ftpd: allow implicit overwrite if user has delete perms

the spec doesn't say what you're supposed to do if the target filename of an upload is already taken, but this seems to be the most common behavior on other ftp servers, and is required by wondows 2000 (otherwise it'll freak out and issue a delete and then not actually upload it, nice)

new option `--ftp-no-ow` restores old default behavior of rejecting upload if target filename exists

copyparty/__main__.py

@@ -1034,6 +1034,7 @@ def add_ftp(ap):
     ap2.add_argument("--ftpv", action="store_true", help="verbose")
     ap2.add_argument("--ftp4", action="store_true", help="only listen on IPv4")
     ap2.add_argument("--ftp-ipa", metavar="CIDR", type=u, default="", help="only accept connections from IP-addresses inside \033[33mCIDR\033[0m; specify [\033[32many\033[0m] to disable inheriting \033[33m--ipa\033[0m. Examples: [\033[32mlan\033[0m] or [\033[32m10.89.0.0/16, 192.168.33.0/24\033[0m]")
+    ap2.add_argument("--ftp-no-ow", action="store_true", help="if target file exists, reject upload instead of overwrite")
     ap2.add_argument("--ftp-wt", metavar="SEC", type=int, default=7, help="grace period for resuming interrupted uploads (any client can write to any file last-modified more recently than \033[33mSEC\033[0m seconds ago)")
     ap2.add_argument("--ftp-nat", metavar="ADDR", type=u, help="the NAT address to use for passive connections")
     ap2.add_argument("--ftp-pr", metavar="P-P", type=u, help="the range of TCP ports to use for passive connections, for example \033[32m12000-13000")

copyparty/ftpd.py

@@ -19,6 +19,7 @@ from .__init__ import PY2, TYPE_CHECKING
 from .authsrv import VFS
 from .bos import bos
 from .util import (
+    VF_CAREFUL,
     Daemon,
     ODict,
     Pebkac,
@@ -30,6 +31,7 @@ from .util import (
     runhook,
     sanitize_fn,
     vjoin,
+    wunlink,
 )
 
 if TYPE_CHECKING:
@@ -37,7 +39,7 @@ if TYPE_CHECKING:
 
 if True:  # pylint: disable=using-constant-test
     import typing
-    from typing import Any, Optional
+    from typing import Any, Optional, Union
 
 
 class FSE(FilesystemError):
@@ -139,6 +141,9 @@ class FtpFs(AbstractedFS):
         self.listdirinfo = self.listdir
         self.chdir(".")
 
+    def log(self, msg: str, c: Union[int, str] = 0) -> None:
+        self.hub.log("ftpd", msg, c)
+
     def v2a(
         self,
         vpath: str,
@@ -207,17 +212,37 @@ class FtpFs(AbstractedFS):
         w = "w" in mode or "a" in mode or "+" in mode
 
         ap = self.rv2a(filename, r, w)[0]
+        self.validpath(ap)
         if w:
             try:
                 st = bos.stat(ap)
                 td = time.time() - st.st_mtime
+                need_unlink = True
             except:
+                need_unlink = False
                 td = 0
 
-            if td < -1 or td > self.args.ftp_wt:
+        if w and need_unlink:
-                raise FSE("Cannot open existing file for writing")
+            if td >= -1 and td <= self.args.ftp_wt:
+                # within permitted timeframe; unlink and accept
+                do_it = True
+            elif self.args.no_del or self.args.ftp_no_ow:
+                # file too old, or overwrite not allowed; reject
+                do_it = False
+            else:
+                # allow overwrite if user has delete permission
+                # (avoids win2000 freaking out and deleting the server copy without uploading its own)
+                try:
+                    self.rv2a(filename, False, True, False, True)
+                    do_it = True
+                except:
+                    do_it = False
+
+            if not do_it:
+                raise FSE("File already exists")
+
+            wunlink(self.log, ap, VF_CAREFUL)
 
-        self.validpath(ap)
         return open(fsenc(ap), mode, self.args.iobuf)
 
     def chdir(self, path: str) -> None: