How to parse link header from github API

问题

the github API sends the pagination data for the json results in the http link header:

Link: <https://api.github.com/repos?page=3&per_page=100>; rel="next",
<https://api.github.com/repos?page=50&per_page=100>; rel="last"

since the github API is not the only API using this method (i think) i wanted to ask if someone has a useful little snippet to parse the link header (and convert it to an array for example) so that i can use it for my js app.

i googled around but found nothing useful regarding how to parse pagination from json APIs

回答1:

There is a PageLinks class in the GitHub Java API that shows how to parse the Link header.

回答2:

The parse-link-header NPM module exists for this purpose; its source can be found on github under a MIT license (free for commercial use).

Installation is as simple as:

npm install parse-link-header

Usage looks like the following:

var parse = require('parse-link-header');
var parsed = parse('<https://api.github.com/repos?page=3&per_page=100>; rel="next", <https://api.github.com/repos?page=50&per_page=100>; rel="last"')

...after which one has parsed.next, parsed.last, etc:

{ next:
   { page: '3',
     per_page: '100',
     rel: 'next',
     url: 'https://api.github.com/repos?page=3&per_page=100' },
  last:
   { page: '50',
     per_page: '100',
     rel: 'last',
     url: ' https://api.github.com/repos?page=50&per_page=100' } }

回答3:

I found wombleton/link-headers on github. It appears to be made for the browser, as opposed to being an npm module, but it seems like it wouldn't be hard to modify it to work in a server-side environment. It uses pegjs to generate a real RFC 5988 parser rather than string splits, so it should work well for any link header, rather than just Github's.

回答4:

I found this Gist that:

Parse Github Links header in JavaScript

Tested it out on the Github API and it returns an object like:

var results = {
    last: "https://api.github.com/repositories/123456/issues?access_token=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX&state=open&since=2013-07-24T02%3A12%3A30.309Z&direction=asc&page=4"
    next: "https://api.github.com/repositories/123456/issues?access_token=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX&state=open&since=2013-07-24T02%3A12%3A30.309Z&direction=asc&page=2"
};

回答5:

If you can use Python and don't want to implement full specification, but need to have something what work for Github API, then here we go:

import re
header_link = '<https://api.github.com/repos?page=3&per_page=100>; rel="next", <https://api.github.com/repos?page=50&per_page=100>; rel="last"'
if re.search(r'; rel="next"', header_link):
    print re.sub(r'.*<(.*)>; rel="next".*', r'\1', header_link)

回答6:

I completely understand this is "technically" a JavaScript thread. But, if you're like me and arrived here by Google'ing "how to parse Link header" I thought I'd share my solution for my envinronment (C#).

public class LinkHeader
{
    public string FirstLink { get; set; }
    public string PrevLink { get; set; }
    public string NextLink { get; set; }
    public string LastLink { get; set;}

    public static LinkHeader FromHeader(string linkHeader)
    {
        LinkHeader linkHeader = null;

        if (!string.IsNullOrWhiteSpace(linkHeader))
        {
            string[] linkStrings = linkHeader.Split("\",");

            if (linkStrings != null && linkStrings.Any())
            {
                linkHeader = new LinkHeader();

                foreach (string linkString in linkStrings)
                {
                    var relMatch = Regex.Match(linkString, "(?<=rel=\").+?(?=\")", RegexOptions.IgnoreCase);
                    var linkMatch = Regex.Match(linkString, "(?<=<).+?(?=>)", RegexOptions.IgnoreCase);

                    if (relMatch.Success && linkMatch.Success)
                    {
                        string rel = relMatch.Value.ToUpper();
                        string link = linkMatch.Value;

                        switch (rel)
                        {
                            case "FIRST":
                                linkHeader.FirstLink = link;
                                break;
                            case "PREV":
                                linkHeader.PrevLink = link;
                                break;
                            case "NEXT":
                                linkHeader.NextLink = link;
                                break;
                            case "LAST":
                                linkHeader.LastLink = link;
                                break;
                        }
                    }
                }
            }
        }

        return linkHeader;
    }
}

Testing in a console app, using GitHub's example Link header:

void Main()
{
    string link = "<https://api.github.com/user/repos?page=3&per_page=100>; rel=\"next\",< https://api.github.com/user/repos?page=50&per_page=100>; rel=\"last\"";
    LinkHeader linkHeader = LinkHeader.FromHeader(link);
}

回答7:

Here is a simple javascript function that extracts the useful info from the link in a nice object notation.

var linkParser = (linkHeader) => {
  let re = /<([^\?]+\?[a-z]+=([\d]+))>;[\s]*rel="([a-z]+)"/g;
  let arrRes = [];
  let obj = {};
  while ((arrRes = re.exec(linkHeader)) !== null) {
    obj[arrRes[3]] = {
      url: arrRes[1],
      page: arrRes[2]
    };
  }
  return obj;
}

It will output the result like this ==>

{
  "next": {
    "url": "https://api.github.com/user/9919/repos?page=2",
    "page": "2"
  },
  "last": {
    "url": "https://api.github.com/user/9919/repos?page=10",
    "page": "10"
  }
}

回答8:

Here's a simple bash script with curl and sed to get all pages from a long query

url="https://api.github.com/repos/$GIT_USER/$GIT_REPO/issues"
while [ "$url" ]; do
      echo "$url" >&2
      curl -Ss -n "$url"
      url="$(curl -Ss -I -n "$url" | sed -n -E 's/Link:.*<(.*?)>; rel="next".*/\1/p')"
done > issues.json

来源：https://stackoverflow.com/questions/8735792/how-to-parse-link-header-from-github-api