Problem with handling completion

The following is what I am trying to do:

- Go to a website;

- Read the website content into a String;

- Identify substrings with specific content (multiple hyperlinks);

- Save the list of hyperlinks as an array of Strings.

This is how I am trying to do it:

// Reads a web page into a string and returns a list of hyperlinks
func readWebToString(completion: @escaping ([String]) -> ())
    {
        var finalResult = [String]()
    
        guard let dataURL = URL(string: self.GRIB_URL)
            else
        {
            print("Error")
            return completion(["N/A"])
        }
    
        do
        {
            var contents = ""
        
            let request = URLRequest(url: dataURL)
            let session = URLSession.shared
        
            let task = session.dataTask(with: request) {(data, response, error) -> Void in
                if (data != nil)
                {
                    contents = String(data: data!, encoding:String.Encoding.utf8)!
                
                    print("CONTENTS1:",contents)
                
                    let expression : String = ">gfs\\.\\d+<"
                    let range = NSRange(location: 0, length: contents.characters.count)
                
                    do
                    {
                        let regex = try NSRegularExpression(pattern: expression, options: NSRegularExpression.Options.caseInsensitive)
                        let contentsNS = contents as NSString
                        let matches = regex.matches(in: contents, options: [], range: range)
                    
                        for match in matches
                        {
                            for i in 0..<match.numberOfRanges
                            {
                                let resultingNS = contentsNS.substring(with: (match.rangeAt(i))) as String
                                finalResult.append(resultingNS)
                            }
                        }
                    
                        if (!finalResult.isEmpty)
                        {
                            for i in 0..<finalResult.count
                            {
                                finalResult[i].remove(at: finalResult[i].startIndex)
                                finalResult[i].remove(at: finalResult[i].index(before: finalResult[i].endIndex))
                            }
                        }
                    
                        completion(finalResult)
                    }
                    catch
                    {
                        print("No regex match")
                    }
                }
                else
                {
                    print("No data")
                }
            }
            task.resume()
        }
    }


func makeGribWebAddress() -> [String]
    {
        var finalResult = [String]()
      
        let address1 = "h t t p://xxxxxxxxx"
        let address2 = "xxxxx";
        let address4 = "xxxx"
        let address5 = "xxxxxx"
      

        print("CONTENTS2:")
     
      
        readWebToString() {listOfFiles in
            if (!listOfFiles.isEmpty)
            {
                for i in 0..<listOfFiles.count
                {
                    let address6 = xxxxxx"+listOfFiles[i]
                    let address3 = listOfFiles[i].substring(from:listOfFiles[i].index(listOfFiles[i].endIndex, offsetBy: -2))
                    let addressFull = (address1 + address2 + address3 + address4 + address5 + address6).trimmingCharacters(in: .whitespacesAndNewlines)
                    finalResult.append(addressFull)
                }
            }
        }

        print("CONTENTS3:",finalResult)
      
        return finalResult;
    }

Unfortunately, it does not work. My output is as follows:

CONTENTS2:

CONTENTS3: []

CONTENTS1: website content read successfully

Obviously, the completion is not handled correctly. Any suggestions?

Thank you!