From 9d9f42cc38b06ddc3fe30f4c1695514774b5217e Mon Sep 17 00:00:00 2001
From: Jacek Galowicz <jacek@galowicz.de>
Date: Thu, 2 Nov 2023 15:52:38 +0100
Subject: [PATCH] Remove C-style casts

---
 src/libutil/file-descriptor.cc    |  2 +-
 src/libutil/processes.cc          |  4 ++--
 src/libutil/unix-domain-socket.cc | 18 ++++++++++++++----
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/src/libutil/file-descriptor.cc b/src/libutil/file-descriptor.cc
index 43e3cd979..55d57e29b 100644
--- a/src/libutil/file-descriptor.cc
+++ b/src/libutil/file-descriptor.cc
@@ -114,7 +114,7 @@ void drainFD(int fd, Sink & sink, bool block)
                 throw SysError("reading from file");
         }
         else if (rd == 0) break;
-        else sink({(char *) buf.data(), (size_t) rd});
+        else sink({reinterpret_cast<char *>(buf.data()), size_t(rd)});
     }
 }
 
diff --git a/src/libutil/processes.cc b/src/libutil/processes.cc
index 28f1adcf0..f5d584330 100644
--- a/src/libutil/processes.cc
+++ b/src/libutil/processes.cc
@@ -226,8 +226,8 @@ pid_t startProcess(std::function<void()> fun, const ProcessOptions & options)
         assert(!(options.cloneFlags & CLONE_VM));
 
         size_t stackSize = 1 * 1024 * 1024;
-        auto stack = (char *) mmap(0, stackSize,
-            PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
+        auto stack = static_cast<char *>(mmap(0, stackSize,
+            PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0));
         if (stack == MAP_FAILED) throw SysError("allocating stack");
 
         Finally freeStack([&] { munmap(stack, stackSize); });
diff --git a/src/libutil/unix-domain-socket.cc b/src/libutil/unix-domain-socket.cc
index dc19daf9e..3b6d54a2c 100644
--- a/src/libutil/unix-domain-socket.cc
+++ b/src/libutil/unix-domain-socket.cc
@@ -38,6 +38,14 @@ AutoCloseFD createUnixDomainSocket(const Path & path, mode_t mode)
     return fdSocket;
 }
 
+static struct sockaddr* safeSockAddrPointerCast(struct sockaddr_un *addr) {
+    // Casting between types like these legacy C library interfaces require
+    // is forbidden in C++.
+    // To maintain backwards compatibility, the implementation of the
+    // bind function contains some hints to the compiler that allow for this
+    // special case.
+    return reinterpret_cast<struct sockaddr *>(addr);
+}
 
 void bind(int fd, const std::string & path)
 {
@@ -45,6 +53,7 @@ void bind(int fd, const std::string & path)
 
     struct sockaddr_un addr;
     addr.sun_family = AF_UNIX;
+    auto psaddr {safeSockAddrPointerCast(&addr)};
 
     if (path.size() + 1 >= sizeof(addr.sun_path)) {
         Pid pid = startProcess([&] {
@@ -55,7 +64,7 @@ void bind(int fd, const std::string & path)
             if (base.size() + 1 >= sizeof(addr.sun_path))
                 throw Error("socket path '%s' is too long", base);
             memcpy(addr.sun_path, base.c_str(), base.size() + 1);
-            if (bind(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
+            if (bind(fd, psaddr, sizeof(addr)) == -1)
                 throw SysError("cannot bind to socket '%s'", path);
             _exit(0);
         });
@@ -64,7 +73,7 @@ void bind(int fd, const std::string & path)
             throw Error("cannot bind to socket '%s'", path);
     } else {
         memcpy(addr.sun_path, path.c_str(), path.size() + 1);
-        if (bind(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
+        if (bind(fd, psaddr, sizeof(addr)) == -1)
             throw SysError("cannot bind to socket '%s'", path);
     }
 }
@@ -74,6 +83,7 @@ void connect(int fd, const std::string & path)
 {
     struct sockaddr_un addr;
     addr.sun_family = AF_UNIX;
+    auto psaddr {safeSockAddrPointerCast(&addr)};
 
     if (path.size() + 1 >= sizeof(addr.sun_path)) {
         Pipe pipe;
@@ -88,7 +98,7 @@ void connect(int fd, const std::string & path)
                 if (base.size() + 1 >= sizeof(addr.sun_path))
                     throw Error("socket path '%s' is too long", base);
                 memcpy(addr.sun_path, base.c_str(), base.size() + 1);
-                if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
+                if (connect(fd, psaddr, sizeof(addr)) == -1)
                     throw SysError("cannot connect to socket at '%s'", path);
                 writeFull(pipe.writeSide.get(), "0\n");
             } catch (SysError & e) {
@@ -107,7 +117,7 @@ void connect(int fd, const std::string & path)
         }
     } else {
         memcpy(addr.sun_path, path.c_str(), path.size() + 1);
-        if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
+        if (connect(fd, psaddr, sizeof(addr)) == -1)
             throw SysError("cannot connect to socket at '%s'", path);
     }
 }