Calculate file size on demand

IB-8711, Fixes #682

Signed-off-by: Raul Metsma <[email protected]>

Author: metsma

src/DataFile.cpp

@@ -83,16 +83,17 @@ using namespace std;
 DataFile::DataFile() = default;
 DataFile::~DataFile() = default;
 
+struct DataFilePrivate::Private {
+    optional<unsigned long> size;
+};
 
 DataFilePrivate::DataFilePrivate(unique_ptr<istream> &&is, string filename, string mediatype, string id)
-    : m_is(std::move(is))
+    : d(make_unique<Private>())
+    , m_is(std::move(is))
     , m_id(std::move(id))
     , m_filename(std::move(filename))
     , m_mediatype(std::move(mediatype))
 {
-    m_is->seekg(0, istream::end);
-    istream::pos_type pos = m_is->tellg();
-    m_size = pos < 0 ? 0 : (unsigned long)pos;
 }
 
 void DataFilePrivate::digest(const Digest &digest) const
@@ -109,6 +110,17 @@ vector<unsigned char> DataFilePrivate::calcDigest(const string &method) const
     return d.result();
 }
 
+unsigned long DataFilePrivate::fileSize() const
+{
+    if(d->size.has_value())
+        return d->size.value();
+    m_is->clear();
+    m_is->seekg(0, istream::end);
+    istream::pos_type pos = m_is->tellg();
+    d->size.emplace(pos < 0 ? 0 : (unsigned long)pos);
+    return d->size.value();
+}
+
 void DataFilePrivate::saveAs(const string& path) const
 {
     ofstream ofs(File::encodeName(path), ofstream::binary);

src/DataFile_p.h

@@ -23,6 +23,7 @@
 
 #include <istream>
 #include <memory>
+#include <optional>
 
 namespace digidoc
 {
@@ -31,20 +32,21 @@ class Digest;
 class DataFilePrivate final: public DataFile
 {
 public:
-	DataFilePrivate(std::unique_ptr<std::istream> &&is, std::string filename, std::string mediatype, std::string id = {});
-
-	std::string id() const final { return m_id.empty() ? m_filename : m_id; }
-	std::string fileName() const final { return m_filename; }
-	unsigned long fileSize() const final { return m_size; }
-	std::string mediaType() const final { return m_mediatype; }
-
-	void digest(const Digest &method) const;
-	std::vector<unsigned char> calcDigest(const std::string &method) const final;
-	void saveAs(std::ostream &os) const final;
-	void saveAs(const std::string& path) const final;
-
-	std::unique_ptr<std::istream> m_is;
-	std::string m_id, m_filename, m_mediatype;
-	unsigned long m_size;
+    DataFilePrivate(std::unique_ptr<std::istream> &&is, std::string filename, std::string mediatype, std::string id = {});
+
+    std::string id() const final { return m_id.empty() ? m_filename : m_id; }
+    std::string fileName() const final { return m_filename; }
+    unsigned long fileSize() const final;
+    std::string mediaType() const final { return m_mediatype; }
+
+    void digest(const Digest &method) const;
+    std::vector<unsigned char> calcDigest(const std::string &method) const final;
+    void saveAs(std::ostream &os) const final;
+    void saveAs(const std::string& path) const final;
+
+    struct Private;
+    std::unique_ptr<Private> d;
+    std::unique_ptr<std::istream> m_is;
+    std::string m_id, m_filename, m_mediatype;
 };
 }