cpp: add flush to IWritable

foxglove · Nov 7, 2024 · 570e29c · 570e29c
1 parent ba3c9c0
commit 570e29c
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Showing 3 changed files with 25 additions and 2 deletions.
diff --git a/cpp/mcap/conanfile.py b/cpp/mcap/conanfile.py
@@ -1,4 +1,4 @@
-from conans import ConanFile, tools
+from conan import ConanFile, tools
 
 
 class McapConan(ConanFile):

diff --git a/cpp/mcap/include/mcap/writer.hpp b/cpp/mcap/include/mcap/writer.hpp
@@ -143,6 +143,11 @@ class MCAP_PUBLIC IWritable {
    */
   void resetCrc();
 
+  /**
+   * @brief flushes any buffered data to the output. Defaults to a no-op.
+   */
+  virtual void flush() = 0;
+
 protected:
   virtual void handleWrite(const std::byte* data, uint64_t size) = 0;
 
@@ -162,6 +167,7 @@ class MCAP_PUBLIC FileWriter final : public IWritable {
 
   void handleWrite(const std::byte* data, uint64_t size) override;
   void end() override;
+  void flush() override;
   uint64_t size() const override;
 
 private:
@@ -179,6 +185,7 @@ class MCAP_PUBLIC StreamWriter final : public IWritable {
 
   void handleWrite(const std::byte* data, uint64_t size) override;
   void end() override;
+  void flush() override;
   uint64_t size() const override;
 
 private:
@@ -205,6 +212,7 @@ class MCAP_PUBLIC IChunkWriter : public IWritable {
    * @brief Returns the size in bytes of the uncompressed data.
    */
   virtual uint64_t size() const override = 0;
+
   /**
    * @brief Returns the size in bytes of the compressed data. This will only be
    * called after `end()`.
@@ -230,6 +238,10 @@ class MCAP_PUBLIC IChunkWriter : public IWritable {
    */
   virtual const std::byte* compressedData() const = 0;
 
+  // No-op IWritable::flush() implementation. Chunk writers have no concept of an "underlying
+  // stream" to flush to.
+  void flush() override {}
+
 protected:
   virtual void handleClear() = 0;
 };

diff --git a/cpp/mcap/include/mcap/writer.inl b/cpp/mcap/include/mcap/writer.inl
@@ -61,6 +61,12 @@ void FileWriter::handleWrite(const std::byte* data, uint64_t size) {
   size_ += size;
 }
 
+void FileWriter::flush() {
+  if (file_) {
+    std::fflush(file_);
+  }
+}
+
 void FileWriter::end() {
   if (file_) {
     std::fclose(file_);
@@ -84,10 +90,14 @@ void StreamWriter::handleWrite(const std::byte* data, uint64_t size) {
   size_ += size;
 }
 
-void StreamWriter::end() {
+void StreamWriter::flush() {
   stream_.flush();
 }
 
+void StreamWriter::end() {
+  flush();
+}
+
 uint64_t StreamWriter::size() const {
   return size_;
 }
@@ -921,6 +931,7 @@ uint64_t McapWriter::write(IWritable& output, const Chunk& chunk) {
   write(output, chunk.compression);
   write(output, chunk.compressedSize);
   write(output, chunk.records, chunk.compressedSize);
+  output.flush();
 
   return 9 + recordSize;
 }