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112 lines
3.1 KiB
Markdown
112 lines
3.1 KiB
Markdown
+++
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title = "An intro to MiniUPNP"
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description = "An intro to the MiniUPNP C library."
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date = 2020-04-14
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[taxonomies]
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categories = ["c"]
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+++
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If you have a software that requires port forwarding, you may want to implement UPnP to make things easy for your end users.
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When I wanted to implement it, the first library I found was [MiniUPnP](http://miniupnp.free.fr/files/), sadly it doesn't have much documentation but a quick look at the header files and some examples on the internet I managed to make it work, here is how:
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First the required include directives we need:
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```c
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#include <miniupnpc/miniupnpc.h>
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#include <miniupnpc/upnpcommands.h>
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#include <miniupnpc/upnperrors.h>
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#include <stdio.h>
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```
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The first thing we need to do is discover the UPnP devices on the network, this is done using `upnpDiscover`:
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```c
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int main() {
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struct UPNPDev *upnp_dev = 0;
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int error = 0;
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upnp_dev = upnpDiscover(2000, NULL, NULL, 0, 0, 2, &error);
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if(error != 0) {
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printf("error discovering upnp devices: %s\n", strupnperror(error));
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return 1;
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}
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}
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```
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Then we need to retrieve the Internet Gateway Device we discovered:
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```c
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struct UPNPUrls upnp_urls;
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struct IGDdatas upnp_data;
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char aLanAddr[64];
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const char *pPort = "8000";
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// Retrieve a valid Internet Gateway Device
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int status = UPNP_GetValidIGD(
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upnp_dev,
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&upnp_urls,
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&upnp_data,
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aLanAddr,
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sizeof(aLanAddr)
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);
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printf("status=%d, lan_addr=%s\n", status, aLanAddr);
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```
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We check if we got the correct status and then map the port.
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We also declare the port we want to use, in this case I use the same number for the internal and external ports:
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```c
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if (status == 1)
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{
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printf("found valid IGD: %s\n", upnp_urls.controlURL);
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error =
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UPNP_AddPortMapping(
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upnp_urls.controlURL,
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upnp_data.first.servicetype,
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pPort, // external port
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pPort, // internal port
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aLanAddr, "My Application Name", "UDP",
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0, // remote host
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"0" // lease duration, recommended 0 as some NAT
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// implementations may not support another value
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);
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if (error)
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{
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printf("failed to map port\n");
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printf("error: %s\n", strupnperror(error));
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}
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else
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printf("successfully mapped port\n");
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}
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else
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printf("no valid IGD found\n");
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```
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Now the port is mapped, at this point you can open a socket bound to the internal port and external clients will be able to connect using the external port.
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Then we do some cleanup:
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*Note: The port here is the external one.*
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```c
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error = UPNP_DeletePortMapping(upnp_urls.controlURL,
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upnp_data.first.servicetype,
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pPort,
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"UDP",
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0);
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if (error != 0) {
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printf("port map deletion error: %s\n", strupnperror(error));
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}
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FreeUPNPUrls(&upnp_urls);
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freeUPNPDevlist(upnp_dev);
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return 0;
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```
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Complete source code: [gist](https://gist.github.com/edg-l/98241d2ef929661f0bb20136ebda16cd)
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Compiled using: `cc -lminiupnpc upnp.c` |