Add nxt_file_chown()

This wraps chown(2) but takes the user/owner and group as strings.

It's a little long winded as it uses the thread safe versions of
getpwnam()/getgrname() which require a little more work.

This function will be used by the following commit that allows to set
the permissions of the Unix domain control socket.

We need to cast uid & gid to long in the call to nxt_thread_log_alert()
to appease clang-ast as it's adamant that uid/gid are unsigned ints, but
chown(2) takes -1 for these values to indicate don't change this item,
and it'd be nice to show them in the error message.

Note that getpwnam()/getgrname() don't define "not found" as an error as
per their man page

  The  formulation given above under "RETURN VALUE" is from POSIX.1-2001.
  It does not call "not found" an error, and hence does not specify  what
  value errno might have in this situation.  But that makes it impossible
  to  recognize  errors.   One  might argue that according to POSIX errno
  should be left unchanged if an entry is not found.  Experiments on var‐
  ious UNIX-like systems show that lots of different values occur in this
  situation: 0, ENOENT, EBADF, ESRCH, EWOULDBLOCK,  EPERM,  and  probably
  others.

Thus if we log an error from these functions we can end up with the
slightly humorous error message

  2024/02/12 15:15:12 [alert] 99404#99404 getpwnam_r("noddy", ...) failed (0: Success) (User not found) while creating listening socket on unix:/opt/unit/control.unit.sock

Reviewed-by: Zhidao Hong <z.hong@f5.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

src/nxt_file.c

@@ -325,6 +325,88 @@ nxt_file_set_access(nxt_file_name_t *name, nxt_file_access_t access)
 }
 
 
+nxt_int_t
+nxt_file_chown(nxt_file_name_t *name, const char *owner, const char *group)
+{
+    int    err;
+    char   *buf;
+    long   bufsize;
+    gid_t  gid = ~0;
+    uid_t  uid = ~0;
+
+    if (owner == NULL && group == NULL) {
+        return NXT_OK;
+    }
+
+    if (owner != NULL) {
+        struct passwd  pwd, *result;
+
+        bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
+        if (bufsize == -1) {
+            bufsize = 32768;
+        }
+
+        buf = nxt_malloc(bufsize);
+        if (buf == NULL) {
+            return NXT_ERROR;
+        }
+
+        err = getpwnam_r(owner, &pwd, buf, bufsize, &result);
+        if (result == NULL) {
+            nxt_thread_log_alert("getpwnam_r(\"%s\", ...) failed %E %s",
+                                 owner, nxt_errno,
+                                 err == 0 ? "(User not found)" : "");
+            goto out_err_free;
+        }
+
+        uid = pwd.pw_uid;
+
+        nxt_free(buf);
+    }
+
+    if (group != NULL) {
+        struct group  grp, *result;
+
+        bufsize = sysconf(_SC_GETGR_R_SIZE_MAX);
+        if (bufsize == -1) {
+            bufsize = 32768;
+        }
+
+        buf = nxt_malloc(bufsize);
+        if (buf == NULL) {
+            return NXT_ERROR;
+        }
+
+        err = getgrnam_r(group, &grp, buf, bufsize, &result);
+        if (result == NULL) {
+            nxt_thread_log_alert("getgrnam_r(\"%s\", ...) failed %E %s",
+                                 group, nxt_errno,
+                                 err == 0 ? "(Group not found)" : "");
+            goto out_err_free;
+        }
+
+        gid = grp.gr_gid;
+
+        nxt_free(buf);
+    }
+
+    if (nxt_fast_path(chown((const char *) name, uid, gid) == 0)) {
+        return NXT_OK;
+    }
+
+    nxt_thread_log_alert("chown(\"%FN\", %l, %l) failed %E", name,
+                         owner != NULL ? (long) uid : -1,
+                         group != NULL ? (long) gid : -1, nxt_errno);
+
+    return NXT_ERROR;
+
+out_err_free:
+    nxt_free(buf);
+
+    return NXT_ERROR;
+}
+
+
 nxt_int_t
 nxt_file_rename(nxt_file_name_t *old_name, nxt_file_name_t *new_name)
 {

src/nxt_file.h

@@ -177,6 +177,8 @@ NXT_EXPORT nxt_int_t nxt_file_info(nxt_file_t *file, nxt_file_info_t *fi);
 NXT_EXPORT nxt_int_t nxt_file_delete(nxt_file_name_t *name);
 NXT_EXPORT nxt_int_t nxt_file_set_access(nxt_file_name_t *name,
     nxt_file_access_t access);
+NXT_EXPORT nxt_int_t nxt_file_chown(nxt_file_name_t *name, const char *owner,
+    const char *group);
 NXT_EXPORT nxt_int_t nxt_file_rename(nxt_file_name_t *old_name,
     nxt_file_name_t *new_name);