diff --git a/adb/adb_client.cpp b/adb/adb_client.cpp
index bbc4dc7..db9b710 100644
--- a/adb/adb_client.cpp
+++ b/adb/adb_client.cpp
@@ -295,3 +295,27 @@
     adb_close(fd);
     return true;
 }
+
+std::string format_host_command(const char* command, TransportType type, const char* serial) {
+    if (serial) {
+        return android::base::StringPrintf("host-serial:%s:%s", serial, command);
+    }
+
+    const char* prefix = "host";
+    if (type == kTransportUsb) {
+        prefix = "host-usb";
+    } else if (type == kTransportLocal) {
+        prefix = "host-local";
+    }
+    return android::base::StringPrintf("%s:%s", prefix, command);
+}
+
+bool adb_get_feature_set(FeatureSet* feature_set, std::string* error) {
+    std::string result;
+    if (adb_query(format_host_command("features", __adb_transport, __adb_serial), &result, error)) {
+        *feature_set = StringToFeatureSet(result);
+        return true;
+    }
+    feature_set->clear();
+    return false;
+}
diff --git a/adb/adb_client.h b/adb/adb_client.h
index 5de0638..a9df4d7 100644
--- a/adb/adb_client.h
+++ b/adb/adb_client.h
@@ -18,13 +18,14 @@
 #define _ADB_CLIENT_H_
 
 #include "adb.h"
+#include "transport.h"
 
 #include <string>
 
 // Connect to adb, connect to the named service, and return a valid fd for
 // interacting with that service upon success or a negative number on failure.
-int adb_connect(const std::string& service, std::string* error);
-int _adb_connect(const std::string& service, std::string* error);
+int adb_connect(const std::string& service, std::string* _Nonnull error);
+int _adb_connect(const std::string& service, std::string* _Nonnull error);
 
 // Connect to adb, connect to the named service, returns true if the connection
 // succeeded AND the service returned OKAY. Outputs any returned error otherwise.
@@ -32,24 +33,33 @@
 
 // Connects to the named adb service and fills 'result' with the response.
 // Returns true on success; returns false and fills 'error' on failure.
-bool adb_query(const std::string& service, std::string* result, std::string* error);
+bool adb_query(const std::string& service, std::string* _Nonnull result,
+               std::string* _Nonnull error);
 
 // Set the preferred transport to connect to.
-void adb_set_transport(TransportType type, const char* serial);
+void adb_set_transport(TransportType type, const char* _Nullable serial);
 
 // Set TCP specifics of the transport to use.
 void adb_set_tcp_specifics(int server_port);
 
 // Set TCP Hostname of the transport to use.
-void adb_set_tcp_name(const char* hostname);
+void adb_set_tcp_name(const char* _Nullable hostname);
 
 // Send commands to the current emulator instance. Will fail if there is not
 // exactly one emulator connected (or if you use -s <serial> with a <serial>
 // that does not designate an emulator).
-int adb_send_emulator_command(int argc, const char** argv, const char* serial);
+int adb_send_emulator_command(int argc, const char* _Nonnull* _Nonnull argv,
+                              const char* _Nullable serial);
 
 // Reads a standard adb status response (OKAY|FAIL) and returns true in the
 // event of OKAY, false in the event of FAIL or protocol error.
-bool adb_status(int fd, std::string* error);
+bool adb_status(int fd, std::string* _Nonnull error);
+
+// Create a host command corresponding to selected transport type/serial.
+std::string format_host_command(const char* _Nonnull command, TransportType type,
+                                const char* _Nullable serial);
+
+// Get the feature set of the current preferred transport.
+bool adb_get_feature_set(FeatureSet* _Nonnull feature_set, std::string* _Nonnull error);
 
 #endif
diff --git a/adb/commandline.cpp b/adb/commandline.cpp
index 5679711..85ab4d1 100644
--- a/adb/commandline.cpp
+++ b/adb/commandline.cpp
@@ -428,49 +428,6 @@
     free(buf);
 }
 
-static std::string format_host_command(const char* command,
-                                       TransportType type, const char* serial) {
-    if (serial) {
-        return android::base::StringPrintf("host-serial:%s:%s", serial, command);
-    }
-
-    const char* prefix = "host";
-    if (type == kTransportUsb) {
-        prefix = "host-usb";
-    } else if (type == kTransportLocal) {
-        prefix = "host-local";
-    }
-    return android::base::StringPrintf("%s:%s", prefix, command);
-}
-
-namespace {
-
-enum class ErrorAction {
-    kPrintToStderr,
-    kDoNotPrint
-};
-
-}  // namespace
-
-// Fills |feature_set| using the target indicated by |transport_type| and |serial|. Returns false
-// and clears |feature_set| on failure. |error_action| selects whether to also print error messages
-// on failure.
-static bool GetFeatureSet(TransportType transport_type, const char* serial, FeatureSet* feature_set,
-                          ErrorAction error_action) {
-    std::string result, error;
-
-    if (adb_query(format_host_command("features", transport_type, serial), &result, &error)) {
-        *feature_set = StringToFeatureSet(result);
-        return true;
-    }
-
-    if (error_action == ErrorAction::kPrintToStderr) {
-        fprintf(stderr, "error: %s\n", error.c_str());
-    }
-    feature_set->clear();
-    return false;
-}
-
 static void send_window_size_change(int fd, std::unique_ptr<ShellProtocol>& shell) {
     // Old devices can't handle window size changes.
     if (shell == nullptr) return;
@@ -738,10 +695,12 @@
     return exit_code;
 }
 
-static int adb_shell(int argc, const char** argv,
-                     TransportType transport_type, const char* serial) {
+static int adb_shell(int argc, const char** argv) {
     FeatureSet features;
-    if (!GetFeatureSet(transport_type, serial, &features, ErrorAction::kPrintToStderr)) {
+    std::string error;
+
+    if (!adb_get_feature_set(&features, &error)) {
+        fprintf(stderr, "error: %s\n", error.c_str());
         return 1;
     }
 
@@ -1129,7 +1088,8 @@
         // Use shell protocol if it's supported and the caller doesn't explicitly disable it.
         if (!disable_shell_protocol) {
             FeatureSet features;
-            if (GetFeatureSet(transport_type, serial, &features, ErrorAction::kDoNotPrint)) {
+            std::string error;
+            if (adb_get_feature_set(&features, &error)) {
                 use_shell_protocol = CanUseFeature(features, kFeatureShell2);
             } else {
                 // Device was unreachable.
@@ -1608,7 +1568,7 @@
         return adb_send_emulator_command(argc, argv, serial);
     }
     else if (!strcmp(argv[0], "shell")) {
-        return adb_shell(argc, argv, transport_type, serial);
+        return adb_shell(argc, argv);
     }
     else if (!strcmp(argv[0], "exec-in") || !strcmp(argv[0], "exec-out")) {
         int exec_in = !strcmp(argv[0], "exec-in");
@@ -1764,7 +1724,9 @@
     else if (!strcmp(argv[0], "install")) {
         if (argc < 2) return usage();
         FeatureSet features;
-        if (!GetFeatureSet(transport_type, serial, &features, ErrorAction::kPrintToStderr)) {
+        std::string error;
+        if (!adb_get_feature_set(&features, &error)) {
+            fprintf(stderr, "error: %s\n", error.c_str());
             return 1;
         }
 
@@ -1780,7 +1742,9 @@
     else if (!strcmp(argv[0], "uninstall")) {
         if (argc < 2) return usage();
         FeatureSet features;
-        if (!GetFeatureSet(transport_type, serial, &features, ErrorAction::kPrintToStderr)) {
+        std::string error;
+        if (!adb_get_feature_set(&features, &error)) {
+            fprintf(stderr, "error: %s\n", error.c_str());
             return 1;
         }
 
@@ -1883,7 +1847,9 @@
     else if (!strcmp(argv[0], "features")) {
         // Only list the features common to both the adb client and the device.
         FeatureSet features;
-        if (!GetFeatureSet(transport_type, serial, &features, ErrorAction::kPrintToStderr)) {
+        std::string error;
+        if (!adb_get_feature_set(&features, &error)) {
+            fprintf(stderr, "error: %s\n", error.c_str());
             return 1;
         }
 
diff --git a/adb/sysdeps.h b/adb/sysdeps.h
index d89f0de..5942592 100644
--- a/adb/sysdeps.h
+++ b/adb/sysdeps.h
@@ -61,6 +61,10 @@
 
 #ifdef _WIN32
 
+// Clang-only nullability specifiers
+#define _Nonnull
+#define _Nullable
+
 #include <ctype.h>
 #include <direct.h>
 #include <dirent.h>