[thread-host] add set country code api (#2550)

This commit adds the `SetCountryCode` method to `ThreadHost`.

The commit implements this method for `RcpHost`. The implementation
for NCP will be added later.

src/ncp/ncp_host.cpp

@@ -166,6 +166,14 @@ void NcpHost::SetThreadEnabled(bool aEnabled, const AsyncResultReceiver aReceive
     mTaskRunner.Post([aReceiver](void) { aReceiver(OT_ERROR_NOT_IMPLEMENTED, "Not implemented!"); });
 }
 
+void NcpHost::SetCountryCode(const std::string &aCountryCode, const AsyncResultReceiver &aReceiver)
+{
+    OT_UNUSED_VARIABLE(aCountryCode);
+
+    // TODO: Implement SetCountryCode under NCP mode.
+    mTaskRunner.Post([aReceiver](void) { aReceiver(OT_ERROR_NOT_IMPLEMENTED, "Not implemented!"); });
+}
+
 void NcpHost::Process(const MainloopContext &aMainloop)
 {
     mSpinelDriver.Process(&aMainloop);

src/ncp/ncp_host.hpp

@@ -91,6 +91,7 @@ class NcpHost : public MainloopProcessor, public ThreadHost, public NcpNetworkPr
     void ScheduleMigration(const otOperationalDatasetTlvs &aPendingOpDatasetTlvs,
                            const AsyncResultReceiver       aReceiver) override;
     void SetThreadEnabled(bool aEnabled, const AsyncResultReceiver aReceiver) override;
+    void SetCountryCode(const std::string &aCountryCode, const AsyncResultReceiver &aReceiver) override;
     CoprocessorType GetCoprocessorType(void) override { return OT_COPROCESSOR_NCP; }
     const char     *GetCoprocessorVersion(void) override;
     const char     *GetInterfaceName(void) const override { return mConfig.mInterfaceName; }

src/ncp/rcp_host.cpp

@@ -480,6 +480,26 @@ void RcpHost::DisableThreadAfterDetach(void)
     SafeInvokeAndClear(mSetThreadEnabledReceiver, error, errorMsg);
 }
 
+void RcpHost::SetCountryCode(const std::string &aCountryCode, const AsyncResultReceiver &aReceiver)
+{
+    static constexpr int kCountryCodeLength = 2;
+    otError              error              = OT_ERROR_NONE;
+    std::string          errorMsg;
+    uint16_t             countryCode;
+
+    VerifyOrExit((aCountryCode.length() == kCountryCodeLength) && isalpha(aCountryCode[0]) && isalpha(aCountryCode[1]),
+                 error = OT_ERROR_INVALID_ARGS, errorMsg = "The country code is invalid");
+
+    otbrLogInfo("Set country code: %c%c", aCountryCode[0], aCountryCode[1]);
+    VerifyOrExit(mInstance != nullptr, error = OT_ERROR_INVALID_STATE, errorMsg = "OT is not initialized");
+
+    countryCode = static_cast<uint16_t>((aCountryCode[0] << 8) | aCountryCode[1]);
+    SuccessOrExit(error = otLinkSetRegion(mInstance, countryCode), errorMsg = "Failed to set the country code");
+
+exit:
+    mTaskRunner.Post([aReceiver, error, errorMsg](void) { aReceiver(error, errorMsg); });
+}
+
 /*
  * Provide, if required an "otPlatLog()" function
  */

src/ncp/rcp_host.hpp

@@ -209,6 +209,7 @@ class RcpHost : public MainloopProcessor, public ThreadHost, public OtNetworkPro
     void ScheduleMigration(const otOperationalDatasetTlvs &aPendingOpDatasetTlvs,
                            const AsyncResultReceiver       aReceiver) override;
     void SetThreadEnabled(bool aEnabled, const AsyncResultReceiver aReceiver) override;
+    void SetCountryCode(const std::string &aCountryCode, const AsyncResultReceiver &aReceiver) override;
 
     CoprocessorType GetCoprocessorType(void) override
     {

src/ncp/thread_host.hpp

@@ -157,6 +157,18 @@ class ThreadHost : virtual public NetworkProperties
      */
     virtual void SetThreadEnabled(bool aEnabled, const AsyncResultReceiver aReceiver) = 0;
 
+    /**
+     * This method sets the country code.
+     *
+     * The country code refers to the 2-alpha code defined in ISO-3166.
+     *
+     * 1. If @p aCountryCode isn't valid, @p aReceiver will be invoked with error OT_ERROR_INVALID_ARGS.
+     * 2. If the host hasn't been initialized, @p aReceiver will be invoked with error OT_ERROR_INVALID_STATE.
+     *
+     * @param[in] aCountryCode  The country code.
+     */
+    virtual void SetCountryCode(const std::string &aCountryCode, const AsyncResultReceiver &aReceiver) = 0;
+
     /**
      * Returns the co-processor type.
      */