Add support for spanned archives

Without it, assimp would crash on some inputs by jumping to a NULL
opendisk function. This commit adds an opendisk implementation, which
required adding a filename member to ZipFile.

Fix https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=38873
Fix #4229

code/Common/ZipArchiveIOSystem.cpp

@@ -59,11 +59,38 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 namespace Assimp {
 
+// ----------------------------------------------------------------
+// A read-only file inside a ZIP
+
+class ZipFile : public IOStream {
+    friend class ZipFileInfo;
+    explicit ZipFile(std::string &filename, size_t size);
+
+public:
+    std::string m_Filename;
+    virtual ~ZipFile();
+
+    // IOStream interface
+    size_t Read(void *pvBuffer, size_t pSize, size_t pCount) override;
+    size_t Write(const void * /*pvBuffer*/, size_t /*pSize*/, size_t /*pCount*/) override { return 0; }
+    size_t FileSize() const override;
+    aiReturn Seek(size_t pOffset, aiOrigin pOrigin) override;
+    size_t Tell() const override;
+    void Flush() override {}
+
+private:
+    size_t m_Size = 0;
+    size_t m_SeekPtr = 0;
+    std::unique_ptr<uint8_t[]> m_Buffer;
+};
+
+
 // ----------------------------------------------------------------
 // Wraps an existing Assimp::IOSystem for unzip
 class IOSystem2Unzip {
 public:
     static voidpf open(voidpf opaque, const char *filename, int mode);
+    static voidpf opendisk(voidpf opaque, voidpf stream, uint32_t number_disk, int mode);
     static uLong read(voidpf opaque, voidpf stream, void *buf, uLong size);
     static uLong write(voidpf opaque, voidpf stream, const void *buf, uLong size);
     static long tell(voidpf opaque, voidpf stream);
@@ -92,6 +119,28 @@ voidpf IOSystem2Unzip::open(voidpf opaque, const char *filename, int mode) {
     return (voidpf)io_system->Open(filename, mode_fopen);
 }
 
+voidpf IOSystem2Unzip::opendisk(voidpf opaque, voidpf stream, uint32_t number_disk, int mode) {
+    ZipFile *io_stream = (ZipFile *)stream;
+    voidpf ret = NULL;
+    size_t i;
+
+    char *disk_filename = (char*)malloc(io_stream->m_Filename.length() + 1);
+    strncpy(disk_filename, io_stream->m_Filename.c_str(), io_stream->m_Filename.length() + 1);
+    for (i = io_stream->m_Filename.length() - 1; i >= 0; i -= 1)
+    {
+        if (disk_filename[i] != '.')
+            continue;
+        snprintf(&disk_filename[i], io_stream->m_Filename.length() - i, ".z%02u", number_disk + 1);
+        break;
+    }
+
+    if (i >= 0)
+        ret = open(opaque, disk_filename, mode);
+
+    free(disk_filename);
+    return ret;
+}
+
 uLong IOSystem2Unzip::read(voidpf /*opaque*/, voidpf stream, void *buf, uLong size) {
     IOStream *io_stream = (IOStream *)stream;
 
@@ -147,6 +196,7 @@ zlib_filefunc_def IOSystem2Unzip::get(IOSystem *pIOHandler) {
     zlib_filefunc_def mapping;
 
     mapping.zopen_file = (open_file_func)open;
+    mapping.zopendisk_file = (opendisk_file_func)opendisk;
     mapping.zread_file = (read_file_func)read;
     mapping.zwrite_file = (write_file_func)write;
     mapping.ztell_file = (tell_file_func)tell;
@@ -159,30 +209,6 @@ zlib_filefunc_def IOSystem2Unzip::get(IOSystem *pIOHandler) {
     return mapping;
 }
 
-// ----------------------------------------------------------------
-// A read-only file inside a ZIP
-
-class ZipFile : public IOStream {
-    friend class ZipFileInfo;
-    explicit ZipFile(size_t size);
-
-public:
-    virtual ~ZipFile();
-
-    // IOStream interface
-    size_t Read(void *pvBuffer, size_t pSize, size_t pCount) override;
-    size_t Write(const void * /*pvBuffer*/, size_t /*pSize*/, size_t /*pCount*/) override { return 0; }
-    size_t FileSize() const override;
-    aiReturn Seek(size_t pOffset, aiOrigin pOrigin) override;
-    size_t Tell() const override;
-    void Flush() override {}
-
-private:
-    size_t m_Size = 0;
-    size_t m_SeekPtr = 0;
-    std::unique_ptr<uint8_t[]> m_Buffer;
-};
-
 // ----------------------------------------------------------------
 // Info about a read-only file inside a ZIP
 class ZipFileInfo {
@@ -190,7 +216,7 @@ public:
     explicit ZipFileInfo(unzFile zip_handle, size_t size);
 
     // Allocate and Extract data from the ZIP
-    ZipFile *Extract(unzFile zip_handle) const;
+    ZipFile *Extract(std::string &filename, unzFile zip_handle) const;
 
 private:
     size_t m_Size = 0;
@@ -206,7 +232,7 @@ ZipFileInfo::ZipFileInfo(unzFile zip_handle, size_t size) :
     unzGetFilePos(zip_handle, &(m_ZipFilePos));
 }
 
-ZipFile *ZipFileInfo::Extract(unzFile zip_handle) const {
+ZipFile *ZipFileInfo::Extract(std::string &filename, unzFile zip_handle) const {
     // Find in the ZIP. This cannot fail
     unz_file_pos_s *filepos = const_cast<unz_file_pos_s *>(&(m_ZipFilePos));
     if (unzGoToFilePos(zip_handle, filepos) != UNZ_OK)
@@ -215,7 +241,7 @@ ZipFile *ZipFileInfo::Extract(unzFile zip_handle) const {
     if (unzOpenCurrentFile(zip_handle) != UNZ_OK)
         return nullptr;
 
-    ZipFile *zip_file = new ZipFile(m_Size);
+    ZipFile *zip_file = new ZipFile(filename, m_Size);
 
     // Unzip has a limit of UINT16_MAX bytes buffer
     uint16_t unzipBufferSize = zip_file->m_Size <= UINT16_MAX ? static_cast<uint16_t>(zip_file->m_Size) : UINT16_MAX;
@@ -245,8 +271,8 @@ ZipFile *ZipFileInfo::Extract(unzFile zip_handle) const {
     return zip_file;
 }
 
-ZipFile::ZipFile(size_t size) :
+ZipFile::ZipFile(std::string &filename, size_t size) :
-        m_Size(size) {
+        m_Filename(filename), m_Size(size) {
     ai_assert(m_Size != 0);
     m_Buffer = std::unique_ptr<uint8_t[]>(new uint8_t[m_Size]);
 }
@@ -422,7 +448,7 @@ IOStream *ZipArchiveIOSystem::Implement::OpenFile(std::string &filename) {
         return nullptr;
 
     const ZipFileInfo &zip_file = (*zip_it).second;
-    return zip_file.Extract(m_ZipFileHandle);
+    return zip_file.Extract(filename, m_ZipFileHandle);
 }
 
 inline void ReplaceAll(std::string &data, const std::string &before, const std::string &after) {