[adb] Don't copy features set on each get()

The features are already cached in a static and don't change.
Let's return the cached set instead of copying it every time.

Bug: 150183149
Test: manual
Change-Id: Ifdca852cc3b32e09e50ea4771f7878987c46cce8
diff --git a/adb/client/adb_client.cpp b/adb/client/adb_client.cpp
index c859d75..0ad0465 100644
--- a/adb/client/adb_client.cpp
+++ b/adb/client/adb_client.cpp
@@ -37,6 +37,7 @@
 #include <vector>
 
 #include <android-base/file.h>
+#include <android-base/no_destructor.h>
 #include <android-base/stringprintf.h>
 #include <android-base/strings.h>
 #include <android-base/thread_annotations.h>
@@ -415,18 +416,14 @@
     return android::base::StringPrintf("%s:%s", prefix, command);
 }
 
-bool adb_get_feature_set(FeatureSet* feature_set, std::string* error) {
-    static FeatureSet* features = nullptr;
-    if (!features) {
+const FeatureSet& adb_get_feature_set() {
+    static const android::base::NoDestructor<FeatureSet> features([] {
         std::string result;
-        if (adb_query(format_host_command("features"), &result, error)) {
-            features = new FeatureSet(StringToFeatureSet(result));
+        if (!adb_query(format_host_command("features"), &result, &result)) {
+            fprintf(stderr, "failed to get feature set: %s\n", result.c_str());
+            return FeatureSet{};
         }
-    }
-    if (features) {
-        *feature_set = *features;
-        return true;
-    }
-    feature_set->clear();
-    return false;
+        return StringToFeatureSet(result);
+    }());
+    return *features;
 }
diff --git a/adb/client/adb_client.h b/adb/client/adb_client.h
index 1c6cde7..bf0be40 100644
--- a/adb/client/adb_client.h
+++ b/adb/client/adb_client.h
@@ -76,7 +76,7 @@
 std::string format_host_command(const char* _Nonnull command);
 
 // Get the feature set of the current preferred transport.
-bool adb_get_feature_set(FeatureSet* _Nonnull feature_set, std::string* _Nonnull error);
+const FeatureSet& adb_get_feature_set();
 
 #if defined(__linux__)
 // Get the path of a file containing the path to the server executable, if the socket spec set via
diff --git a/adb/client/adb_install.cpp b/adb/client/adb_install.cpp
index da3154e..3810cc8 100644
--- a/adb/client/adb_install.cpp
+++ b/adb/client/adb_install.cpp
@@ -57,10 +57,8 @@
 }
 
 static bool can_use_feature(const char* feature) {
-    FeatureSet features;
-    std::string error;
-    if (!adb_get_feature_set(&features, &error)) {
-        fprintf(stderr, "error: %s\n", error.c_str());
+    auto&& features = adb_get_feature_set();
+    if (features.empty()) {
         return false;
     }
     return CanUseFeature(features, feature);
diff --git a/adb/client/commandline.cpp b/adb/client/commandline.cpp
index ceb21d5..6a7493f 100644
--- a/adb/client/commandline.cpp
+++ b/adb/client/commandline.cpp
@@ -672,10 +672,8 @@
 }
 
 static int adb_shell(int argc, const char** argv) {
-    FeatureSet features;
-    std::string error_message;
-    if (!adb_get_feature_set(&features, &error_message)) {
-        fprintf(stderr, "error: %s\n", error_message.c_str());
+    auto&& features = adb_get_feature_set();
+    if (features.empty()) {
         return 1;
     }
 
@@ -779,13 +777,10 @@
 }
 
 static int adb_abb(int argc, const char** argv) {
-    FeatureSet features;
-    std::string error_message;
-    if (!adb_get_feature_set(&features, &error_message)) {
-        fprintf(stderr, "error: %s\n", error_message.c_str());
+    auto&& features = adb_get_feature_set();
+    if (features.empty()) {
         return 1;
     }
-
     if (!CanUseFeature(features, kFeatureAbb)) {
         error_exit("abb is not supported by the device");
     }
@@ -1164,9 +1159,8 @@
         // Use shell protocol if it's supported and the caller doesn't explicitly
         // disable it.
         if (!disable_shell_protocol) {
-            FeatureSet features;
-            std::string error;
-            if (adb_get_feature_set(&features, &error)) {
+            auto&& features = adb_get_feature_set();
+            if (!features.empty()) {
                 use_shell_protocol = CanUseFeature(features, kFeatureShell2);
             } else {
                 // Device was unreachable.
@@ -1816,10 +1810,8 @@
         }
         return adb_connect_command(android::base::StringPrintf("tcpip:%d", port));
     } else if (!strcmp(argv[0], "remount")) {
-        FeatureSet features;
-        std::string error;
-        if (!adb_get_feature_set(&features, &error)) {
-            fprintf(stderr, "error: %s\n", error.c_str());
+        auto&& features = adb_get_feature_set();
+        if (features.empty()) {
             return 1;
         }
 
@@ -2042,10 +2034,8 @@
     } else if (!strcmp(argv[0], "track-jdwp")) {
         return adb_connect_command("track-jdwp");
     } else if (!strcmp(argv[0], "track-app")) {
-        FeatureSet features;
-        std::string error;
-        if (!adb_get_feature_set(&features, &error)) {
-            fprintf(stderr, "error: %s\n", error.c_str());
+        auto&& features = adb_get_feature_set();
+        if (features.empty()) {
             return 1;
         }
         if (!CanUseFeature(features, kFeatureTrackApp)) {
@@ -2074,10 +2064,8 @@
         return 0;
     } else if (!strcmp(argv[0], "features")) {
         // Only list the features common to both the adb client and the device.
-        FeatureSet features;
-        std::string error;
-        if (!adb_get_feature_set(&features, &error)) {
-            fprintf(stderr, "error: %s\n", error.c_str());
+        auto&& features = adb_get_feature_set();
+        if (features.empty()) {
             return 1;
         }
 
diff --git a/adb/client/file_sync_client.cpp b/adb/client/file_sync_client.cpp
index 6816734..f2c673a 100644
--- a/adb/client/file_sync_client.cpp
+++ b/adb/client/file_sync_client.cpp
@@ -225,13 +225,14 @@
 
 class SyncConnection {
   public:
-    SyncConnection() : acknowledgement_buffer_(sizeof(sync_status) + SYNC_DATA_MAX) {
+    SyncConnection()
+        : acknowledgement_buffer_(sizeof(sync_status) + SYNC_DATA_MAX),
+          features_(adb_get_feature_set()) {
         acknowledgement_buffer_.resize(0);
         max = SYNC_DATA_MAX; // TODO: decide at runtime.
 
-        std::string error;
-        if (!adb_get_feature_set(&features_, &error)) {
-            Error("failed to get feature set: %s", error.c_str());
+        if (features_.empty()) {
+            Error("failed to get feature set");
         } else {
             have_stat_v2_ = CanUseFeature(features_, kFeatureStat2);
             have_ls_v2_ = CanUseFeature(features_, kFeatureLs2);
@@ -239,6 +240,7 @@
             have_sendrecv_v2_brotli_ = CanUseFeature(features_, kFeatureSendRecv2Brotli);
             have_sendrecv_v2_lz4_ = CanUseFeature(features_, kFeatureSendRecv2LZ4);
             have_sendrecv_v2_dry_run_send_ = CanUseFeature(features_, kFeatureSendRecv2DryRunSend);
+            std::string error;
             fd.reset(adb_connect("sync:", &error));
             if (fd < 0) {
                 Error("connect failed: %s", error.c_str());
@@ -919,7 +921,7 @@
   private:
     std::deque<std::pair<std::string, std::string>> deferred_acknowledgements_;
     Block acknowledgement_buffer_;
-    FeatureSet features_;
+    const FeatureSet& features_;
     bool have_stat_v2_;
     bool have_ls_v2_;
     bool have_sendrecv_v2_;