The option «--dump-header» does not work correctly.

[u20221022]

I did this

Start PowerShell 7.3.0 under the MS Windows and execute commands:
PS >

.\curl.exe --progress-bar `
    --remote-name `
    --dump-header "Header32.txt" `
    "https://curl.se/windows/dl-7.86.0_2/curl-7.86.0_2-win32-mingw.zip" `
--next `
    --remote-name `
    --dump-header "Header64.txt" `
    "https://curl.se/windows/dl-7.86.0_2/curl-7.86.0_2-win64-mingw.zip" `
--next `
    --remote-name `
    --dump-header "Header96.txt" `
    "https://curl.se/windows/dl-7.86.0_2/curl-7.86.0_2-win64a-mingw.zip"

32, 64, 96 | %{(Get-Content -LiteralPath Header$_.txt).Count}

################################################################################ 100,0%
################################################################################ 100,0%
################################################################################ 100,0%
22
22
22

Repeat all above:
22
44
44

Repeat again:
22
66
66

And so on. All but the first header dump has incorrect content.

I expected the following

All header dumps contain an equal number of lines (22). Always.

curl/libcurl version

Build: 7.86.0_2
[curl -V output]
curl 7.86.0 (x86_64-w64-mingw32) libcurl/7.86.0 OpenSSL/3.0.7 (Schannel) zlib/1.2.13 brotli/1.0.9 zstd/1.5.2 WinIDN libssh2/1.10.0 nghttp2/1.51.0 ngtcp2/0.11.0 nghttp3/0.7.1 libgsasl/2.2.0
Release-Date: 2022-10-26
Protocols: dict file ftp ftps gopher gophers http https imap imaps ldap ldaps mqtt pop3 pop3s rtsp scp sftp smb smbs smtp smtps telnet tftp ws wss
Features: alt-svc AsynchDNS brotli gsasl HSTS HTTP2 HTTP3 HTTPS-proxy IDN IPv6 Kerberos Largefile libz MultiSSL NTLM SPNEGO SSL SSPI threadsafe TLS-SRP UnixSockets zstd

operating system

MS Windows 10 last version with all updates

[gvanem]

All header dumps contain an equal number of lines (22). Always.

I get 21 lines in all headers when using another shell. A Powershell issue?

[u20221022]

Repeat without manual deleting of dumps. Read more carefully: repeat some times. Repeat. Is the PowerShell clearing the file content? PowerShell does start external program and send options. Nothing more.

Console of Cmd.exe:

curl.exe --progress-bar --remote-name --dump-header "Header32.txt" -y 20 -Y 1024 "https://curl.se/windows/dl-7.86.0_2/curl-7.86.0_2-win32-mingw.zip" --next --remote-name --dump-header "Header64.txt" -y 20 -Y 1024 "https://curl.se/windows/dl-7.86.0_2/curl-7.86.0_2-win64-mingw.zip" --next --remote-name --dump-header "Header96.txt" -y 20 -Y 1024 "https://curl.se/windows/dl-7.86.0_2/curl-7.86.0_2-win64a-mingw.zip"
Dir Header??.txt

10.12.2022 14:25 802 Header32.txt
10.12.2022 14:26 4 818 Header64.txt
10.12.2022 14:27 4 807 Header96.txt

[u20221022]

I get 21 lines in all headers when using another shell. A Powershell issue?

Using another arithmetics. An arithmetics issue? Empty line as end of dump you can not calculate? 1+20+1=22. The cURL does report, that num_headers=20.

[bagder]

This line (brought by #4762) looks wrong:

curl/src/tool_operate.c

Line 972 in 99f72c0

newfile = fopen(config->headerfile, per->prev == NULL?"wb":"ab");

It assumes that the same file is used repeatedly and thus appends in all but the first fopen() calls.

[jay]

Yes this one is a bug. @emilengler

[cvengler]

See #4753

[cvengler]

I looked at the regarding PRs and issues from 3 years ago.

#4753 (comment)
#10074 (comment)

@jay: If I follow your logic correctly, I see a contradiction in these two comments. Could you elaborate?

[u20221022]

If you add, then to everyone. Why not add to the first?

[bagder]

@emilengler there's a difference:

This should put the headers from both transfers into the same file:

curl -D file $URL1 $URL2

This should (probably) not append the headers to the files if they exist before the command line is invoked:

curl -D file1 $URL1 --next -D file2 $URL2