From e8828c152dfe20305e2c16bf85f42b8cba65d164 Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <github@carlo.cab>
Date: Wed, 13 Aug 2025 13:55:33 +0800
Subject: [PATCH] Apply review suggestions for `pid_path.rb`

Co-authored-by: MikeMcQuaid <125011+MikeMcQuaid@users.noreply.github.com>
---
 Library/Homebrew/utils/pid_path.rb | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/Library/Homebrew/utils/pid_path.rb b/Library/Homebrew/utils/pid_path.rb
index 1ae07a78fe..73f7505b68 100755
--- a/Library/Homebrew/utils/pid_path.rb
+++ b/Library/Homebrew/utils/pid_path.rb
@@ -2,22 +2,31 @@
 # typed: strict
 # frozen_string_literal: true
 
+pid = ARGV[0]&.to_i
+exit 1 unless pid
+
 require "fiddle"
 
 libproc = Fiddle.dlopen("/usr/lib/libproc.dylib")
 
-proc_pidpath = Fiddle::Function.new(
+libproc_proc_pidpath_function = Fiddle::Function.new(
   libproc["proc_pidpath"],
   [Fiddle::TYPE_INT, Fiddle::TYPE_VOIDP, Fiddle::TYPE_UINT32_T],
   Fiddle::TYPE_INT,
 )
 
-pid = ARGV[0]&.to_i
-exit 1 unless pid
+# We have to allocate a (char) buffer of exactly `PROC_PIDPATHINFO_MAXSIZE` to use `proc_pidpath`
+# From `include/sys/proc_info.h`, PROC_PIDPATHINFO_MAXSIZE = 4 * MAXPATHLEN
+# From `include/sys/param.h`, MAXPATHLEN = PATH_MAX
+# From `include/sys/syslimits.h`, PATH_MAX = 1024
+# https://github.com/apple-oss-distributions/xnu/blob/e3723e1f17661b24996789d8afc084c0c3303b26/libsyscall/wrappers/libproc/libproc.c#L268-L275
+buffer_size = 4 * 1024 # PROC_PIDPATHINFO_MAXSIZE = 4 * MAXPATHLEN
+buffer = "\0" * buffer_size
+pointer_to_buffer = Fiddle::Pointer.to_ptr(buffer)
 
-bufsize = 4 * 1024 # PROC_PIDPATHINFO_MAXSIZE = 4 * MAXPATHLEN
-buf = "\0" * bufsize
-ptr = Fiddle::Pointer.to_ptr(buf)
-
-ret = proc_pidpath.call(pid, ptr, bufsize)
-puts ptr.to_s.strip if ret.positive?
+# `proc_pidpath` returns a positive value on success. See:
+# https://stackoverflow.com/a/8149198
+# https://github.com/chromium/chromium/blob/86df41504a235f9369f6f53887da12a718a19db4/base/process/process_handle_mac.cc#L37-L44
+# https://github.com/apple-oss-distributions/xnu/blob/e3723e1f17661b24996789d8afc084c0c3303b26/libsyscall/wrappers/libproc/libproc.c#L263-L283
+return_value = libproc_proc_pidpath_function.call(pid, pointer_to_buffer, buffer_size)
+puts pointer_to_buffer.to_s.strip if return_value.positive?