Go

When app is started from command line, config.json is loaded and values are read from it.
Ports and Targets are processed from the above file. Targets are processed in a way that a new struct targetServer is initialised which implements the Target interface.
The Target interface has necessary methods needed for querying remote address information.
To listen into every port from the config file, a new goroutine is created to setup the proxy server.
Setup method basically resolves the local address i.e our port and starts listening to it while checking for any connections.
To check for new connections it is run in an infinite loop and the proxy server is ran in a different goroutine.
Loadbalancing is done using a simple roundrobin algorithm. It checks for active host and if the host is not present, it moves on to a different host i.e remote address.
After active remote address is found, a new TCP connection is made via proxy.
Bidirectional copy of data is done, so that client and server can both see the response sent from the remote address.

eBPF

BPF kernel code resides in bpf/bpf_proxy_dispatch.c
There are 2 maps defined proxy_ports of type BPF_MAP_TYPE_HASH and proxy_sock of type BPF_MAP_TYPE_SOCKMAP.
proxy_ports map store information about the ports that are inside the config.json
proxy_sock store the information about the fd of the proxifie's listerner socket.
SEC contains that code that will be loaded into the memory.
bpf_prog is the program name that get's attached to the kernel.
port number is found by ctx->local_port and if the port is not inside the proxy_ports map the socket connection is passed forward.
sk contains the information about proxy_sock map's 0'th element which is our fd of proxifie's listerner socket.
bpf_sk_assign assgns the ctx to our socket sk
Package tracer has all the information how to load eBPF program.
Once the proxify application is run by sudo ./proxify -b. Userspace side loads the bpf ELF file bpf_proxy_dispatch.o. The function NewTracer inside pkg/tracer/tracer.go helps in achieving that.
After that userspace loads both the maps, initialise and populate them with respective values and creates a link between network ns and eBPF program. This is done by RegisterIface function.