martin-g commented on code in PR #190:
URL: https://github.com/apache/avro-rs/pull/190#discussion_r2064388162
##########
avro/src/headers.rs:
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@@ -0,0 +1,163 @@
+//! Handling of Avro magic headers
+use uuid::Uuid;
+
+use crate::{rabin::Rabin, schema::SchemaFingerprint, AvroResult, Schema};
+
+/// This trait represents that an object is able to construct an Avro message
header. It is
+/// implemented for some known header types already. If you need a header type
that is not already
+/// included here, then you can create your own struct and implement this
trait.
+pub trait HeaderBuilder {
+ fn build_header(&self) -> Vec<u8>;
+}
+
+/// HeaderBuilder based on the Rabin schema fingerprint
+///
+/// This is the default, and will be used automatically by the `new` impls in
+/// `GenericSingleObjectReader` and `GenericSingleObjectWriter`.
+pub struct RabinFingerprintHeader {
+ fingerprint: SchemaFingerprint,
+}
+
+impl RabinFingerprintHeader {
+ /// Use this helper to build an instance from an existing Avro `Schema`.
+ pub fn from_schema(schema: &Schema) -> Self {
+ let fingerprint = schema.fingerprint::<Rabin>();
+ RabinFingerprintHeader { fingerprint }
+ }
+}
+
+impl HeaderBuilder for RabinFingerprintHeader {
+ fn build_header(&self) -> Vec<u8> {
+ vec![
+ 0xC3,
+ 0x01,
+ self.fingerprint.bytes[0],
+ self.fingerprint.bytes[1],
+ self.fingerprint.bytes[2],
+ self.fingerprint.bytes[3],
+ self.fingerprint.bytes[4],
+ self.fingerprint.bytes[5],
+ self.fingerprint.bytes[6],
+ self.fingerprint.bytes[7],
+ ]
+ }
+}
+
+/// HeaderBuilder based on Glue schema UUID
+///
+/// See the function docs for usage details
+pub struct GlueSchemaUuidHeader {
+ schema_uuid: Uuid,
+}
+
+impl GlueSchemaUuidHeader {
+ /// Create an instance of the struct from a Glue Schema UUID
+ ///
+ /// Code for writing messages will most likely want to use this. You will
need to determine
+ /// via other means the correct Glue schema UUID and use it with this
method to be able to
+ /// create Avro-encoded messages with the correct headers.
+ pub fn from_uuid(schema_uuid: Uuid) -> Self {
+ GlueSchemaUuidHeader { schema_uuid }
+ }
+
+ /// Create an instance of the struct based on parsing the UUID out of the
header of a raw
+ /// message
+ ///
+ /// Code for reading messages will most likely want to use this. Once you
receive the raw bytes
+ /// of a message, use this function to build the struct from it. That
struct can then be used
+ /// with the below `schema_uuid` function to retrieve the UUID in order to
retrieve the correct
+ /// schema for the message. You can then use the raw message, the schema,
and the struct
+ /// instance to read the message.
+ pub fn parse_from_raw_avro(message_payload: &[u8]) -> AvroResult<Self> {
+ if message_payload.len() < 19 {
Review Comment:
Why `19` ?
The special prefix (`3, 0`) needs two bytes + 16 for the Uuid. What is the
19th ?
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