Provide basic read only access to dictzip files

`dictzip::Istream` and `dictzip::IstreamBuf` are forked from `alpinocorpus::DzIstream` and `alpinocorpus::DzIstreamBuf` of rug-compling/alpinocorpus.

1 files changed, 58 insertions, 0 deletions

diff --git a/src/istream/buffer.h b/src/istream/buffer.h
new file mode 100644
index 0000000..91bb53f
--- /dev/null
+++ b/src/istream/buffer.h
@@ -0,0 +1,58 @@
+#pragma once
+
+#include <cstdio>
+#include <iostream>
+#include <streambuf>
+#include <vector>
+
+namespace dictzip {
+
+// Warning: The inherent statefulness of stream buffers interferes with
+// multithreaded access. Users of this class should perform appropriate
+// locking, since they are in a better position to do so.
+class IstreamBuf : public std::streambuf {
+private:
+	struct Chunk {
+		Chunk(size_t offset, size_t size):
+			offset(offset),
+			size(size) {};
+
+		const size_t offset;
+		const size_t size;
+	};
+
+	FILE* dictzip_file_;
+
+	std::vector<unsigned char> buffer_;
+	std::vector<unsigned char> header_;
+	std::vector<Chunk>  chunks_;
+
+	size_t chunk_length_;
+	long data_offset_;
+	long curr_chunk_;
+
+	void readChunk(long n);
+	void readHeader();
+	void readExtra();
+	void skipOptional();
+
+protected:
+	int underflow();
+	std::streamsize xsgetn(char *dest, std::streamsize n);
+
+public:
+	using pos_type = std::streambuf::pos_type;
+	using off_type = std::streambuf::off_type;
+
+	typedef std::ios::seekdir  seekdir;
+	typedef std::ios::openmode openmode;
+
+	IstreamBuf(char const* filename);
+	~IstreamBuf();
+
+	pos_type seekoff(off_type off, seekdir dir, openmode);
+	pos_type seekpos(pos_type off, openmode mode);
+
+};
+
+}