API: nvim_get_proc()

TODO: "exepath" field (win32: QueryFullProcessImageName())

On unix-likes `ps` is used because the platform-specific APIs are
a nightmare.  For reference, below is a (incomplete) attempt:

diff --git a/src/nvim/os/process.c b/src/nvim/os/process.c
index 09769925aca5..99afbbf290c1 100644
--- a/src/nvim/os/process.c
+++ b/src/nvim/os/process.c
@@ -208,3 +210,60 @@ int os_proc_children(int ppid, int **proc_list, size_t *proc_count)
   return 0;
 }

+/// Gets various properties of the process identified by `pid`.
+///
+/// @param pid Process to inspect.
+/// @return Map of process properties, empty on error.
+Dictionary os_proc_info(int pid)
+{
+  Dictionary pinfo = ARRAY_DICT_INIT;
+#ifdef WIN32
+
+#elif defined(__APPLE__)
+  char buf[PROC_PIDPATHINFO_MAXSIZE];
+  if (proc_pidpath(pid, buf, sizeof(buf))) {
+    name = getName(buf);
+    PUT(pinfo, "exepath", STRING_OBJ(cstr_to_string(buf)));
+    return name;
+  } else {
+    ILOG("proc_pidpath() failed for pid: %d", pid);
+  }
+#elif defined(BSD)
+# if defined(__FreeBSD__)
+#  define KP_COMM(o) o.ki_comm
+# else
+#  define KP_COMM(o) o.p_comm
+# endif
+  struct kinfo_proc *proc = kinfo_getproc(pid);
+  if (proc) {
+    PUT(pinfo, "name", cstr_to_string(KP_COMM(proc)));
+    xfree(proc);
+  } else {
+    ILOG("kinfo_getproc() failed for pid: %d", pid);
+  }
+
+#elif defined(__linux__)
+  char fname[256] = { 0 };
+  char buf[MAXPATHL];
+  snprintf(fname, sizeof(fname), "/proc/%d/comm", pid);
+  FILE *fp = fopen(fname, "r");
+  // FileDescriptor *f = file_open_new(&error, fname, kFileReadOnly, 0);
+  // ptrdiff_t file_read(FileDescriptor *const fp, char *const ret_buf,
+  //                     const size_t size)
+  if (fp == NULL) {
+    ILOG("fopen() of /proc/%d/comm failed", pid);
+  } else {
+    size_t n = fread(buf, sizeof(char), sizeof(buf) - 1, fp);
+    if (n == 0) {
+      WLOG("fread() of /proc/%d/comm failed", pid);
+    } else {
+      size_t end = MIN(sizeof(buf) - 1, n);
+      end = (end > 0 && buf[end - 1] == '\n') ? end - 1 : end;
+      buf[end] = '\0';
+      PUT(pinfo, "name", STRING_OBJ(cstr_to_string(buf)));
+    }
+  }
+  fclose(fp);
+#endif
+  return pinfo;
+}

src/nvim/api/vim.c

@@ -1482,11 +1482,11 @@ Array nvim_list_uis(void)
 
 /// Gets the immediate children of process `pid`.
 ///
-/// @return Array of child process ids. Empty array if process not found.
+/// @return Array of child process ids, empty if process not found.
 Array nvim_get_proc_children(Integer pid, Error *err)
   FUNC_API_SINCE(4)
 {
-  Array proc_array = ARRAY_DICT_INIT;
+  Array rvobj = ARRAY_DICT_INIT;
   int *proc_list = NULL;
 
   if (pid <= 0 || pid > INT_MAX) {
@@ -1498,6 +1498,7 @@ Array nvim_get_proc_children(Integer pid, Error *err)
   int rv = os_proc_children((int)pid, &proc_list, &proc_count);
   if (rv != 0) {
     // syscall failed (possibly because of kernel options), try shelling out.
+    DLOG("fallback to vim._os_proc_children()");
     Array a = ARRAY_DICT_INIT;
     ADD(a, INTEGER_OBJ(pid));
     String s = cstr_to_string("return vim._os_proc_children(select(1, ...))");
@@ -1505,7 +1506,7 @@ Array nvim_get_proc_children(Integer pid, Error *err)
     api_free_string(s);
     api_free_array(a);
     if (o.type == kObjectTypeArray) {
-      proc_array = o.data.array;
+      rvobj = o.data.array;
     } else if (!ERROR_SET(err)) {
       api_set_error(err, kErrorTypeException,
                     "Failed to get process children. pid=%" PRId64 " error=%d",
@@ -1515,10 +1516,49 @@ Array nvim_get_proc_children(Integer pid, Error *err)
   }
 
   for (size_t i = 0; i < proc_count; i++) {
-    ADD(proc_array, INTEGER_OBJ(proc_list[i]));
+    ADD(rvobj, INTEGER_OBJ(proc_list[i]));
   }
 
 end:
   xfree(proc_list);
-  return proc_array;
+  return rvobj;
+}
+
+/// Gets info describing process `pid`.
+///
+/// @return Map of process properties, or NIL if process not found.
+Object nvim_get_proc(Integer pid, Error *err)
+  FUNC_API_SINCE(4)
+{
+  Object rvobj = OBJECT_INIT;
+  rvobj.data.dictionary = (Dictionary)ARRAY_DICT_INIT;
+  rvobj.type = kObjectTypeDictionary;
+
+  if (pid <= 0 || pid > INT_MAX) {
+    api_set_error(err, kErrorTypeException, "Invalid pid: %" PRId64, pid);
+    return NIL;
+  }
+#ifdef WIN32
+  rvobj.data.dictionary = os_proc_info((int)pid);
+  if (rvobj.data.dictionary.size == 0) {  // Process not found.
+    return NIL;
+  }
+#else
+  // Cross-platform process info APIs are miserable, so use `ps` instead.
+  Array a = ARRAY_DICT_INIT;
+  ADD(a, INTEGER_OBJ(pid));
+  String s = cstr_to_string("return vim._os_proc_info(select(1, ...))");
+  Object o = nvim_execute_lua(s, a, err);
+  api_free_string(s);
+  api_free_array(a);
+  if (o.type == kObjectTypeArray && o.data.array.size == 0) {
+    return NIL;  // Process not found.
+  } else if (o.type == kObjectTypeDictionary) {
+    rvobj.data.dictionary = o.data.dictionary;
+  } else if (!ERROR_SET(err)) {
+    api_set_error(err, kErrorTypeException,
+                  "Failed to get process info. pid=%" PRId64, pid);
+  }
+#endif
+  return rvobj;
 }

src/nvim/lua/vim.lua

@@ -1,18 +1,54 @@
--- Gets the children of process `ppid` via the shell.
+-- Internal-only until comments in #8107 are addressed.
+-- Returns:
+--    {errcode}, {output}
+local function _system(cmd)
+  local out = vim.api.nvim_call_function('system', { cmd })
+  local err = vim.api.nvim_get_vvar('shell_error')
+  return err, out
+end
+
+-- Gets process info from the `ps` command.
+-- Used by nvim_get_proc() as a fallback.
+local function _os_proc_info(pid)
+  if pid == nil or pid <= 0 or type(pid) ~= 'number' then
+    error('invalid pid')
+  end
+  local cmd = { 'ps', '-p', pid, '-o', 'ucomm=', }
+  local err, name = _system(cmd)
+  if 1 == err and string.gsub(name, '%s*', '') == '' then
+    return {}  -- Process not found.
+  elseif 0 ~= err then
+    local args_str = vim.api.nvim_call_function('string', { cmd })
+    error('command failed: '..args_str)
+  end
+  local _, ppid = _system({ 'ps', '-p', pid, '-o', 'ppid=', })
+  -- Remove trailing whitespace.
+  name = string.gsub(name, '%s+$', '')
+  ppid = string.gsub(ppid, '%s+$', '')
+  ppid = tonumber(ppid) == nil and -1 or tonumber(ppid)
+  return {
+    name = name,
+    pid = pid,
+    ppid = ppid,
+  }
+end
+
+-- Gets process children from the `pgrep` command.
 -- Used by nvim_get_proc_children() as a fallback.
 local function _os_proc_children(ppid)
   if ppid == nil or ppid <= 0 or type(ppid) ~= 'number' then
     error('invalid ppid')
   end
-  local out = vim.api.nvim_call_function('system', { 'pgrep -P '..ppid })
+  local cmd = { 'pgrep', '-P', ppid, }
-  local err = vim.api.nvim_get_vvar('shell_error')
+  local err, rv = _system(cmd)
-  if 1 == err and out == '' then
+  if 1 == err and string.gsub(rv, '%s*', '') == '' then
     return {}  -- Process not found.
   elseif 0 ~= err then
-    error('pgrep failed')
+    local args_str = vim.api.nvim_call_function('string', { cmd })
+    error('command failed: '..args_str)
   end
   local children = {}
-  for s in string.gmatch(out, '%S+') do
+  for s in string.gmatch(rv, '%S+') do
     local i = tonumber(s)
     if i ~= nil then
       table.insert(children, i)
@@ -81,8 +117,12 @@ local function _update_package_paths()
   end
   last_nvim_paths = cur_nvim_paths
 end
---{{{1 Module definition
+
-return {
+local module = {
   _update_package_paths = _update_package_paths,
   _os_proc_children = _os_proc_children,
+  _os_proc_info = _os_proc_info,
+  _system = _system,
 }
+
+return module

src/nvim/os/fileio.c

@@ -4,7 +4,7 @@
 /// @file fileio.c
 ///
 /// Buffered reading/writing to a file. Unlike fileio.c this is not dealing with
-/// Neovim stuctures for buffer, with autocommands, etc: just fopen/fread/fwrite
+/// Nvim stuctures for buffer, with autocommands, etc: just fopen/fread/fwrite
 /// replacement.
 
 #include <assert.h>
@@ -43,7 +43,7 @@
 /// @param[in]  mode  Permissions for the newly created file (ignored if flags
 ///                   does not have kFileCreate\*).
 ///
-/// @return Error code (@see os_strerror()) or 0.
+/// @return Error code, or 0 on success. @see os_strerror()
 int file_open(FileDescriptor *const ret_fp, const char *const fname,
               const int flags, const int mode)
   FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT
@@ -115,8 +115,7 @@ int file_open_fd(FileDescriptor *const ret_fp, const int fd, const bool wr)
 
 /// Like file_open(), but allocate and return ret_fp
 ///
-/// @param[out]  error  Error code, @see os_strerror(). Is set to zero on
+/// @param[out]  error  Error code, or 0 on success. @see os_strerror()
-///                     success.
 /// @param[in]  fname  File name to open.
 /// @param[in]  flags  Flags, @see FileOpenFlags.
 /// @param[in]  mode  Permissions for the newly created file (ignored if flags
@@ -137,8 +136,7 @@ FileDescriptor *file_open_new(int *const error, const char *const fname,
 
 /// Like file_open_fd(), but allocate and return ret_fp
 ///
-/// @param[out]  error  Error code, @see os_strerror(). Is set to zero on
+/// @param[out]  error  Error code, or 0 on success. @see os_strerror()
-///                     success.
 /// @param[in]  fd  File descriptor to wrap.
 /// @param[in]  wr  True if fd is opened for writing only, false if it is read
 ///                 only.

src/nvim/os/process.c

@@ -1,6 +1,11 @@
 // This is an open source non-commercial project. Dear PVS-Studio, please check
 // it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
 
+/// OS process functions
+///
+/// psutil is a good reference for cross-platform syscall voodoo:
+/// https://github.com/giampaolo/psutil/tree/master/psutil/arch
+
 #include <uv.h>  // for HANDLE (win32)
 
 #ifdef WIN32
@@ -18,10 +23,12 @@
 # include <pwd.h>
 #endif
 
+#include "nvim/globals.h"
 #include "nvim/log.h"
 #include "nvim/os/process.h"
 #include "nvim/os/os.h"
 #include "nvim/os/os_defs.h"
+#include "nvim/api/private/helpers.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "os/process.c.generated.h"
@@ -104,11 +111,6 @@ bool os_proc_tree_kill(int pid, int sig)
 /// @return 0 on success, 1 if process not found, 2 on other error.
 int os_proc_children(int ppid, int **proc_list, size_t *proc_count)
 {
-  //
-  // psutil is a good reference for cross-platform syscall voodoo:
-  // https://github.com/giampaolo/psutil/tree/master/psutil/arch
-  //
-
   if (ppid < 0) {
     return 2;
   }
@@ -208,3 +210,44 @@ int os_proc_children(int ppid, int **proc_list, size_t *proc_count)
   return 0;
 }
 
+#ifdef WIN32
+/// Gets various properties of the process identified by `pid`.
+///
+/// @param pid Process to inspect.
+/// @return Map of process properties, empty on error.
+Dictionary os_proc_info(int pid)
+{
+  Dictionary pinfo = ARRAY_DICT_INIT;
+  PROCESSENTRY32 pe;
+
+  // Snapshot of all processes.  This is used instead of:
+  //    OpenProcess(PROCESS_QUERY_INFORMATION | PROCESS_VM_READ, …)
+  // to avoid ERROR_PARTIAL_COPY.  https://stackoverflow.com/a/29942376
+  HANDLE h = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
+  if (h == INVALID_HANDLE_VALUE) {
+    return pinfo;  // Return empty.
+  }
+
+  pe.dwSize = sizeof(PROCESSENTRY32);
+  // Get root process.
+  if (!Process32First(h, &pe)) {
+    CloseHandle(h);
+    return pinfo;  // Return empty.
+  }
+  // Find the process.
+  do {
+    if (pe.th32ProcessID == (DWORD)pid) {
+      break;
+    }
+  } while (Process32Next(h, &pe));
+  CloseHandle(h);
+
+  if (pe.th32ProcessID == (DWORD)pid) {
+    PUT(pinfo, "pid", INTEGER_OBJ(pid));
+    PUT(pinfo, "ppid", INTEGER_OBJ((int)pe.th32ParentProcessID));
+    PUT(pinfo, "name", STRING_OBJ(cstr_to_string(pe.szExeFile)));
+  }
+
+  return pinfo;
+}
+#endif

src/nvim/os/process.h

@@ -2,6 +2,7 @@
 #define NVIM_OS_PROCESS_H
 
 #include <stddef.h>
+#include "nvim/api/private/defs.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "os/process.h.generated.h"

test/functional/api/proc_spec.lua

@@ -1,10 +1,14 @@
 local helpers = require('test.functional.helpers')(after_each)
 
-local clear, eq = helpers.clear, helpers.eq
+local clear = helpers.clear
+local eq = helpers.eq
 local funcs = helpers.funcs
+local iswin = helpers.iswin
 local nvim_argv = helpers.nvim_argv
+local ok = helpers.ok
 local request = helpers.request
 local retry = helpers.retry
+local NIL = helpers.NIL
 
 describe('api', function()
   before_each(clear)
@@ -43,11 +47,35 @@ describe('api', function()
       eq(false, status)
       eq("Invalid pid: 0", string.match(rv, "Invalid.*"))
 
-      -- Assume PID 99999999 does not exist.
+      -- Assume PID 99999 does not exist.
-      status, rv = pcall(request, "nvim_get_proc_children", 99999999)
+      status, rv = pcall(request, "nvim_get_proc_children", 99999)
       eq(true, status)
       eq({}, rv)
     end)
   end)
 
+  describe('nvim_get_proc', function()
+    it('returns process info', function()
+      local pid = funcs.getpid()
+      local pinfo = request('nvim_get_proc', pid)
+      eq((iswin() and 'nvim.exe' or 'nvim'), pinfo.name)
+      ok(pinfo.pid == pid)
+      ok(type(pinfo.ppid) == 'number' and pinfo.ppid ~= pid)
+    end)
+
+    it('validates input', function()
+      local status, rv = pcall(request, "nvim_get_proc", -1)
+      eq(false, status)
+      eq("Invalid pid: -1", string.match(rv, "Invalid.*"))
+
+      status, rv = pcall(request, "nvim_get_proc", 0)
+      eq(false, status)
+      eq("Invalid pid: 0", string.match(rv, "Invalid.*"))
+
+      -- Assume PID 99999 does not exist.
+      status, rv = pcall(request, "nvim_get_proc", 99999)
+      eq(true, status)
+      eq(NIL, rv)
+    end)
+  end)
 end)