[cli] update borderagent discover to allow network interface selection for mDNS binding

src/app/border_agent_functions_mock.cpp

@@ -43,9 +43,9 @@ void ClearBorderAgentFunctionsMock()
     gBorderAgentFunctionsMock = nullptr;
 }
 
-Error DiscoverBorderAgent(BorderAgentHandler aBorderAgentHandler, size_t aTimeout)
+Error DiscoverBorderAgent(BorderAgentHandler aBorderAgentHandler, size_t aTimeout, const std::string &aNetIf)
 {
-    return gBorderAgentFunctionsMock->DiscoverBorderAgent(aBorderAgentHandler, aTimeout);
+    return gBorderAgentFunctionsMock->DiscoverBorderAgent(aBorderAgentHandler, aTimeout, aNetIf);
 }
 
 } // namespace commissioner

src/app/border_agent_functions_mock.hpp

@@ -45,7 +45,7 @@ class BorderAgentFunctionsMock
 public:
     virtual ~BorderAgentFunctionsMock() = default;
 
-    MOCK_METHOD(Error, DiscoverBorderAgent, (BorderAgentHandler, size_t));
+    MOCK_METHOD(Error, DiscoverBorderAgent, (BorderAgentHandler, size_t, const std::string&));
 };
 
 void SetBorderAgentFunctionsMock(ot::commissioner::BorderAgentFunctionsMock *ptr);

src/app/br_discover.cpp

@@ -29,16 +29,19 @@
 #include "br_discover.hpp"
 
 #include <chrono>
+#include <sys/socket.h>
 #include <thread>
 
 #include "common/error_macros.hpp"
 #include "common/utils.hpp"
 
+#define SO_BINDTODEVICE 25
+
 namespace ot {
 
 namespace commissioner {
 
-Error DiscoverBorderAgent(BorderAgentHandler aBorderAgentHandler, size_t aTimeout)
+Error DiscoverBorderAgent(BorderAgentHandler aBorderAgentHandler, size_t aTimeout, const std::string &aNetIf)
 {
     static constexpr size_t             kDefaultBufferSize = 1024 * 16;
     static constexpr mdns_record_type_t kMdnsQueryType     = MDNS_RECORDTYPE_PTR;
@@ -52,6 +55,11 @@ Error DiscoverBorderAgent(BorderAgentHandler aBorderAgentHandler, size_t aTimeou
     int socket = mdns_socket_open_ipv4();
     VerifyOrExit(socket >= 0, error = ERROR_IO_ERROR("failed to open mDNS IPv4 socket"));
 
+    if (!aNetIf.empty() && setsockopt(socket, SOL_SOCKET, SO_BINDTODEVICE, &aNetIf[0], sizeof(aNetIf)) < 0)
+    {
+        ExitNow(error = ERROR_INVALID_ARGS("failed to bind network interface {}: {}", aNetIf, strerror(errno)));
+    }
+
     if (mdns_query_send(socket, kMdnsQueryType, kServiceName, strlen(kServiceName), buf, sizeof(buf)) != 0)
     {
         ExitNow(error = ERROR_IO_ERROR("failed to send mDNS query"));

src/app/br_discover.hpp

@@ -56,9 +56,11 @@ using BorderAgentHandler = std::function<void(const BorderAgent *aBorderAgent, c
  * @param[in] aBorderAgentHandler  The handler of a single Border Agent response.
  * @param[in] aTimeout             The time to wait for mDNS responses. Any
  *                                 response not within the interval is ignored.
+ * @param[in] aNetIf               The specified network interface for mDNS binding. Can be an empty string
+ *
  *
  */
-Error DiscoverBorderAgent(BorderAgentHandler aBorderAgentHandler, size_t aTimeout);
+Error DiscoverBorderAgent(BorderAgentHandler aBorderAgentHandler, size_t aTimeout, const std::string &aNetIf);
 
 } // namespace commissioner
 

src/app/cli/README.md

@@ -377,7 +377,7 @@ The command `borderagent` provides access to Border Agent information and scans
 ```shell
 > help borderagent
 usage:
-borderagent discover [<timeout-in-milliseconds>]
+borderagent discover [<timeout-in-milliseconds>] [<specified-network-interface>]
 borderagent get locator
 [done]
 >

src/app/cli/interpreter.cpp

@@ -1787,14 +1787,20 @@ Interpreter::Value Interpreter::ProcessBorderAgent(const Expression &aExpr)
 
     if (CaseInsensitiveEqual(aExpr[1], "discover"))
     {
-        uint64_t timeout = 4000;
+        uint64_t    timeout = 4000;
+        std::string netIf   = "";
 
         if (aExpr.size() >= 3)
         {
             SuccessOrExit(value = ParseInteger(timeout, aExpr[2]));
         }
 
-        SuccessOrExit(value = DiscoverBorderAgent(BorderAgentHandler, static_cast<size_t>(timeout)));
+        if (aExpr.size() == 4)
+        {
+            netIf = aExpr[3];
+        }
+
+        SuccessOrExit(value = DiscoverBorderAgent(BorderAgentHandler, static_cast<size_t>(timeout), netIf));
     }
     else if (CaseInsensitiveEqual(aExpr[1], "get"))
     {

src/app/cli/interpreter_test.cpp

@@ -1629,7 +1629,7 @@ TEST_F(InterpreterTestSuite, PC_BorderagentDiscover)
     BorderAgentFunctionsMock bafm;
     SetBorderAgentFunctionsMock(&bafm);
 
-    EXPECT_CALL(bafm, DiscoverBorderAgent(_, _)).WillOnce(Return(Error{}));
+    EXPECT_CALL(bafm, DiscoverBorderAgent(_, _, _)).WillOnce(Return(Error{}));
 
     Interpreter::Expression expr;
     Interpreter::Value      value;