adb: shell: add -n flag to not read from stdin.

Shell scripts of the following form do not work properly with adb:
    echo "foo\nbar\nbaz" | {
        read FOO
        while [ "$FOO" != "" ]; do
            adb shell echo $FOO
            read FOO
        done
    }
The first run of adb shell will consume all of the contents of stdin,
causing the loop to immediately end. ssh solves this by providing a -n
flag that causes it to not read from stdin. This commit adds the same.

Bug: http://b/25817224
Change-Id: Id74ca62ef520bcf03678b50f4bf203916fd81038

5 files changed, 30 insertions, 26 deletions

diff --git a/adb_utils.cpp b/adb_utils.cpp
index 42f1c7d..1c3526b 100644
--- a/adb_utils.cpp
+++ b/adb_utils.cpp
@@ -30,12 +30,31 @@
 #include <base/stringprintf.h>
 #include <base/strings.h>
 
+#include "adb.h"
 #include "adb_trace.h"
 #include "sysdeps.h"
 
 ADB_MUTEX_DEFINE(basename_lock);
 ADB_MUTEX_DEFINE(dirname_lock);
 
+#if defined(_WIN32)
+constexpr char kNullFileName[] = "NUL";
+#else
+constexpr char kNullFileName[] = "/dev/null";
+#endif
+
+void close_stdin() {
+    int fd = unix_open(kNullFileName, O_RDONLY);
+    if (fd == -1) {
+        fatal_errno("failed to open %s", kNullFileName);
+    }
+
+    if (TEMP_FAILURE_RETRY(dup2(fd, STDIN_FILENO)) == -1) {
+        fatal_errno("failed to redirect stdin to %s", kNullFileName);
+    }
+    unix_close(fd);
+}
+
 bool getcwd(std::string* s) {
   char* cwd = getcwd(nullptr, 0);
   if (cwd != nullptr) *s = cwd;
diff --git a/adb_utils.h b/adb_utils.h
index 537d0e4..388d7dd 100644
--- a/adb_utils.h
+++ b/adb_utils.h
@@ -19,6 +19,8 @@
 
 #include <string>
 
+void close_stdin();
+
 bool getcwd(std::string* cwd);
 bool directory_exists(const std::string& path);
 
diff --git a/client/main.cpp b/client/main.cpp
index 04b9882..1ac6e82 100644
--- a/client/main.cpp
+++ b/client/main.cpp
@@ -34,11 +34,10 @@
 #include "adb.h"
 #include "adb_auth.h"
 #include "adb_listeners.h"
+#include "adb_utils.h"
 #include "transport.h"
 
 #if defined(_WIN32)
-static const char kNullFileName[] = "NUL";
-
 static BOOL WINAPI ctrlc_handler(DWORD type) {
     // TODO: Consider trying to kill a starting up adb server (if we're in
     // launch_server) by calling GenerateConsoleCtrlEvent().
@@ -66,24 +65,11 @@ static std::string GetLogFilePath() {
     return temp_path_utf8 + log_name;
 }
 #else
-static const char kNullFileName[] = "/dev/null";
-
 static std::string GetLogFilePath() {
     return std::string("/tmp/adb.log");
 }
 #endif
 
-static void close_stdin() {
-    int fd = unix_open(kNullFileName, O_RDONLY);
-    if (fd == -1) {
-        fatal("cannot open '%s': %s", kNullFileName, strerror(errno));
-    }
-    if (dup2(fd, STDIN_FILENO) == -1) {
-        fatal("cannot redirect stdin: %s", strerror(errno));
-    }
-    unix_close(fd);
-}
-
 static void setup_daemon_logging(void) {
     const std::string log_file_path(GetLogFilePath());
     int fd = unix_open(log_file_path.c_str(), O_WRONLY | O_CREAT | O_APPEND, 0640);
diff --git a/commandline.cpp b/commandline.cpp
index bd3813e..a43b6ab 100644
--- a/commandline.cpp
+++ b/commandline.cpp
@@ -112,9 +112,10 @@ static void help() {
         "                                 (-a preserves file timestamp and mode)\n"
         "  adb sync [ <directory> ]     - copy host->device only if changed\n"
         "                                 (-l means list but don't copy)\n"
-        "  adb shell [-e escape] [-Tt] [-x] [command]\n"
+        "  adb shell [-e escape] [-n] [-Tt] [-x] [command]\n"
         "                               - run remote shell command (interactive shell if no command given)\n"
         "                                 (-e: choose escape character, or \"none\"; default '~')\n"
+        "                                 (-n: don't read from stdin)\n"
         "                                 (-T: disable PTY allocation)\n"
         "                                 (-t: force PTY allocation)\n"
         "                                 (-x: disable remote exit codes and stdout/stderr separation)\n"
@@ -733,6 +734,11 @@ static int adb_shell(int argc, const char** argv,
             use_shell_protocol = false;
             --argc;
             ++argv;
+        } else if (!strcmp(argv[0], "-n")) {
+            close_stdin();
+
+            --argc;
+            ++argv;
         } else {
             break;
         }
diff --git a/daemon/main.cpp b/daemon/main.cpp
index f4e054e..a56d1dc 100644
--- a/daemon/main.cpp
+++ b/daemon/main.cpp
@@ -34,6 +34,7 @@
 #include "adb.h"
 #include "adb_auth.h"
 #include "adb_listeners.h"
+#include "adb_utils.h"
 #include "transport.h"
 
 static const char* root_seclabel = nullptr;
@@ -217,16 +218,6 @@ int adbd_main(int server_port) {
     return 0;
 }
 
-static void close_stdin() {
-    int fd = unix_open("/dev/null", O_RDONLY);
-    if (fd == -1) {
-        perror("failed to open /dev/null, stdin will remain open");
-        return;
-    }
-    dup2(fd, STDIN_FILENO);
-    unix_close(fd);
-}
-
 int main(int argc, char** argv) {
     while (true) {
         static struct option opts[] = {