[starter] Add a process starter for use by the installer for launching tools (#4931)

processstarter/src/main/native/linux/main.cpp

@@ -0,0 +1,86 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include <poll.h>
+#include <spawn.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <climits>
+#include <cstdio>
+#include <cstring>
+#include <filesystem>
+
+int main(int argc, char* argv[]) {
+  char path[PATH_MAX];
+  char dest[PATH_MAX];
+  std::memset(dest, 0, sizeof(dest));  // readlink does not null terminate!
+  pid_t pid = getpid();
+  std::snprintf(path, PATH_MAX, "/proc/%d/exe", pid);
+  int readlink_len = readlink(path, dest, PATH_MAX);
+  if (readlink_len < 0) {
+    std::perror("readlink");
+    return 1;
+  } else if (readlink_len == PATH_MAX) {
+    std::printf("Truncation occured\n");
+    return 1;
+  }
+
+  std::filesystem::path exePath{dest};
+  if (exePath.empty()) {
+    return 1;
+  }
+
+  if (!exePath.has_stem()) {
+    return 1;
+  }
+
+  if (!exePath.has_parent_path()) {
+    return 1;
+  }
+
+  std::filesystem::path jarPath{exePath};
+  jarPath.replace_extension("jar");
+  std::filesystem::path parentPath{exePath.parent_path()};
+
+  if (!parentPath.has_parent_path()) {
+    return 1;
+  }
+  std::filesystem::path toolsFolder{parentPath.parent_path()};
+
+  std::filesystem::path Java = toolsFolder / "jdk" / "bin" / "java";
+
+  pid = 0;
+  std::string data = jarPath;
+  std::string jarArg = "-jar";
+  char* const arguments[] = {jarArg.data(), data.data(), nullptr};
+
+  int status =
+      posix_spawn(&pid, Java.c_str(), nullptr, nullptr, arguments, environ);
+  if (status != 0) {
+    char* home = std::getenv("JAVA_HOME");
+    std::string javaLocal = "java";
+    if (home != nullptr) {
+      std::filesystem::path javaHomePath{home};
+      javaHomePath /= "bin";
+      javaHomePath /= "java";
+      javaLocal = javaHomePath;
+    }
+
+    status = posix_spawn(&pid, javaLocal.c_str(), nullptr, nullptr, arguments,
+                         environ);
+    if (status != 0) {
+      return 1;
+    }
+  }
+
+  int childPid = syscall(SYS_pidfd_open, pid, 0);
+  if (childPid <= 0) {
+    return 1;
+  }
+
+  struct pollfd pfd = {childPid, POLLIN, 0};
+  return poll(&pfd, 1, 3000);
+}