feat(common): streaming raw deflate and CRC-32 in ZCompression

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

dCommon/ZCompression.h

@@ -1,6 +1,8 @@
 #pragma once
 
 #include <cstdint>
+#include <functional>
+#include <memory>
 #include <optional>
 #include <string>
 #include <string_view>
@@ -20,5 +22,34 @@ namespace ZCompression {
 
 	// Raw deflate data (no zlib or gzip header, as in zip files) that inflates to `size` bytes; nullopt when it doesn't
 	std::optional<std::string> InflateRaw(std::string_view data, size_t size);
-}
 
+	// CRC-32 (as in zip and gzip files) of `data`, continuing from `crc` (0 to start)
+	uint32_t Crc32(uint32_t crc, std::string_view data);
+
+	/**
+	 * Raw deflate (as in zip files) of data given a piece at a time, so a big file never has to sit in memory: each
+	 * Write and Finish hands what's compressed so far to `sink`.
+	 */
+	class RawDeflater {
+	public:
+		using Sink = std::function<bool(std::string_view)>; // false stops (e.g. the disk is full)
+		explicit RawDeflater(Sink sink, int level = 6);
+		~RawDeflater();
+		RawDeflater(const RawDeflater&) = delete;
+		RawDeflater& operator=(const RawDeflater&) = delete;
+
+		bool Write(std::string_view data);
+		// The rest of the compressed data; the deflater can't be written to afterwards
+		bool Finish();
+		uint64_t BytesIn() const { return m_In; }
+		uint64_t BytesOut() const { return m_Out; }
+
+	private:
+		bool Run(std::string_view data, int flush);
+		struct State;
+		std::unique_ptr<State> m_State;
+		Sink m_Sink;
+		uint64_t m_In{};
+		uint64_t m_Out{};
+	};
+}