client/adb_client.cpp - SHIFTPHONES/android_packages_modules_adb - Gitiles

 /*
  * Copyright (C) 2015 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #define TRACE_TAG ADB

 #include "sysdeps.h"
 #include "adb_client.h"

 #include <errno.h>
 #include <inttypes.h>
 #include <limits.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/types.h>

 #include <condition_variable>
 #include <mutex>
 #include <optional>
 #include <string>
 #include <thread>
 #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>
 #include <cutils/sockets.h>

 #include "adb_io.h"
 #include "adb_utils.h"
 #include "socket_spec.h"
 #include "sysdeps/chrono.h"

 static TransportType __adb_transport = kTransportAny;
 static const char* __adb_serial = nullptr;
 static TransportId __adb_transport_id = 0;

 static const char* __adb_server_socket_spec;

 void adb_set_transport(TransportType type, const char* serial, TransportId transport_id) {
     __adb_transport = type;
     __adb_serial = serial;
     __adb_transport_id = transport_id;
 }

 void adb_get_transport(TransportType* type, const char** serial, TransportId* transport_id) {
     if (type) *type = __adb_transport;
     if (serial) *serial = __adb_serial;
     if (transport_id) *transport_id = __adb_transport_id;
 }

 void adb_set_socket_spec(const char* socket_spec) {
     if (__adb_server_socket_spec) {
         LOG(FATAL) << "attempted to reinitialize adb_server_socket_spec " << socket_spec << " (was " << __adb_server_socket_spec << ")";
     }
     __adb_server_socket_spec = socket_spec;
 }

 static std::optional<TransportId> switch_socket_transport(int fd, std::string* error) {
     TransportId result;
     bool read_transport = true;

     std::string service;
     if (__adb_transport_id) {
         read_transport = false;
         service += "host:transport-id:";
         service += std::to_string(__adb_transport_id);
         result = __adb_transport_id;
     } else if (__adb_serial) {
         service += "host:tport:serial:";
         service += __adb_serial;
     } else {
         const char* transport_type = "???";
         switch (__adb_transport) {
           case kTransportUsb:
               transport_type = "usb";
               break;
           case kTransportLocal:
               transport_type = "local";
               break;
           case kTransportAny:
               transport_type = "any";
               break;
           case kTransportHost:
             // no switch necessary
             return 0;
         }
         service += "host:tport:";
         service += transport_type;
     }

     if (!SendProtocolString(fd, service)) {
         *error = perror_str("write failure during connection");
         return std::nullopt;
     }

     LOG(DEBUG) << "Switch transport in progress: " << service;

     if (!adb_status(fd, error)) {
         D("Switch transport failed: %s", error->c_str());
         return std::nullopt;
     }

     if (read_transport) {
         if (!ReadFdExactly(fd, &result, sizeof(result))) {
             *error = "failed to read transport id from server";
             return std::nullopt;
         }
     }

     D("Switch transport success");
     return result;
 }

 bool adb_status(borrowed_fd fd, std::string* error) {
     char buf[5];
     if (!ReadFdExactly(fd, buf, 4)) {
         *error = perror_str("protocol fault (couldn't read status)");
         return false;
     }

     if (!memcmp(buf, "OKAY", 4)) {
         return true;
     }

     if (memcmp(buf, "FAIL", 4)) {
         *error = android::base::StringPrintf("protocol fault (status %02x %02x %02x %02x?!)",
                                              buf[0], buf[1], buf[2], buf[3]);
         return false;
     }

     ReadProtocolString(fd, error, error);
     return false;
 }

 static int _adb_connect(std::string_view service, TransportId* transport, std::string* error,
                         bool force_switch = false) {
     LOG(DEBUG) << "_adb_connect: " << service;
     if (service.empty() || service.size() > MAX_PAYLOAD) {
         *error = android::base::StringPrintf("bad service name length (%zd)", service.size());
         return -1;
     }

     std::string reason;
     unique_fd fd;
     if (!socket_spec_connect(&fd, __adb_server_socket_spec, nullptr, nullptr, &reason)) {
         *error = android::base::StringPrintf("cannot connect to daemon at %s: %s",
                                              __adb_server_socket_spec, reason.c_str());
         return -2;
     }

     if (!service.starts_with("host") || force_switch) {
         std::optional<TransportId> transport_result = switch_socket_transport(fd.get(), error);
         if (!transport_result) {
             return -1;
         }

         if (transport) {
             *transport = *transport_result;
         }
     }

     if (!SendProtocolString(fd.get(), service)) {
         *error = perror_str("write failure during connection");
         return -1;
     }

     if (!adb_status(fd.get(), error)) {
         return -1;
     }

     D("_adb_connect: return fd %d", fd.get());
     return fd.release();
 }

 bool adb_kill_server() {
     D("adb_kill_server");
     std::string reason;
     unique_fd fd;
     if (!socket_spec_connect(&fd, __adb_server_socket_spec, nullptr, nullptr, &reason)) {
         fprintf(stderr, "cannot connect to daemon at %s: %s\n", __adb_server_socket_spec,
                 reason.c_str());
         return true;
     }

     if (!SendProtocolString(fd.get(), "host:kill")) {
         fprintf(stderr, "error: write failure during connection: %s\n", strerror(errno));
         return false;
     }

     char buf[4];
     if (!ReadFdExactly(fd.get(), buf, 4)) {
         fprintf(stderr, "error: failed to read response from server\n");
         return false;
     }

     if (memcmp(buf, "OKAY", 4) == 0) {
         // Nothing to do.
     } else if (memcmp(buf, "FAIL", 4) == 0) {
         std::string output, error;
         if (!ReadProtocolString(fd.get(), &output, &error)) {
             fprintf(stderr, "error: %s\n", error.c_str());
             return false;
         }

         fprintf(stderr, "error: %s\n", output.c_str());
         return false;
     }

     // Now that no more data is expected, wait for socket orderly shutdown or error, indicating
     // server death.
     ReadOrderlyShutdown(fd.get());
     return true;
 }

 int adb_connect(std::string_view service, std::string* error) {
     return adb_connect(nullptr, service, error);
 }

 #if defined(__linux__)
 std::optional<std::string> adb_get_server_executable_path() {
     int port;
     std::string error;
     if (!parse_tcp_socket_spec(__adb_server_socket_spec, nullptr, &port, nullptr, &error)) {
         return {};
     }

     return adb_get_android_dir_path() + OS_PATH_SEPARATOR + "adb." + std::to_string(port);
 }
 #endif

 static bool __adb_check_server_version(std::string* error) {
     unique_fd fd(_adb_connect("host:version", nullptr, error));

     bool local = is_local_socket_spec(__adb_server_socket_spec);
     if (fd == -2 && !local) {
         fprintf(stderr, "* cannot start server on remote host\n");
         // error is the original network connection error
         return false;
     } else if (fd == -2) {
         fprintf(stderr, "* daemon not running; starting now at %s\n", __adb_server_socket_spec);
     start_server:
         if (launch_server(__adb_server_socket_spec)) {
             fprintf(stderr, "* failed to start daemon\n");
             // launch_server() has already printed detailed error info, so just
             // return a generic error string about the overall adb_connect()
             // that the caller requested.
             *error = "cannot connect to daemon";
             return false;
         } else {
             fprintf(stderr, "* daemon started successfully\n");
         }
         // The server will wait until it detects all of its connected devices before acking.
         // Fall through to _adb_connect.
     } else {
         // If a server is already running, check its version matches.
         int version = 0;

         // If we have a file descriptor, then parse version result.
         if (fd >= 0) {
             std::string version_string;
             if (!ReadProtocolString(fd, &version_string, error)) {
                 return false;
             }

             ReadOrderlyShutdown(fd);

             if (sscanf(&version_string[0], "%04x", &version) != 1) {
                 *error = android::base::StringPrintf("cannot parse version string: %s",
                                                      version_string.c_str());
                 return false;
             }
         } else {
             // If fd is -1 check for "unknown host service" which would
             // indicate a version of adb that does not support the
             // version command, in which case we should fall-through to kill it.
             if (*error != "unknown host service") {
                 return false;
             }
         }

         if (version != ADB_SERVER_VERSION) {
 #if defined(__linux__)
             if (version > ADB_SERVER_VERSION && local) {
                 // Try to re-exec the existing adb server's binary.
                 constexpr const char* adb_reexeced = "adb (re-execed)";
                 if (strcmp(adb_reexeced, *__adb_argv) != 0) {
                     __adb_argv[0] = adb_reexeced;
                     std::optional<std::string> server_path_path = adb_get_server_executable_path();
                     std::string server_path;
                     if (server_path_path &&
                         android::base::ReadFileToString(*server_path_path, &server_path)) {
                         if (execve(server_path.c_str(), const_cast<char**>(__adb_argv),
                                    const_cast<char**>(__adb_envp)) == -1) {
                             LOG(ERROR) << "failed to exec newer version at " << server_path;
                         }

                         // Fall-through to restarting the server.
                     }
                 }
             }
 #endif

             fprintf(stderr, "adb server version (%d) doesn't match this client (%d); killing...\n",
                     version, ADB_SERVER_VERSION);
             adb_kill_server();
             goto start_server;
         }
     }

     return true;
 }

 bool adb_check_server_version(std::string* error) {
     // Only check the version once per process, since this isn't atomic anyway.
     static std::once_flag once;
     static bool result;
     static std::string* err;
     std::call_once(once, []() {
         err = new std::string();
         result = __adb_check_server_version(err);
     });
     *error = *err;
     return result;
 }

 int adb_connect(TransportId* transport, std::string_view service, std::string* error,
                 bool force_switch_device) {
     LOG(DEBUG) << "adb_connect: service: " << service;

     // Query the adb server's version.
     if (!adb_check_server_version(error)) {
         return -1;
     }

     // if the command is start-server, we are done.
     if (service == "host:start-server") {
         return 0;
     }

     unique_fd fd(_adb_connect(service, transport, error, force_switch_device));
     if (fd == -1) {
         D("_adb_connect error: %s", error->c_str());
     } else if(fd == -2) {
         fprintf(stderr, "* daemon still not running\n");
     }
     D("adb_connect: return fd %d", fd.get());

     return fd.release();
 }

 bool adb_command(const std::string& service) {
     std::string error;
     unique_fd fd(adb_connect(service, &error));
     if (fd < 0) {
         fprintf(stderr, "error: %s\n", error.c_str());
         return false;
     }

     if (!adb_status(fd.get(), &error)) {
         fprintf(stderr, "error: %s\n", error.c_str());
         return false;
     }

     ReadOrderlyShutdown(fd.get());
     return true;
 }

 bool adb_query(const std::string& service, std::string* result, std::string* error) {
     D("adb_query: %s", service.c_str());
     unique_fd fd(adb_connect(service, error));
     if (fd < 0) {
         return false;
     }

     result->clear();
     if (!ReadProtocolString(fd.get(), result, error)) {
         return false;
     }

     ReadOrderlyShutdown(fd.get());
     return true;
 }

 std::string format_host_command(const char* command) {
     if (__adb_transport_id) {
         return android::base::StringPrintf("host-transport-id:%" PRIu64 ":%s", __adb_transport_id,
                                            command);
     } else if (__adb_serial) {
         return android::base::StringPrintf("host-serial:%s:%s", __adb_serial, command);
     }

     const char* prefix = "host";
     if (__adb_transport == kTransportUsb) {
         prefix = "host-usb";
     } else if (__adb_transport == kTransportLocal) {
         prefix = "host-local";
     }
     return android::base::StringPrintf("%s:%s", prefix, command);
 }

 const std::optional<FeatureSet>& adb_get_feature_set(std::string* error) {
     static std::mutex feature_mutex [[clang::no_destroy]];
     static std::optional<FeatureSet> features [[clang::no_destroy]] GUARDED_BY(feature_mutex);
     std::lock_guard<std::mutex> lock(feature_mutex);
     if (!features) {
         std::string result;
         std::string err;
         if (adb_query(format_host_command("features"), &result, &err)) {
             features = StringToFeatureSet(result);
         } else {
             if (error) {
                 *error = err;
             }
         }
     }
     return features;
 }
	/*
	* Copyright (C) 2015 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#define TRACE_TAG ADB

	#include "sysdeps.h"
	#include "adb_client.h"

	#include <errno.h>
	#include <inttypes.h>
	#include <limits.h>
	#include <stdarg.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>
	#include <sys/stat.h>
	#include <sys/types.h>

	#include <condition_variable>
	#include <mutex>
	#include <optional>
	#include <string>
	#include <thread>
	#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>
	#include <cutils/sockets.h>

	#include "adb_io.h"
	#include "adb_utils.h"
	#include "socket_spec.h"
	#include "sysdeps/chrono.h"

	static TransportType __adb_transport = kTransportAny;
	static const char* __adb_serial = nullptr;
	static TransportId __adb_transport_id = 0;

	static const char* __adb_server_socket_spec;

	void adb_set_transport(TransportType type, const char* serial, TransportId transport_id) {
	__adb_transport = type;
	__adb_serial = serial;
	__adb_transport_id = transport_id;
	}

	void adb_get_transport(TransportType* type, const char** serial, TransportId* transport_id) {
	if (type) *type = __adb_transport;
	if (serial) *serial = __adb_serial;
	if (transport_id) *transport_id = __adb_transport_id;
	}

	void adb_set_socket_spec(const char* socket_spec) {
	if (__adb_server_socket_spec) {
	LOG(FATAL) << "attempted to reinitialize adb_server_socket_spec " << socket_spec << " (was " << __adb_server_socket_spec << ")";
	}
	__adb_server_socket_spec = socket_spec;
	}

	static std::optional<TransportId> switch_socket_transport(int fd, std::string* error) {
	TransportId result;
	bool read_transport = true;

	std::string service;
	if (__adb_transport_id) {
	read_transport = false;
	service += "host:transport-id:";
	service += std::to_string(__adb_transport_id);
	result = __adb_transport_id;
	} else if (__adb_serial) {
	service += "host:tport:serial:";
	service += __adb_serial;
	} else {
	const char* transport_type = "???";
	switch (__adb_transport) {
	case kTransportUsb:
	transport_type = "usb";
	break;
	case kTransportLocal:
	transport_type = "local";
	break;
	case kTransportAny:
	transport_type = "any";
	break;
	case kTransportHost:
	// no switch necessary
	return 0;
	}
	service += "host:tport:";
	service += transport_type;
	}

	if (!SendProtocolString(fd, service)) {
	*error = perror_str("write failure during connection");
	return std::nullopt;
	}

	LOG(DEBUG) << "Switch transport in progress: " << service;

	if (!adb_status(fd, error)) {
	D("Switch transport failed: %s", error->c_str());
	return std::nullopt;
	}

	if (read_transport) {
	if (!ReadFdExactly(fd, &result, sizeof(result))) {
	*error = "failed to read transport id from server";
	return std::nullopt;
	}
	}

	D("Switch transport success");
	return result;
	}

	bool adb_status(borrowed_fd fd, std::string* error) {
	char buf[5];
	if (!ReadFdExactly(fd, buf, 4)) {
	*error = perror_str("protocol fault (couldn't read status)");
	return false;
	}

	if (!memcmp(buf, "OKAY", 4)) {
	return true;
	}

	if (memcmp(buf, "FAIL", 4)) {
	*error = android::base::StringPrintf("protocol fault (status %02x %02x %02x %02x?!)",
	buf[0], buf[1], buf[2], buf[3]);
	return false;
	}

	ReadProtocolString(fd, error, error);
	return false;
	}

	static int _adb_connect(std::string_view service, TransportId* transport, std::string* error,
	bool force_switch = false) {
	LOG(DEBUG) << "_adb_connect: " << service;
	if (service.empty() \|\| service.size() > MAX_PAYLOAD) {
	*error = android::base::StringPrintf("bad service name length (%zd)", service.size());
	return -1;
	}

	std::string reason;
	unique_fd fd;
	if (!socket_spec_connect(&fd, __adb_server_socket_spec, nullptr, nullptr, &reason)) {
	*error = android::base::StringPrintf("cannot connect to daemon at %s: %s",
	__adb_server_socket_spec, reason.c_str());
	return -2;
	}

	if (!service.starts_with("host") \|\| force_switch) {
	std::optional<TransportId> transport_result = switch_socket_transport(fd.get(), error);
	if (!transport_result) {
	return -1;
	}

	if (transport) {
	transport = transport_result;
	}
	}

	if (!SendProtocolString(fd.get(), service)) {
	*error = perror_str("write failure during connection");
	return -1;
	}

	if (!adb_status(fd.get(), error)) {
	return -1;
	}

	D("_adb_connect: return fd %d", fd.get());
	return fd.release();
	}

	bool adb_kill_server() {
	D("adb_kill_server");
	std::string reason;
	unique_fd fd;
	if (!socket_spec_connect(&fd, __adb_server_socket_spec, nullptr, nullptr, &reason)) {
	fprintf(stderr, "cannot connect to daemon at %s: %s\n", __adb_server_socket_spec,
	reason.c_str());
	return true;
	}

	if (!SendProtocolString(fd.get(), "host:kill")) {
	fprintf(stderr, "error: write failure during connection: %s\n", strerror(errno));
	return false;
	}

	char buf[4];
	if (!ReadFdExactly(fd.get(), buf, 4)) {
	fprintf(stderr, "error: failed to read response from server\n");
	return false;
	}

	if (memcmp(buf, "OKAY", 4) == 0) {
	// Nothing to do.
	} else if (memcmp(buf, "FAIL", 4) == 0) {
	std::string output, error;
	if (!ReadProtocolString(fd.get(), &output, &error)) {
	fprintf(stderr, "error: %s\n", error.c_str());
	return false;
	}

	fprintf(stderr, "error: %s\n", output.c_str());
	return false;
	}

	// Now that no more data is expected, wait for socket orderly shutdown or error, indicating
	// server death.
	ReadOrderlyShutdown(fd.get());
	return true;
	}

	int adb_connect(std::string_view service, std::string* error) {
	return adb_connect(nullptr, service, error);
	}

	#if defined(__linux__)
	std::optional<std::string> adb_get_server_executable_path() {
	int port;
	std::string error;
	if (!parse_tcp_socket_spec(__adb_server_socket_spec, nullptr, &port, nullptr, &error)) {
	return {};
	}

	return adb_get_android_dir_path() + OS_PATH_SEPARATOR + "adb." + std::to_string(port);
	}
	#endif

	static bool __adb_check_server_version(std::string* error) {
	unique_fd fd(_adb_connect("host:version", nullptr, error));

	bool local = is_local_socket_spec(__adb_server_socket_spec);
	if (fd == -2 && !local) {
	fprintf(stderr, "* cannot start server on remote host\n");
	// error is the original network connection error
	return false;
	} else if (fd == -2) {
	fprintf(stderr, "* daemon not running; starting now at %s\n", __adb_server_socket_spec);
	start_server:
	if (launch_server(__adb_server_socket_spec)) {
	fprintf(stderr, "* failed to start daemon\n");
	// launch_server() has already printed detailed error info, so just
	// return a generic error string about the overall adb_connect()
	// that the caller requested.
	*error = "cannot connect to daemon";
	return false;
	} else {
	fprintf(stderr, "* daemon started successfully\n");
	}
	// The server will wait until it detects all of its connected devices before acking.
	// Fall through to _adb_connect.
	} else {
	// If a server is already running, check its version matches.
	int version = 0;

	// If we have a file descriptor, then parse version result.
	if (fd >= 0) {
	std::string version_string;
	if (!ReadProtocolString(fd, &version_string, error)) {
	return false;
	}

	ReadOrderlyShutdown(fd);

	if (sscanf(&version_string[0], "%04x", &version) != 1) {
	*error = android::base::StringPrintf("cannot parse version string: %s",
	version_string.c_str());
	return false;
	}
	} else {
	// If fd is -1 check for "unknown host service" which would
	// indicate a version of adb that does not support the
	// version command, in which case we should fall-through to kill it.
	if (*error != "unknown host service") {
	return false;
	}
	}

	if (version != ADB_SERVER_VERSION) {
	#if defined(__linux__)
	if (version > ADB_SERVER_VERSION && local) {
	// Try to re-exec the existing adb server's binary.
	constexpr const char* adb_reexeced = "adb (re-execed)";
	if (strcmp(adb_reexeced, *__adb_argv) != 0) {
	__adb_argv[0] = adb_reexeced;
	std::optional<std::string> server_path_path = adb_get_server_executable_path();
	std::string server_path;
	if (server_path_path &&
	android::base::ReadFileToString(*server_path_path, &server_path)) {
	if (execve(server_path.c_str(), const_cast<char**>(__adb_argv),
	const_cast<char**>(__adb_envp)) == -1) {
	LOG(ERROR) << "failed to exec newer version at " << server_path;
	}

	// Fall-through to restarting the server.
	}
	}
	}
	#endif

	fprintf(stderr, "adb server version (%d) doesn't match this client (%d); killing...\n",
	version, ADB_SERVER_VERSION);
	adb_kill_server();
	goto start_server;
	}
	}

	return true;
	}

	bool adb_check_server_version(std::string* error) {
	// Only check the version once per process, since this isn't atomic anyway.
	static std::once_flag once;
	static bool result;
	static std::string* err;
	std::call_once(once, []() {
	err = new std::string();
	result = __adb_check_server_version(err);
	});
	error = err;
	return result;
	}

	int adb_connect(TransportId* transport, std::string_view service, std::string* error,
	bool force_switch_device) {
	LOG(DEBUG) << "adb_connect: service: " << service;

	// Query the adb server's version.
	if (!adb_check_server_version(error)) {
	return -1;
	}

	// if the command is start-server, we are done.
	if (service == "host:start-server") {
	return 0;
	}

	unique_fd fd(_adb_connect(service, transport, error, force_switch_device));
	if (fd == -1) {
	D("_adb_connect error: %s", error->c_str());
	} else if(fd == -2) {
	fprintf(stderr, "* daemon still not running\n");
	}
	D("adb_connect: return fd %d", fd.get());

	return fd.release();
	}

	bool adb_command(const std::string& service) {
	std::string error;
	unique_fd fd(adb_connect(service, &error));
	if (fd < 0) {
	fprintf(stderr, "error: %s\n", error.c_str());
	return false;
	}

	if (!adb_status(fd.get(), &error)) {
	fprintf(stderr, "error: %s\n", error.c_str());
	return false;
	}

	ReadOrderlyShutdown(fd.get());
	return true;
	}

	bool adb_query(const std::string& service, std::string* result, std::string* error) {
	D("adb_query: %s", service.c_str());
	unique_fd fd(adb_connect(service, error));
	if (fd < 0) {
	return false;
	}

	result->clear();
	if (!ReadProtocolString(fd.get(), result, error)) {
	return false;
	}

	ReadOrderlyShutdown(fd.get());
	return true;
	}

	std::string format_host_command(const char* command) {
	if (__adb_transport_id) {
	return android::base::StringPrintf("host-transport-id:%" PRIu64 ":%s", __adb_transport_id,
	command);
	} else if (__adb_serial) {
	return android::base::StringPrintf("host-serial:%s:%s", __adb_serial, command);
	}

	const char* prefix = "host";
	if (__adb_transport == kTransportUsb) {
	prefix = "host-usb";
	} else if (__adb_transport == kTransportLocal) {
	prefix = "host-local";
	}
	return android::base::StringPrintf("%s:%s", prefix, command);
	}

	const std::optional<FeatureSet>& adb_get_feature_set(std::string* error) {
	static std::mutex feature_mutex [[clang::no_destroy]];
	static std::optional<FeatureSet> features [[clang::no_destroy]] GUARDED_BY(feature_mutex);
	std::lock_guard<std::mutex> lock(feature_mutex);
	if (!features) {
	std::string result;
	std::string err;
	if (adb_query(format_host_command("features"), &result, &err)) {
	features = StringToFeatureSet(result);
	} else {
	if (error) {
	*error = err;
	}
	}
	}
	return features;
	}