wrapper: implement xopen()

A common usage pattern of open() is to check if it was successful, and
die() if it was not:

int fd = open(path, O_WRONLY | O_CREAT, 0777);
if (fd < 0)
die_errno(_("Could not open '%s' for writing."), path);

Implement a wrapper function xopen() that does the above so that we can
save a few lines of code, and make the die() messages consistent.

Helped-by: Torsten Bögershausen <tboegi@web.de>
Helped-by: Jeff King <peff@peff.net>
Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/git-compat-util.h b/git-compat-util.h
index c6d391f86490b94e4df667d64d54323e1915c477..e168dfd68b57be2d44951e1d5f8c8e8526cfef7c 100644 (file)
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -717,6 +717,7 @@ extern void *xrealloc(void *ptr, size_t size);
 extern void *xcalloc(size_t nmemb, size_t size);
 extern void *xmmap(void *start, size_t length, int prot, int flags, int fd, off_t offset);
 extern void *xmmap_gently(void *start, size_t length, int prot, int flags, int fd, off_t offset);
+extern int xopen(const char *path, int flags, ...);
 extern ssize_t xread(int fd, void *buf, size_t len);
 extern ssize_t xwrite(int fd, const void *buf, size_t len);
 extern ssize_t xpread(int fd, void *buf, size_t len, off_t offset);

diff --git a/wrapper.c b/wrapper.c
index ff49807948f3c406fe73511cec4ef4e2b2df186a..0a4502d232344e1af9b7df67cd29a9f51a6d3181 100644 (file)
--- a/wrapper.c
+++ b/wrapper.c
@@ -189,6 +189,41 @@ void *xcalloc(size_t nmemb, size_t size)
 # endif
 #endif
 
+/**
+ * xopen() is the same as open(), but it die()s if the open() fails.
+ */
+int xopen(const char *path, int oflag, ...)
+{
+       mode_t mode = 0;
+       va_list ap;
+
+       /*
+        * va_arg() will have undefined behavior if the specified type is not
+        * compatible with the argument type. Since integers are promoted to
+        * ints, we fetch the next argument as an int, and then cast it to a
+        * mode_t to avoid undefined behavior.
+        */
+       va_start(ap, oflag);
+       if (oflag & O_CREAT)
+               mode = va_arg(ap, int);
+       va_end(ap);
+
+       for (;;) {
+               int fd = open(path, oflag, mode);
+               if (fd >= 0)
+                       return fd;
+               if (errno == EINTR)
+                       continue;
+
+               if ((oflag & O_RDWR) == O_RDWR)
+                       die_errno(_("could not open '%s' for reading and writing"), path);
+               else if ((oflag & O_WRONLY) == O_WRONLY)
+                       die_errno(_("could not open '%s' for writing"), path);
+               else
+                       die_errno(_("could not open '%s' for reading"), path);
+       }
+}
+
 /*
  * xread() is the same a read(), but it automatically restarts read()
  * operations with a recoverable error (EAGAIN and EINTR). xread()