From 159f51b12b91ec046fcdd02133d57b7ba771b3a0 Mon Sep 17 00:00:00 2001
From: ed <s@ocv.me>
Date: Fri, 25 Oct 2024 22:05:59 +0000
Subject: [PATCH] http 304: if-range, backdating

add support for the `If-Range` header which is generally used to
prevent resuming a partial download after the source file on the
server has been modified, by returning HTTP 200 instead of a 206

also simplifies `If-Modified-Since` and `If-Range` handling;
previously this was a spec-compliant lexical comparison,
now it's a basic string-comparison instead. The server will now
reply 200 also when the server mtime is older than the client's.
This is technically not according to spec, but should be safer,
as it allows backdating timestamps without purging client cache
---
 copyparty/httpcli.py | 53 ++++++++++++++++++++++++--------------------
 1 file changed, 29 insertions(+), 24 deletions(-)

diff --git a/copyparty/httpcli.py b/copyparty/httpcli.py
index 4a8b97d3..5d58ead1 100644
--- a/copyparty/httpcli.py
+++ b/copyparty/httpcli.py
@@ -2,7 +2,6 @@
 from __future__ import print_function, unicode_literals
 
 import argparse  # typechk
-import calendar
 import copy
 import errno
 import gzip
@@ -19,7 +18,6 @@ import threading  # typechk
 import time
 import uuid
 from datetime import datetime
-from email.utils import parsedate
 from operator import itemgetter
 
 import jinja2  # typechk
@@ -3409,26 +3407,26 @@ class HttpCli(object):
         self.reply(response.encode("utf-8"))
         return True
 
-    def _chk_lastmod(self, file_ts: int) -> tuple[str, bool]:
+    def _chk_lastmod(self, file_ts: int) -> tuple[str, bool, bool]:
+        # ret: lastmod, do_send, can_range
         file_lastmod = formatdate(file_ts)
-        cli_lastmod = self.headers.get("if-modified-since")
-        if cli_lastmod:
-            try:
-                # some browser append "; length=573"
-                cli_lastmod = cli_lastmod.split(";")[0].strip()
-                cli_dt = parsedate(cli_lastmod)
-                assert cli_dt  # !rm
-                cli_ts = calendar.timegm(cli_dt)
-                return file_lastmod, int(file_ts) > int(cli_ts)
-            except Exception as ex:
-                self.log(
-                    "lastmod {}\nremote: [{}]\n local: [{}]".format(
-                        repr(ex), cli_lastmod, file_lastmod
-                    )
-                )
-                return file_lastmod, file_lastmod != cli_lastmod
+        c_ifrange = self.headers.get("if-range")
+        c_lastmod = self.headers.get("if-modified-since")
 
-        return file_lastmod, True
+        if not c_ifrange and not c_lastmod:
+            return file_lastmod, True, True
+
+        if c_ifrange and c_ifrange != file_lastmod:
+            t = "sending entire file due to If-Range; cli(%s) file(%s)"
+            self.log(t % (c_ifrange, file_lastmod), 6)
+            return file_lastmod, True, False
+
+        do_send = c_lastmod != file_lastmod
+        if do_send and c_lastmod:
+            t = "sending body due to If-Modified-Since cli(%s) file(%s)"
+            self.log(t % (c_lastmod, file_lastmod), 6)
+
+        return file_lastmod, do_send, True
 
     def _use_dirkey(self, vn: VFS, ap: str) -> bool:
         if self.can_read or not self.can_get:
@@ -3578,7 +3576,7 @@ class HttpCli(object):
         # if-modified
 
         if file_ts > 0:
-            file_lastmod, do_send = self._chk_lastmod(int(file_ts))
+            file_lastmod, do_send, _ = self._chk_lastmod(int(file_ts))
             self.out_headers["Last-Modified"] = file_lastmod
             if not do_send:
                 status = 304
@@ -3740,7 +3738,7 @@ class HttpCli(object):
         #
         # if-modified
 
-        file_lastmod, do_send = self._chk_lastmod(int(file_ts))
+        file_lastmod, do_send, can_range = self._chk_lastmod(int(file_ts))
         self.out_headers["Last-Modified"] = file_lastmod
         if not do_send:
             status = 304
@@ -3784,7 +3782,14 @@ class HttpCli(object):
 
         # let's not support 206 with compression
         # and multirange / multipart is also not-impl (mostly because calculating contentlength is a pain)
-        if do_send and not is_compressed and hrange and file_sz and "," not in hrange:
+        if (
+            do_send
+            and not is_compressed
+            and hrange
+            and can_range
+            and file_sz
+            and "," not in hrange
+        ):
             try:
                 if not hrange.lower().startswith("bytes"):
                     raise Exception()
@@ -4255,7 +4260,7 @@ class HttpCli(object):
             sz_md = len(lead) + len(fullfile)
 
         file_ts = int(max(ts_md, self.E.t0))
-        file_lastmod, do_send = self._chk_lastmod(file_ts)
+        file_lastmod, do_send, _ = self._chk_lastmod(file_ts)
         self.out_headers["Last-Modified"] = file_lastmod
         self.out_headers.update(NO_CACHE)
         status = 200 if do_send else 304