--libcurl fails to reproduce binary data from --data-binary input that contains null bytes

[smuehlst]

I did this

I came across this when I tried to convert a curl command line tool invocation into a corresponding libcurl program. The use case was to retrieve a time-stamp from a time-stamp server. The attached file is only for demonstration purposes and does not contain an actual time-stamp request. The file contains null bytes and is six bytes large:

E:\Users\stm\Documents\GitHub\curl [master ≡ +4 ~0 -0 !]> wsl xxd bindata.gif
00000000: 6100 0000 0062

curl command line tool invocation:

E:\Users\stm\Documents\GitHub\curl [master ≡ +4 ~0 -0 !]> .\build\src\Debug\curl.exe --libcurl - -s -H "Content-Type: application/timestamp-query" --data-binary "@bindata.gif" -o response.tsr http://zeitstempel.dfn.de
/********* Sample code generated by the curl command line tool **********
 * All curl_easy_setopt() options are documented at:
 * https://curl.haxx.se/libcurl/c/curl_easy_setopt.html
 ************************************************************************/
...
  curl_easy_setopt(hnd, CURLOPT_POSTFIELDS, "a");
  curl_easy_setopt(hnd, CURLOPT_POSTFIELDSIZE_LARGE, (curl_off_t)6);
...

Note that the value supplied for CURLOPT_POSTFIELDSIZE_LARGE does not match the length of the data supplied via CURLOPT_POSTFIELDS.

I expected the following

I expected that the string passed via CURLOPT_POSTFIELDS contains the full data from the input file, e.g.:

curl_easy_setopt(hnd, CURLOPT_POSTFIELDS, "a\000\000\000\000b");

curl/libcurl version

Curl built from commit 7920be9.

E:\Users\stm\Documents\GitHub\curl [master ≡ +4 ~0 -0 !]> .\build\src\Debug\curl.exe -V
curl 7.73.0-DEV (Windows) libcurl/7.73.0-DEV
Release-Date: [unreleased]
Protocols: dict file ftp gopher http imap ldap mqtt pop3 rtsp smb smtp telnet tftp
Features: AsynchDNS IPv6 Largefile NTLM

operating system

Windows 10 Version 2004, but also reproduced on Linux.