(PureBasic) Refresh Access Token on 401 Unauthorized and Retry (Service Account)

See more Google Cloud Storage Examples

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 PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkBinData.pb"
IncludeFile "CkHttp.pb"
IncludeFile "CkFileAccess.pb"
IncludeFile "CkSocket.pb"
IncludeFile "CkStringBuilder.pb"
IncludeFile "CkAuthGoogle.pb"

Procedure ChilkatExample()

    ; 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..
    sbToken.i = CkStringBuilder::ckCreate()
    If sbToken.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i = CkStringBuilder::ckLoadFile(sbToken,"qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8")
    If success = 0
        Debug "Failed to load access token."
        CkStringBuilder::ckDispose(sbToken)
        ProcedureReturn
    EndIf

    http.i = CkHttp::ckCreate()
    If http.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkHttp::setCkAuthToken(http, CkStringBuilder::ckGetAsString(sbToken))

    ; Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
    CkHttp::ckSetUrlVar(http,"bucket_name","chilkat-ocean")
    CkHttp::ckSetUrlVar(http,"object_name","starfish.jpg")
    url.s = "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..
    fileData.i = CkBinData::ckCreate()
    If fileData.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkHttp::ckDownloadBd(http,url,fileData)
    responseCode.i = CkHttp::ckLastStatus(http)
    If (success = 0) AND (responseCode <> 401)
        Debug CkHttp::ckLastErrorText(http)
        CkStringBuilder::ckDispose(sbToken)
        CkHttp::ckDispose(http)
        CkBinData::ckDispose(fileData)
        ProcedureReturn
    EndIf

    If responseCode = 401
        Debug "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.
        fac.i = CkFileAccess::ckCreate()
        If fac.i = 0
            Debug "Failed to create object."
            ProcedureReturn
        EndIf

        jsonKey.s = CkFileAccess::ckReadEntireTextFile(fac,"qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json","utf-8")
        If CkFileAccess::ckLastMethodSuccess(fac) <> 1
            Debug CkFileAccess::ckLastErrorText(fac)
            CkStringBuilder::ckDispose(sbToken)
            CkHttp::ckDispose(http)
            CkBinData::ckDispose(fileData)
            CkFileAccess::ckDispose(fac)
            ProcedureReturn
        EndIf

        gAuth.i = CkAuthGoogle::ckCreate()
        If gAuth.i = 0
            Debug "Failed to create object."
            ProcedureReturn
        EndIf

        CkAuthGoogle::setCkJsonKey(gAuth, jsonKey)
        CkAuthGoogle::setCkScope(gAuth, "https://www.googleapis.com/auth/cloud-platform")
        CkAuthGoogle::setCkExpireNumSeconds(gAuth, 3600)
        CkAuthGoogle::setCkSubEmailAddress(gAuth, "")

        tlsSock.i = CkSocket::ckCreate()
        If tlsSock.i = 0
            Debug "Failed to create object."
            ProcedureReturn
        EndIf

        success = CkSocket::ckConnect(tlsSock,"www.googleapis.com",443,1,5000)
        If success <> 1
            Debug CkSocket::ckLastErrorText(tlsSock)
            CkStringBuilder::ckDispose(sbToken)
            CkHttp::ckDispose(http)
            CkBinData::ckDispose(fileData)
            CkFileAccess::ckDispose(fac)
            CkAuthGoogle::ckDispose(gAuth)
            CkSocket::ckDispose(tlsSock)
            ProcedureReturn
        EndIf

        success = CkAuthGoogle::ckObtainAccessToken(gAuth,tlsSock)
        If success <> 1
            Debug CkAuthGoogle::ckLastErrorText(gAuth)
            CkStringBuilder::ckDispose(sbToken)
            CkHttp::ckDispose(http)
            CkBinData::ckDispose(fileData)
            CkFileAccess::ckDispose(fac)
            CkAuthGoogle::ckDispose(gAuth)
            CkSocket::ckDispose(tlsSock)
            ProcedureReturn
        EndIf

        CkFileAccess::ckWriteEntireTextFile(fac,"qa_data/tokens/googleCloudStorageAccessToken.txt",CkAuthGoogle::ckAccessToken(gAuth),"utf-8",0)

        ; Retry the original request.
        CkHttp::setCkAuthToken(http, CkAuthGoogle::ckAccessToken(gAuth))
        success = CkHttp::ckDownloadBd(http,url,fileData)
        If success = 0
            Debug CkHttp::ckLastErrorText(http)
            CkStringBuilder::ckDispose(sbToken)
            CkHttp::ckDispose(http)
            CkBinData::ckDispose(fileData)
            CkFileAccess::ckDispose(fac)
            CkAuthGoogle::ckDispose(gAuth)
            CkSocket::ckDispose(tlsSock)
            ProcedureReturn
        EndIf

    EndIf

    If responseCode <> 200
        ; Get the error response
        sbErrorResponse.i = CkStringBuilder::ckCreate()
        If sbErrorResponse.i = 0
            Debug "Failed to create object."
            ProcedureReturn
        EndIf

        CkStringBuilder::ckAppendBd(sbErrorResponse,fileData,"utf-8",0,0)
        Debug "Error response code = " + Str(responseCode)
        Debug "Error:"
        Debug CkStringBuilder::ckGetAsString(sbErrorResponse)
        CkStringBuilder::ckDispose(sbToken)
        CkHttp::ckDispose(http)
        CkBinData::ckDispose(fileData)
        CkFileAccess::ckDispose(fac)
        CkAuthGoogle::ckDispose(gAuth)
        CkSocket::ckDispose(tlsSock)
        CkStringBuilder::ckDispose(sbErrorResponse)
        ProcedureReturn
    EndIf

    Debug "Success."

    ; Save the downloaded data to a file.
    success = CkBinData::ckWriteFile(fileData,"qa_output/starfish.jpg")


    CkStringBuilder::ckDispose(sbToken)
    CkHttp::ckDispose(http)
    CkBinData::ckDispose(fileData)
    CkFileAccess::ckDispose(fac)
    CkAuthGoogle::ckDispose(gAuth)
    CkSocket::ckDispose(tlsSock)
    CkStringBuilder::ckDispose(sbErrorResponse)


    ProcedureReturn
EndProcedure