1 files changed, 77 insertions, 2 deletions
diff --git a/zen/zlib_wrap.cpp b/zen/zlib_wrap.cpp
index fbbe2f09..9eb4302f 100755..100644
--- a/zen/zlib_wrap.cpp
+++ b/zen/zlib_wrap.cpp
@@ -6,9 +6,9 @@
 
 #include "zlib_wrap.h"
 //Windows:     use the SAME zlib version that wxWidgets is linking against! //C:\Data\Projects\wxWidgets\Source\src\zlib\zlib.h
-//Linux/macOS: use zlib system header for both wxWidgets and Curl (zlib is required for HTTP)
+//Linux/macOS: use zlib system header for both wxWidgets and libcurl (zlib is required for HTTP)
 //             => don't compile wxWidgets with: --with-zlib=builtin
-#include <zlib.h>
+#include <zlib.h> //https://www.zlib.net/manual.html
 
 using namespace zen;
 
@@ -51,3 +51,78 @@ size_t zen::impl::zlib_decompress(const void* src, size_t srcLen, void* trg, siz
         throw ZlibInternalError();
     return bufferSize;
 }
+
+
+class InputStreamAsGzip::Impl
+{
+public:
+    Impl(const std::function<size_t(void* buffer, size_t bytesToRead)>& readBlock /*throw X*/) : //throw ZlibInternalError; returning 0 signals EOF: Posix read() semantics
+        readBlock_(readBlock)
+    {
+        const int windowBits = MAX_WBITS + 16; //"add 16 to windowBits to write a simple gzip header"
+
+        //"memLevel=1 uses minimum memory but is slow and reduces compression ratio; memLevel=9 uses maximum memory for optimal speed.
+        const int memLevel = 9; //test; 280 MB installer file: level 9 shrinks runtime by ~8% compared to level 8 (==DEF_MEM_LEVEL) at the cost of 128 KB extra memory
+        static_assert(memLevel <= MAX_MEM_LEVEL);
+
+        const int rv = ::deflateInit2(&gzipStream_,          //z_streamp strm
+                                      3 /*see db_file.cpp*/, //int level
+                                      Z_DEFLATED,            //int method
+                                      windowBits,            //int windowBits
+                                      memLevel,              //int memLevel
+                                      Z_DEFAULT_STRATEGY);   //int strategy
+        if (rv != Z_OK)
+            throw ZlibInternalError();
+    }
+
+    ~Impl()
+    {
+        const int rv = ::deflateEnd(&gzipStream_);
+        assert(rv == Z_OK);
+        (void)rv;
+    }
+
+    size_t read(void* buffer, size_t bytesToRead) //throw ZlibInternalError, X; return "bytesToRead" bytes unless end of stream!
+    {
+        if (bytesToRead == 0) //"read() with a count of 0 returns zero" => indistinguishable from end of file! => check!
+            throw std::logic_error("Contract violation! " + std::string(__FILE__) + ":" + numberTo<std::string>(__LINE__));
+
+        gzipStream_.next_out  = static_cast<Bytef*>(buffer);
+        gzipStream_.avail_out = static_cast<uInt>(bytesToRead);
+
+        for (;;)
+        {
+            if (gzipStream_.avail_in == 0 && !eof_)
+            {
+                if (bufIn_.size() < bytesToRead)
+                    bufIn_.resize(bytesToRead);
+
+                const size_t bytesRead = readBlock_(&bufIn_[0], bufIn_.size()); //throw X; returning 0 signals EOF: Posix read() semantics
+                gzipStream_.next_in  = reinterpret_cast<z_const Bytef*>(&bufIn_[0]);
+                gzipStream_.avail_in = static_cast<uInt>(bytesRead);
+                if (bytesRead == 0)
+                    eof_ = true;
+            }
+
+            const int rv = ::deflate(&gzipStream_, eof_ ? Z_FINISH : Z_NO_FLUSH);
+            if (rv == Z_STREAM_END)
+                return bytesToRead - gzipStream_.avail_out;
+            if (rv != Z_OK)
+                throw ZlibInternalError();
+
+            if (gzipStream_.avail_out == 0)
+                return bytesToRead;
+        }
+    }
+
+private:
+    const std::function<size_t(void* buffer, size_t bytesToRead)> readBlock_; //throw X
+    bool eof_ = false;
+    std::vector<std::byte> bufIn_;
+    z_stream gzipStream_ = {};
+};
+
+
+zen::InputStreamAsGzip::InputStreamAsGzip(const std::function<size_t(void* buffer, size_t bytesToRead)>& readBlock /*throw X*/) : pimpl_(std::make_unique<Impl>(readBlock)) {} //throw ZlibInternalError
+zen::InputStreamAsGzip::~InputStreamAsGzip() {}
+size_t zen::InputStreamAsGzip::read(void* buffer, size_t bytesToRead) { return pimpl_->read(buffer, bytesToRead); } //throw ZlibInternalError, X