diff --git a/adb/adb.cpp b/adb/adb.cpp
index ad85184f..b09e853 100644
--- a/adb/adb.cpp
+++ b/adb/adb.cpp
@@ -838,10 +838,10 @@
             }
         }
 
-        const char* err;
-        transport = acquire_one_transport(CS_ANY, ttype, serial, &err);
+        std::string error_msg;
+        transport = acquire_one_transport(CS_ANY, ttype, serial, &error_msg);
         if (!transport) {
-            sendfailmsg(reply_fd, err);
+            sendfailmsg(reply_fd, error_msg.c_str());
             return 1;
         }
 
@@ -910,14 +910,14 @@
             serial = service;
         }
 
-        const char* error_string = "unknown failure";
-        transport = acquire_one_transport(CS_ANY, type, serial, &error_string);
+        std::string error_msg = "unknown failure";
+        transport = acquire_one_transport(CS_ANY, type, serial, &error_msg);
 
         if (transport) {
             s->transport = transport;
             adb_write(reply_fd, "OKAY", 4);
         } else {
-            sendfailmsg(reply_fd, error_string);
+            sendfailmsg(reply_fd, error_msg.c_str());
         }
         return 1;
     }
@@ -975,7 +975,7 @@
     if(!strncmp(service,"get-serialno",strlen("get-serialno"))) {
         const char *out = "unknown";
         transport = acquire_one_transport(CS_ANY, ttype, serial, NULL);
-       if (transport && transport->serial) {
+        if (transport && transport->serial) {
             out = transport->serial;
         }
         send_msg_with_okay(reply_fd, out, strlen(out));
@@ -984,7 +984,7 @@
     if(!strncmp(service,"get-devpath",strlen("get-devpath"))) {
         const char *out = "unknown";
         transport = acquire_one_transport(CS_ANY, ttype, serial, NULL);
-       if (transport && transport->devpath) {
+        if (transport && transport->devpath) {
             out = transport->devpath;
         }
         send_msg_with_okay(reply_fd, out, strlen(out));
diff --git a/adb/services.cpp b/adb/services.cpp
index 12eb406..e58100f 100644
--- a/adb/services.cpp
+++ b/adb/services.cpp
@@ -559,12 +559,12 @@
 
     D("wait_for_state %d\n", sinfo->state);
 
-    const char* err = "unknown error";
-    atransport *t = acquire_one_transport(sinfo->state, sinfo->transport, sinfo->serial, &err);
-    if(t != 0) {
+    std::string error_msg = "unknown error";
+    atransport* t = acquire_one_transport(sinfo->state, sinfo->transport, sinfo->serial, &error_msg);
+    if (t != 0) {
         WriteFdExactly(fd, "OKAY", 4);
     } else {
-        sendfailmsg(fd, err);
+        sendfailmsg(fd, error_msg.c_str());
     }
 
     if (sinfo->serial)
diff --git a/adb/sockets.cpp b/adb/sockets.cpp
index 48d02d6..e52d6b1 100644
--- a/adb/sockets.cpp
+++ b/adb/sockets.cpp
@@ -827,12 +827,11 @@
     }
 #else /* !ADB_HOST */
     if (s->transport == NULL) {
-        const char* error_string = "unknown failure";
-        s->transport = acquire_one_transport (CS_ANY,
-                kTransportAny, NULL, &error_string);
+        std::string error_msg = "unknown failure";
+        s->transport = acquire_one_transport(CS_ANY, kTransportAny, NULL, &error_msg);
 
         if (s->transport == NULL) {
-            sendfailmsg(s->peer->fd, error_string);
+            sendfailmsg(s->peer->fd, error_msg.c_str());
             goto fail;
         }
     }
diff --git a/adb/transport.cpp b/adb/transport.cpp
index 4b9eeeb..f3e6461 100644
--- a/adb/transport.cpp
+++ b/adb/transport.cpp
@@ -800,22 +800,20 @@
     return !*to_test;
 }
 
-atransport *acquire_one_transport(int state, transport_type ttype,
-                                  const char* serial, const char** error_out)
+atransport* acquire_one_transport(int state, transport_type ttype,
+                                  const char* serial, std::string* error_out)
 {
     atransport *t;
     atransport *result = NULL;
     int ambiguous = 0;
 
 retry:
-    if (error_out)
-        *error_out = "device not found";
+    if (error_out) *error_out = "device not found";
 
     adb_mutex_lock(&transport_lock);
     for (t = transport_list.next; t != &transport_list; t = t->next) {
         if (t->connection_state == CS_NOPERM) {
-        if (error_out)
-            *error_out = "insufficient permissions for device";
+            if (error_out) *error_out = "insufficient permissions for device";
             continue;
         }
 
@@ -827,8 +825,7 @@
                 qual_match(serial, "model:", t->model, true) ||
                 qual_match(serial, "device:", t->device, false)) {
                 if (result) {
-                    if (error_out)
-                        *error_out = "more than one device";
+                    if (error_out) *error_out = "more than one device";
                     ambiguous = 1;
                     result = NULL;
                     break;
@@ -838,8 +835,7 @@
         } else {
             if (ttype == kTransportUsb && t->type == kTransportUsb) {
                 if (result) {
-                    if (error_out)
-                        *error_out = "more than one device";
+                    if (error_out) *error_out = "more than one device";
                     ambiguous = 1;
                     result = NULL;
                     break;
@@ -847,8 +843,7 @@
                 result = t;
             } else if (ttype == kTransportLocal && t->type == kTransportLocal) {
                 if (result) {
-                    if (error_out)
-                        *error_out = "more than one emulator";
+                    if (error_out) *error_out = "more than one emulator";
                     ambiguous = 1;
                     result = NULL;
                     break;
@@ -856,8 +851,7 @@
                 result = t;
             } else if (ttype == kTransportAny) {
                 if (result) {
-                    if (error_out)
-                        *error_out = "more than one device and emulator";
+                    if (error_out) *error_out = "more than one device and emulator";
                     ambiguous = 1;
                     result = NULL;
                     break;
@@ -870,29 +864,33 @@
 
     if (result) {
         if (result->connection_state == CS_UNAUTHORIZED) {
-            if (error_out)
-                *error_out = "device unauthorized. Please check the confirmation dialog on your device.";
+            if (error_out) {
+                *error_out = "device unauthorized.\n";
+                char* ADB_VENDOR_KEYS = getenv("ADB_VENDOR_KEYS");
+                *error_out += "This adbd's $ADB_VENDOR_KEYS is ";
+                *error_out += ADB_VENDOR_KEYS ? ADB_VENDOR_KEYS : "not set";
+                *error_out += "; try 'adb kill-server' if that seems wrong.\n";
+                *error_out += "Otherwise check for a confirmation dialog on your device.";
+            }
             result = NULL;
         }
 
-         /* offline devices are ignored -- they are either being born or dying */
+        /* offline devices are ignored -- they are either being born or dying */
         if (result && result->connection_state == CS_OFFLINE) {
-            if (error_out)
-                *error_out = "device offline";
+            if (error_out) *error_out = "device offline";
             result = NULL;
         }
-         /* check for required connection state */
+
+        /* check for required connection state */
         if (result && state != CS_ANY && result->connection_state != state) {
-            if (error_out)
-                *error_out = "invalid device state";
+            if (error_out) *error_out = "invalid device state";
             result = NULL;
         }
     }
 
     if (result) {
         /* found one that we can take */
-        if (error_out)
-            *error_out = NULL;
+        if (error_out) *error_out = "success";
     } else if (state != CS_ANY && (serial || !ambiguous)) {
         adb_sleep_ms(1000);
         goto retry;
diff --git a/adb/transport.h b/adb/transport.h
index 36a0e40..a2077e8 100644
--- a/adb/transport.h
+++ b/adb/transport.h
@@ -17,14 +17,11 @@
 #ifndef __TRANSPORT_H
 #define __TRANSPORT_H
 
-#include <stdbool.h>
 #include <sys/types.h>
 
-#include "adb.h"
+#include <string>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+#include "adb.h"
 
 #if ADB_TRACE
 void dump_hex(const unsigned char* ptr, size_t  len);
@@ -37,7 +34,7 @@
  * If no suitable transport is found, error is set.
  */
 atransport* acquire_one_transport(int state, transport_type ttype,
-                                  const char* serial, const char** error_out);
+                                  const char* serial, std::string* error_out);
 void add_transport_disconnect(atransport* t, adisconnect* dis);
 void remove_transport_disconnect(atransport* t, adisconnect* dis);
 void kick_transport(atransport* t);
@@ -74,8 +71,4 @@
 
 asocket* create_device_tracker(void);
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif   /* __TRANSPORT_H */