linux: add Get/SetHandlerSocket()

These methods are used to connect additional clients to an existing
handler process.

Bug: crashpad:285
Change-Id: Iefa5b0d8f5fd7d4799140ff9a7c2f79ac65da738
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/1759281
Commit-Queue: Joshua Peraza <jperaza@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>

client/crashpad_client.h

@@ -24,6 +24,7 @@
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "build/build_config.h"
+#include "util/file/file_io.h"
 #include "util/misc/capture_context.h"
 
 #if defined(OS_MACOSX)
@@ -116,6 +117,30 @@ class CrashpadClient {
                     bool restartable,
                     bool asynchronous_start);
 
+#if defined(OS_ANDROID) || defined(OS_LINUX) || DOXYGEN
+  //! \brief Retrieve the socket and process ID for the handler.
+  //!
+  //! `StartHandler()` must have successfully been called before calling this
+  //!     method.
+  //!
+  //! \param[out] sock The socket connected to the handler.
+  //! \param[out] pid The handler's process ID.
+  //! \return `true` on success. Otherwise `false` with a message logged.
+  static bool GetHandlerSocket(int* sock, pid_t* pid);
+
+  //! \brief Sets the socket to a presumably-running Crashpad handler process
+  //!      which was started with StartHandler().
+  //!
+  //! This method installs a signal handler to request crash dumps on \a sock.
+  //!
+  //! \param[in] sock A socket connected to a Crashpad handler.
+  //! \param[in] pid The process ID of the handler, used to set the handler as
+  //!     this process' ptracer. 0 indicates it is not necessary to set the
+  //!     handler as this process' ptracer. -1 indicates that the handler's
+  //!     process ID should be determined by communicating over the socket.
+  static bool SetHandlerSocket(ScopedFileHandle sock, pid_t pid);
+#endif  // OS_ANDROID || OS_LINUX || DOXYGEN
+
 #if defined(OS_ANDROID) || DOXYGEN
   //! \brief Installs a signal handler to execute `/system/bin/app_process` and
   //!     load a Java class in response to a crash.

client/crashpad_client_linux.cc

@@ -284,9 +284,19 @@ class RequestCrashDumpHandler : public SignalHandler {
       return false;
     }
     sock_to_handler_.reset(sock.release());
+    handler_pid_ = pid;
     return Install();
   }
 
+  bool GetHandlerSocket(int* sock, pid_t* pid) {
+    if (!sock_to_handler_.is_valid()) {
+      return false;
+    }
+    *sock = sock_to_handler_.get();
+    *pid = handler_pid_;
+    return true;
+  }
+
   void HandleCrashImpl() override {
     ExceptionHandlerProtocol::ClientInformation info = {};
     info.exception_information_address =
@@ -302,6 +312,7 @@ class RequestCrashDumpHandler : public SignalHandler {
   ~RequestCrashDumpHandler() = delete;
 
   ScopedFileHandle sock_to_handler_;
+  pid_t handler_pid_ = -1;
 
   DISALLOW_COPY_AND_ASSIGN(RequestCrashDumpHandler);
 };
@@ -343,6 +354,20 @@ bool CrashpadClient::StartHandler(
   return signal_handler->Initialize(std::move(client_sock), -1);
 }
 
+#if defined(OS_ANDROID) || defined(OS_LINUX)
+// static
+bool CrashpadClient::GetHandlerSocket(int* sock, pid_t* pid) {
+  auto signal_handler = RequestCrashDumpHandler::Get();
+  return signal_handler->GetHandlerSocket(sock, pid);
+}
+
+// static
+bool CrashpadClient::SetHandlerSocket(ScopedFileHandle sock, pid_t pid) {
+  auto signal_handler = RequestCrashDumpHandler::Get();
+  return signal_handler->Initialize(std::move(sock), pid);
+}
+#endif  // OS_ANDROID || OS_LINUX
+
 #if defined(OS_ANDROID)
 
 // static