gurl

README

ᵍ🆄🆁🅻

Combinator library for network I/O

---

The library implements a pure functional style to express communication behavior by hiding the networking complexity using combinators. This construction decorates http i/o pipeline(s) with "programmable commas", allowing to make http requests with few interesting properties such as composition and laziness.

User Guide | Playground | Examples | API Specification

Inspiration

Microservices have become a design style to evolve system architecture in parallel, implement stable and consistent interfaces. An expressive language is required to design the variety of network communication use-cases. Pure functional languages fit very well to express intent of communication behavior. These languages give rich abstractions to hide the networking complexity and help us to compose a chain of network operations and represent them as pure computation, building new things from small reusable elements. This library is implemented after Erlang's m_http

The library attempts to adapt a human-friendly logging syntax of HTTP I/O used by curl and Behavior as a Code paradigm, which connects cause-and-effect (Given/When/Then) with the networking (Input/Process/Output).

> GET / HTTP/1.1
> Host: example.com
> User-Agent: curl/7.54.0
> Accept: application/json
>
< HTTP/1.1 200 OK
< Content-Type: text/html; charset=UTF-8
< Server: ECS (phd/FD58)
< ...

Given semantic provides an intuitive approach to specify HTTP requests and expected responses. Adoption of this syntax as Go native code provides a rich capabilities for network programming.

Key features

Standard Golang packages implement a low-level HTTP interface, which requires knowledge about the protocol itself, understanding of Golang implementation aspects, and a bit of boilerplate coding. It also misses standardized chaining (composition) of individual requests. ᵍ🆄🆁🅻 inherits an ability of pure functional languages to express communication behavior by hiding the networking complexity using combinators. Combinators make a chain of network operations as a pure computation.

• cause-and-effect abstraction of HTTP I/O using Golang naive do-notation
• composition of individual HTTP requests to complex networking computations
• human-friendly, Go native and declarative syntax to depict HTTP operations
• implements a declarative approach for testing of RESTful interfaces
• automatically encodes/decodes Golang native HTTP payload using Content-Type hints
• supports generic transformation to algebraic data types

Getting started

The library requires Go 1.18 or later

The latest version of the library is available at its main branch. All development, including new features and bug fixes, take place on the main branch using forking and pull requests as described in contribution guidelines. The stable version is available via Golang modules.

Use go get to retrieve the library and add it as dependency to your application.

go get -u github.com/fogfish/gurl

Quick Example

The following code snippet demonstrates a typical usage scenario. See runnable http request example.

import (
  "context"

  "github.com/fogfish/gurl/v2/http"
  ø "github.com/fogfish/gurl/v2/http/send"
  ƒ "github.com/fogfish/gurl/v2/http/recv"
)

// Declare the type, used for networking I/O.
type Payload struct {
  Origin string `json:"origin"`
  Url    string `json:"url"`
}

// Define the variable holds results of network I/O
var data Payload

// Declare HTTP I/O specification
lazy := http.GET(
  // specify HTTP request
  ø.GET.URL("http://httpbin.org/get"),
  ø.Accept.JSON,

  // assert HTTP response and "recv" JSON to the variable
  ƒ.Status.OK,
  ƒ.ContentType.JSON,
  ƒ.Recv(&data),
)

// instance of HTTP stack
stack := http.New()

// evaluate HTTP I/O specification
err := stack.IO(context.Background(), lazy)

Next steps

• Study User Guide if defines library concepts and guides about api usage;
• Use examples as a reference for further development.

Extensions

The library supplies extensions

• x/awsapi enables AWS Signature V4 for HTTP I/O. Allows to use AWS API Gateway with IAM authentication.
• x/xhtml enables fetching and parsing xHTML content.

How To Contribute

The library is MIT licensed and accepts contributions via GitHub pull requests:

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

The build and testing process requires Go version 1.18 or later.

Build and test the library in your development console.

git clone https://github.com/fogfish/gurl
cd gurl
go test ./...

commit message

The commit message helps us to write a good release note, speed-up review process. The message should address two questions what changed and why. The project follows the template defined by chapter Contributing to a Project of Git book.

Short (50 chars or less) summary of changes

More detailed explanatory text, if necessary. Wrap it to about 72 characters or so. In some contexts, the first line is treated as the subject of an email and the rest of the text as the body. The blank line separating the summary from the body is critical (unless you omit the body entirely); tools like rebase can get confused if you run the two together.

Further paragraphs come after blank lines.

Bullet points are okay, too

Typically a hyphen or asterisk is used for the bullet, preceded by a single space, with blank lines in between, but conventions vary here

bugs

If you experience any issues with the library, please let us know via GitHub issues. We appreciate detailed and accurate reports that help us to identity and replicate the issue.

• Specify the configuration of your environment. Include which operating system you use and the versions of runtime environments.

• Attach logs, screenshots and exceptions, if possible.

• Reveal the steps you took to reproduce the problem, include code snippet or links to your project.

License

Documentation

Overview

Package gurl is a class of High Order Component which can do http requests with few interesting property such as composition and laziness. The library implements rough and naive Haskell's equivalent of do-notation, so called monadic binding form. This construction decorates http i/o pipeline(s) with "programmable commas".

Inspiration

Microservices have become a design style to evolve system architecture in parallel, implement stable and consistent interfaces. An expressive language is required to design the variety of network communication use-cases. A pure functional languages fits very well to express communication behavior. The language gives a rich techniques to hide the networking complexity using monads as abstraction. The IO-monads helps us to compose a chain of network operations and represent them as pure computation, build a new things from small reusable elements. The library is implemented after Erlang's https://github.com/fogfish/m_http

The library attempts to adapts a human-friendly syntax of HTTP request/response logging/definition used by curl with Behavior as a Code paradigm. It tries to connect cause-and-effect (Given/When/Then) with the networking (Input/Process/Output).

> GET / HTTP/1.1
> Host: example.com
> User-Agent: curl/7.54.0
> Accept: application/json
>
< HTTP/1.1 200 OK
< Content-Type: text/html; charset=UTF-8
< Server: ECS (phd/FD58)
< ...

This semantic provides an intuitive approach to specify HTTP requests/responses. Adoption of this syntax as Go native code provides a rich capability to network programming.

Key features

↣ cause-and-effect abstraction of HTTP request/response, naive do-notation

↣ high-order composition of individual HTTP requests to complex networking computations

↣ human-friendly, Go native and declarative syntax to depict HTTP operations

↣ implements a declarative approach for testing of RESTful interfaces

↣ automatically encodes/decodes Go native HTTP payload using Content-Type hints

↣ supports generic transformation to algebraic data types

↣ simplify error handling with naive Either implementation

IO Category

Standard Golang packages implements low-level HTTP interface, which requires knowledge about protocol itself, aspects of Golang implementation, a bit of boilerplate coding and lack of standardized chaining (composition) of individual requests.

gurl library inherits an ability of pure functional languages to express communication behavior by hiding the networking complexity using category pattern (aka "do"-notation). This pattern helps us to compose a chain of network operations and represent them as pure computation, build a new things from small reusable elements. This library uses the "do"-notation, so called monadic binding form. It is well know in functional programming languages such as Haskell and Scala. The networking becomes a collection of composed "do"-notation in context of a state monad.

A composition of HTTP primitives within the category are written with the following syntax.

gurl.Join(arrows ...Arrow) Arrow

Here, each arrow is a morphism applied to HTTP protocol. The implementation defines an abstraction of the protocol environments and lenses to focus inside it. In other words, the category represents the environment as an "invisible" side-effect of the composition.

`gurl.Join(arrows ...Arrow) Arrow` and its composition implements lazy I/O. It only returns a "promise", you have to evaluate it in the context of IO instance.

io := gurl.IO()
fn := gurl.Join( ... )
fn(io)

Basics

The following code snippet demonstrates a typical usage scenario.

import (
  "github.com/fogfish/gurl"
  "github.com/fogfish/gurl/http"
  ƒ "github.com/fogfish/gurl/http/recv"
  ø "github.com/fogfish/gurl/http/send"
)

// You can declare any types and use them as part of networking I/O.
type Payload struct {
  Origin string `json:"origin"`
  Url    string `json:"url"`
}

var data Payload
var lazy := http.Join(
  // declares HTTP method and destination URL
  ø.GET.URL("http://httpbin.org/get"),
  // HTTP content negotiation, declares acceptable types
  ø.Accept.JSON,

  // requires HTTP Status Code to be 200 OK
  ƒ.Status.OK,
  // requites HTTP Header to be Content-Type: application/json
  ƒ.ContentType.JSON,
  // unmarshal JSON to the variable
  ƒ.Recv(&data),
)

// Note: http do not hold yet, a results of HTTP I/O
//       it is just a composable "promise", you have to
//       evaluate a side-effect of HTTP "computation"
if lazy(gurl.IO( ... )).Fail != nil {
  // error handling
}

The evaluation of "program" fails if either networking fails or expectations do not match actual response. There are no needs to check error code after each operation. The composition is smart enough to terminate "program" execution.

See User Guide about the library at https://github.com/fogfish/gurl

Index

• Constants
• type NoMatch
  • func (e *NoMatch) Error() string
• type NotSupported
  • func (e *NotSupported) Error() string

Constants

const Version = "v2.10.0"

Types

type NoMatch

type NoMatch struct {
	ID       string // unique ID of failed combinator
	Protocol any    // protocol primitive caused failure
	Diff     string // human readable difference between expected & actual values
	Expect   any    // expected value
	Actual   any    // actual value
}

Mismatch is returned by api if expectation at body value is failed

func (*NoMatch) Error

func (e *NoMatch) Error() string

type NotSupported

type NotSupported struct{ URL string }

NotSupported is returned if communication schema is not supported.

func (*NotSupported) Error

func (e *NotSupported) Error() string