(Swift 3,4,5...) Refresh Access Token on 401 Unauthorized and Retry

Demonstrates how to handle an expired access token error, refresh the token, and retry the request. (In this case, the request is to download an object from Google Cloud Storage.)

Chilkat Downloads for the Swift Programming Language MAC OS X (Cocoa) Objective-C/Swift Libs iOS Objective-C/Swift Libs

func chilkatTest() {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // This example uses a previously obtained access token having permission for the 
    // scope "https://www.googleapis.com/auth/cloud-platform"

    // In this example, Get Google Cloud Storage OAuth2 Access Token, 
    // the service account access token was saved to a text file.  This example fetches the access token from the file..
    let sbToken = CkoStringBuilder()!
    var success: Bool = sbToken.loadFile("qa_data/tokens/googleCloudStorageAccessToken.txt", charset: "utf-8")
    if success == false {
        print("Failed to load access token.")
        return
    }

    let http = CkoHttp()!

    http.authToken = sbToken.getAsString()

    // Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
    http.setUrlVar("bucket_name", value: "chilkat-ocean")
    http.setUrlVar("object_name", value: "starfish.jpg")
    var url: String? = "https://www.googleapis.com/storage/v1/b/{$bucket_name}/o/{$object_name}?alt=media"

    // If there is an error response, then we didn't actually download the file data,
    // but instead we downloaded an error response..
    let fileData = CkoBinData()!
    success = http.downloadBd(url, binData: fileData)
    var responseCode: Int = http.lastStatus.intValue
    if (success == false) && (responseCode != 401) {
        print("\(http.lastErrorText!)")
        return
    }

    if responseCode == 401 {
        print("Received 401 Unauthorized response. Attempting to refresh the access token...")

        // May be that the access token expired.
        // Load our JSON key and request a new access token, then retry the original request.
        let fac = CkoFileAccess()!
        var jsonKey: String? = fac.readEntireTextFile("qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json", charset: "utf-8")
        if fac.lastMethodSuccess != true {
            print("\(fac.lastErrorText!)")
            return
        }

        let gAuth = CkoAuthGoogle()!
        gAuth.jsonKey = jsonKey
        gAuth.scope = "https://www.googleapis.com/auth/cloud-platform"
        gAuth.expireNumSeconds = 3600
        gAuth.subEmailAddress = ""

        let tlsSock = CkoSocket()!
        success = tlsSock.connect("www.googleapis.com", port: 443, ssl: true, maxWaitMs: 5000)
        if success != true {
            print("\(tlsSock.lastErrorText!)")
            return
        }

        success = gAuth.obtainAccessToken(tlsSock)
        if success != true {
            print("\(gAuth.lastErrorText!)")
            return
        }

        fac.writeEntireTextFile("qa_data/tokens/googleCloudStorageAccessToken.txt", fileData: gAuth.accessToken, charset: "utf-8", includePreamble: false)

        // Retry the original request.
        http.authToken = gAuth.accessToken
        success = http.downloadBd(url, binData: fileData)
        if success == false {
            print("\(http.lastErrorText!)")
            return
        }

    }

    if responseCode != 200 {
        // Get the error response
        let sbErrorResponse = CkoStringBuilder()!
        sbErrorResponse.appendBd(fileData, charset: "utf-8", offset: 0, numBytes: 0)
        print("Error response code = \(responseCode)")
        print("Error:")
        print("\(sbErrorResponse.getAsString()!)")
        return
    }

    print("Success.")

    // Save the downloaded data to a file.
    success = fileData.writeFile("qa_output/starfish.jpg")

}