Another alternative. This uses only HTTP and requires no special software, except the server. Elegant, IMHO. Extremely robust in fact.

https://github.com/nwtgck/go-piping-server

After starting the server, a few options.

Method 1: Visit https://127.0.0.1:8080 in a Javascript-enabled browser and fill out HTML form

Method 2: Visit https://127.0.0.1:8080/noscript in any browser and fill out HTML form

Method 3: Use any TCP or HTTP client. For example here is a quick and dirty shell script

       #!/bin/sh 
       test $1||exec echo usage: $0 something file
       test $2||exec echo usage: $0 something file
       x=$(stat -c %s $2)
       {
       printf 'POST /'$1' HTTP/1.1\r\n'
       printf 'Host: 127.0.0.1\r\n'
       printf 'Content-Type: multipart/form-data; boundary=\"yxxxxzxxxzxxxzzxyxzx\"\r\n'
       printf 'Content-Length: '$x'\r\n'
       printf 'Connection: close\r\n'
       printf '\r\n'
       cat $2
       echo ---yxxxxzxxxzxxxzzxyxzx
       } \
       |nc -vvn 127.1 8080
     
       laptop> 1.sh whatever 1.pdf
       phone> curl http://127.0.0.1:8080/whatever > 1.pdf 
       laptop> 1.sh 1.pdf 1.pdf
       On phone, type into browser: https://127.0.0.1:8080/1.pdf
       This file is saved as 1.pdf
       YMMV

There is also a Rust version.