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stasberkov/ProtobufFaker.cs

Created January 30, 2025 16:07
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  1. stasberkov created this gist Jan 30, 2025.
    173 changes: 173 additions & 0 deletions ProtobufFaker.cs
    View file
    Original file line number Diff line number Diff line change
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    using System;
    using System.Collections.Generic;
    using System.Linq;
    using Google.Protobuf;
    using Google.Protobuf.Reflection;
    using Google.Protobuf.Collections;
    using Google.Protobuf.WellKnownTypes;
    using System.Collections;

    public class ProtobufFaker {
    private readonly Random _random;
    private readonly int _maxCollectionSize;
    private readonly int _stringMaxLength;

    public ProtobufFaker(int? seed = null, int maxCollectionSize = 5, int stringMaxLength = 20) {
    _random = seed.HasValue ? new Random(seed.Value) : new Random();
    _maxCollectionSize = maxCollectionSize;
    _stringMaxLength = stringMaxLength;
    }

    public T Generate<T>() where T : IMessage, new() {
    var message = new T();
    PopulateMessage(message);
    return message;
    }

    public void PopulateMessage(IMessage message) {
    var descriptor = message.Descriptor;
    foreach (var fieldDescriptor in descriptor.Fields.InDeclarationOrder()) {
    if (fieldDescriptor.IsRepeated) {
    var list = (IList)fieldDescriptor.Accessor.GetValue(message);
    var count = _random.Next(1, _maxCollectionSize + 1);
    for (int i = 0; i < count; i++) {
    var value = GenerateSingleValue(fieldDescriptor);
    if (value != null) {
    list.Add(value);
    }
    }
    }
    else {
    var value = GenerateFieldValue(fieldDescriptor);
    if (value != null) {
    fieldDescriptor.Accessor.SetValue(message, value);
    }
    }
    }
    }

    private object? GenerateFieldValue(FieldDescriptor field) {
    if (field.IsMap) {
    return GenerateMapField(field);
    }

    // Handle oneof fields
    if (field.ContainingOneof != null) {
    // Randomly decide whether to set this oneof field
    if (_random.Next(2) == 0) {
    return null;
    }
    }

    return GenerateSingleValue(field);
    }

    private object? GenerateSingleValue(FieldDescriptor field) {
    if (field.FieldType == FieldType.Message && field.MessageType.FullName == "google.protobuf.Timestamp") {
    return GenerateTimestamp();
    }

    return field.FieldType switch {
    FieldType.Double => _random.NextDouble() * 1000,
    FieldType.Float => (float)(_random.NextDouble() * 1000),
    FieldType.Int64 or FieldType.SInt64 or FieldType.SFixed64 => (long)_random.Next(1, 1000),
    FieldType.UInt64 or FieldType.Fixed64 => (ulong)_random.Next(1, 1000),
    FieldType.Int32 or FieldType.SInt32 or FieldType.SFixed32 => _random.Next(1, 1000),
    FieldType.Fixed32 or FieldType.UInt32 => (uint)_random.Next(1, 1000),
    FieldType.Bool => _random.Next(2) == 1,
    FieldType.String => GenerateRandomString(),
    FieldType.Bytes => GenerateRandomBytes(),
    FieldType.Enum => GenerateEnumValue(field.EnumType),
    FieldType.Message => GenerateNestedMessage(field.MessageType),
    _ => null,
    };
    }

    private object? GenerateMapField(FieldDescriptor field) {
    var count = _random.Next(1, _maxCollectionSize + 1);
    var mapField = field.Accessor.GetValue((IMessage?)Activator.CreateInstance(field.ContainingType.ClrType));
    var mapDescriptor = field.MessageType;
    var keyDescriptor = mapDescriptor.FindFieldByNumber(1); // Key is always field 1
    var valueDescriptor = mapDescriptor.FindFieldByNumber(2); // Value is always field 2

    var addMethod = mapField.GetType().GetMethod("Add");
    if (addMethod == null) { return null; }

    for (int i = 0; i < count; i++) {
    var key = GenerateSingleValue(keyDescriptor);
    var value = GenerateSingleValue(valueDescriptor);

    if (key != null && value != null) {
    addMethod.Invoke(mapField, [key, value]);
    }
    }

    return mapField;
    }

    private IMessage? GenerateNestedMessage(MessageDescriptor messageDescriptor) {
    var message = (IMessage?)Activator.CreateInstance(messageDescriptor.ClrType);
    if (message == null) { return null; }
    PopulateMessage(message);
    return message;
    }

    private object GenerateEnumValue(EnumDescriptor enumDescriptor) {
    var values = enumDescriptor.Values;
    var randomIndex = _random.Next(values.Count);
    return values[randomIndex].Number;
    }

    private Timestamp GenerateTimestamp() {
    var now = DateTime.UtcNow;
    var daysOffset = _random.Next(-365 * 2, 365 * 2); // ±2 years from now
    var hoursOffset = _random.Next(-24, 24);
    var minutesOffset = _random.Next(-60, 60);

    var randomTime = now
    .AddDays(daysOffset)
    .AddHours(hoursOffset)
    .AddMinutes(minutesOffset);

    return Timestamp.FromDateTime(randomTime);
    }

    private string GenerateRandomString() {
    const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    var length = _random.Next(1, _stringMaxLength + 1);
    return new string(Enumerable.Repeat(chars, length)
    .Select(s => s[_random.Next(s.Length)]).ToArray());
    }

    private ByteString GenerateRandomBytes() {
    var length = _random.Next(1, _stringMaxLength + 1);
    var bytes = new byte[length];
    _random.NextBytes(bytes);
    return ByteString.CopyFrom(bytes);
    }
    }

    // Example usage:
    /*
    public class Program
    {
    public static void Main()
    {
    var faker = new ProtobufFaker();
    // Generate fake data for any protobuf message
    var message = faker.Generate<YourProtobufMessage>();
    // The faker will properly handle:
    // - All protobuf field types
    // - Repeated fields
    // - Map fields
    // - Oneof fields
    // - Nested messages
    // - Enums
    // - Optional fields
    Console.WriteLine(message.ToString());
    }
    }
    */