Add an integration test for the cmsg(3) functions.

Since these are defined in C as macros, they must be reimplemented in
libc as Rust functions.  They're hard to get exactly right, and they
vary from platform to platform.  The test builds custom C code that uses
the real macros, and compares its output to the Rust versions' output
for various inputs.

Author: asomers

Cargo.lock

@@ -9,6 +9,7 @@ path = ".."
 default-features = false
 
 [build-dependencies]
+cc = "1.0"
 ctest = "0.2.8"
 
 [features]
@@ -26,3 +27,7 @@ name = "linux-fcntl"
 path = "test/linux_fcntl.rs"
 harness = false
 
+[[test]]
+name = "cmsg"
+path = "test/cmsg.rs"
+harness = true

libc-test/Cargo.toml

@@ -1,10 +1,17 @@
 #![deny(warnings)]
 
+extern crate cc;
 extern crate ctest;
 
 use std::env;
 
-fn main() {
+fn do_cc() {
+    cc::Build::new()
+        .file("src/cmsg.c")
+        .compile("cmsg");
+}
+
+fn do_ctest() {
     let target = env::var("TARGET").unwrap();
     let aarch64 = target.contains("aarch64");
     let i686 = target.contains("i686");
@@ -973,3 +980,8 @@ fn main() {
     }
     cfg.generate("../src/lib.rs", "linux_fcntl.rs");
 }
+
+fn main() {
+    do_cc();
+    do_ctest();
+}

libc-test/build.rs

@@ -0,0 +1,27 @@
+#include <sys/socket.h>
+
+// Since the cmsg(3) macros are macros instead of functions, they aren't
+// available to FFI.  libc must reimplement them, which is error-prone.  This
+// file provides FFI access to the actual macros so they can be tested against
+// the Rust reimplementations.
+
+struct cmsghdr *cmsg_firsthdr(struct msghdr *msgh) {
+	return CMSG_FIRSTHDR(msgh);
+}
+
+struct cmsghdr *cmsg_nxthdr(struct msghdr *msgh, struct cmsghdr *cmsg) {
+	return CMSG_NXTHDR(msgh, cmsg);
+}
+
+size_t cmsg_space(size_t length) {
+	return CMSG_SPACE(length);
+}
+
+size_t cmsg_len(size_t length) {
+	return CMSG_LEN(length);
+}
+
+unsigned char *cmsg_data(struct cmsghdr *cmsg) {
+	return CMSG_DATA(cmsg);
+}
+

libc-test/src/cmsg.c

@@ -0,0 +1,88 @@
+//! Compare libc's CMSG(3) family of functions against the actual C macros, for
+//! various inputs.
+
+extern crate libc;
+use libc::{c_uchar, c_uint, c_void, cmsghdr, msghdr};
+use std::{mem, ptr};
+
+extern {
+    pub fn cmsg_firsthdr(msgh: *const msghdr) -> *mut cmsghdr;
+    pub fn cmsg_nxthdr(mhdr: *const msghdr,
+                       cmsg: *const cmsghdr) -> *mut cmsghdr;
+    pub fn cmsg_space(length: c_uint) -> usize;
+    pub fn cmsg_len(length: c_uint) -> usize;
+    pub fn cmsg_data(cmsg: *const cmsghdr) -> *mut c_uchar;
+}
+
+#[test]
+fn test_cmsg_data() {
+    for l in 0..128 {
+        let pcmsghdr = l as *const cmsghdr;
+        unsafe {
+            assert_eq!(libc::CMSG_DATA(pcmsghdr), cmsg_data(pcmsghdr));
+        }
+    }
+}
+
+#[test]
+fn test_cmsg_firsthdr() {
+    let mut mhdr: msghdr = unsafe{mem::zeroed()};
+    mhdr.msg_control = 0xdeadbeef as *mut c_void;
+    let pmhdr = &mhdr as *const msghdr;
+    for l in 0..128 {
+        mhdr.msg_controllen = l;
+        unsafe {
+            assert_eq!(libc::CMSG_FIRSTHDR(pmhdr), cmsg_firsthdr(pmhdr));
+        }
+    }
+}
+
+#[test]
+fn test_cmsg_len() {
+    for l in 0..128 {
+        unsafe {
+            assert_eq!(libc::CMSG_LEN(l) as usize, cmsg_len(l));
+        }
+    }
+}
+
+#[test]
+fn test_cmsg_nxthdr() {
+    let mut buffer = [0u8; 256];
+    let mut mhdr: msghdr = unsafe{mem::zeroed()};
+    let pmhdr = &mhdr as *const msghdr;
+    for start_ofs in 0..64 {
+        let pcmsghdr = &mut buffer[start_ofs] as *mut u8 as *mut cmsghdr;
+        mhdr.msg_control = pcmsghdr as *mut c_void;
+        mhdr.msg_controllen = (160 - start_ofs) as _;
+        for cmsg_len in 0..64 {
+            for next_cmsg_len in 0..32 {
+                for i in buffer[start_ofs..].iter_mut() {
+                    *i = 0;
+                }
+                unsafe {
+                    (*pcmsghdr).cmsg_len = cmsg_len;
+                    let libc_next = libc::CMSG_NXTHDR(pmhdr, pcmsghdr);
+                    let next = cmsg_nxthdr(pmhdr, pcmsghdr);
+                    assert_eq!(libc_next, next);
+
+                    if libc_next != ptr::null_mut() {
+                        (*libc_next).cmsg_len = next_cmsg_len;
+                        let libc_next = libc::CMSG_NXTHDR(pmhdr, pcmsghdr);
+                        let next = cmsg_nxthdr(pmhdr, pcmsghdr);
+                        assert_eq!(libc_next, next);
+                    }
+                }
+            }
+        }
+    }
+}
+
+#[test]
+fn test_cmsg_space() {
+    unsafe {
+        for l in 0..128 {
+            assert_eq!(libc::CMSG_SPACE(l) as usize, cmsg_space(l));
+        }
+    }
+}