From ea268d3158637e7d57f76d182cda72bc0adef22c Mon Sep 17 00:00:00 2001
From: Dustin Decker <dustin@trufflesec.com>
Date: Thu, 10 Mar 2022 21:15:49 -0800
Subject: [PATCH] Add AvailableMemory for Linux

---
 doc.go            | 10 ++++++++++
 memory_bsd.go     |  5 +++++
 memory_darwin.go  |  5 +++++
 memory_linux.go   | 16 ++++++++++++++++
 memory_windows.go |  5 +++++
 5 files changed, 41 insertions(+)

diff --git a/doc.go b/doc.go
index 4e4f984..862d8a1 100644
--- a/doc.go
+++ b/doc.go
@@ -22,3 +22,13 @@ func TotalMemory() uint64 {
 func FreeMemory() uint64 {
 	return sysFreeMemory()
 }
+
+// AvailableMemory returns the total free+freeable system memory in bytes.
+//
+// The total available memory is the free memory + freeable memory
+// such as buffer and cache.
+//
+// If available memory size could not be determined, then 0 is returned.
+func AvailableMemory() uint64 {
+	return sysAvailableMemory()
+}
diff --git a/memory_bsd.go b/memory_bsd.go
index 49d808a..ed18ff1 100644
--- a/memory_bsd.go
+++ b/memory_bsd.go
@@ -1,3 +1,4 @@
+//go:build freebsd || openbsd || dragonfly || netbsd
 // +build freebsd openbsd dragonfly netbsd
 
 package memory
@@ -17,3 +18,7 @@ func sysFreeMemory() uint64 {
 	}
 	return s
 }
+
+func sysAvailableMemory() uint64 {
+	return sysFreeMemory()
+}
diff --git a/memory_darwin.go b/memory_darwin.go
index a3f4576..5019cfd 100644
--- a/memory_darwin.go
+++ b/memory_darwin.go
@@ -1,3 +1,4 @@
+//go:build darwin
 // +build darwin
 
 package memory
@@ -47,3 +48,7 @@ func sysFreeMemory() uint64 {
 	}
 	return freePages * pageSize
 }
+
+func sysAvailableMemory() uint64 {
+	return sysFreeMemory()
+}
diff --git a/memory_linux.go b/memory_linux.go
index 3d07711..ad75f20 100644
--- a/memory_linux.go
+++ b/memory_linux.go
@@ -1,3 +1,4 @@
+//go:build linux
 // +build linux
 
 package memory
@@ -27,3 +28,18 @@ func sysFreeMemory() uint64 {
 	// So we always convert to uint64 to match signature.
 	return uint64(in.Freeram) * uint64(in.Unit)
 }
+
+func sysAvailableMemory() uint64 {
+	in := &syscall.Sysinfo_t{}
+	err := syscall.Sysinfo(in)
+	if err != nil {
+		return 0
+	}
+	// If this is a 32-bit system, then these fields are
+	// uint32 instead of uint64.
+	// So we always convert to uint64 to match signature.
+	// Buffer/cache ram is included on linux since the kernel
+	// will free this memory for applications if needed, and tends
+	// to use almost all free memory for itself when it can.
+	return (uint64(in.Freeram) + uint64(in.Bufferram)) * uint64(in.Unit)
+}
diff --git a/memory_windows.go b/memory_windows.go
index c8500cc..fa8014e 100644
--- a/memory_windows.go
+++ b/memory_windows.go
@@ -1,3 +1,4 @@
+//go:build windows
 // +build windows
 
 package memory
@@ -58,3 +59,7 @@ func sysFreeMemory() uint64 {
 	}
 	return msx.ullAvailPhys
 }
+
+func sysAvailableMemory() uint64 {
+	return sysFreeMemory()
+}