From 5546086ca9c7494449552784d8acf08e833ed2e7 Mon Sep 17 00:00:00 2001
From: Richard Hodges <hodges.r@gmail.com>
Date: Thu, 13 May 2021 21:06:40 +0200
Subject: [PATCH] Remove use of POSIX-only constant

fixes #2233
refs #2231
---
 CHANGELOG.md                                 |  4 ++++
 include/boost/beast/core/impl/file_posix.ipp | 16 ++++++++++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ac1d5791..f3c8bfff 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+* Remove use of POSIX-only constant.
+
+--------------------------------------------------------------------------------
+
 Version 317:
 
 * Remove travis CI.
diff --git a/include/boost/beast/core/impl/file_posix.ipp b/include/boost/beast/core/impl/file_posix.ipp
index 61a33a52..1bb7ae10 100644
--- a/include/boost/beast/core/impl/file_posix.ipp
+++ b/include/boost/beast/core/impl/file_posix.ipp
@@ -270,8 +270,12 @@ read(void* buffer, std::size_t n, error_code& ec) const
     std::size_t nread = 0;
     while(n > 0)
     {
-        auto const amount = static_cast<ssize_t>((std::min)(
-            n, static_cast<std::size_t>(SSIZE_MAX)));
+        // <limits> not required to define SSIZE_MAX so we avoid it
+        constexpr auto ssmax =
+            static_cast<std::size_t>((std::numeric_limits<
+                decltype(::read(fd_, buffer, n))>::max)());
+        auto const amount = (std::min)(
+            n, ssmax);
         auto const result = ::read(fd_, buffer, amount);
         if(result == -1)
         {
@@ -305,8 +309,12 @@ write(void const* buffer, std::size_t n, error_code& ec)
     std::size_t nwritten = 0;
     while(n > 0)
     {
-        auto const amount = static_cast<ssize_t>((std::min)(
-            n, static_cast<std::size_t>(SSIZE_MAX)));
+        // <limits> not required to define SSIZE_MAX so we avoid it
+        constexpr auto ssmax =
+            static_cast<std::size_t>((std::numeric_limits<
+                decltype(::write(fd_, buffer, n))>::max)());
+        auto const amount = (std::min)(
+            n, ssmax);
         auto const result = ::write(fd_, buffer, amount);
         if(result == -1)
         {