I just tried to disable the
"curl_easy_setopt(curl, CURLOPT_INFILESIZE_LARGE, file_info.st_size);"
and the fun is that it now works like a charm (See trace.log at the end).

(Just got Daniel's mail) : you're right, I did not pass curl_off_t
argument : there is not such a conversion in "ftpupload.c" example. Now,
that I have added it to my code, it works ok !

Maybe it's worth updating it in the docs/examples section.

Thanks a lot !

See the trace.log :
*********************************************************
== Info: About to connect() to localhost port 9021
== Info: Trying 127.0.0.1... == Info: connected
== Info: Connected to localhost (127.0.0.1) port 9021
<= Recv header, 53 bytes (0x35)
0000: 220 Msy-w00-3704 X2 WS_FTP Server 5.0.0 (544962717)
=> Send header, 16 bytes (0x10)
0000: USER anonymous
<= Recv header, 23 bytes (0x17)
0000: 331 Password required
=> Send header, 29 bytes (0x1d)
0000: PASS curl_by_daniel_at_haxx.se
<= Recv header, 20 bytes (0x14)
0000: 230 user logged in
== Info: We have successfully logged in
=> Send header, 5 bytes (0x5)
0000: PWD
<= Recv header, 30 bytes (0x1e)
0000: 257 "/" is current directory
== Info: Entry path is '/'
=> Send header, 9 bytes (0x9)
0000: CWD top
<= Recv header, 20 bytes (0x14)
0000: 250 CWD successful
=> Send header, 6 bytes (0x6)
0000: EPSV
<= Recv header, 21 bytes (0x15)
0000: 500 illegal command
=> Send header, 6 bytes (0x6)
0000: PASV
<= Recv header, 47 bytes (0x2f)
0000: 227 Entering Passive Mode (127,0,0,1,14,150).
== Info: Trying 127.0.0.1... == Info: connected
== Info: Connecting to 127.0.0.1 (127.0.0.1) port 3734
== Info: Connected the data stream with PASV!
=> Send header, 8 bytes (0x8)
0000: TYPE I
<= Recv header, 24 bytes (0x18)
0000: 200 Type set to IMAGE.
=> Send header, 18 bytes (0x12)
0000: STOR tmpfile.csp
<= Recv header, 52 bytes (0x34)
0000: 150 Opening BINARY data connection for tmpfile.csp
*** We read 1 bytes from file
=> Send data, 1 bytes (0x1)
0000: !
*** We read 0 bytes from file
<= Recv header, 23 bytes (0x17)
0000: 226 transfer complete
=> Send header, 23 bytes (0x17)
0000: RNFR /top/tmpfile.csp
<= Recv header, 23 bytes (0x17)
0000: 350 ok, send new name
=> Send header, 24 bytes (0x18)
0000: RNTO /top/testfile.txt
<= Recv header, 13 bytes (0xd)
0000: 250 renamed
== Info: Connection #0 to host localhost left intact
Curl_easy_perform returns 0=> Send header, 6 bytes (0x6)
0000: QUIT
<= Recv header, 14 bytes (0xe)
0000: 221 Good-Bye
== Info: Closing connection #0
*********************************************************
Received on 2005-01-20