diff --git a/copyparty/szip.py b/copyparty/szip.py
new file mode 100644
index 00000000..9c7a5e05
--- /dev/null
+++ b/copyparty/szip.py
@@ -0,0 +1,239 @@
+import os
+import time
+import zlib
+import struct
+from datetime import datetime
+
+from .util import fsenc
+
+
+def dostime2unix(buf):
+    t, d = struct.unpack("<HH", buf)
+
+    ts = (t & 0x1F) * 2
+    tm = (t >> 5) & 0x3F
+    th = t >> 11
+
+    dd = d & 0x1F
+    dm = (d >> 5) & 0xF
+    dy = (d >> 9) + 1980
+
+    tt = (dy, dm, dd, th, tm, ts)
+    tf = "{:04d}-{:02d}-{:02d} {:02d}:{:02d}:{:02d}"
+    iso = tf.format(*tt)
+
+    dt = datetime.strptime(iso, "%Y-%m-%d %H:%M:%S")
+    return int(dt.timestamp())
+
+
+def unixtime2dos(ts):
+    tt = time.gmtime(ts)
+    dy, dm, dd, th, tm, ts = list(tt)[:6]
+
+    bd = ((dy - 1980) << 9) + (dm << 5) + dd
+    bt = (th << 11) + (tm << 5) + ts // 2
+    return struct.pack("<HH", bt, bd)
+
+
+def gen_fdesc(sz, crc32, z64):
+    ret = b"\x50\x4b\x07\x08"
+    fmt = "<LQQ" if z64 else "<LLL"
+    ret += struct.pack(fmt, crc32, sz, sz)
+    return ret
+
+
+def gen_hdr(h_pos, fn, sz, lastmod, utf8, crc32, pre_crc):
+    """
+    does regular file headers
+    and the central directory meme if h_pos is set
+    (h_pos = absolute position of the regular header)
+    """
+
+    # appnote 4.5 / zip 3.0 (2008) / unzip 6.0 (2009) says to add z64
+    # extinfo for values which exceed H, but that becomes an off-by-one
+    # (can't tell if it was clamped or exactly maxval), make it obvious
+    z64 = sz >= 0xFFFFFFFF
+    z64v = [sz, sz] if z64 else []
+    if h_pos and h_pos >= 0xFFFFFFFF:
+        # central, also consider ptr to original header
+        z64v.append(h_pos)
+
+    # confusingly this doesn't bump if h_pos
+    req_ver = b"\x2d\x00" if z64 else b"\x0a\x00"
+
+    if crc32:
+        crc32 = struct.pack("<L", crc32)
+    else:
+        crc32 = b"\x00" * 4
+
+    if h_pos is None:
+        # 4b magic, 2b min-ver
+        ret = b"\x50\x4b\x03\x04" + req_ver
+    else:
+        # 4b magic, 2b spec-ver, 2b min-ver
+        ret = b"\x50\x4b\x01\x02\x1e\x03" + req_ver
+
+    ret += b"\x00" if pre_crc else b"\x08"  # streaming
+    ret += b"\x08" if utf8 else b"\x00"  # appnote 6.3.2 (2007)
+
+    # 2b compression, 4b time, 4b crc
+    ret += b"\x00\x00" + unixtime2dos(lastmod) + crc32
+
+    # spec says to put zeros when !crc if bit3 (streaming)
+    # however infozip does actual sz and it even works on winxp
+    # (same reasning for z64 extradata later)
+    vsz = 0xFFFFFFFF if z64 else sz
+    ret += struct.pack("<LL", vsz, vsz)
+
+    bfn = fn.encode("utf-8" if utf8 else "cp437", "replace")
+
+    z64_len = len(z64v) * 8 + 4 if z64v else 0
+    ret += struct.pack("<HH", len(bfn), z64_len)
+
+    if h_pos is not None:
+        # 2b comment, 2b diskno, 2b internal.attr,
+        # 4b external.attr (infozip-linux: 0000(a481|ff81)) idk
+        ret += b"\x00" * 10
+
+        # 4b local-header-ofs
+        ret += struct.pack("<L", min(h_pos, 0xFFFFFFFF))
+
+    ret += bfn
+
+    if z64v:
+        ret += struct.pack("<HH" + "Q" * len(z64v), 1, len(z64v) * 8, *z64v)
+
+    return ret
+
+
+def gen_ecdr(items, cdir_pos, cdir_end):
+    """
+    summary of all file headers,
+    usually the zipfile footer unless something clamps
+    """
+
+    ret = b"\x50\x4b\x05\x06"
+
+    # 2b ndisk, 2b disk0
+    ret += b"\x00" * 4
+
+    cdir_sz = cdir_end - cdir_pos
+
+    nitems = min(0xFFFF, len(items))
+    csz = min(0xFFFFFFFF, cdir_sz)
+    cpos = min(0xFFFFFFFF, cdir_pos)
+
+    need_64 = nitems == 0xFFFF or 0xFFFFFFFF in [csz, cpos]
+
+    # 2b tnfiles, 2b dnfiles, 4b dir sz, 4b dir pos
+    ret += struct.pack("<HHLL", nitems, nitems, csz, cpos)
+
+    # 2b comment length
+    ret += b"\x00\x00"
+
+    return [ret, need_64]
+
+
+def gen_ecdr64(items, cdir_pos, cdir_end):
+    """
+    z64 end of central directory
+    added when numfiles or a headerptr clamps
+    """
+
+    ret = b"\x50\x4b\x06\x06"
+
+    # 8b own length from hereon
+    ret += b"\x2c" + b"\x00" * 7
+
+    # 2b spec-ver, 2b min-ver
+    ret += b"\x1e\x03\x2d\x00"
+
+    # 4b ndisk, 4b disk0
+    ret += b"\x00" * 8
+
+    # 8b tnfiles, 8b dnfiles, 8b dir sz, 8b dir pos
+    cdir_sz = cdir_end - cdir_pos
+    ret += struct.pack("<QQQQ", len(items), len(items), cdir_sz, cdir_pos)
+
+    return ret
+
+
+def gen_ecdr64_loc(ecdr64_pos):
+    """
+    z64 end of central directory locator
+    points to ecdr64
+    why
+    """
+
+    ret = b"\x50\x4b\x06\x07"
+
+    # 4b cdisk, 8b start of ecdr64, 4b ndisks
+    ret += struct.pack("<LQL", 0, ecdr64_pos, 1)
+
+    return ret
+
+
+class StreamZip(object):
+    def __init__(self, top, fgen, utf8, pre_crc):
+        self.top = top
+        self.fgen = fgen
+        self.utf8 = utf8
+        self.pre_crc = pre_crc
+
+        self.pos = 0
+        self.items = []
+
+    def _ct(self, buf):
+        self.pos += len(buf)
+        return buf
+
+    def gen(self):
+        for f in self.fgen:
+            src = f["a"]
+            name = f["n"]
+
+            st = os.stat(fsenc(src))
+            sz = st.st_size
+            ts = st.st_mtime + 1
+
+            h_pos = self.pos
+            buf = gen_hdr(None, name, sz, ts, self.utf8, None, self.pre_crc)
+            yield self._ct(buf)
+
+            crc = 0
+            with open(src, "rb") as f:
+                while True:
+                    buf = f.read(32768)
+                    if not buf:
+                        break
+
+                    crc = zlib.crc32(buf, crc)
+                    yield self._ct(buf)
+
+            crc &= 0xFFFFFFFF
+
+            self.items.append([name, sz, ts, crc, h_pos])
+
+            z64 = sz >= 4 * 1024 * 1024 * 1024
+
+            if z64 or not self.pre_crc:
+                buf = gen_fdesc(sz, crc, z64)
+                yield self._ct(buf)
+
+        cdir_pos = self.pos
+        for name, sz, ts, crc, h_pos in self.items:
+            buf = gen_hdr(h_pos, name, sz, ts, self.utf8, crc, self.pre_crc)
+            yield self._ct(buf)
+        cdir_end = self.pos
+
+        _, need_64 = gen_ecdr(self.items, cdir_pos, cdir_end)
+        if need_64:
+            ecdir64_pos = self.pos
+            buf = gen_ecdr64(self.items, cdir_pos, cdir_end)
+            yield self._ct(buf)
+
+            buf = gen_ecdr64_loc(ecdir64_pos)
+            yield self._ct(buf)
+
+        ecdr, _ = gen_ecdr(self.items, cdir_pos, cdir_end)
+        yield self._ct(ecdr)