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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the License for the
// specific language governing permissions and limitations
// under the License.
//! # A primer on Apache Avro
//!
//! Avro is a schema based encoding system, like Protobuf. This means that if you have raw Avro data
//! without a schema, you are unable to decode it. It also means that the format is very space
//! efficient.
//!
//! ## Schemas
//!
//! Schemas are defined in JSON and look like this:
//! ```json
//! {
//! "type": "record",
//! "name": "example",
//! "fields": [
//! {"name": "a", "type": "long", "default": 42},
//! {"name": "b", "type": "string"}
//! ]
//! }
//! ```
//! For all possible types and extra attributes, see [the schema section of the specification].
//!
//! Schemas can depend on each other. For example, the schema defined above can be used again or a
//! schema can include itself:
//! ```json
//! {
//! "type": "record",
//! "name": "references",
//! "fields": [
//! {"name": "a", "type": "example"},
//! {"name": "b", "type": "bytes"},
//! {"name": "recursive", "type": ["null", "references"]}
//! ]
//! }
//! ```
//!
//! Schemas are represented using the [`Schema`](crate::Schema) type.
//!
//! [the schema section of the specification]: https://avro.apache.org/docs/++version++/specification/#schema-declaration
//!
//! ## Data serialization and deserialization
//! There are various formats to encode and decode Avro data. Most formats use the Avro binary encoding.
//!
//! #### [Object Container File](https://avro.apache.org/docs/++version++/specification/#object-container-files)
//! This is the most common file format used for Avro, it uses the binary encoding. It includes the
//! schema in the file, and can therefore be decoded by a reader who doesn't have the schema. It includes
//! many records in one file.
//!
//! This file format can be used via the [`Reader`](crate::Reader) and [`Writer`](crate::Writer) types.
//!
//! #### [Single Object Encoding](https://avro.apache.org/docs/++version++/specification/#single-object-encoding)
//! This file format also uses the binary encoding, but the schema is not included directly. It instead
//! includes a fingerprint of the schema, which a reader can look up in a schema database or compare
//! with the fingerprint that the reader is expecting. This file format always contains one record.
//!
//! This file format can be used via the [`GenericSingleObjectReader`](crate::GenericSingleObjectReader),
//! [`GenericSingleObjectWriter`](crate::GenericSingleObjectWriter), [`SpecificSingleObjectReader`](crate::SpecificSingleObjectReader),
//! and [`SpecificSingleObjectWriter`](crate::SpecificSingleObjectWriter) types.
//!
//! #### Avro datums
//! This is not really a file format, as it's just the raw Avro binary data. It does not include a
//! schema and can therefore not be decoded without the reader knowing **exactly** which schema was
//! used to write it.
//!
//! This file format can be used via the [`to_avro_datum`](crate::to_avro_datum), [`from_avro_datum`](crate::from_avro_datum),
//! [`to_avro_datum_schemata`](crate::to_avro_datum_schemata), [`from_avro_datum_schemata`](crate::from_avro_datum_schemata),
//! [`from_avro_datum_reader_schemata`](crate::from_avro_datum_reader_schemata), and
//! [`write_avro_datum_ref`](crate::write_avro_datum_ref) functions.
//!
//! #### [Avro JSON](https://avro.apache.org/docs/++version++/specification/#json-encoding)
//! Not be confused with the schema definition which is also in JSON. This is the Avro data encoded
//! in JSON.
//!
//! It can be used via the [`From<serde_json::Value> for Value`](crate::types::Value) and
//! [`TryFrom<Value> for serde_json::Value`](crate::types::Value) implementations.
//!
//! ## Compression
//! For records with low entropy it can be useful to compress the encoded data. Using the [Object Container File format](#object-container-file)
//! this is directly possible in Avro. Avro supports various compression codecs:
//!
//! - deflate
//! - bzip2
//! - Snappy
//! - XZ
//! - Zstandard
//!
//! All readers are required to implement the `deflate` codec, but most implementations implement most
//! codecs.
//!