add memory_istream

src/io/memory_istream.hpp

@@ -0,0 +1,34 @@
+#pragma once
+
+#include <istream>
+#include "util/Buffer.hpp"
+
+class memory_istream : public std::istream {
+public:
+    explicit memory_istream(util::Buffer<char> buffer)
+        : std::istream(&buf), buf(std::move(buffer)) {}
+
+private:
+    class memory_streambuf : public std::streambuf {
+    public:
+        explicit memory_streambuf(util::Buffer<char> buffer)
+            : buffer(std::move(buffer)) {
+            char* base = this->buffer.data();
+            char* end = base + this->buffer.size();
+            setg(base, base, end);
+        }
+        
+        memory_streambuf(const memory_streambuf&) = delete;
+        memory_streambuf& operator=(const memory_streambuf&) = delete;
+    
+    protected:
+        int_type underflow() override {
+            return traits_type::eof();
+        }
+    
+    private:
+        util::Buffer<char> buffer;
+    };
+    
+    memory_streambuf buf;
+};

test/io/memory_istream.cpp

@@ -0,0 +1,19 @@
+#include <gtest/gtest.h>
+
+#include "io/memory_istream.hpp"
+
+TEST(io, memory_istream) {
+    const char data[] = "Hello, world!";
+    const int n = std::strlen(data);
+
+    util::Buffer<char> buffer(data, n);
+    memory_istream stream(std::move(buffer));
+
+    ASSERT_TRUE(stream.good());
+
+    std::string text(n, '\0');
+    stream.read(text.data(), n);
+    ASSERT_EQ(text, std::string(data));
+    stream.read(text.data(), 1);
+    ASSERT_TRUE(stream.eof());
+}