From d9a4020a92db3fdc92163fa1bdb8b46ce13fae86 Mon Sep 17 00:00:00 2001
From: chriseth <chris@ethereum.org>
Date: Wed, 1 Dec 2021 12:31:21 +0100
Subject: [PATCH] Function to read a number of bytes from an input stream.

---
 libsolutil/CommonIO.cpp      | 11 +++++++++++
 libsolutil/CommonIO.h        |  4 ++++
 test/libsolutil/CommonIO.cpp |  9 +++++++++
 3 files changed, 24 insertions(+)

diff --git a/libsolutil/CommonIO.cpp b/libsolutil/CommonIO.cpp
index 9da5b2422..6089f4db6 100644
--- a/libsolutil/CommonIO.cpp
+++ b/libsolutil/CommonIO.cpp
@@ -79,6 +79,17 @@ string solidity::util::readUntilEnd(istream& _stdin)
 	return ss.str();
 }
 
+string solidity::util::readBytes(istream& _input, size_t _length)
+{
+	string output;
+	output.resize(_length);
+	_input.read(output.data(), static_cast<streamsize>(_length));
+	// If read() reads fewer bytes it sets failbit in addition to eofbit.
+	if (_input.fail())
+		output.resize(static_cast<size_t>(_input.gcount()));
+	return output;
+}
+
 #if defined(_WIN32)
 class DisableConsoleBuffering
 {
diff --git a/libsolutil/CommonIO.h b/libsolutil/CommonIO.h
index ab0000f86..e6cd0c161 100644
--- a/libsolutil/CommonIO.h
+++ b/libsolutil/CommonIO.h
@@ -57,6 +57,10 @@ std::string readFileAsString(boost::filesystem::path const& _file);
 /// Retrieves and returns the whole content of the specified input stream (until EOF).
 std::string readUntilEnd(std::istream& _stdin);
 
+/// Tries to read exactly @a _length bytes from @a _input.
+/// Returns a string containing as much data as has been read.
+std::string readBytes(std::istream& _input, size_t _length);
+
 /// Retrieves and returns a character from standard input (without waiting for EOL).
 int readStandardInputChar();
 
diff --git a/test/libsolutil/CommonIO.cpp b/test/libsolutil/CommonIO.cpp
index ce1a24a41..8b8c3d326 100644
--- a/test/libsolutil/CommonIO.cpp
+++ b/test/libsolutil/CommonIO.cpp
@@ -90,6 +90,15 @@ BOOST_AUTO_TEST_CASE(readUntilEnd_empty)
 	BOOST_TEST(readUntilEnd(inputStream) == "");
 }
 
+BOOST_AUTO_TEST_CASE(readBytes_past_end)
+{
+	istringstream inputStream("abc");
+	BOOST_CHECK_EQUAL(readBytes(inputStream, 0), "");
+	BOOST_CHECK_EQUAL(readBytes(inputStream, 1), "a");
+	BOOST_CHECK_EQUAL(readBytes(inputStream, 20), "bc");
+	BOOST_CHECK_EQUAL(readBytes(inputStream, 20), "");
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 } // namespace solidity::util::test