<h1 align="center">Link Preview JS</h1>

<div align="center">
<img src="https://user-images.githubusercontent.com/1634213/127743288-9f8a99f3-75d8-42c5-9a69-b47c661b7e18.jpg" height="500"/>

<pre align="center">
npm i link-preview-js
</pre>

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**Before creating an issue**

It's more than likely there is nothing wrong with the library:

- It's very simple; fetch html, parse html, look for OpenGraph html tags.
- Unless HTML or the OpenGraph standard change, the library will not break
- If the target website you are trying to preview redirects you to a login page **the preview will "fail"**, becuase it will parse the login page
- If the target website does not have OpenGraph tags **the preview will most likely "fail"**, there are some fallbacks but in general it will not work
- **You cannot preview (fetch) another web page from YOUR web page. This is an intentional security feature of browsers called CORS**

Any opened issue that does not take this points into account will just be closed.

# Link Preview

Allows you to extract information from a HTTP url/link (or parse a HTML string) and retrieve meta information such as title, description, images, videos, etc. via **OpenGraph** tags.

## GOTCHAs

- You cannot request a different domain from your web app (Browsers block cross-origin-requests). If you don't know how _same-origin-policy_ works, [here is a good intro](https://dev.to/lydiahallie/cs-visualized-cors-5b8h), therefore **this library works on node (back-end environments) and certain mobile run-times (cordova or react-native)**.
- **This library acts as if the user would visit the page, sites might re-direct you to sign-up pages, consent screens, etc.** You can try to change the user-agent header (try with `google-bot` or with `Twitterbot`), but you need to work around these issues yourself.

## API

`getLinkPreview`: you have to pass a string, doesn't matter if it is just a URL or a piece of text that contains a URL, the library will take care of parsing it and returning the info of first valid HTTP(S) URL info it finds.

`getPreviewFromContent`: useful for passing a pre-fetched Response object from an existing async/etc. call. Refer to example below for required object values.

```typescript
import { getLinkPreview, getPreviewFromContent } from "link-preview-js";

// pass the link directly
getLinkPreview("https://www.youtube.com/watch?v=MejbOFk7H6c").then((data) =>
  console.debug(data)
);

////////////////////////// OR //////////////////////////

// pass a chunk of text
getLinkPreview(
  "This is a text supposed to be parsed and the first link displayed https://www.youtube.com/watch?v=MejbOFk7H6c"
).then((data) => console.debug(data));

////////////////////////// OR //////////////////////////

// pass a pre-fetched response object
// The passed response object should include, at minimum:
// {
//   data: '<!DOCTYPE...><html>...',     // response content
//   headers: {
//     ...
//     // should include content-type
//     content-type: "text/html; charset=ISO-8859-1",
//     ...
//   },
//   url: 'https://domain.com/'          // resolved url
// }
yourAjaxCall(url, (response) => {
  getPreviewFromContent(response).then((data) => console.debug(data));
});
```

## Options

Additionally you can pass an options object which should add more functionality to the parsing of the link

| Property Name                                                                          |                                                                                             Result                                                                                              |
| -------------------------------------------------------------------------------------- | :---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------: |
| imagesPropertyType (**optional**) (ex: 'og')                                           |                                                 Fetches images only with the specified property, `meta[property='${imagesPropertyType}:image']`                                                 |
| headers (**optional**) (ex: { 'user-agent': 'googlebot', 'Accept-Language': 'en-US' }) |                                                                                Add request headers to fetch call                                                                                |
| timeout (**optional**) (ex: 1000)                                                      |                                                                                 Timeout for the request to fail                                                                                 |
| followRedirects (**optional**) (default 'error')                                       | For security reasons, the library does not automatically follow redirects ('error' value), a malicious agent can exploit redirects to steal data, posible values: ('error', 'follow', 'manual') |
| handleRedirects (**optional**) (with followRedirects 'manual')                         |                         When followRedirects is set to 'manual' you need to pass a function that validates if the redirectinon is secure, below you can find an example                         |
| resolveDNSHost (**optional**)                                                          |                                                   Function that resolves the final address of the detected/parsed URL to prevent SSRF attacks                                                   |

```javascript
getLinkPreview("https://www.youtube.com/watch?v=MejbOFk7H6c", {
  imagesPropertyType: "og", // fetches only open-graph images
  headers: {
    "user-agent": "googlebot" // fetches with googlebot crawler user agent
    "Accept-Language": "fr-CA", // fetches site for French language
    // ...other optional HTTP request headers
  },
  timeout: 1000
}).then(data => console.debug(data));
```

## SSRF Concerns

Doing requests on behalf of your users or using user provided URLs is dangerous. One of such attacks is a trying to fetch a domain which redirects to localhost and so the users getting the contents of your server (doesn't affect mobile runtimes). In order to mittigate this attack you can use the resolveDNSHost option:

```ts
// example how to use node's dns resolver
const dns = require("node:dns");
getLinkPreview("http://maliciousLocalHostRedirection.com", {
  resolveDNSHost: async (url: string) => {
    return new Promise((resolve, reject) => {
      const hostname = new URL(url).hostname;
      dns.lookup(hostname, (err, address, family) => {
        if (err) {
          reject(err);
          return;
        }

        resolve(address); // if address resolves to localhost or '127.0.0.1' library will throw an error
      });
    });
  },
}).catch((e) => {
  // will throw a detected redirection to localhost
});
```

This might add some latency to your request but prevents loopback attacks.

## Redirections

Same as SSRF, following redirections is dangerous, the library errors by default when the response tries to redirect the user. There are however some simple redirections which are valid (e.g. http to https) and you might want to allow, you can do it via:

```ts
await getLinkPreview(`http://google.com/`, {
  followRedirects: `manual`,
  handleRedirects: (baseURL: string, forwardedURL: string) => {
    const urlObj = new URL(baseURL);
    const forwardedURLObj = new URL(forwardedURL);
    if (
      forwardedURLObj.hostname === urlObj.hostname ||
      forwardedURLObj.hostname === "www." + urlObj.hostname ||
      "www." + forwardedURLObj.hostname === urlObj.hostname
    ) {
      return true;
    } else {
      return false;
    }
  },
});
```

## Response

Returns a Promise that resolves with an object describing the provided link.
The info object returned varies depending on the content type (MIME type) returned
in the HTTP response (see below for variations of response). Rejects with an error if response can not be parsed or if there was no URL in the text provided.

### Text/HTML URL

```javascript
{
  url: "https://www.youtube.com/watch?v=MejbOFk7H6c",
  title: "OK Go - Needing/Getting - Official Video - YouTube",
  siteName: "YouTube",
  description: "Buy the video on iTunes: https://itunes.apple.com/us/album/needing-getting-bundle-ep/id508124847 See more about the guitars at: http://www.gretschguitars.com...",
  images: ["https://i.ytimg.com/vi/MejbOFk7H6c/maxresdefault.jpg"],
  mediaType: "video.other",
  contentType: "text/html; charset=utf-8",
  videos: [],
  favicons:["https://www.youtube.com/yts/img/favicon_32-vflOogEID.png","https://www.youtube.com/yts/img/favicon_48-vflVjB_Qk.png","https://www.youtube.com/yts/img/favicon_96-vflW9Ec0w.png","https://www.youtube.com/yts/img/favicon_144-vfliLAfaB.png","https://s.ytimg.com/yts/img/favicon-vfl8qSV2F.ico"]
}
```

### Image URL

```javascript
{
  url: "https://media.npr.org/assets/img/2018/04/27/gettyimages-656523922nunes-4bb9a194ab2986834622983bb2f8fe57728a9e5f-s1100-c15.jpg",
  mediaType: "image",
  contentType: "image/jpeg",
  favicons: [ "https://media.npr.org/favicon.ico" ]
}
```

### Audio URL

```javascript
{
  url: "https://ondemand.npr.org/anon.npr-mp3/npr/atc/2007/12/20071231_atc_13.mp3",
  mediaType: "audio",
  contentType: "audio/mpeg",
  favicons: [ "https://ondemand.npr.org/favicon.ico" ]
}
```

### Video URL

```javascript
{
  url: "https://www.w3schools.com/html/mov_bbb.mp4",
  mediaType: "video",
  contentType: "video/mp4",
  favicons: [ "https://www.w3schools.com/favicon.ico" ]
}
```

### Application URL

```javascript
{
  url: "https://assets.curtmfg.com/masterlibrary/56282/installsheet/CME_56282_INS.pdf",
  mediaType: "application",
  contentType: "application/pdf",
  favicons: [ "https://assets.curtmfg.com/favicon.ico" ]
}
```

## License

MIT license
