Crate prost_reflect

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This crate provides support for dynamic protobuf messages. These are useful when the protobuf type definition is not known ahead of time.

The main entry points into the API of this crate are:

Example - decoding

DynamicMessage does not implement Default since it needs a message descriptor to function. To decode a protobuf byte stream into an instance of this type, use DynamicMessage::decode to create a default value for the MessageDescriptor instance and merge into it:

use prost::Message;
use prost_types::FileDescriptorSet;
use prost_reflect::{DynamicMessage, DescriptorPool, Value};

let pool = DescriptorPool::decode(include_bytes!("file_descriptor_set.bin").as_ref()).unwrap();
let message_descriptor = pool.get_message_by_name("package.MyMessage").unwrap();

let dynamic_message = DynamicMessage::decode(message_descriptor, b"\x08\x96\x01".as_ref()).unwrap();

assert_eq!(dynamic_message.get_field_by_name("foo").unwrap().as_ref(), &Value::I32(150));

Implementing ReflectMessage

The ReflectMessage trait provides a .descriptor() method to get type information for a message. By default it is just implemented for DynamicMessage.

The ReflectMessage trait provides a .descriptor() method to get type information for a message. It is implemented for DynamicMessage and the well-known-types provided by prost-types.

When the derive feature is enabled, it can be derived for Message implementations. The derive macro takes the following parameters:

NameValue
descriptor_poolAn expression that resolves to a DescriptorPool containing the message type. The descriptor should be cached to avoid re-building it. Either this or file_descriptor_pool_bytes must be set
file_descriptor_pool_bytesAn expression that resolves to an implementation of Buf containing an encoded file descriptor set. This will be automatically added to the global descriptor pool the first time ReflectMessage::descriptor() is called.
message_nameThe full name of the message, used to look it up within DescriptorPool.
use prost::Message;
use prost_reflect::{DescriptorPool, ReflectMessage};
use once_cell::sync::Lazy;

static DESCRIPTOR_POOL: Lazy<DescriptorPool>
    = Lazy::new(|| DescriptorPool::decode(include_bytes!("file_descriptor_set.bin").as_ref()).unwrap());

#[derive(Message, ReflectMessage)]
#[prost_reflect(descriptor_pool = "DESCRIPTOR_POOL", message_name = "package.MyMessage")]
pub struct MyMessage {}

let message = MyMessage {};
assert_eq!(message.descriptor().full_name(), "package.MyMessage");

If you are using prost-build, the prost-reflect-build crate provides helpers to generate ReflectMessage implementations:

prost_reflect_build::Builder::new()
    .compile_protos(&["src/package.proto"], &["src"])
    .unwrap();

Re-exports

Structs

Enums

Traits

Derive Macros