2 files changed, 104 insertions, 0 deletions
diff --git a/lib/embed.cpp b/lib/embed.cpp
new file mode 100644
index 0000000..c3b0286
--- /dev/null
+++ b/lib/embed.cpp
@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2016-present, Yann Collet, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under both the BSD-style license (found in the
+ * LICENSE file in the root directory of this source tree) and the GPLv2 (found
+ * in the COPYING file in the root directory of this source tree).
+ * You may select, at your option, one of the above-listed licenses.
+ */
+
+#include "embed.h"
+#include <zstd.h>      // presumes zstd library is installed
+#include <cassert>
+
+using namespace embed;
+
+ZSTD_DDict* dictPtr = nullptr;
+
+Resources::Resources(const ResourceData &info)
+    : m_info(info)
+{
+    if(!info.dictionary.empty()) {
+        dictPtr = ZSTD_createDDict(info.dictionary.data(), info.dictionary.size());
+    }
+}
+
+Resources::~Resources()
+{
+    if(dictPtr != nullptr) {
+        ZSTD_freeDDict(dictPtr);
+    }
+}
+
+[[nodiscard]] std::span<unsigned char> Resources::decompress(const std::span<const unsigned char> &entry)
+{
+    /* Read the content size from the frame header. For simplicity we require
+     * that it is always present. By default, zstd will write the content size
+     * in the header when it is known. If you can't guarantee that the frame
+     * content size is always written into the header, either use streaming
+     * decompression, or ZSTD_decompressBound().
+     */
+    unsigned long long const rSize = ZSTD_getFrameContentSize(entry.data(), entry.size());
+    assert(rSize != ZSTD_CONTENTSIZE_ERROR); //, "%s: not compressed by zstd!", fname);
+    assert(rSize != ZSTD_CONTENTSIZE_UNKNOWN); //, "%s: original size unknown!", fname);
+    auto* rBuff = new unsigned char[(size_t) rSize];
+
+    /* Check that the dictionary ID matches.
+     * If a non-zstd dictionary is used, then both will be zero.
+     * By default zstd always writes the dictionary ID into the frame.
+     * Zstd will check if there is a dictionary ID mismatch as well.
+     */
+    unsigned const expectedDictID = ZSTD_getDictID_fromDDict(dictPtr);
+    unsigned const actualDictID = ZSTD_getDictID_fromFrame(entry.data(), entry.size());
+    assert(actualDictID == expectedDictID); //"DictID mismatch: expected %u got %u",
+
+    /* Decompress using the dictionary.
+     * If you need to control the decompression parameters, then use the
+     * advanced API: ZSTD_DCtx_setParameter(), ZSTD_DCtx_refDDict(), and
+     * ZSTD_decompressDCtx().
+     */
+    ZSTD_DCtx* const dctx = ZSTD_createDCtx();
+    assert(dctx != NULL); //, "ZSTD_createDCtx() failed!");
+    size_t const dSize = ZSTD_decompress_usingDDict(dctx, rBuff, rSize, entry.data(), entry.size(), dictPtr);
+    /* When zstd knows the content size, it will error if it doesn't match. */
+    assert(dSize == rSize); //, "Impossible because zstd will check this condition!");
+
+    ZSTD_freeDCtx(dctx);
+    return std::span(rBuff, rSize);
+}
+
diff --git a/lib/embed.h b/lib/embed.h
new file mode 100644
index 0000000..566b14c
--- /dev/null
+++ b/lib/embed.h
@@ -0,0 +1,34 @@
+#pragma once
+
+#include <span>
+#include <string>
+#include <unordered_map>
+#include <frozen/unordered_map.h>
+#include <frozen/string.h>
+
+namespace embed {
+
+enum Compression {
+    None,
+    Zstd
+};
+
+struct ResourceData {
+    Compression compression = None;
+    std::span<const unsigned char> dictionary;
+};
+
+class Resources {
+public:
+    explicit Resources(const ResourceData &info);
+    ~Resources();
+
+    [[nodiscard]]
+    std::span<unsigned char> decompress(const std::span<const unsigned char> &entry);
+
+private:
+    const ResourceData m_info;
+}; // class
+
+}
+