_acl
+\snippet{doc} utils.cpp cli_long_manager_address
+\snippet{doc} utils.cpp cli_long_mtu
+\snippet{doc} utils.cpp cli_long_help
+\snippet{doc} utils.cpp cli_long_plugin
+\snippet{doc} utils.cpp cli_long_plugin_opts
+\snippet{doc} utils.cpp cli_long_password
+\snippet{doc} utils.cpp cli_long_key
+\snippet{doc} utils.cpp cli_long_mptcp
+\snippet{doc} utils.cpp cli_long_nftables_sets
 [cli-options] */
     static struct option long_options[] = {
         { "config", required_argument, NULL, 'c' },
diff --git a/src/ss_event.c b/src/ss_event.cpp
similarity index 100%
rename from src/ss_event.c
rename to src/ss_event.cpp
diff --git a/src/tunnel.c b/src/tunnel.cpp
similarity index 95%
rename from src/tunnel.c
rename to src/tunnel.cpp
index 576ee74a..4015a7ee 100644
--- a/src/tunnel.c
+++ b/src/tunnel.cpp
@@ -1,5 +1,5 @@
 /*
- * tunnel.c - Setup a local port forwarding through remote shadowsocks server
+ * tunnel.cpp - Setup a local port forwarding through remote shadowsocks server
  *
  * Copyright (C) 2013 - 2019, Max Lv <max.c.lv@gmail.com>
  *
@@ -1043,60 +1043,60 @@ Same behavior as `-V`; see that option for details. Short alias: `-V`.
 [cli_long_vpn] */
 
 /* [cli-options]
-\snippet{doc} utils.c cli_short_f
-\snippet{doc} utils.c cli_short_s
-\snippet{doc} utils.c cli_short_p
-\snippet{doc} utils.c cli_short_l
-\snippet{doc} utils.c cli_short_k
-\snippet{doc} utils.c cli_short_t
-\snippet{doc} utils.c cli_short_m
-\snippet{doc} utils.c cli_short_i
-\snippet{doc} utils.c cli_short_c
-\snippet{doc} utils.c cli_short_b
-\snippet{doc} utils.c cli_short_L
-\snippet{doc} utils.c cli_short_a
-\snippet{doc} utils.c cli_short_n
-\snippet{doc} utils.c cli_short_h
-\snippet{doc} utils.c cli_short_u
-\snippet{doc} utils.c cli_short_U
-\snippet{doc} utils.c cli_short_v
-\snippet{doc} utils.c cli_short_V
-\snippet{doc} utils.c cli_short_6
-\snippet{doc} utils.c cli_short_A
-\snippet{doc} tunnel.c cli_long_config
-\snippet{doc} tunnel.c cli_long_cipher
-\snippet{doc} tunnel.c cli_long_timeout
-\snippet{doc} tunnel.c cli_long_user
-\snippet{doc} tunnel.c cli_long_pid_file
-\snippet{doc} tunnel.c cli_long_nofile
-\snippet{doc} tunnel.c cli_long_udp
-\snippet{doc} tunnel.c cli_long_udp_only
-\snippet{doc} tunnel.c cli_long_ipv6_first
-\snippet{doc} tunnel.c cli_long_verbose
-\snippet{doc} tunnel.c cli_long_server
-\snippet{doc} tunnel.c cli_long_server_port
-\snippet{doc} tunnel.c cli_long_listen_address
-\snippet{doc} tunnel.c cli_long_listen_port
-\snippet{doc} tunnel.c cli_long_interface
-\snippet{doc} tunnel.c cli_long_destination
-\snippet{doc} utils.c cli_long_version
-\snippet{doc} utils.c cli_long_tcp_only
-\snippet{doc} utils.c cli_long_ipv4_first
-\snippet{doc} tunnel.c cli_long_vpn
-\snippet{doc} utils.c cli_long_fast_open
-\snippet{doc} utils.c cli_long_mtu
-\snippet{doc} utils.c cli_long_no_delay
-\snippet{doc} utils.c cli_long_mptcp
-\snippet{doc} utils.c cli_long_plugin
-\snippet{doc} utils.c cli_long_plugin_opts
-\snippet{doc} utils.c cli_long_reuse_port
-\snippet{doc} utils.c cli_long_tcp_incoming_sndbuf
-\snippet{doc} utils.c cli_long_tcp_incoming_rcvbuf
-\snippet{doc} utils.c cli_long_tcp_outgoing_sndbuf
-\snippet{doc} utils.c cli_long_tcp_outgoing_rcvbuf
-\snippet{doc} utils.c cli_long_password
-\snippet{doc} utils.c cli_long_key
-\snippet{doc} utils.c cli_long_help
+\snippet{doc} utils.cpp cli_short_f
+\snippet{doc} utils.cpp cli_short_s
+\snippet{doc} utils.cpp cli_short_p
+\snippet{doc} utils.cpp cli_short_l
+\snippet{doc} utils.cpp cli_short_k
+\snippet{doc} utils.cpp cli_short_t
+\snippet{doc} utils.cpp cli_short_m
+\snippet{doc} utils.cpp cli_short_i
+\snippet{doc} utils.cpp cli_short_c
+\snippet{doc} utils.cpp cli_short_b
+\snippet{doc} utils.cpp cli_short_L
+\snippet{doc} utils.cpp cli_short_a
+\snippet{doc} utils.cpp cli_short_n
+\snippet{doc} utils.cpp cli_short_h
+\snippet{doc} utils.cpp cli_short_u
+\snippet{doc} utils.cpp cli_short_U
+\snippet{doc} utils.cpp cli_short_v
+\snippet{doc} utils.cpp cli_short_V
+\snippet{doc} utils.cpp cli_short_6
+\snippet{doc} utils.cpp cli_short_A
+\snippet{doc} tunnel.cpp cli_long_config
+\snippet{doc} tunnel.cpp cli_long_cipher
+\snippet{doc} tunnel.cpp cli_long_timeout
+\snippet{doc} tunnel.cpp cli_long_user
+\snippet{doc} tunnel.cpp cli_long_pid_file
+\snippet{doc} tunnel.cpp cli_long_nofile
+\snippet{doc} tunnel.cpp cli_long_udp
+\snippet{doc} tunnel.cpp cli_long_udp_only
+\snippet{doc} tunnel.cpp cli_long_ipv6_first
+\snippet{doc} tunnel.cpp cli_long_verbose
+\snippet{doc} tunnel.cpp cli_long_server
+\snippet{doc} tunnel.cpp cli_long_server_port
+\snippet{doc} tunnel.cpp cli_long_listen_address
+\snippet{doc} tunnel.cpp cli_long_listen_port
+\snippet{doc} tunnel.cpp cli_long_interface
+\snippet{doc} tunnel.cpp cli_long_destination
+\snippet{doc} utils.cpp cli_long_version
+\snippet{doc} utils.cpp cli_long_tcp_only
+\snippet{doc} utils.cpp cli_long_ipv4_first
+\snippet{doc} tunnel.cpp cli_long_vpn
+\snippet{doc} utils.cpp cli_long_fast_open
+\snippet{doc} utils.cpp cli_long_mtu
+\snippet{doc} utils.cpp cli_long_no_delay
+\snippet{doc} utils.cpp cli_long_mptcp
+\snippet{doc} utils.cpp cli_long_plugin
+\snippet{doc} utils.cpp cli_long_plugin_opts
+\snippet{doc} utils.cpp cli_long_reuse_port
+\snippet{doc} utils.cpp cli_long_tcp_incoming_sndbuf
+\snippet{doc} utils.cpp cli_long_tcp_incoming_rcvbuf
+\snippet{doc} utils.cpp cli_long_tcp_outgoing_sndbuf
+\snippet{doc} utils.cpp cli_long_tcp_outgoing_rcvbuf
+\snippet{doc} utils.cpp cli_long_password
+\snippet{doc} utils.cpp cli_long_key
+\snippet{doc} utils.cpp cli_long_help
 [cli-options] */
     static struct option long_options[] = {
         { "config", required_argument, NULL, 'c' },
diff --git a/src/udprelay.c b/src/udprelay.cpp
similarity index 99%
rename from src/udprelay.c
rename to src/udprelay.cpp
index 5857a421..f4b0b90b 100644
--- a/src/udprelay.c
+++ b/src/udprelay.cpp
@@ -1,5 +1,5 @@
 /*
- * udprelay.c - Setup UDP relay for both client and server
+ * udprelay.cpp - Setup UDP relay for both client and server
  *
  * Copyright (C) 2013 - 2019, Max Lv <max.c.lv@gmail.com>
  *
diff --git a/src/utils.c b/src/utils.cpp
similarity index 99%
rename from src/utils.c
rename to src/utils.cpp
index b6f95f9c..24052734 100644
--- a/src/utils.c
+++ b/src/utils.cpp
@@ -1,5 +1,5 @@
 /*
- * utils.c - Misc utilities
+ * utils.cpp - Misc utilities
  *
  * Copyright (C) 2013 - 2019, Max Lv <max.c.lv@gmail.com>
  *
@@ -860,7 +860,7 @@ get_default_conf(void)
     // If not, fall back to the system-wide config.
     return sysconf;
 #else
-    return "config.json";
+    return (char *)"config.json";
 #endif
 }
 
diff --git a/src/utils.h b/src/utils.h
index a582a6de..1ffe1801 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -207,7 +207,7 @@ extern int use_syslog;
 #endif
 #define ERROR(s) ss_error(s)
 
-// Implemented in winsock.c
+// Implemented in winsock.cpp
 void ss_error(const char *s);
 void ss_color_info(void);
 void ss_color_error(void);
diff --git a/src/winsock.c b/src/winsock.cpp
similarity index 99%
rename from src/winsock.c
rename to src/winsock.cpp
index ef6e7cb5..c0997030 100644
--- a/src/winsock.c
+++ b/src/winsock.cpp
@@ -1,5 +1,5 @@
 /*
- * winsock.c - Windows socket compatibility layer
+ * winsock.cpp - Windows socket compatibility layer
  *
  * Copyright (C) 2013 - 2019, Max Lv <max.c.lv@gmail.com>
  *
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 7b0befa8..d6aeb456 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -20,8 +20,8 @@ endif()
 
 # Helper function to add a unit test
 function(ss_add_test name sources libs)
-    if(WIN32 AND "${sources}" MATCHES "utils.c")
-        list(APPEND sources ${PROJECT_SOURCE_DIR}/src/winsock.c)
+    if(WIN32 AND "${sources}" MATCHES "utils.cpp")
+        list(APPEND sources ${PROJECT_SOURCE_DIR}/src/winsock.cpp)
     endif()
     add_executable(${name} ${sources})
     target_compile_definitions(${name} PRIVATE -DHAVE_CONFIG_H)
@@ -95,9 +95,9 @@ ss_add_test(test_base64
     "test_base64.c;${PROJECT_SOURCE_DIR}/src/base64.cpp"
     "")
 
-# test_utils - needs sodium (for ss_malloc -> uses sodium in utils.c)
+# test_utils - needs sodium (for ss_malloc -> uses sodium in utils.cpp)
 ss_add_test(test_utils
-    "test_utils.c;${PROJECT_SOURCE_DIR}/src/utils.c"
+    "test_utils.c;${PROJECT_SOURCE_DIR}/src/utils.cpp"
     "ss_sodium")
 
 # test_json - standalone json parser
@@ -107,7 +107,7 @@ ss_add_test(test_json
 
 # test_ssurl - ss:// URI parsing (SIP002 and legacy)
 ss_add_test(test_ssurl
-    "test_ssurl.c;${PROJECT_SOURCE_DIR}/src/ssurl.cpp;${PROJECT_SOURCE_DIR}/src/base64.cpp;${PROJECT_SOURCE_DIR}/src/utils.c"
+    "test_ssurl.c;${PROJECT_SOURCE_DIR}/src/ssurl.cpp;${PROJECT_SOURCE_DIR}/src/base64.cpp;${PROJECT_SOURCE_DIR}/src/utils.cpp"
     "ss_sodium")
 
 # test_netutils - address parsing and resolver integration
@@ -117,19 +117,19 @@ set(TEST_NETUTILS_LIBS
     ss_cares
 )
 ss_add_test(test_netutils
-    "test_netutils.c;${PROJECT_SOURCE_DIR}/src/netutils.cpp;${PROJECT_SOURCE_DIR}/src/utils.c"
+    "test_netutils.c;${PROJECT_SOURCE_DIR}/src/netutils.cpp;${PROJECT_SOURCE_DIR}/src/utils.cpp"
     "${TEST_NETUTILS_LIBS}")
 
 # test_cache - expiration uses a platform monotonic clock
 ss_add_test(test_cache
-    "test_cache.c;${PROJECT_SOURCE_DIR}/src/cache.cpp;${PROJECT_SOURCE_DIR}/src/utils.c"
+    "test_cache.c;${PROJECT_SOURCE_DIR}/src/cache.cpp;${PROJECT_SOURCE_DIR}/src/utils.cpp"
     "ss_sodium")
 
 # test_ppbloom - needs bloom
 set(TEST_PPBLOOM_LIBS "")
 list(APPEND TEST_PPBLOOM_LIBS bloom)
 ss_add_test(test_ppbloom
-    "test_ppbloom.c;${PROJECT_SOURCE_DIR}/src/ppbloom.cpp;${PROJECT_SOURCE_DIR}/src/utils.c"
+    "test_ppbloom.c;${PROJECT_SOURCE_DIR}/src/ppbloom.cpp;${PROJECT_SOURCE_DIR}/src/utils.cpp"
     "${TEST_PPBLOOM_LIBS};ss_sodium;${SS_MATH_LIBRARY}")
 
 if(SS_ENABLE_REGEX)
@@ -139,13 +139,13 @@ set(TEST_RULE_LIBS
     ss_sodium
 )
 ss_add_test(test_rule
-    "test_rule.c;${PROJECT_SOURCE_DIR}/src/rule.cpp;${PROJECT_SOURCE_DIR}/src/utils.c"
+    "test_rule.c;${PROJECT_SOURCE_DIR}/src/rule.cpp;${PROJECT_SOURCE_DIR}/src/utils.cpp"
     "${TEST_RULE_LIBS}")
 
 # test_acl - ACL precedence and prefix matching
 set(TEST_ACL_LIBS ${TEST_RULE_LIBS})
 ss_add_test(test_acl
-    "test_acl.c;${PROJECT_SOURCE_DIR}/src/acl.cpp;${PROJECT_SOURCE_DIR}/src/ipset.cpp;${PROJECT_SOURCE_DIR}/src/rule.cpp;${PROJECT_SOURCE_DIR}/src/utils.c"
+    "test_acl.c;${PROJECT_SOURCE_DIR}/src/acl.cpp;${PROJECT_SOURCE_DIR}/src/ipset.cpp;${PROJECT_SOURCE_DIR}/src/rule.cpp;${PROJECT_SOURCE_DIR}/src/utils.cpp"
     "${TEST_ACL_LIBS}")
 
 endif()
@@ -157,7 +157,7 @@ set(TEST_JCONF_LIBS
     ss_cares
 )
 ss_add_test(test_jconf
-    "test_jconf.c;${PROJECT_SOURCE_DIR}/src/jconf.cpp;${PROJECT_SOURCE_DIR}/src/json.cpp;${PROJECT_SOURCE_DIR}/src/utils.c;${PROJECT_SOURCE_DIR}/src/netutils.cpp"
+    "test_jconf.c;${PROJECT_SOURCE_DIR}/src/jconf.cpp;${PROJECT_SOURCE_DIR}/src/json.cpp;${PROJECT_SOURCE_DIR}/src/utils.cpp;${PROJECT_SOURCE_DIR}/src/netutils.cpp"
     "${TEST_JCONF_LIBS};${SS_MATH_LIBRARY}")
 
 # Crypto sources shared by the tests that link the crypto layer. The AEAD-2022
@@ -171,7 +171,7 @@ set(SS_CRYPTO_TEST_SOURCES
     ${PROJECT_SOURCE_DIR}/src/ppbloom.cpp
     ${PROJECT_SOURCE_DIR}/src/cache.cpp
     ${PROJECT_SOURCE_DIR}/src/base64.cpp
-    ${PROJECT_SOURCE_DIR}/src/utils.c
+    ${PROJECT_SOURCE_DIR}/src/utils.cpp
 )
 
 if(SS_ENABLE_LEGACY)
@@ -220,16 +220,16 @@ add_test(NAME test_ss_setup
 set_tests_properties(test_ss_setup PROPERTIES LABELS "integration")
 
 ss_add_test(test_ipset
-    "test_ipset.c;${PROJECT_SOURCE_DIR}/src/ipset.cpp;${PROJECT_SOURCE_DIR}/src/utils.c"
+    "test_ipset.c;${PROJECT_SOURCE_DIR}/src/ipset.cpp;${PROJECT_SOURCE_DIR}/src/utils.cpp"
     "ss_sodium")
 
 ss_add_test(test_process
-    "test_process.c;${PROJECT_SOURCE_DIR}/src/process.cpp;${PROJECT_SOURCE_DIR}/src/utils.c"
+    "test_process.c;${PROJECT_SOURCE_DIR}/src/process.cpp;${PROJECT_SOURCE_DIR}/src/utils.cpp"
     "ss_sodium")
 set_tests_properties(test_process PROPERTIES TIMEOUT 20)
 
 ss_add_test(test_resolv
-    "test_resolv.c;${PROJECT_SOURCE_DIR}/src/resolv.cpp;${PROJECT_SOURCE_DIR}/src/utils.c"
+    "test_resolv.c;${PROJECT_SOURCE_DIR}/src/resolv.cpp;${PROJECT_SOURCE_DIR}/src/utils.cpp"
     "ss_ev;ss_cares;ss_sodium")
 set_tests_properties(test_resolv PROPERTIES TIMEOUT 20)
 
@@ -238,13 +238,13 @@ if(SS_ENABLE_REGEX)
     list(APPEND TEST_LITERAL_LIBS ss_pcre2)
 endif()
 ss_add_test(test_acl_literal
-    "test_acl_literal.c;${PROJECT_SOURCE_DIR}/src/acl.cpp;${PROJECT_SOURCE_DIR}/src/ipset.cpp;${PROJECT_SOURCE_DIR}/src/rule.cpp;${PROJECT_SOURCE_DIR}/src/utils.c"
+    "test_acl_literal.c;${PROJECT_SOURCE_DIR}/src/acl.cpp;${PROJECT_SOURCE_DIR}/src/ipset.cpp;${PROJECT_SOURCE_DIR}/src/rule.cpp;${PROJECT_SOURCE_DIR}/src/utils.cpp"
     "${TEST_LITERAL_LIBS}")
 
 ss_add_test(test_event "test_event.c" "ss_ev")
 set_tests_properties(test_event PROPERTIES TIMEOUT 30)
 ss_add_test(test_resolv_async
-    "test_resolv_async.c;${PROJECT_SOURCE_DIR}/src/resolv.cpp;${PROJECT_SOURCE_DIR}/src/utils.c"
+    "test_resolv_async.c;${PROJECT_SOURCE_DIR}/src/resolv.cpp;${PROJECT_SOURCE_DIR}/src/utils.cpp"
     "ss_ev;ss_cares;ss_sodium")
 set_tests_properties(test_resolv_async PROPERTIES TIMEOUT 30)
 
diff --git a/tests/test_cli_docs.py b/tests/test_cli_docs.py
index 8b0032c3..eab32687 100644
--- a/tests/test_cli_docs.py
+++ b/tests/test_cli_docs.py
@@ -19,7 +19,7 @@ class CliDocsTests(unittest.TestCase):
         self.root = Path(self.temp.name)
         (self.root / 'src').mkdir()
         (self.root / 'doc').mkdir()
-        for name in ('local.c', 'server.c', 'tunnel.c', 'redir.c', 'manager.c', 'utils.c', 'ss-nat'):
+        for name in ('local.cpp', 'server.cpp', 'tunnel.cpp', 'redir.cpp', 'manager.cpp', 'utils.cpp', 'ss-nat'):
             shutil.copyfile(ROOT / 'src' / name, self.root / 'src' / name)
         for path in (ROOT / 'doc').glob('*.md'):
             shutil.copyfile(path, self.root / 'doc' / path.name)
@@ -33,32 +33,32 @@ class CliDocsTests(unittest.TestCase):
     def test_current_documentation_matches_all_variants(self):
         DOCS.check(self.root)
         sources = {p.name: p.read_text(encoding='utf-8') for p in (self.root / 'src').iterdir()}
-        local = DOCS.documented_options('local.c', sources)
+        local = DOCS.documented_options('local.cpp', sources)
         self.assertIn('-S', local)
         self.assertIn('-V', local)
-        self.assertIn('--nftables-sets', DOCS.documented_options('server.c', sources))
+        self.assertIn('--nftables-sets', DOCS.documented_options('server.cpp', sources))
         self.assertIn('-I', DOCS.documented_options('ss-nat', sources))
-        self.assertNotIn('-p', DOCS.documented_options('manager.c', sources))
+        self.assertNotIn('-p', DOCS.documented_options('manager.cpp', sources))
 
     def test_new_option_requires_documentation(self):
-        self.change('src/local.c', '"reuse-port",', '"new-option",')
+        self.change('src/local.cpp', '"reuse-port",', '"new-option",')
         with self.assertRaisesRegex(ValueError, 'missing documentation.*new-option'):
             DOCS.check(self.root)
 
     def test_argument_arity_is_checked(self):
-        self.change('src/local.c', '"reuse-port",  no_argument',
+        self.change('src/local.cpp', '"reuse-port",  no_argument',
                     '"reuse-port",  required_argument')
         with self.assertRaisesRegex(ValueError, 'argument mismatch.*reuse-port'):
             DOCS.check(self.root)
 
     def test_unknown_parser_syntax_fails_closed(self):
-        self.change('src/local.c', '"reuse-port",  no_argument',
+        self.change('src/local.cpp', '"reuse-port",  no_argument',
                     '"reuse-port",  optional_argument')
         with self.assertRaisesRegex(ValueError, 'Unsupported long_options'):
             DOCS.check(self.root)
 
     def test_nonliteral_short_options_fail_closed(self):
-        self.change('src/local.c', '":f:s:p:l:k:t:m:i:c:b:a:n:huUv6A"', 'SHORT_OPTIONS')
+        self.change('src/local.cpp', '":f:s:p:l:k:t:m:i:c:b:a:n:huUv6A"', 'SHORT_OPTIONS')
         with self.assertRaisesRegex(ValueError, 'literal getopt_long'):
             DOCS.check(self.root)
 
@@ -68,17 +68,17 @@ class CliDocsTests(unittest.TestCase):
             DOCS.check(self.root)
 
     def test_missing_snippet_is_rejected(self):
-        self.change('src/local.c', 'utils.c cli_long_reuse_port', 'utils.c missing_snippet')
+        self.change('src/local.cpp', 'utils.cpp cli_long_reuse_port', 'utils.cpp missing_snippet')
         with self.assertRaisesRegex(ValueError, 'Missing snippet'):
             DOCS.check(self.root)
 
     def test_duplicate_option_is_rejected(self):
-        self.change('src/local.c', 'utils.c cli_long_reuse_port', 'utils.c cli_short_f')
+        self.change('src/local.cpp', 'utils.cpp cli_long_reuse_port', 'utils.cpp cli_short_f')
         with self.assertRaisesRegex(ValueError, 'Duplicate documented option'):
             DOCS.check(self.root)
 
     def test_manual_must_include_parser_options(self):
-        self.change('doc/ss-local.md', 'local.c cli-options', 'local.c missing-options')
+        self.change('doc/ss-local.md', 'local.cpp cli-options', 'local.cpp missing-options')
         with self.assertRaisesRegex(ValueError, 'manual must include'):
             DOCS.check(self.root)