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Visual FoxPro Examples

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(Visual FoxPro) 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 ActiveX Downloads

ActiveX for 32-bit and 64-bit Windows

LOCAL loSbToken
LOCAL lnSuccess
LOCAL loHttp
LOCAL lcUrl
LOCAL loFileData
LOCAL lnResponseCode
LOCAL loFac
LOCAL lcJsonKey
LOCAL loGAuth
LOCAL loTlsSock
LOCAL loSbErrorResponse

* 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..
loSbToken = CreateObject('Chilkat_9_5_0.StringBuilder')
lnSuccess = loSbToken.LoadFile("qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8")
IF (lnSuccess = 0) THEN
    ? "Failed to load access token."
    RELEASE loSbToken
    CANCEL
ENDIF

loHttp = CreateObject('Chilkat_9_5_0.Http')

loHttp.AuthToken = loSbToken.GetAsString()

* Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
loHttp.SetUrlVar("bucket_name","chilkat-ocean")
loHttp.SetUrlVar("object_name","starfish.jpg")
lcUrl = "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..
loFileData = CreateObject('Chilkat_9_5_0.BinData')
lnSuccess = loHttp.DownloadBd(lcUrl,loFileData)
lnResponseCode = loHttp.LastStatus
IF ((lnSuccess = 0) AND (lnResponseCode <> 401)) THEN
    ? loHttp.LastErrorText
    RELEASE loSbToken
    RELEASE loHttp
    RELEASE loFileData
    CANCEL
ENDIF

IF (lnResponseCode = 401) THEN
    ? "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.
    loFac = CreateObject('Chilkat_9_5_0.FileAccess')
    lcJsonKey = loFac.ReadEntireTextFile("qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json","utf-8")
    IF (loFac.LastMethodSuccess <> 1) THEN
        ? loFac.LastErrorText
        RELEASE loSbToken
        RELEASE loHttp
        RELEASE loFileData
        RELEASE loFac
        CANCEL
    ENDIF

    loGAuth = CreateObject('Chilkat_9_5_0.AuthGoogle')
    loGAuth.JsonKey = lcJsonKey
    loGAuth.Scope = "https://www.googleapis.com/auth/cloud-platform"
    loGAuth.ExpireNumSeconds = 3600
    loGAuth.SubEmailAddress = ""

    loTlsSock = CreateObject('Chilkat_9_5_0.Socket')
    lnSuccess = loTlsSock.Connect("www.googleapis.com",443,1,5000)
    IF (lnSuccess <> 1) THEN
        ? loTlsSock.LastErrorText
        RELEASE loSbToken
        RELEASE loHttp
        RELEASE loFileData
        RELEASE loFac
        RELEASE loGAuth
        RELEASE loTlsSock
        CANCEL
    ENDIF

    lnSuccess = loGAuth.ObtainAccessToken(loTlsSock)
    IF (lnSuccess <> 1) THEN
        ? loGAuth.LastErrorText
        RELEASE loSbToken
        RELEASE loHttp
        RELEASE loFileData
        RELEASE loFac
        RELEASE loGAuth
        RELEASE loTlsSock
        CANCEL
    ENDIF

    loFac.WriteEntireTextFile("qa_data/tokens/googleCloudStorageAccessToken.txt",loGAuth.AccessToken,"utf-8",0)

    * Retry the original request.
    loHttp.AuthToken = loGAuth.AccessToken
    lnSuccess = loHttp.DownloadBd(lcUrl,loFileData)
    IF (lnSuccess = 0) THEN
        ? loHttp.LastErrorText
        RELEASE loSbToken
        RELEASE loHttp
        RELEASE loFileData
        RELEASE loFac
        RELEASE loGAuth
        RELEASE loTlsSock
        CANCEL
    ENDIF

ENDIF

IF (lnResponseCode <> 200) THEN
    * Get the error response
    loSbErrorResponse = CreateObject('Chilkat_9_5_0.StringBuilder')
    loSbErrorResponse.AppendBd(loFileData,"utf-8",0,0)
    ? "Error response code = " + STR(lnResponseCode)
    ? "Error:"
    ? loSbErrorResponse.GetAsString()
    RELEASE loSbToken
    RELEASE loHttp
    RELEASE loFileData
    RELEASE loFac
    RELEASE loGAuth
    RELEASE loTlsSock
    RELEASE loSbErrorResponse
    CANCEL
ENDIF

? "Success."

* Save the downloaded data to a file.
lnSuccess = loFileData.WriteFile("qa_output/starfish.jpg")

RELEASE loSbToken
RELEASE loHttp
RELEASE loFileData
RELEASE loFac
RELEASE loGAuth
RELEASE loTlsSock
RELEASE loSbErrorResponse


 

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