property |NSURL| : a reference to current application’s |NSURL|
property NSString : a reference to current application’s NSString
property NSURLSession : a reference to current application’s NSURLSession
property NSJSONSerialization : a reference to current application’s NSJSONSerialization
property NSMutableURLRequest : a reference to current application’s NSMutableURLRequest
property NSUTF8StringEncoding : a reference to current application’s NSUTF8StringEncoding
property NSURLSessionConfiguration : a reference to current application’s NSURLSessionConfiguration

property retData : missing value
property retCode : 0
property retHeaders : 0
property drecF : false

set aURL to "http://piyocast.com/as/"
set uRes to chekURLExistence(aURL) of me
–> true

on chekURLExistence(aURL as string)
　　set webRes to callRestGETAPIAndParseResults(aURL, 5) of me
　　return ((retCode of webRes) as integer = 200)
end chekURLExistence

— 指定URLにファイル（画像など）が存在するかチェック
–> {存在確認結果（boolean）, レスポンスヘッダー(NSDictionary), データ(NSData)}
on callRestGETAPIAndParseResults(reqURLStr as string, timeOutSec as real)
　　set (my retData) to false
　　set (my retCode) to 0
　　set (my retHeaders) to {}
　　set (my drecF) to false
　　
　　set aURL to |NSURL|’s URLWithString:reqURLStr
　　set aRequest to NSMutableURLRequest’s requestWithURL:aURL
　　aRequest’s setHTTPMethod:"GET"
　　aRequest’s setValue:"gzip" forHTTPHeaderField:"Content-Encoding"
　　aRequest’s setValue:"application/json; charset=UTF-8" forHTTPHeaderField:"Content-Type"
　　
　　set aConfig to NSURLSessionConfiguration’s defaultSessionConfiguration()
　　set aSession to NSURLSession’s sessionWithConfiguration:aConfig delegate:(me) delegateQueue:(missing value)
　　set aTask to aSession’s dataTaskWithRequest:aRequest
　　
　　set hitF to false
　　aTask’s resume() –Start URL Session
　　
　　repeat (1000 * timeOutSec) times
　　　　if (my drecF) = true then
　　　　　　set hitF to true
　　　　　　exit repeat
　　　　end if
　　　　delay ("0.001" as real)
　　end repeat
　　
　　if hitF = false then error "REST API Timeout Error"
　　
　　return {retData:retData, retCode:retCode, retHeaders:retHeaders}
end callRestGETAPIAndParseResults

on URLSession:tmpSession dataTask:tmpTask didReceiveData:tmpData
　　parseSessionResults(tmpSession, tmpTask, tmpData) of me
　　set (my drecF) to true
end URLSession:dataTask:didReceiveData:

–ないとエラーになるので足した。とくに何もしていない
on URLSession:tmpSession dataTask:tmpTask willCacheResponse:cacheRes completionHandler:aHandler
　　—
end URLSession:dataTask:willCacheResponse:completionHandler:

on parseSessionResults(aSession, aTask, tmpData)
　　set aRes to aTask’s response()
　　set (my retCode) to aRes’s statusCode()
　　set (my retHeaders) to aRes’s allHeaderFields()
　　
　　set resStr to NSString’s alloc()’s initWithData:tmpData encoding:(NSUTF8StringEncoding)
　　set jsonString to NSString’s stringWithString:(resStr)
　　
　　set jsonData to jsonString’s dataUsingEncoding:(NSUTF8StringEncoding)
　　set aJsonDict to NSJSONSerialization’s JSONObjectWithData:jsonData options:0 |error|:(missing value)
　　
　　set (my retData) to aJsonDict as anything
end parseSessionResults