From 9389d63a5f2e64759c91a5dd114aebb14032de4d Mon Sep 17 00:00:00 2001
From: MihailRis <mexaruc@gmail.com>
Date: Sat, 22 Feb 2025 07:03:18 +0300
Subject: [PATCH] add deflate_istream

---
 src/io/deflate_istream.hpp | 101 +++++++++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)
 create mode 100644 src/io/deflate_istream.hpp

diff --git a/src/io/deflate_istream.hpp b/src/io/deflate_istream.hpp
new file mode 100644
index 00000000..ecbc738a
--- /dev/null
+++ b/src/io/deflate_istream.hpp
@@ -0,0 +1,101 @@
+#pragma once
+
+#define ZLIB_CONST
+#include <zlib.h>
+#include <istream>
+#include <memory>
+#include <array>
+#include <stdexcept>
+
+class deflate_istream : public std::istream {
+public:
+    explicit deflate_istream(std::unique_ptr<std::istream> src)
+        : std::istream(&buf), source(std::move(src)), buf(*source) {}
+
+private:
+    class deflate_streambuf : public std::streambuf {
+    public:
+        explicit deflate_streambuf(std::istream& src) : src(src) {
+            zstream.zalloc = Z_NULL;
+            zstream.zfree = Z_NULL;
+            zstream.opaque = Z_NULL;
+            zstream.avail_in = 0;
+            zstream.next_in = Z_NULL;
+            
+            int ret = inflateInit2(&zstream, -15);
+            if (ret != Z_OK) {
+                throw std::runtime_error("zlib init failed");
+            }
+        }
+
+        ~deflate_streambuf() {
+            inflateEnd(&zstream);
+        }
+
+        deflate_streambuf(const deflate_streambuf&) = delete;
+        deflate_streambuf& operator=(const deflate_streambuf&) = delete;
+
+    protected:
+        int_type underflow() override {
+            if (gptr() < egptr()) {
+                return traits_type::to_int_type(*gptr());
+            }
+
+            if (eof) {
+                return traits_type::eof();
+            }
+
+            zstream.next_out = reinterpret_cast<Bytef*>(outBuf.data());
+            zstream.avail_out = outBuf.size();
+
+            do {
+                if (zstream.avail_in == 0) {
+                    src.read(inBuf.data(), inBuf.size());
+                    zstream.avail_in = static_cast<uInt>(src.gcount());
+                    zstream.next_in = reinterpret_cast<Bytef*>(inBuf.data());
+                    
+                    if (src.bad()) {
+                        return traits_type::eof();
+                    }
+                }
+
+                int ret = inflate(&zstream, Z_NO_FLUSH);
+                if (ret == Z_STREAM_END) {
+                    eof = true;
+                } else if (ret != Z_OK) {
+                    if (ret == Z_BUF_ERROR && zstream.avail_out == outBuf.size()) {
+                        continue;
+                    }
+                    return traits_type::eof();
+                }
+
+                const auto decompressed = outBuf.size() - zstream.avail_out;
+                if (decompressed > 0) {
+                    setg(outBuf.data(), 
+                         outBuf.data(), 
+                         outBuf.data() + decompressed);
+                    return traits_type::to_int_type(*gptr());
+                }
+
+                if (eof) {
+                    return traits_type::eof();
+                }
+
+            } while (zstream.avail_in > 0 || !src.eof());
+
+            return traits_type::eof();
+        }
+
+    private:
+        static constexpr size_t BUFFER_SIZE = 16384;
+
+        std::istream& src;
+        z_stream zstream {};
+        std::array<char, BUFFER_SIZE> inBuf {};
+        std::array<char, BUFFER_SIZE> outBuf {};
+        bool eof = false;
+    };
+
+    std::unique_ptr<std::istream> source;
+    deflate_streambuf buf;
+};