Method build

arrow-ipc/src/reader.rs:1222–1290

Build [`FileReader`] with given reader.

(self, mut reader: R)

    /// Build [`FileReader`] with given reader.
    pub fn build<R: Read + Seek>(self, mut reader: R) -> Result<FileReader<R>, ArrowError> {
        // Space for ARROW_MAGIC (6 bytes) and length (4 bytes)
        let mut buffer = [0; 10];
        reader.seek(SeekFrom::End(-10))?;
        reader.read_exact(&mut buffer)?;

        let footer_len = read_footer_length(buffer)?;

        // read footer
        let mut footer_data = vec![0; footer_len];
        reader.seek(SeekFrom::End(-10 - footer_len as i64))?;
        reader.read_exact(&mut footer_data)?;

        let verifier_options = VerifierOptions {
            max_tables: self.max_footer_fb_tables,
            max_depth: self.max_footer_fb_depth,
            ..Default::default()
        };
        let footer = crate::root_as_footer_with_opts(&verifier_options, &footer_data[..]).map_err(
            |err| ArrowError::ParseError(format!("Unable to get root as footer: {err:?}")),
        )?;

        let blocks = footer.recordBatches().ok_or_else(|| {
            ArrowError::ParseError("Unable to get record batches from IPC Footer".to_string())
        })?;

        let total_blocks = blocks.len();

        let ipc_schema = footer.schema().unwrap();
        if !ipc_schema.endianness().equals_to_target_endianness() {
            return Err(ArrowError::IpcError(
                "the endianness of the source system does not match the endianness of the target system.".to_owned()
            ));
        }

        let schema = crate::convert::fb_to_schema(ipc_schema);

        let mut custom_metadata = HashMap::new();
        if let Some(fb_custom_metadata) = footer.custom_metadata() {
            for kv in fb_custom_metadata.into_iter() {
                custom_metadata.insert(
                    kv.key().unwrap().to_string(),
                    kv.value().unwrap().to_string(),
                );
            }
        }

        let mut decoder = FileDecoder::new(Arc::new(schema), footer.version());
        if let Some(projection) = self.projection {
            decoder = decoder.with_projection(projection)
        }

        // Create an array of optional dictionary value arrays, one per field.
        if let Some(dictionaries) = footer.dictionaries() {
            for block in dictionaries {
                let buf = read_block(&mut reader, block)?;
                decoder.read_dictionary(block, &buf)?;
            }