protovalidate-python is the Python implementation of protovalidate, designed to validate Protobuf messages at runtime based on user-defined validation constraints. Powered by Google's Common Expression Language (CEL), it provides a flexible and efficient foundation for defining and evaluating custom validation rules. The primary goal of protovalidate is to help developers ensure data consistency and integrity across the network without requiring generated code.

Head over to the core protovalidate repository for:

• The API definition: used to describe validation constraints
• Documentation: how to apply protovalidate effectively
• Migration tooling: incrementally migrate from protoc-gen-validate
• Conformance testing utilities: for acceptance testing of protovalidate implementations

Other protovalidate runtime implementations include:

• Go: protovalidate-go
• C++: protovalidate-cc
• Java: protovalidate-java

And others coming soon:

• TypeScript: protovalidate-ts

To install the package, use pip:

pip install protovalidate

Make sure you have the latest version of protovalidate-python by checking the project's PyPI page.

Validation constraints are defined directly within .proto files. Documentation for adding constraints can be found in the protovalidate project README and its comprehensive docs.

syntax = "proto3";

package my.package;

import "google/protobuf/timestamp.proto";
import "buf/validate/validate.proto";

message Transaction {
  uint64 id = 1 [(buf.validate.field).uint64.gt = 999];
  google.protobuf.Timestamp purchase_date = 2;
  google.protobuf.Timestamp delivery_date = 3;

  string price = 4 [(buf.validate.field).cel = {
    id: "transaction.price",
    message: "price must be positive and include a valid currency symbol ($ or £)",
    expression: "(this.startswith('$') or this.startswith('£')) and float(this[1:]) > 0"
  }];

  option (buf.validate.message).cel = {
    id: "transaction.delivery_date",
    message: "delivery date must be after purchase date",
    expression:

 "this.delivery_date > this.purchase_date"
  };
}

When using the runtime library after installing it with pip, it's necessary to generate the Python code for the core buf.protovalidate Protobuf package. buf provides an efficient method for this:

1. Initialize a New Configuration File:

   buf mod init

   This initializes the buf.yaml configuration file at the root of the Protobuf source files.

2. Module Configuration and Dependencies:

   # buf.yaml
   version: v1
   deps: 
     - buf.build/bufbuild/protovalidate

   Ensure your dependencies are up-to-date with:

   buf mod update

3. Setup Code Generation:

   # buf.gen.yaml
   version: v1
   plugins:
     - plugin: buf.build/protocolbuffers/python:v23.4
       out: gen

4. Generate Code: To generate the required Python code:

   buf generate --include-imports

If your goal is to generate code specifically for the buf.protovalidate Protobuf package, run:

buf generate buf.build/bufbuild/protovalidate

Note: For users familiar with protoc, while it's an alternative to buf, it is recommended to use tooling or frameworks like Bazel for direct code generation, as it provides an encapsulated environment for such tasks.

import protovalidate
from google.protobuf.timestamp_pb2 import Timestamp
from my.package import Transaction

transaction = Transaction()
transaction.id = 1234
transaction.price = "$5.67"
transaction.purchase_date.CopyFrom(Timestamp())
transaction.delivery_date.CopyFrom(Timestamp())

try:
    protovalidate.validate(transaction)
except protovalidate.ValidationError as e:
# Report the violations

• protovalidate core repository
• Buf
• CEL Spec

Offered under the Apache 2 license.