Features

Features are built-in behaviours that can be customized through their configurers. Small features can be named as Configuration or Option. When they only configure an existing behaviour, such as DatabaseConfiguration, it is a Configuration. When they provide nothing to configure other than enable/disable, such as UtcOption, it is an Option.

• Audit : Audit your service requests and entities
• Authentication : Learn what alternatives you have in Gazel to provide authentication in your projects
• Authorization : TBD
• Cache : TBD
• Concurrency Limiter : Provides a default concurrency limiter for your backend to perform well under high loads.
• Cors : Allows you to configure Cross-Origin request polices.
• Crypto : Crypto provides a built-in way to encrypt & decrypt sensitive data
• Exception Handling : Gazel has a prebuilt code & message system that converts exceptions into data
• File System : File system gives a nice abstraction for your application to read & write file
• Hashing : TBD
• Localization : TBD
• Logging : TBD
• Message Queue : TBD
• Remote Call : TBD
• Secure Call : TBD
• Transaction : TBD
• Configurations : List of all configuration type features
• Options : List of all option type features
• Implement a new feature : TBD

Below sample illustrates how you can configure a service application;

builder.Services.AddGazelServiceApplication(cfg,
    ...
    service: c => ...,
    audit: c => ...,
    authentication: c => ...,
    ...
);

In this section we will go through every feature available in Gazel and explain how you can configure them using their configurers.

Audit

Audit feature allows you to audit persistent classes and business services. To configure this feature you can use Enabled() and Disabled() options. Default option is Enabled().

audit: c => c.Enabled()

audit: c => c.Disabled()

Auditing Business Services

Add [Audit] attribute to a business service method to make it auditable. When a request is made to an audited business service, it will be intercepted and several calls will be made to your IAuditManager implementation.

[Audit]
public async Task RequestWithAudit() => ...;

Audit services will require a valid request ID for each service call. If you want a request ID to be auto generated, you can set RequestId property to RequestIdMode.Optional.

[Audit(RequestIdMode.Optional)]
public async Task RequestWithAudit() => ...;

Implementing IAuditManager

For audit attribute to work, you need to have an implementation of IAuditManager interface in one of your business modules. In this implementation you can define the behaviour of audit feature.

public class AuditManager : IAuditManager
{
    void IAuditManager.SaveRequest(Guid requestId, string serviceInstance, string serviceName, string serviceParameters) => ...;
    void IAuditManager.SaveSuccessfulResponse(Guid requestId, string serviceResponse) => ...;
    void IAuditManager.SaveFailedResponse(Guid requestId, Exception exception) => ...;
    int IAuditManager.GetDailyRequestCount(string serviceInstance, string serviceName, Date date) => ...;
    int IAuditManager.GetMaxDailyRequestCount(string serviceInstance, string serviceName) => ...;
}

• SaveRequest(): During every request interceptor calls the SaveRequest() method. You can use this method to keep a request log.
• SaveSuccessfulResponse(): You can use this method to save the information of requests with successful response.
• SaveFailedResponse(): You can use this method to save the information of requests with failed response.
• GetDailyRequestCount(): Using the request log stored in SaveRequest() you can return the request count for each service.
• GetMaxDailyRequestCount(): You can use this method to limit number of requests to a business service within a day.

Limiting Daily Request

This feature is enabled by default to allow you to limit number of requests to a business service within a day. When there is a service request, interceptor uses GetDailyRequestCount() to get the daily request count and if it exceeds the maximum daily request amount it will throw an exception.

You can disable this behaviour like below;

audit: c => c.Enabled(limitDailyRequest: false)

Auditing Persistent Classes

To audit a persistent class, implement IAuditable interface and add the AuditInfo type property to your persistent class. AuditInfo is a composite user type that is mapped to 5 columns, CreateDate, CreateUserId, ModifyDate, ModifyUserId, ModifyHost.

AuditInfo is readonly and values for these 5 properties are managed by this feature automatically.

• CreateDate: The time this record is inserted
• CreateUserId: Id of the user in context.Session.Account when this record is inserted
• ModifyDate: The last time this record is updated
• ModifyUserId: Id of the last user that updates this record
• ModifyHost: Value of context.Session.Host when this record is inserted or updated

Below is a sample implementation of IAuditable interface;

public class PersistentClass : IAuditable
{
    private readonly IRepository<PersistentClass> _repository;
    private readonly IModuleContext _context;
    protected PersistentClass() { }
    public PersistentClass(IRepository<PersistentClass> repository, IModuleContext context)
    {
        _repository = repository;
        _context = context;
    }
    public virtual int Id { get; protected set; }
    public virtual AuditInfo AuditInfo { get; protected set; }
}

Authentication

In this section, you will learn about how authentication is implemented in Gazel.

Authentication is enabled by default in Service Application. All requests from outside of your host project require an token. When you run your App.Service project, you will see an Authorization text box in request headers section which configures an HTTP authorization header for every request.

Below you can see a sequence diagram explaining how gazel interacts with your code through interfaces;

Here you can see that for every request;

• It first calls GetSession() to retrieve session object
• Then it invokes Validate() to enable validation logic
• If everything is ok, it sets your session object to request scope.

ISessionManager interface

When authentication is enabled, Gazel requires an implementation of ISessionManager interface. Once you implement it in any module, it will be registered automatically.

ISessionManager is basically responsible for finding an ISession instance from a given AppToken. An example implementation is as follows;

public class SessionManager : ISessionManager
{
    ...
    public ISession GetSession(AppToken appToken) =>
        _context.Query<Sessions>().SingleByAppToken(appToken);
    ...
}

public class SessionManager : ISessionManager
{
    ...
    private ISession GetSession(AppToken appToken) { ... }
    ...
    ISession ISessionManager.GetSession(AppToken appToken) => GetSession(appToken);
    ...
}

ISession interface

Just like a web session, ISession represents a session of a user. Unlike a web session it is not stored in cookies nor in a file. ISessionManager creates it before every request and puts it in the request scope. After every request, session instances are destroyed along with its request.

public interface ISession
{
    AppToken Token { get; } // The unique identifier of the session
    string Host { get; } // A text to represent client's host if needed
    IAccount Account { get; } // The account that this session is attached to
    void Validate(); // The method that is invoked before every request
}

Here is an example implementation of ISession interface;

public class Session : ISession
{
    private readonly IRepository<Session> _repository;
    private readonly IModuleContext _context;
    protected Session() { }
    public Session(IRepository<Session> repository, IModuleContext context)
    {
        _repository = repository;
        _context = context;
    }
    public virtual int Id { get; protected set; }
    public virtual AppToken Token { get; protected set; }
    public virtual Account Account { get; protected set; }
    public virtual string Host { get; protected set; }
    public virtual DateTime ExpireTime { get; protected set; }
    protected internal virtual Session With(Account account)
    {
        Account = account;
        Token = _context.System.NewAppToken();
        Host = _context.Request.Host.ToString();
        ExpireTime = _context.System.Now.AddMinutes(30);
        _repository.Insert(this);
        return this;
    }
    protected virtual void Validate()
    {
        if(ExpireTime < _context.System.Now)
        {
            throw new AuthenticationRequiredException();
        }
    }
    //implemented explicitly to return IAccount
    IAccount ISession.Account => Account;
    //implemented explicitly to make Validate protected
    void ISession.Validate() => Validate();
}
public class Sessions : Query<Session>
{
    public Sessions(IModuleContext context) : base(context) { }
    internal Session SingleByAppToken(AppToken appToken) =>
        SingleBy(s => s.AppToken == appToken);
}

IAccount interface

IAccount represents an account in your application.

public interface IAccount
{
    int Id { get; } // Id of the account
    string DisplayName { get; } // A text to represent the account
    // The method that is invoked before every request if authorization is enabled
    bool HasAccess(IResource resource);
}

Here is an example implementation of IAccount interface;

public class Account : IAccount
{
    private readonly IRepository<Account> _repository;
    private readonly IModuleContext _context;
    protected Account() { }
    public Account(IRepository<Account> repository, IModuleContext context)
    {
        _repository = repository;
        _context = context;
    }
    public virtual int Id { get; protected set; }
    public virtual string FullName { get; protected set; }
    protected internal virtual Account With(string fullName)
    {
        FullName = fullName;
        _repository.Insert(this);
        return this;
    }
    //implemented explicitly to map DisplayName on FullName
    string IAccount.DisplayName => FullName;
    //give access to everything for this sample
    bool IAccount.HasAccess(IResource resource) => true;
}
public class Accounts : Query<Account> { ... }

Accessing User Session

When you finish setting up your authentication mechanism, you can access user session using IModuleContext.Session property.

public class CompanyManager
{
    private readonly IModuleContext _context;
    public CompanyManager(IModuleContext context)
    {
        _context = context;
    }
    public Company CreateCompany(string name)
    {
        return _context.New<Company>().With(
           name: name,
           createdBy: _context.Session.Account.DisplayName
        );
    }
}

Overriding Current Session

You may need to override the session in some specific cases. You can use IModuleContext.OverrideSession method as shown below.

public class Company
{
    private readonly IRepository<Company> _repository;
    private readonly IModuleContext _context;
    protected Company() { }
    public Company(IRepository<Company> repository, IModuleContext context)
    {
        _repository = repository;
        _context = context;
    }
    protected internal virtual Company With(string name, string address)
    {
        //this level uses current session
        //assume we need an admin session here
        var adminSession = _context.New<Session>().WithAdminRights();
        _context.OverrideSession(adminSession, () =>
        {
            //here _context.Session returns adminSession
            //do some admin stuff
        });
        //back to current session
        Name = name;
        Address = address;
        _repository.Insert(this);
        return this;
    }
}

...
protected internal virtual Company With(string name, string address)
{
    //this level uses current session
    _context.OverrideSession(innerSession, () =>
    {
        //this level uses inner session
        _context.OverrideSession(nestedSession, () =>
        {
            //this level uses nested session
        });
    });
    //this level uses current session
    return this;
}
...

Concurrency Limiter

Concurrency limiter provides a way to limit number of requests that are being handled in parallel. To make this happen, Gazel makes use of Microsoft.AspNetCore.ConcurrencyLimiter package.

Configuration

There are two main settings;

• MaxConcurrentRequests: Maximum number of concurrent requests allowed from outside of the application. Default is 20. Your application will still be able to accept context.Remote and queue callback requests internally.
• RequestQueueLimit: This is the limit of your wait queue. Default is 1000. When exceeded, your application will reject further requests with 503 Service Unavailable.

Below is a sample configuration;

builder.Services.AddGazelServiceApplication(
    ...
    concurrencyLimiter: c => c.AspNetCore(
        maxConcurrentRequests: 20,
        requestQueueLimit: 1000
    ),
    ...
);

You may want to reduce the number of concurrent requests for development environment. To achieve this you can use settings file;

concurrencyLimiter: c => c.AspNetCore(
    maxConcurrentRequests: cfg.Setting("ConcurrencyLimiter", 20)
),

Thread Count Calculation

Number of minimum threads is calculated using given MaxConcurrentRequests value. For 20 concurrent requests;

• Min threads is set to 40 worker, 80 completion port threads
• Max threads is set to 80 worker, 160 completion port threads

This way we ensure that your application handles async call returns, internal remote & system calls and internal queue callbak requests for every request from outside.

Cors

This feature adds Cors extension to your application. In this document, it states that UseCors call must be placed somewhere between UseRouting and UseEndpoints calls. With this feature, Gazel ensures this call order.

Applications that use ApiApplication template have this feature enabled and allows requests from any domain by default.

You may disable this when you don't want your application to allow requests from other domains;

cors: c => c.Disabled()

Adding Default Policy

You can add a custom policy as default;

cors: c => c.Enabled(
    o => o.AddDefaultPolicy(policy => policy.WithOrigins("http://example.com"))
)

Adding Named Policies

You may also add multiple policies, so that they can be selected later from settings;

cors: c => c.Enabled(
    o =>
    {
        o.AddPolicy("Production", policy => policy.WithOrigins(cfg.Setting("Cors.Production")));
        o.AddPolicy("Staging", policy => policy.WithOrigins(cfg.Setting("Cors.Staging")));
    },
    cfg.Setting("Cors.PolicyName")
)

For more information about how to add policy to cors you can refer to Microsoft Cors Document .

Crypto

Crypto feature provides a basic encryption/decryption capability to store sensitive data in configuration file or database. It also provides an API to be used in accepting an input in a more secure way. Let's dive in to see how you can use this feature to make your back-end functionality more secure.

Crypto API

This API consists of two main types ICryptographer and EncryptedString providing ways to encrypt/decrypt data and represent encrypted data, respectively.

ICryptographer interface

This interface is a gateway facade to an underlying security mechanism provided by .NET. Behind the scenes, this interface uses a X.509 certificate with a an public / private key pair (for more information see X.509 and RSA ). This way you can make use of asymmetric encryption where needed. There are two types of usage; Encrypt / Decrypt and Sign / Verify.

Encrypt & Decrypt

First and most basic type of usage is to encrypt data using the public key, and decrypt it using the private key. For example, you can use this to encrypt sensitive data to save it in somewhere unsafe so that you can retrieve and decrypt it later.

public class CryptoManager
{
    private readonly ICryptographer _crypto;
    public FileManager(ICryptographer crypto) => _crypto = crypto;
    public Binary GetSensitiveData()
    {
        var sensitive = "something to hide".ToUtf8Binary();
        return _crypto.Encrypt(sensitive);
    }
    public bool CheckSensitiveData(Binary binary)
    {
        var sensitive = _crypto.Decrypt(binary).ToUtf8String();
        return sensitive == "something to hide";
    }
}

ICryptographer also has helper methods to make string conversions easier.

...
public string GetSensitiveData()
{
    // returns base64 representation of encrypted binary
    return _crypto.Encrypt("something to hide");
}
public bool CheckSensitiveData(string encryptedSensitive)
{
    return _crypto.DecryptUnsecure(encryptedSensitive) == "something to hide";
}
...

Above code uses DecryptUnsecure method, which returns a regular string object. There is also a Decrypt method which returns a SecureString. SecureString is a class that encrypts given string with a symmetric key and stores in memory so that a it is safely kept in memory.

...
public bool CheckSensitiveData(string encryptedSensitive)
{
    var sensitive = _crypto.Decrypt(encryptedSensitive);
    return sensitive.Decrypt() == "something to hide";
}
...

Notice that data is decrypted twice; first time it is done by using your X.509 certificate, second time it is done on SecureString object by using a symmetric key that .NET generates.

Sign & Verify

Sign & verify is like the opposite usage of encrypt & decrypt. Decryption can only happen on the side that has the private key, which is back-end side in this case. So encryption is made with a public key, decryption is made with the corresponding private key.

On the contrary, here, signing is done using a private key, and verifying is done using its corresponding public key. So in this usage it's not about hiding information from outside, rather it's about signing data to make it possible for retrievers to verify that data is signed by, thus coming from, the trusted source.

...
public string[] GetSignedData()
{
    var sensitive = "something to be signed";
    var hasher = HashAlgorithm.Create("SHA256");
    hasher.ComputeHash(sensitive.ToUtf8Binary());
    // Signing is done using the private key
    var signature = _crypto.Sign(hasher.Hash, "SHA256");
    return new[] { sensitive, signature };
}
public bool Verify(string[] signedData)
{
    var sensitive = signedData[0];
    var signature = signedData[1];
    var hasher = HashAlgorithm.Create("SHA256");
    hasher.ComputeHash(sensitive.ToUtf8Binary());
    // Verification is done with the public key
    return _crypto.Verify(hasher.Hash, "SHA256", signature);
}
...

EncryptedString struct

This struct acts like a wrapper type for SecureString class from .NET, (see SecureString ). It conforms to the parseable value type convention just like rest of the value types from Gazel.Primitives package. There are three ways to create an EncryptedString instance.

1. Parse method, when you have a plain string object;

   var encrypted = EncryptedString.Parse("something sensitive");

2. FromEncrypted method, when you have an encrypted value;

   var encrypted = EncryptedString.FromEncrypted(encryptedBinary, b => _crypto.DecryptUnsecure(b));

   Second parameter is decryptDelegate in case EncryptedString.Decrypt or Encrypted.ToString() method are called on this instance. Without a decrypt delegate it would not be able to decrpyt its value.
3. Use a SecureString instance. You can cast it to an EncryptedString;

   var encrypted = (EncryptedString)secureString;

   or use constructor;

   var encrypted = new EncryptedString(secureString);

This struct either stores given encrypted binary value, or a secure string instance so that sensitive information is securly kept in memory. You may read How secure is SecureString section from .NET documentation to learn more.

Mapping to a Table Column

You can map EncryptedString just like any other value type.

public class Secret
{
    ...
    public virtual int Id { get; protected set; }
    public virtual string Name { get; protected set; }
    public virtual EncryptedString Value { get; protected set; }
    ...
}

If you intend to use an encrypted string property, please read below information carefully;

• Only encrypted binary value is stored in database so that nobody can see the value without a proper certificate. So it is highly recommended for you to use a different certificate for each environment (Development, Production etc.), and never expose private key of your Production certificate to the people that have access to your production database.
• Value is not decrypted until you explicitly call Decrypt or ToString. This is because decryption is costly and retrieving a list of persistent objects should not decrypt automatically. DataAccessLayer uses FromEncrypted method to create EncryptedString instances when data is retrieved from database.
• Since EncryptedString is expected to store sensitive data, it will never appear in a response directly. So you don't need to make it protected internal or [Internal].

Below is an example of how you can generate and store a sensitive information;

public class Secret
{
    ...
    protected internal SecretToken With(string name)
    {
        Name = name;
        Value = EncryptedString.Parse($"{system.NewGuid()}");
        _repository.Insert(this);
        return this;
    }
    ...
}

As a Service Parameter

You may use EncryptedString as a service parameter just like any other value type. Below you can see a simple example;

public class Secret
{
    ...
    public virtual void UpdateValue(EncryptedString value)
    {
        Value = value;
    }
    ...
}

Although EncryptedString is accepted as a service parameter, a method that returns EncryptedString cannot be registered as a business service (a.k.a. operation), and cannot be called from outside. And also, a property with its type as EncryptedString cannot be registered in service layer as a business data as well.

Reading from Settings

This feature allows you to read an encrypted string from settings using GetEncryptedString method of ICryptographer interface. Let's revisit the previous example from ICryptographer Interface section.

public Binary GetSensitiveData()
{
    var sensitive = "something to hide".ToUtf8Binary();
    return _crypto.Encrypt(sensitive);
}

Here you can see that sensitive information is exposed as a constant string, which makes this sensitive information available to anyone who has access to this code. To prevent this we can read it from settings.

public Binary GetSensitiveData()
{
    var sensitive = _crypto.GetEncryptedString("Sensitive");
    return sensitive.EncryptedValue;
}

Encrypt a sensitive data using your certificate and put its encrypted value to configuration file in base64 format. This way only someone with private key will be able to know actual value of sensitive data.

{
  "Sensitive": { "Decrypted": "something to hide" }
}

Configuration

There are three ways to load a certificate, X509Store, X509CertificateFromP12File and X509CertificateFromPem. There is also a fourth, and the default, AutoResolve option which uses configuration file to decide which one to use.

X509Store

This option uses certificate store of operating system to load a certificate. If you use this option you will have to install your certificate to every OS that will run your back-end system.

You can choose this option as follows;

crypto: c => c.X509Store()

X509Store requires storeName and storeLocation information to know in which store to look for a certificate. It also requires an extra search parameter to locate certificate in the specified store. By default this option looks for StoreName, StoreLocation and SubjectName in configuration file under Gazel.Certificate section like the following;

{
    "Gazel": {
        "Certificate": {
            "StoreName": "TrustedPublisher",
            "StoreLocation": "LocalComputer",
            "SubjectName": "Gazel"
        }
    }
}

If no configuration was given, storeName defaults to TrustedPublisher, storeLocation defaults to LocalComputer. Possible values to these parameters can be found at StoreName and StoreLocation pages.

You can override this configuration directly from configurer as well;

crypto: c => c.X509Store(
    storeName: StoreName.TrustedPublisher,
    storeLocation: StoreLocation.LocalMachine
)

For the extra search parameter, you may give any of search criteria defined in X509FindType . All values of X509FindType enum starts with FindBy prefix, which is removed in configuration keys. For example if you use FindByIssuerName and use Inventiv as its value, you should change configuration as follows;

{
    "Gazel": {
        "Certificate": {
            "StoreName": "TrustedPublisher",
            "StoreLocation": "LocalComputer",
            "IssuerName": "Inventiv"
        }
    }
}

X509CertificateFromP12File

This option enables you to load a PKCS #12 certificate from .p12 file using configured IFileSystem instance (see File System ) and suitable in non-Windows operating systems. Below code enables this option;

crypto: c => c.X509CertificateFromP12File()

It requires path and passwordFile information to load a certificate from given path and use private key with the password specified in given password file. By default it looks for Path and PasswordFile keys in configuration under Gazel.Certificate section as follows;

{
    "Gazel": {
        "Certificate": {
            "Path": "Gazel.p12",
            "PasswordFile": ".CERTPASS"
        }
    }
}

When configuration does not contain these keys, path defaults to Gazel.p12 and passwordFile defaults to .CERTPASS.

You may override these configurations to be set directly from configurer;

crypto: c => c.X509CertificateFromP12File(
    path: "Inventiv.p12",
    passwordFile: ".Inventiv.p12.pass"
)

X509CertificateFromPem

This option enables you to give certificate information directly from configuration file or configurer. Gazel uses this option to register a stub certificate during unit test runs. Below code enables this option;

crypto: c => c.X509CertificateFromPem()

This option requires certPem, keyPem and passwordFile information to be used. By default it looks for these information configuration file using CertPem, KeyPem and PasswordFile keys, respectively, under Gazel.Certificate section. Certificate contents usually start with -----BEGIN CERTIFICATE----- and has new lines in them. To handle this you need to use \n character in json string, an example is as follows;

{
    "Gazel": {
        "Certificate": {
            "CertPem": "-----BEGIN CERTIFICATE-----\nMIIC7zCCAdegAwIBAgIQhaAixfnuiK5HBHMC+kz4zTANBgkqhkiG9w0BAQsFADAQ\nMQ4wDAYDVQQDEwVHYXplbDAeFw0xODAxMTcxMDMxMDFaFw0zOTEyMzEyMzU5NTla...",
            "KeyPem": "-----BEGIN ENCRYPTED PRIVATE KEY-----\nMIIFHDBOBgkqhkiG9w0BBQ0wQTApBgkqhkiG9w0BBQwwHAQIG7xEAxkSK6gCAggA\nMAwGCCqGSIb3DQIJBQAwFAYIKoZIhvcNAwcECEmeebmmTgQsBIIEyJGTsjMc2869...",
            "PasswordFile": ".CERTPASS"
        }
    }
}

Gazel does not have a default certificate so certPem and keyPem do not have a default. Just like previous option, passwordFile defaults to .CERTPASS.

crypto: c => c.X509CertificateFromPem(
    certPem: @"
-----BEGIN CERTIFICATE-----
MIIC7zCCAdegAwIBAgIQhaAixfnuiK5HBHMC+kz4zTANBgkqhkiG9w0BAQsFADAQ
MQ4wDAYDVQQDEwVHYXplbDAeFw0xODAxMTcxMDMxMDFaFw0zOTEyMzEyMzU5NTla
...
-----END CERTIFICATE-----
",
    keyPem: @"
-----BEGIN ENCRYPTED PRIVATE KEY-----
MIIFHDBOBgkqhkiG9w0BBQ0wQTApBgkqhkiG9w0BBQwwHAQIG7xEAxkSK6gCAggA
MAwGCCqGSIb3DQIJBQAwFAYIKoZIhvcNAwcECEmeebmmTgQsBIIEyJGTsjMc2869
...
-----END ENCRYPTED PRIVATE KEY-----
",
    passwordFile: ".CERTIFICATE_PASSWORD"
)

Above example illustrates how you can override default configuratiion directly from configurer.

AutoResolve

This option is the default option for crypto feature and enables you to configure crypto feature completely through configuration file. You don't have to select this option explicitly but you can still choose to do it as shown below;

crypto: c => c.AutoResolve()

It does not accept any parameters. Default behaviour is to use X509Store on Windows and X509CertificateFromP12File on unix-like operating systems. To explicitly specify which option to use, you can add Type key under Gazel.Certificate section;

{
    "Gazel": {
        "Certificate": {
            "Type": "X509Store"
        }
    }
}

Option names are the same as previous sections; X509Store, X509CertificateFromP12File and X509CertificateFromPem. Each option expects its own keys as explained in previous sections. Below example uses store option and specifies certificate information under same conffiguration section;

{
    "Gazel": {
        "Certificate": {
            "Type": "X509Store",
            "SubjectName": "Inventiv"
        }
    }
}

{
    "Gazel": {
        "Certificate": {
            "SubjectName": "Inventiv",
            "Path": "Inventiv.p12",
        }
    }
}

Configuring certificates for a Gazel CLI process

Gazel CLI allows you to generate a schema from a bin directory. When you use this option Gazel CLI will render given bin directory including your configuration files and configurers in your Program.cs. This means that if you use crypto feature, especially in configuration files, it might require a correct configuration for crypto feature as well.

Gazel CLI uses Development for environment by default. However if you face a problem while generating schema, code or dll because of encryption problems, you can make use of --environment option to set environment during Gazel CLI process.

g schemagen bin/net6.0/Debug --environment GazelCLI

This, for example, sets environment to GazelCLI so that you can create a appsettings.GazelCLI.json file and specify your certificate option in this configuration under Gazel.Certificate section.

Exception Handling

Exception handling feature provides a way for your services to respond with a code and a message for every request. To set an error code and message in your response you simply implement an exception class that extends ServiceException and throw an instance of that exception class in your business code.

But before you start writing exception classes and use them right away, we want to describe result code system in Gazel.

Result Codes

Result codes are reserved numbers starting from 0 to 99999 that will represent a response status of a service in your system. There are 5 types of result codes;

Result Code Blocks

There are two main concerns about result codes that need to be addressed;

1. To be unique and static so that they can be documented
2. To be organized so that they are easily used

There are 10K info, 10K warning codes and 70K error codes. To organize these numbers without breaking uniqueness you may split those codes into blocks, so that for every result code block there are 100 info, 100 warning and 700 error codes. Here is the table for result codes organized using result code blocks;

To create a result code block extend ResultCodeBlocks class like this;

public class ResultCodes : ResultCodeBlocks
{
    public static readonly ResultCodeBlock MyBlock = CreateBlock(1, "MyBlock");
}

Now that we've created a block called MyBlock at index 1, let's use this block to create a unique result code within its code ranges;

using static MyProduct.ResultCodes;

MyBlock.Info(0); // 101
MyBlock.Info(10); // 111
MyBlock.Warn(0); // 10101
MyBlock.Warn(10); // 10111
MyBlock.Err(0); // 20701
MyBlock.Err(10); // 20711

You may use one block per business module in your project. This way, errors will be organized by the domain they belong to.

Response Status

Response status is managed by Status property of IResponse to which you can access through IModuleContext.

_context.Response.Status

Type of this property is IResponseStatus, which is the interface to represent all response statuses. There are 3 base classes that implements this interface;

• ServiceInformation for information
• ServiceWarning for warnings
• ServiceException for errors

Implementing a response status

For every message and status extend one of the response status base classes with a proper result code.

using static MyProduct.ResultCodes;
...
public static class MyExceptions
{
    public class ThisIsWrong : ServiceException
    {
        public ThisIsWrong() : base(MyBlock.Err(0)) { }
    }
}
public static class MyWarnings
{
    public class YouAreWarned : ServiceWarning
    {
        public YouAreWarned() : base(MyBlock.Warn(0)) { }
    }
}

Throwing exceptions

When you implement an exception class that extends ServiceException you may throw it just like any .NET exception;

using static MyProduct.MyExceptions;
...
public class MyManager
{
    public void GiveMeError()
    {
         throw new ThisIsWrong();
    }
}

Exception handling mechanism catches this exception and automatically sets it as a response status.

Setting response status

You may also directly set _context.Response.Status property with an IResponseStatus instance. Below is an example of setting status to a warning;

using static MyProduct.MyWarnings;
...
public class MyManager
{
    private readonly IModuleContext _context;
    public MyManager(IModuleContext context) => _context = context;
    public void GiveMeStatus()
    {
        _context.Response.Status = new YouAreWarned();
    }
}

Log Levels

• Handled exceptions, responses with error codes, are logged in Warning level.
• Unhandled exceptions, responses with fatal code , are logged in Error level.
• Other statuses are not logged separately.

Localizing messages

Every result code should have a corresponding message in localization. Exception handling uses ILocalizer to retrieve message format using a key with type and code such as ERR-20001, WAR-10001. Once message format is retrieved, it is formatted using message parameters in response status object.

Let's say you defined another exception in MyBlock;

...
public class RequiredParameter : ServiceException
{
    public RequiredParameter(string parameterName) : base(MyBlock.Err(1), parameterName) { }
}

This would have a localization key ERR-20702.

Assume your localization has a message like this;

{
    "ERR-20702": "Parameter is required: '{0}'"
}

When you throw this exception;

public void CreateEmployee(string ssid)
{
    if(string.IsNullOrWhitespace(ssid))
    {
        throw new RequiredParameter(nameof(ssid));
    }
    ...
}

You will send a response with code 20702 and message;

Parameter is required: 'ssid'

Including extra data

ServiceException class has a special property called ExtraData to enable you to include extra data along with code and message so that client applications can use this information to handle some business logic in exception case.

Assume you have a Withdraw service that withdraws money from an account. You may return current balance in extra data, when withdraw operation throws insufficient balance exception so that client application can use it to provide some further functionality.

Built-in Errors

Below you can see built-in exceptions and their defined error codes;

Information and Warnings

Customization

Exception handling mechanism is a core feature of Gazel framework. You cannot change the underlying mechanism nor you cannot disable it. However, you can extend it to provide additional exception handlers.

Creating a custom handler

Exception handling is done through IExceptionHandler interface. If you want to provide a custom mechanism to handle errors, you must implement this interface and register it to IKernel.

When an exception is thrown, exception handling feature loops through all exception handlers to find a way to convert the exception into ServiceException. If it can, then it means exception is handled with an error code, if it cannot, then it means it is an unhandled exception with the fatal code.

Below is an example of a custom exception handler for ArgumentException;

public class MyHandler : IExceptionHandler
{
    public bool Handles(Exception ex) => ex is ArgumentException;
    public ServiceException Handle(Exception ex) => new ServiceException(90001)
    ExceptionInfo GetExceptionInfo(int resultCode) =>
        resultCode == 90001
            ? new ExceptionInfo(typeof(ArgumentException))
            : null;
}

File System

File system feature basically enables you to read/write file content from/to a file storage.

IFileSystem interface

When an application has this feature, you can directly inject IFileSystem interface into your business objects. Below is a simple example;

public class FileManager
{
    private readonly IFileSystem _file;
    public FileManager(IFileSystem file) => _file = file;
    public await Task<Binary> FetchContent(string path)
    {
        return await _file.ReadAsync(path);
    }
}

Configuration

Gazel has a built-in implementation that uses local storage.

builder.Services.AddGazelServiceApplication(
    ...
    fileSystem: c => c.Local(rootPath: "files"),
    ...
);

When rootPath is given, all files will be stored under this folder. You might pass an absolute path as well.

c => c.Local(rootPath: "/absolute-path"),

Customization

When you want to store files in a different type of storage, you can implement IFileSystem interface and register it using Custom configurer in FileSystemConfigurer.

Assume you've made an S3 implementation of file system interface, you can register it as below;

c => c.Custom<S3FileSystem>()

Configurations

Here you can find how to configure small features, Configurations. When configuring an application you can always check which ones are available from the optional parameters.

Every sample code in this section is in the same format as service feature configuration shown below;

service: c => c.Routine(
  serviceUrlBase: ServiceUrl.Localhost(7028)
)

Examples will only include configuration line to avoid repetitive samples like below;

builder.Services.AddGazelServiceApplication(cfg,
    ...
    service: c => c.Routine(
      serviceUrlBase: ServiceUrl.Localhost(7028)
    )
    ...
);

Application Assemblies

You may change which assemblies are used for an application via this configuration. By default Gazel loads all assemblies starting with the root namespace of your entry assembly. Assume your Program.cs is in a project named MyCompany.MyComponent.App.Service, then the root namespace is MyCompany.

Each application configurer has a configuration named applicationAssemblies which provides Assemblies instance as a parameter and expects List<Assembly> as a result. Below you can find default configuration;

applicationAssemblies: c => c.All

There are several ways to determine which assemblies to use;

Filtering All

You can directly filter out unwanted assemblies returned by All property.

applicationAssemblies: c => c.All.Where(predicate: a => !a.FullName.Contains(value: "Exclude")).ToList()

Find By Namespace

There is a method on Assemblies class called Find that takes a namespace predicate as a parameter;

applicationAssemblies: c => c.Find(namespaceFilter: ns => ns.StartsWith(value: "MyCompany"))

Find By Regex

You can also provide a namespace regex;

applicationAssemblies: c => c.Find(namespaceRegex: "^MyCompany.*$")

Find By AssemblyType

You can make use of AssemblyType class.

applicationAssemblies: c => c.Find(type: AssemblyType.Module)

Application Session

ApplicationSessionConfiguration allows you to provide a token for a middle application (such as Gateway Application) to be used when sending requests to its backing application (such as Service Application). When there is a need for your application to authenticate its requests to the other application before a user session is established you can use this configuration.

You can find this configuration under applicationSession: parameter and provide an AppToken.

applicationSession: c => c.Use(token: cfg.Setting<AppToken>("ApplicationSession.Token"))

Or you can leave your application session token empty by using UseEmptyToken().

applicationSession: c => c.UseEmptyToken()

Business Logic

Using BusinessLogicConfiguration you can configure Routine's developmentMode and maxFetchDepth options.

businessLogic: c => c.Routine(
  developmentMode: builder.Environment.IsDevelopment(), // defaults to false
  maxFetchDepth: 10 // defaults to 10
)

There is also an extra includeComponentNameInModuleName: option which enables your application to use the component part of your module project as well as its module name. To use this option your module projects must be named in this convention: <Company>.<Component>.Module.<ModuleName>.

businessLogic: c => c.Routine(
  includeComponentNameInModuleName: true // defaults to false
)

To give an example, if you have a module project named Inventiv.Sample.Module.Todo, name of this module in service layer is Todo by default. If you set this option to true, module name in service layer will be Sample.Todo. It is useful when you have a large enough project with more than one component.

Command Line

Allows you to configure which assembly to use when searching for command classes. You can use AssemblyType (similar to Application Assemblies ) for this configuration.

commandLine: c => c.CommandLineParser(commandAssembly: AssemblyType.All),

For more information visit Command Line Layer .

Database

Gateway

Configures Gateway Layer . Serves internal business services under given rootPath. You can also restrict access to business services by using allow and deny regex patterns.

// This sample configuration allows all services and denies nothing.
// Example url: http://localhost:5000/gw/{module}.{entity/query}/{business}
gateway: c => c.Routine(
    rootPath: "gw",
    allow: ".*",
    deny: "^!$"
)

Default configuration serves under /, the root url of your application, and allows every business service with no restriction.

Http Header

HttpHeader configuration lets you expose custom headers in your public application and map them to the headers of your internal business services. Exposed headers are called public headers. Once mapped for every request they will be forwarded to the business services using their internal header name. Internal response headers will be mapped back to their corresponding public header as well.

This configuration is an example for creating a custom request and response headers;

httpHeader: c => c.Custom(h => h
    .RequestHeader(
        publicHeaderName: "X-Public-Req",
        internalHeader: "X-Internal-Req"
    )
    .ResponseHeader(
        publicHeaderName: "X-Public-Res",
        internalHeader: "X-Internal-Res"
    )
)

Below diagram illustrates mapping flow of this example;

You may also manipulate header value via a conversion function. Adding conversion functions to configuration from previous example;

httpHeader: c => c.Custom(h => h
    .RequestHeader(
        publicHeaderName: "X-Public-Req",
        internalHeader: "X-Internal-Req",
        conversionFunc: public => public.ToUpperInvariant()
    )s
    .ResponseHeader(
        publicHeaderName: "X-Public-Res",
        internalHeader: "X-Internal-Res",
        conversionFunc: internal => internal.ToLowerInvariant()
    )
)

Below is another example to illustrate what you can achieve using this configuration;

Configuration of this is as follows;

httpHeader: c => c.Custom(h => h
    .RequestHeader(
      publicHeaderName: "Accept-Language",
      internalHeader: Header.LanguageCode,
      conversionFunc: header => header.Before(",")
    )
    // Result code and result message headers are added by default.
    // To override existing configuration, you need to clear response headers.
    .ClearResponseHeaders()
    .ResponseHeader(
      publicHeaderName: "X-Code",
      internalHeader: Header.ResultCode
    )
    .ResponseHeader(
      publicHeaderName: "X-Description",
      internalHeader: Header.ResultMessage
    )
    .ResponseHeader(
      publicHeaderName: "X-Link",
      internalHeader: Header.ResultCode,
      conversionFunc: header => header == "0" ? null : $"https://your-doc-site.com/result-codes/{header}"
    )
)

Rest Api

Service

You can configure service url base and request timeout values for a service application to let it consume its own services as follows;

service: c => c.Routine(
    serviceUrlBase: "http://localhost:5000/service",
    requestTimeout: TimeSpan.FromSeconds(5.0)
)

// http://localhost:5000/service
ServiceUrl.Localhost(5000)
// http://sample.inventiv.com.tr/service
ServiceUrl.Build("http://sample.inventiv.com.tr")

Service Client

Service client configuration allows you to configure a downstream service application information;

serviceClient: c => c.Routine(
    serviceUrlBase: "http://localhost:5000/service"
    requestTimeout: TimeSpan.FromSeconds(5.0)
)

// http://localhost:5000/service
ServiceUrl.Localhost(5000)
// http://sample.inventiv.com.tr/service
ServiceUrl.Build("http://sample.inventiv.com.tr")

Options

Options are features that you can only enable or disable. Below is a sample option configuration;

// e.g. Decimal point has built in Always or AfterTwoDigits configuration options
decimalPoint: c => c.Always()

Decimal Point

Decimal point lets you change the way Money and MoneyRange value types are serialized in service layer. It gives you two options Always and AfterTwoDigits, default configuration is Always().

Use Always, when you always expect decimal point separator;

// While parsing, this option expects decimal point
// only when there are decimal digits.
// 100USD -> $100
// 1.00USD -> $1.00
decimalPoint: c => c.Always()

Use AfterTwoDigits when you want last two digits to be treated automatically as decimal digits;

// While parsing, this option treats last two digits
// as decimal digits even if there is no decimal point
// separator and expect decimal point separator only
// when there are more than two decimal digits
// 100USD -> $1.00
// 1.001USD -> $1.001
decimalPoint: c => c.AfterTwoDigits(),

UTC

You can choose if ISystem.Now property will use UTC time or local time using this option.

// Uses Utc time
utc: c => c.UseUtcTime()

// Uses local time
utc: c => c.UseLocalTime()