url-verifier

🔗 A Go library for URL validation and verification: does this URL actually work?

Features

• URL Validation: validates whether a string is a valid URL.
• Different Validation Types: validates whether the URL is valid according to a "human" definition of a correct URL, strict compliance with RFC3986 (Uniform Resource Identifier (URI): Generic Syntax), and/or compliance with RFC3986 with the addition of a schema e.g. HTTPS.
• Reachability: verifies whether the URL is actually reachable via an HTTP GET request and provides the status code returned.

Rationale

There are several methods of validating URLs in Go depending on what you're trying to achieve. Strict, technical validation can be done through a simple call to url.Parse in Go's Standard library or a more "human" definition of a valid URL using govalidator (which is what this library uses internally for syntax verification).

However, this will successfully validate all types of URLs, from relative paths through to hostnames without a scheme. Often, when building user-facing applications, what we actually want is a way to check whether the URL input provided will actually work i.e. it's valid, it resolves, and it can be loaded in a web browser.

Install

Use go get to install this package.

go get -u github.com/davidmytton/url-verifier

Usage

Basic usage

Use Verify to check whether a URL is correct:

package main

import (
 "fmt"

 urlverifier "github.com/davidmytton/url-verifier"
)

func main() {
 url := "https://example.com/"

 verifier := urlverifier.NewVerifier()
 ret, err := verifier.Verify(url)

 if err != nil {
  fmt.Errorf("Error: %s", err)
 }

 fmt.Printf("Result: %+v\n", ret)
 /*
   Result: &{
    URL:https://example.com/
    URLComponents:https://example.com/
    IsURL:true
    IsRFC3986URL:true
    IsRFC3986URI:true
    HTTP:<nil>
   }
 */
}

URL reachability check

Call EnableHTTPCheck() to issue a GET request to the HTTP or HTTPS URL and check whether it is reachable and successfully returns a response (a success (2xx) or success-like code (3xx)). Non-HTTP(S) URLs will return an error.

package main

import (
 "fmt"

 urlverifier "github.com/davidmytton/url-verifier"
)

func main() {
 url := "https://example.com/"

 verifier := urlverifier.NewVerifier()
 verifier.EnableHTTPCheck()
 ret, err := verifier.Verify(url)

 if err != nil {
  fmt.Errorf("Error: %s", err)
 }

 fmt.Printf("Result: %+v\n", ret)
 fmt.Printf("HTTP: %+v\n", ret.HTTP)

 if ret.HTTP.IsSuccess {
  fmt.Println("The URL is reachable with status code", ret.HTTP.StatusCode)
 }
 /*
   Result: &{
    URL:https://example.com/
    URLComponents:https://example.com/
    IsURL:true
    IsRFC3986URL:true
    IsRFC3986URI:true
    HTTP:0x140000b6a50
   }
   HTTP: &{
    Reachable:true
    StatusCode:200
    IsSuccess:true
   }
   The URL is reachable with status code 200
 */
}

HTTP checks against internal URLs

By default, the reachability checks are only executed if the host resolves to a non-internal IP address. An internal IP address is defined as any of: private, loopback, link-local unicast, link-local multicast, interface-local multicast, or unspecified.

This is one layer of protection against Server Side Request Forgery (SSRF) requests.

To allow internal HTTP checks, call verifier.AllowHTTPCheckInternal():

urlToCheck := "http://localhost:3000"

verifier := NewVerifier()
verifier.EnableHTTPCheck()
// Danger: Makes SSRF easier!
verifier.AllowHTTPCheckInternal()
ret, err := verifier.Verify(urlToCheck)
...

Credits

This library is heavily inspired by email-verifier.

License

This package is licensed under the MIT License.