From 4ef8fe8794d6dce8ca83eeae5a364eaec11c934e Mon Sep 17 00:00:00 2001
From: Paul Hollinsky <phollinsky@intrepidcs.com>
Date: Mon, 28 Feb 2022 01:54:21 -0500
Subject: [PATCH] Disk: Predictable behavior for zero length reads

---
 disk/diskreaddriver.cpp      |  3 +++
 disk/diskwritedriver.cpp     |  3 +++
 test/diskdriverreadtest.cpp  |  9 +++++++++
 test/diskdriverwritetest.cpp | 11 +++++++++++
 4 files changed, 26 insertions(+)

diff --git a/disk/diskreaddriver.cpp b/disk/diskreaddriver.cpp
index b795dc6..d37e34d 100644
--- a/disk/diskreaddriver.cpp
+++ b/disk/diskreaddriver.cpp
@@ -6,6 +6,9 @@ using namespace icsneo::Disk;
 
 optional<uint64_t> ReadDriver::readLogicalDisk(Communication& com, device_eventhandler_t report,
 	uint64_t pos, uint8_t* into, uint64_t amount, std::chrono::milliseconds timeout) {
+	if(amount == 0)
+		return 0;
+
 	optional<uint64_t> ret;
 
 	// Read into here if we can't read directly into the user buffer
diff --git a/disk/diskwritedriver.cpp b/disk/diskwritedriver.cpp
index 58b0fd9..fe4ab46 100644
--- a/disk/diskwritedriver.cpp
+++ b/disk/diskwritedriver.cpp
@@ -9,6 +9,9 @@ const APIEvent::Severity WriteDriver::NonatomicSeverity = APIEvent::Severity::Ev
 
 optional<uint64_t> WriteDriver::writeLogicalDisk(Communication& com, device_eventhandler_t report, ReadDriver& readDriver,
 	uint64_t pos, const uint8_t* from, uint64_t amount, std::chrono::milliseconds timeout) {
+	if(amount == 0)
+		return 0;
+
 	optional<uint64_t> ret;
 
 	const uint32_t idealBlockSize = getBlockSizeBounds().second;
diff --git a/test/diskdriverreadtest.cpp b/test/diskdriverreadtest.cpp
index 1449f20..c6070b8 100644
--- a/test/diskdriverreadtest.cpp
+++ b/test/diskdriverreadtest.cpp
@@ -11,6 +11,15 @@ TEST_F(DiskDriverTest, Read) {
 	EXPECT_EQ(driver->readCalls, 1u);
 }
 
+TEST_F(DiskDriverTest, ReadZero) {
+	uint8_t b = 0xCDu;
+	const auto amountRead = readLogicalDisk(0, &b, 0);
+	EXPECT_TRUE(amountRead.has_value());
+	EXPECT_EQ(amountRead, 0u);
+	EXPECT_EQ(b, 0xCDu);
+	EXPECT_EQ(driver->readCalls, 0u);
+}
+
 TEST_F(DiskDriverTest, ReadUnaligned) {
 	std::array<uint8_t, 120> buf;
 	buf.fill(0u);
diff --git a/test/diskdriverwritetest.cpp b/test/diskdriverwritetest.cpp
index 493e14c..1da8435 100644
--- a/test/diskdriverwritetest.cpp
+++ b/test/diskdriverwritetest.cpp
@@ -12,6 +12,17 @@ TEST_F(DiskDriverTest, Write) {
 	EXPECT_EQ(driver->writeCalls, 1u);
 }
 
+TEST_F(DiskDriverTest, WriteZero) {
+	uint8_t b = 0xCDu;
+	const auto amountWritten = writeLogicalDisk(0, &b, 0);
+	EXPECT_TRUE(amountWritten.has_value());
+	EXPECT_EQ(amountWritten, 0u);
+	EXPECT_EQ(driver->mockDisk[0], TEST_STRING[0]);
+	EXPECT_EQ(driver->atomicityChecks, 0u);
+	EXPECT_EQ(driver->readCalls, 0u);
+	EXPECT_EQ(driver->writeCalls, 0u);
+}
+
 TEST_F(DiskDriverTest, WriteNoAtomicityCheck) {
 	driver->supportsAtomic = false;
 	expectedErrors.push({ APIEvent::Type::AtomicOperationCompletedNonatomically, APIEvent::Severity::EventInfo });