Sync remote eXistdb with github repository automatically using github webhooks.

git-sync.xql

xquery version "3.0";

(:module namespace gitsync = "http://syriaca.org/ns/gitsync";:)

(:~ 
 : XQuery endpoint to respond to Github webhook requests. Query responds only to push requests.
 
 : The EXPath Crypto library supplies the HMAC-SHA1 algorithm for matching Github secret. 

 :
 : Secret can be stored as environmental variable.
 : Will need to be run with administrative privileges, suggest creating a git user with privileges only to relevant app.
 :
 : @author Winona Salesky
 : @version 1.1 
 :
 : @see https://github.com/joewiz/xqjson   
 : @see http://expath.org/spec/crypto 
 : @see http://expath.org/spec/http-client
 : 
 :)
 
import module namespace xdb="http://exist-db.org/xquery/xmldb";
import module namespace templates="http://exist-db.org/xquery/templates" ;
import module namespace xqjson="http://xqilla.sourceforge.net/lib/xqjson";
import module namespace crypto="http://expath.org/ns/crypto";
import module namespace http="http://expath.org/ns/http-client";

declare option exist:serialize "method=xml media-type=text/xml indent=yes";

(:~
 
 : Recursively creates new collections if necessary
 
 : @param $uri url to resource being added to db 
 :)
declare function local:create-collections($uri as xs:string){
let $collection-uri := substring($uri,1)
for $collections in tokenize($collection-uri, '/')
let $current-path := concat('/',substring-before($collection-uri, $collections),$collections)
let $parent-collection := substring($current-path, 1, string-length($current-path) - string-length(tokenize($current-path, '/')[last()]))
return 
    if (xmldb:collection-available($current-path)) then ()
    else xmldb:create-collection($parent-collection, $collections)
};

(:~
 : Updates files in eXistdb with github data
 : @param $commits serilized json data
 : @param $contents-url string pointing to resource on github
:)
declare function local:do-update($commits as node()*, $contents-url as xs:string?){
for $modified in $commits/descendant::*/*:pair[@name="modified"]/*:item/text()
let $file-path := concat($contents-url, $modified)
let $req := <http:request href="{xs:anyURI($file-path)}" method="get"/>
let $file := http:send-request($req)[2]
let $file-info := 
    let $payload := util:base64-decode($file) 
    let $parse-payload := xqjson:parse-json($payload)
    return $parse-payload 
let $file-data := $file-info//*:pair[@name="content"]
let $collection := xs:anyURI('/db/apps/srophe') 
let $file-name := $file-info//*:pair[@name="name"]/text()
let $resource-path := substring-before(replace($modified,'srophe-app/',''),$file-name)
let $collection-uri := concat($collection,'/',$resource-path)
return
    try {
         if(xmldb:collection-available($collection-uri)) then 
            <response status="okay">
                <message>{xmldb:store($collection-uri, xmldb:encode-uri($file-name), xs:base64Binary($file-data))}</message>
            </response>
         else (local:create-collections($collection-uri),xmldb:store($collection-uri, xmldb:encode-uri($file-name), xs:base64Binary($file-data)))
    } catch * {
        <response status="fail">
            <message>Failed to update resource: {concat($err:code, ": ", $err:description)}</message>
        </response>
    }
};

(:~
 : Adds new files to eXistdb. Changes permissions for group write. 
 : Pulls data from github repository, parses file information and passes data to xmldb:store
 : @param $commits serilized json data
 : @param $contents-url string pointing to resource on github
 : NOTE permission changes could happen in a db trigger after files are created
:)
declare function local:do-add($commits as node()*, $contents-url as xs:string?){
for $modified in $commits/descendant::*/*:pair[@name="added"]/*:item/text()
let $file-path := concat($contents-url, $modified)
let $req := <http:request href="{xs:anyURI($file-path)}" method="get"/>
let $file := http:send-request($req)[2]
let $file-info := 
    let $payload := util:base64-decode($file) 
    let $parse-payload := xqjson:parse-json($payload)
    return $parse-payload 
let $file-data := $file-info//*:pair[@name="content"]
let $collection := xs:anyURI('/db/apps/srophe') 
let $file-name := $file-info//*:pair[@name="name"]/text()
let $resource-path := substring-before(replace($modified,'srophe-app/',''),$file-name)
let $collection-uri := concat($collection,'/',$resource-path)
return 
    try {
             if(xmldb:collection-available($collection-uri)) then 
                 <response status="okay">
                    <message>
                    {
                    (
                       xmldb:store($collection-uri, xmldb:encode-uri($file-name), xs:base64Binary($file-data)),
                       sm:chmod(xs:anyURI(concat($collection-uri,$file-name)), 'rwxrwxr-x'),
                       sm:chgrp(xs:anyURI(concat($collection-uri,$file-name)), 'srophe')
                    )
                    }
                    </message>
                 </response>
             else 
                <response status="okay">
                   <message>
                   {
                   (
                      local:create-collections($collection-uri),
                      xmldb:store($collection-uri, xmldb:encode-uri($file-name), xs:base64Binary($file-data)),
                      sm:chmod(xs:anyURI(concat($collection-uri,$file-name)), 'rwxrwxr-x'),
                      sm:chgrp(xs:anyURI(concat($collection-uri,$file-name)), 'srophe')
                   )}
                   </message>
                </response>
    } catch * {
        <response status="fail">
            <message>Failed to add resource: {concat($err:code, ": ", $err:description)}</message>
        </response>
    }
};

(:~
 : Removes files from the database uses xmldb:remove
 : Pulls data from github repository, parses file information and passes data to xmldb:store
 : @param $commits serilized json data
 : @param $contents-url string pointing to resource on github
:)
declare function local:do-delete($commits as node()*, $contents-url as xs:string?){
for $modified in $commits/descendant::*/*:pair[@name="removed"]/*:item/text()
let $file-path := concat($contents-url, $modified)
let $collection := xs:anyURI('/db/apps/srophe') 
let $file-name := tokenize($modified,'/')[last()]
let $resource-path := substring-before(replace($modified,'srophe-app/',''),$file-name)
let $collection-uri := replace(concat($collection,'/',$resource-path),'/$','')
return 
    try {
        <response status="okay">
            <message>{xmldb:remove($collection-uri, $file-name)}</message>
        </response>
    } catch * {
        <response status="fail">
            <message>Failed to remove resource: {concat($err:code, ": ", $err:description)}</message>
        </response>
    }
   
};

(:~
 : Parse request data and pass to appropriate local functions
 : @param $json-data github response serializing as xml xqjson:parse-json()  
 :)
declare function local:parse-request($json-data){
let $contents-url := substring-before($json-data//*:pair[@name="contents_url"]/text(),'{')   
return
    try {
        if($json-data//*:pair[@name="ref"] = "refs/heads/master") then
            if($json-data//*:pair[@name="commits"]) then 
                let $commits := $json-data//*:pair[@name="commits"]
                return
                    (if($commits/descendant::*/*:pair[@name="modified"]/*:item/text()) then
                        local:do-update($commits, $contents-url)  
                    else (),
                    if($commits/descendant::*/*:pair[@name="added"]/*:item/text()) then
                        local:do-add($commits, $contents-url)
                    else (),
                    if($commits/descendant::*/*:pair[@name="removed"]/*:item/text()) then
                        local:do-delete($commits, $contents-url)
                    else ())
            else <response status="fail"><message>This is a GitHub request, however there were no commits.</message></response>
         else <response status="fail"><message>Not from the master branch.</message></response>   
    } catch * {
        <response status="fail">
            <message>{concat($err:code, ": ", $err:description)}</message>
        </response>
    }
};

(:~
 : Validate github post request.
 : Check user agent and github event, only accept push events from master branch.
 : Check git hook secret against secret stored in environmental variable
 : @param $GIT_TOKEN environment variable storing github secret
 :)

let $post-data := request:get-data()
return 
if(not(empty($post-data))) then 
    let $payload := util:base64-decode(request:get-data())
    let $json-data := xqjson:parse-json($payload)
    return   
    try {
        if(matches(request:get-header('User-Agent'), '^GitHub-Hookshot/')) then
            if(request:get-header('X-GitHub-Event') = 'push') then 
                let $signiture := request:get-header('X-Hub-Signature')
                let $expected-result := <expected-result>{request:get-header('X-Hub-Signature')}</expected-result>
                let $private-key := string(environment-variable('GIT_TOKEN'))
                let $actual-result :=
                    <actual-result>
                        {concat('sha1=',crypto:hmac($payload, $private-key, "HMAC-SHA-1", "hex"))}
                    </actual-result>
                let $condition := normalize-space($expected-result/text()) = normalize-space($actual-result/text())                	
                return
                    if ($condition) then 
                            local:parse-request($json-data)
    			             else 
    			               <response status="fail"><message>Invalid secret.</message></response>
            else <response status="fail"><message>Invalid trigger.</message></response>
        else <response status="fail"><message>This is not a GitHub request.</message></response>    
    } catch * {
        <response status="fail">
            <message>Unacceptable headers {concat($err:code, ": ", $err:description)}</message>
        </response>
    }
 else    
            <response status="fail">
                <message>No post data recieved</message>
            </response>

To solve the request limits for unauthorized requests, you will need to generate either a github personal access token or register your application as an OAuth application via you settings. I used the personal access token. You can then add the following:

let $gitToken:= 'YOUR TOKEN'
let $send :=
    <http:request href="https://api.github.com" method="GET">
        <http:header name="Authorization" value="{concat('token ',$gitToken)}"/>
    </http:request>
return http:send-request($send)    

This will increase you rate limit to 5,000.