Add function preconditionIsNotBlacklistedErrno (#1201)

Motivation:

Certain POSIX error numbers mean the NIO program is broken beyond repair and should crash. One such value is EBADF, which indicates that the file descriptor that NIO passed to the kernel is invalid for some reason. SR-11557 was discovered in part because debug builds of NIO crash for this.
I have promoted these checks from an assertion to a precondition adding a function preconditionIsNotBlacklistedErrno. Issue was raised in issue #1156

Modifications:

- Add function preconditionIsNotBlacklistedErrno to enable option to stop program execution in both debug mode and release mode if the errno is blacklisted.
- Update assertIsNotBlacklistedErrno to all preconditionIsNotBlacklistedErrno when the program is in debug mode
- Update wrapSyscallMayBlock, wrapSyscall, wrapErrorIsNullReturnCall, and close to call preconditionIsNotBlacklistedErrno in stead of assertIsNotBlacklistedErrno

Result:

Functions wrapSyscallMayBlock, wrapSyscall, wrapErrorIsNullReturnCall, and close will stop the execution in both debug mode and release mode if the errno is blacklisted.

IntegrationTests/tests_02_syscall_wrappers/test_02_blacklisted_errnos.sh

@@ -70,10 +70,8 @@ for mode in debug release; do
         else
             exit_code=$?
             # expecting illegal instruction as it should fail with a blacklisted errno
-            if [[ "$mode" == "release" ]]; then
-                assert_equal 42 $exit_code
-            else
-                assert_equal $(( 128 + 4 )) $exit_code  # 4 == SIGILL
+            assert_equal $(( 128 + 4 )) $exit_code  # 4 == SIGILL
+            if [[ "$mode" == "debug" ]]; then
                 grep -q blacklisted\ errno "$temp_file"
             fi
         fi

Sources/NIO/System.swift

@@ -107,9 +107,9 @@ private func isBlacklistedErrno(_ code: Int32) -> Bool {
     }
 }
 
-private func assertIsNotBlacklistedErrno(err: CInt, where function: StaticString) -> Void {
+private func preconditionIsNotBlacklistedErrno(err: CInt, where function: StaticString) -> Void {
     // strerror is documented to return "Unknown error: ..." for illegal value so it won't ever fail
-    assert(!isBlacklistedErrno(err), "blacklisted errno \(err) \(String(cString: strerror(err)!)) in \(function))")
+    precondition(!isBlacklistedErrno(err), "blacklisted errno \(err) \(String(cString: strerror(err)!)) in \(function))")
 }
 
 /* Sorry, we really try hard to not use underscored attributes. In this case however we seem to break the inlining threshold which makes a system call take twice the time, ie. we need this exception. */
@@ -125,7 +125,7 @@ internal func wrapSyscallMayBlock<T: FixedWidthInteger>(where function: StaticSt
             case EWOULDBLOCK:
                 return .wouldBlock(0)
             default:
-                assertIsNotBlacklistedErrno(err: err, where: function)
+                preconditionIsNotBlacklistedErrno(err: err, where: function)
                 throw IOError(errnoCode: err, function: function)
             }
 
@@ -145,7 +145,7 @@ internal func wrapSyscall<T: FixedWidthInteger>(where function: StaticString = #
             if err == EINTR {
                 continue
             }
-            assertIsNotBlacklistedErrno(err: err, where: function)
+            preconditionIsNotBlacklistedErrno(err: err, where: function)
             throw IOError(errnoCode: err, function: function)
         }
         return res
@@ -161,7 +161,7 @@ internal func wrapErrorIsNullReturnCall<T>(where function: StaticString = #funct
             if err == EINTR {
                 continue
             }
-            assertIsNotBlacklistedErrno(err: err, where: function)
+            preconditionIsNotBlacklistedErrno(err: err, where: function)
             throw IOError(errnoCode: err, function: function)
         }
         return res
@@ -244,7 +244,7 @@ internal enum Posix {
             //     - https://bugs.chromium.org/p/chromium/issues/detail?id=269623
             //     - https://lwn.net/Articles/576478/
             if err != EINTR {
-                assertIsNotBlacklistedErrno(err: err, where: #function)
+                preconditionIsNotBlacklistedErrno(err: err, where: #function)
                 throw IOError(errnoCode: err, function: "close")
             }
         }