Method make_decoder

arrow-avro/src/reader/mod.rs:1035–1146

(
        &self,
        header: Option<&Header>,
        reader_schema: Option<&AvroSchema>,
    )

    }

    fn make_decoder(
        &self,
        header: Option<&Header>,
        reader_schema: Option<&AvroSchema>,
    ) -> Result<Decoder, AvroError> {
        if let Some(hdr) = header {
            let writer_schema = hdr.schema()?.ok_or_else(|| {
                AvroError::ParseError("No Avro schema present in file header".into())
            })?;
            let projected_reader_schema = self
                .projection
                .as_deref()
                .map(|projection| {
                    let base_schema = if let Some(reader_schema) = reader_schema {
                        reader_schema.clone()
                    } else {
                        let raw = hdr.get(SCHEMA_METADATA_KEY).ok_or_else(|| {
                            AvroError::ParseError(
                                "No Avro schema present in file header".to_string(),
                            )
                        })?;
                        let json_string = std::str::from_utf8(raw)
                            .map_err(|e| {
                                AvroError::ParseError(format!(
                                    "Invalid UTF-8 in Avro schema header: {e}"
                                ))
                            })?
                            .to_string();
                        AvroSchema::new(json_string)
                    };
                    base_schema.project(projection)
                })
                .transpose()?;
            let effective_reader_schema = projected_reader_schema.as_ref().or(reader_schema);
            let record_decoder =
                self.make_record_decoder_from_schemas(&writer_schema, effective_reader_schema)?;
            return Ok(Decoder::from_parts(
                self.batch_size,
                record_decoder,
                None,
                IndexMap::new(),
                FingerprintAlgorithm::Rabin,
            ));
        }
        let store = self.writer_schema_store.as_ref().ok_or_else(|| {
            AvroError::ParseError("Writer schema store required for raw Avro".into())
        })?;
        let fingerprints = store.fingerprints();
        if fingerprints.is_empty() {
            return Err(AvroError::ParseError(
                "Writer schema store must contain at least one schema".into(),
            ));
        }
        let start_fingerprint = self
            .active_fingerprint
            .or_else(|| fingerprints.first().copied())
            .ok_or_else(|| {
                AvroError::ParseError("Could not determine initial schema fingerprint".into())