From 5c3617b9e9088ecd9b81b02095ba7b41d6766edc Mon Sep 17 00:00:00 2001
From: Finagolfin <repo@butta.fastem.com>
Date: Fri, 24 Nov 2023 18:59:06 +0530
Subject: [PATCH 1/4] Android: update pread/pwrite for nullability annotations
 in NDK 26

---
 Sources/System/Internals/Syscalls.swift | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Sources/System/Internals/Syscalls.swift b/Sources/System/Internals/Syscalls.swift
index 9fcb2f90..3d375a52 100644
--- a/Sources/System/Internals/Syscalls.swift
+++ b/Sources/System/Internals/Syscalls.swift
@@ -71,7 +71,7 @@ internal func system_pread(
 #if ENABLE_MOCKING
   if mockingEnabled { return _mockInt(fd, buf, nbyte, offset) }
 #endif
-  return pread(fd, buf, nbyte, offset)
+  return pread(fd, buf!, nbyte, offset)
 }
 
 // lseek
@@ -101,7 +101,7 @@ internal func system_pwrite(
 #if ENABLE_MOCKING
   if mockingEnabled { return _mockInt(fd, buf, nbyte, offset) }
 #endif
-  return pwrite(fd, buf, nbyte, offset)
+  return pwrite(fd, buf!, nbyte, offset)
 }
 
 internal func system_dup(_ fd: Int32) -> Int32 {

From c2e8f24c7c81c1842af8a556f7940abf96ec3a5f Mon Sep 17 00:00:00 2001
From: Guillaume Lessard <guillaume.lessard@apple.com>
Date: Thu, 4 Jan 2024 17:48:48 -0800
Subject: [PATCH 2/4] avoid passing null pointer to pread() or pwrite()

---
 Sources/System/Internals/Syscalls.swift | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Sources/System/Internals/Syscalls.swift b/Sources/System/Internals/Syscalls.swift
index 3d375a52..d4549070 100644
--- a/Sources/System/Internals/Syscalls.swift
+++ b/Sources/System/Internals/Syscalls.swift
@@ -71,7 +71,7 @@ internal func system_pread(
 #if ENABLE_MOCKING
   if mockingEnabled { return _mockInt(fd, buf, nbyte, offset) }
 #endif
-  return pread(fd, buf!, nbyte, offset)
+  return buf.map({ pread(fd, $0, nbyte, offset) }) ?? 0
 }
 
 // lseek
@@ -101,7 +101,7 @@ internal func system_pwrite(
 #if ENABLE_MOCKING
   if mockingEnabled { return _mockInt(fd, buf, nbyte, offset) }
 #endif
-  return pwrite(fd, buf!, nbyte, offset)
+  return buf.map({ pwrite(fd, $0, nbyte, offset) }) ?? 0
 }
 
 internal func system_dup(_ fd: Int32) -> Int32 {

From 14597334dcdad2f0e669909882bddbb6f2762034 Mon Sep 17 00:00:00 2001
From: Guillaume Lessard <guillaume.lessard@apple.com>
Date: Fri, 5 Jan 2024 17:57:14 -0800
Subject: [PATCH 3/4] [test] test reading and writing empty, nil-based buffers

---
 Tests/SystemTests/FileOperationsTest.swift | 24 ++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/Tests/SystemTests/FileOperationsTest.swift b/Tests/SystemTests/FileOperationsTest.swift
index 8062aedc..ca178ba5 100644
--- a/Tests/SystemTests/FileOperationsTest.swift
+++ b/Tests/SystemTests/FileOperationsTest.swift
@@ -86,6 +86,30 @@ final class FileOperationsTest: XCTestCase {
     for test in syscallTestCases { test.runAllTests() }
   }
 
+  func testWriteFromEmptyBuffer() throws {
+    let fd = try FileDescriptor.open(FilePath("/dev/null"), .writeOnly)
+    let written1 = try fd.write(toAbsoluteOffset: 0, .init(start: nil, count: 0))
+    XCTAssertEqual(written1, 0)
+
+    let pointer = UnsafeMutableRawPointer.allocate(byteCount: 8, alignment: 8)
+    defer { pointer.deallocate() }
+    let empty = UnsafeRawBufferPointer(start: pointer, count: 0)
+    let written2 = try fd.write(toAbsoluteOffset: 0, empty)
+    XCTAssertEqual(written2, 0)
+  }
+
+  func testReadToEmptyBuffer() throws {
+    let fd = try FileDescriptor.open(FilePath("/dev/random"), .readOnly)
+    let read1 = try fd.read(fromAbsoluteOffset: 0, into: .init(start: nil, count: 0))
+    XCTAssertEqual(read1, 0)
+
+    let pointer = UnsafeMutableRawPointer.allocate(byteCount: 8, alignment: 8)
+    defer { pointer.deallocate() }
+    let empty = UnsafeMutableRawBufferPointer(start: pointer, count: 0)
+    let read2 = try fd.read(fromAbsoluteOffset: 0, into: empty)
+    XCTAssertEqual(read2, 0)
+  }
+
   func testHelpers() {
     // TODO: Test writeAll, writeAll(toAbsoluteOffset), closeAfter
   }

From 5ca37e7d3997b00e19d4a77d45db7830b18b6f56 Mon Sep 17 00:00:00 2001
From: Guillaume Lessard <guillaume.lessard@apple.com>
Date: Fri, 8 Mar 2024 12:58:48 -0800
Subject: [PATCH 4/4] Android: more targeted approach to unusual nullabilities

---
 Sources/System/Internals/Syscalls.swift | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/Sources/System/Internals/Syscalls.swift b/Sources/System/Internals/Syscalls.swift
index d4549070..236ee6cd 100644
--- a/Sources/System/Internals/Syscalls.swift
+++ b/Sources/System/Internals/Syscalls.swift
@@ -71,7 +71,15 @@ internal func system_pread(
 #if ENABLE_MOCKING
   if mockingEnabled { return _mockInt(fd, buf, nbyte, offset) }
 #endif
-  return buf.map({ pread(fd, $0, nbyte, offset) }) ?? 0
+#if os(Android)
+  var zero = UInt8.zero
+  return withUnsafeMutablePointer(to: &zero) {
+    // this pread has a non-nullable `buf` pointer
+    pread(fd, buf ?? UnsafeMutableRawPointer($0), nbyte, offset)
+  }
+#else
+  return pread(fd, buf, nbyte, offset)
+#endif
 }
 
 // lseek
@@ -101,7 +109,15 @@ internal func system_pwrite(
 #if ENABLE_MOCKING
   if mockingEnabled { return _mockInt(fd, buf, nbyte, offset) }
 #endif
-  return buf.map({ pwrite(fd, $0, nbyte, offset) }) ?? 0
+#if os(Android)
+  var zero = UInt8.zero
+  return withUnsafeMutablePointer(to: &zero) {
+    // this pwrite has a non-nullable `buf` pointer
+    pwrite(fd, buf ?? UnsafeRawPointer($0), nbyte, offset)
+  }
+#else
+  return pwrite(fd, buf, nbyte, offset)
+#endif
 }
 
 internal func system_dup(_ fd: Int32) -> Int32 {