Improved calculation for max packet points

src/pc_writer.rs

@@ -64,19 +64,15 @@ impl<'a, T: Read + Write + Seek> PointCloudWriter<'a, T> {
         // Make sure the prototype is not invalid or incomplete
         Self::validate_prototype(&prototype)?;
 
+        // Calculate max number of points per packet
+        let max_points_per_packet = get_max_packet_points(&prototype);
+
         let mut section_header = CompressedVectorSectionHeader::default();
         let section_offset = writer.physical_position()?;
         section_header.data_offset = section_offset + CompressedVectorSectionHeader::SIZE;
         section_header.section_length = CompressedVectorSectionHeader::SIZE;
         section_header.write(writer)?;
 
-        // Each data packet can contain up to 2^16 bytes, but we need some reserved
-        // space for header data. We also need to consider some "incomplete" bytes
-        // from record value sizes that are not a multiple of 8 bits.
-        // So lets round down a bit to have some spare bytes.
-        let point_size_bits: usize = prototype.iter().map(|p| p.data_type.bit_size()).sum();
-        let max_points_per_packet = (64000 * 8) / point_size_bits;
-
         // Prepare bounds
         let has_cartesian = prototype.iter().any(|p| p.name == RecordName::CartesianX);
         let cartesian_bounds = if has_cartesian {
@@ -686,3 +682,17 @@ fn validate_return(prototype: &[Record]) -> Result<()> {
     }
     Ok(())
 }
+
+/// Calculate maximum number of points per packet.
+/// Each data packet can contain up to 2^16 bytes, but we need some reserved
+/// space for header data. We also need to consider some "incomplete" bytes
+/// from record value sizes that are not a multiple of 8 bits.
+fn get_max_packet_points(prototype: &[Record]) -> usize {
+    const SAFETY_MARGIN: usize = 500;
+    let point_size_bits: usize = prototype.iter().map(|p| p.data_type.bit_size()).sum();
+    let bs_size_headers = prototype.len() * 2; // u16 for each byte stream header
+    let headers_size = DataPacketHeader::SIZE + bs_size_headers;
+    let max_incomplete_bytes = prototype.len();
+    let u16_max = u16::MAX as usize;
+    ((u16_max - headers_size - max_incomplete_bytes - SAFETY_MARGIN) * 8) / point_size_bits
+}

tests/writer_tests.rs

@@ -947,8 +947,8 @@ fn custom_xml_test() {
 }
 
 #[test]
-fn writer_bug_reproduction() {
-    let file = "writer_repro_bug.e57";
+fn writer_bug_regression_test() {
+    let file = "writer_bug_regression.e57";
     {
         let mut writer = e57::E57Writer::from_file(file, "file_uuid").unwrap();
         let proto = vec![
@@ -966,7 +966,8 @@ fn writer_bug_reproduction() {
             },
         ];
         let mut pc_writer = writer.add_pointcloud("pc_guid", proto).unwrap();
-        for _ in 0..4785 {
+        // exactly the the max packet point count of the internal writer
+        for _ in 0..4861 {
             let point = vec![
                 RecordValue::Single(0.0),
                 RecordValue::Single(0.0),