bthportdetect.cpp

// Detect the proper COM ports for paired BT devices by name prefix
// pavel_a@fastmail.fm 12-feb-2019

#include "pch.h"
#define _CRT_SECURE_NO_WARNINGS 1
#include <vector>
#include <tuple>
#include <string>
#include <process.h>
#include <iostream>
using string = std::string;


const char * const sGUID_BTHdev = "{e0cbf06c-cd8b-4647-bb8a-263b43f0f974}";
const char * const sGUID_Port = "{4d36e978-e325-11ce-bfc1-08002be10318}";

#define dbgprintf printf

/// Find all matching BTH devices and their COM ports
/// Returns list of tuples (COMname, BTdevname)
std::vector<std::tuple<string, string > >
find_bth_ports(string BT_name_prefix)
{
    // Match BTH device with its COM port by "Contained ID".
    // The matching port is always the "outgoing" one. The other one is "incoming".
    // Parse output of
    // reg query HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\BTHENUM ...
    // No unicode. Assume a normal ENU system, no weird characters in the spew.
    const char *cmd =
        R"(reg.exe query HKLM\SYSTEM\CurrentControlSet\Enum\BTHENUM /s /t REG_SZ)";

    std::vector<std::tuple<string, string > > resv; // result
    std::vector<std::tuple<string, string > > BTH_devs;
    std::vector<std::tuple<string, string > > Ports;
    string curr_reg_base_subkey; // current subkey of either D or P type
    char state = 'N'; // N=Neutral, D=device, P=port, X=unknown
    string name, container_id, COM_port_name;
    char buf[300];

    auto get_val = [&buf]() {
        // Get the reg. value in the spew line as string:
        //search for REG_xxx<space*>, return all after it, can contain spaces
        char *p = strstr(buf, "REG_");
        if (!p) return string("");
        p = strchr(p, ' ');
        if (!p) return string("");
        while (*p == ' ') p++;
        return string(p);
       };

    FILE *p = _popen(cmd, "rt");
    if (!p) {
        dbgprintf("Error reading registry!");
        return resv;
    }

    while (fgets(buf, sizeof(buf)-1, p)) {
        buf[sizeof(buf) - 1] = 0;
        size_t sl = strlen(buf);
        //remove trailing \n
        if (buf[sl - 1] == '\n') {
            buf[--sl] = 0;
        }
        else {
            dbgprintf("Line too long\n");
        }
        // get rid of tabs
        for(;;) {
           char *q = strchr(buf, '\t');
           if (!q) break;
            *q = ' ';
        }

        if (0 == _strnicmp(buf, "End of...", 6)) {
            // Last line of the spew; fake location to flush the last found node.
            strcpy(buf, R"(HKEY_LOCAL_MACHINE\SYSTEM\end)");
        }

        if (0 == strncmp(buf, R"(HKEY_LOCAL_MACHINE\SYSTEM)", 24)) {
            // KEY/SUBKEY line:
            switch (state) {
            case 'N':
                // Keep the last one, go on.
                curr_reg_base_subkey = std::string(buf);
                continue;
            default:
                if (0 != strncmp(buf, curr_reg_base_subkey.c_str(), curr_reg_base_subkey.length()))
                {
                    // This subtree ended and new one starts. Save the current node
                    if (state == 'P') {
                        // printf("Port found... FN=%s PN=%s\n", name.c_str(), COM_port_name.c_str());
                        Ports.push_back({ container_id, COM_port_name });
                    }
                    else if (state == 'D') {
                        if (0 == name.compare(0, BT_name_prefix.length(), BT_name_prefix)) {
                            //printf("BTH dev found... FN=%s\n", name.c_str());
                            BTH_devs.push_back({ container_id, name });
                        }
                    }
                    // and start new (unknown type) node at this subkey:
                    state = 'N';
                    name = "";
                    curr_reg_base_subkey = buf;
                }
            }
            continue;
        } // subkey line

        if (!strstr(buf, " REG_")) {
            continue; // ignore other non-value lines
        }

        if (state == 'N') {
            state = 'X'; // unknown type
            //printf("Node start->\n%s\n", curr_reg_base_subkey.c_str());
        }
        // Look for interesting properties:
        if (strstr(buf, "ClassGUID")) {
            string cls = get_val();
            char const * pcls = cls.c_str();
            if (0 == _stricmp(pcls, sGUID_BTHdev)) {
                state = 'D';
            }
            else if (0 == _stricmp(pcls, sGUID_Port)) {
                state = 'P';
            }
            continue;
        }

        if (strstr(buf, "ContainerID")) {
            container_id = get_val();
            continue;
        }

        if (strstr(buf, "FriendlyName")) {
            name = get_val();
            continue;
        }

        if (strstr(buf, "PortName")) {
            COM_port_name = get_val();
            continue;
        }
    } // while

    fclose(p);

    //printf("Found ports: %d adapters: %d\n", Ports.size(), BTH_devs.size());
    // Now select all ports that have matching container id with any BTH device:
    for (auto &port : Ports) {
        string port_cid = std::get<0>(port);
        for (auto adp : BTH_devs) {
            if (port_cid == std::get<0>(adp)) {
                //printf("match\n");
                // Return tuple (COM_port_name, adapter_Name)
                resv.push_back({ std::get<1>(port), std::get<1>(adp) });
            }
        }

    }

    return resv;
}


int main(int argc, char *argv[])
{
    char const *adp_prefix = "RNBT";

    if (argc >= 2) {
        adp_prefix = argv[1];
    }

    std::cout << "Looking up COM ports for paired/bonded BTH adapters with names like " << adp_prefix << " ...\n";

    auto result = find_bth_ports(adp_prefix);

    if (!result.size()) {
        std::cout << "No COM ports found for BTH devices with prefix '" << adp_prefix << "'\n";
    }

    for (auto &res : result) {
        string COM_name, adapter_name;
        std::tie(COM_name, adapter_name) = res;
        std::cout << "COM port name: " << COM_name << " for adapter: " << adapter_name << std::endl;
    }

    return result.size() ? 0 : 1;
}

Detection of "outgoing" com port of RN42 bluetooth module. Formatted as standalone program.
Seems to work on win10 1803-09.