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StringJsonConverterFactory.cs
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StringJsonConverterFactory.cs
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// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Text.RegularExpressions;
using Azure.DataApiBuilder.Service.Exceptions;
namespace Azure.DataApiBuilder.Config.Converters;
/// <summary>
/// Custom string json converter factory to replace environment variables of the pattern
/// @env('ENV_NAME') with their value during deserialization.
/// </summary>
public class StringJsonConverterFactory : JsonConverterFactory
{
public override bool CanConvert(Type typeToConvert)
{
return typeToConvert.IsAssignableTo(typeof(string));
}
public override JsonConverter? CreateConverter(Type typeToConvert, JsonSerializerOptions options)
{
return new StringJsonConverter();
}
class StringJsonConverter : JsonConverter<string>
{
// @env\(' : match @env('
// .*? : lazy match any character except newline 0 or more times
// (?='\)) : look ahead for ') which will combine with our lazy match
// ie: in @env('hello')goodbye') we match @env('hello')
// '\) : consume the ') into the match (look ahead doesn't capture)
// This pattern lazy matches any string that starts with @env(' and ends with ')
// ie: fooBAR@env('hello-world')bash)FOO') match: @env('hello-world')
// This matching pattern allows for the @env('<match>') to be safely nested
// within strings that contain ') after our match.
// ie: if the environment variable "Baz" has the value of "Bar"
// fooBarBaz: "('foo@env('Baz')Baz')" would parse into
// fooBarBaz: "('fooBarBaz')"
// Note that there is no escape character currently for ') to exist
// within the name of the environment variable, but that ') is not
// a valid environment variable name in certain shells.
const string ENV_PATTERN = @"@env\('.*?(?='\))'\)";
public override string? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
if (reader.TokenType == JsonTokenType.String)
{
string? value = reader.GetString();
return Regex.Replace(value!, ENV_PATTERN, new MatchEvaluator(ReplaceMatchWithEnvVariable));
}
if (reader.TokenType == JsonTokenType.Null)
{
return null;
}
throw new JsonException();
}
public override void Write(Utf8JsonWriter writer, string value, JsonSerializerOptions options)
{
writer.WriteStringValue(value);
}
private static string ReplaceMatchWithEnvVariable(Match match)
{
// [^@env\(] : any substring that is not @env(
// .* : any char except newline any number of times
// (?=\)) : look ahead for end char of )
// This pattern greedy matches all characters that are not a part of @env()
// ie: @env('hello@env('goodbye')world') match: 'hello@env('goodbye')world'
string innerPattern = @"[^@env\(].*(?=\))";
// strips first and last characters, ie: '''hello'' --> ''hello'
string envName = Regex.Match(match.Value, innerPattern).Value[1..^1];
string? envValue = Environment.GetEnvironmentVariable(envName);
return envValue is not null ? envValue :
throw new DataApiBuilderException(message: $"Environmental Variable, {envName}, not found.",
statusCode: System.Net.HttpStatusCode.ServiceUnavailable,
subStatusCode: DataApiBuilderException.SubStatusCodes.ErrorInInitialization);
}
}
}