(Tcl) Download Binary File to In-Memory Bytes

This example demonstrates how to download the binary content of a file from Google Drive directly into local memory.

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load ./chilkat.dll

set success 1

# It 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 
# Google Drive scope.

set gAuth [new_CkAuthGoogle]

CkAuthGoogle_put_AccessToken $gAuth "GOOGLE-DRIVE-ACCESS-TOKEN"

set rest [new_CkRest]

# Connect using TLS.
# A single REST object, once connected, can be used for many Google Drive REST API calls.
# The auto-reconnect indicates that if the already-established HTTPS connection is closed,
# then it will be automatically re-established as needed.
set bAutoReconnect 1
set success [CkRest_Connect $rest "www.googleapis.com" 443 1 $bAutoReconnect]

# Provide the authentication credentials (i.e. the access token)
CkRest_SetAuthGoogle $rest $gAuth

# ------------------------------------------------------------------------------
# To download a file, we must know the file ID.
# In a previous example (see Build Local Metadata Cache
# we built a local cache to make it easy to lookup file IDs given a file path.
# Let's say we want to download "testFolder/abc/123/penguins.jpg".
# First we lookup the fileId in the cache.  With the fileId, we can download the file.
set gdCache [new_CkCache]

CkCache_put_Level $gdCache 0
CkCache_AddRoot $gdCache "C:/ckCache/googleDrive"

set fileId [CkCache_fetchText $gdCache "testFolder/abc/123/penguins.jpg"]
if {[CkCache_get_LastMethodSuccess $gdCache] != 1} then {
    puts "Filepath not found in cache."
    delete_CkAuthGoogle $gAuth
    delete_CkRest $rest
    delete_CkCache $gdCache
    exit
}

# We need to send a GET request like this:
# GET https://www.googleapis.com/drive/v3/files/fileId?alt=media
# The fileId is part of the path.
set sbPath [new_CkStringBuilder]

CkStringBuilder_Append $sbPath "/drive/v3/files/"
CkStringBuilder_Append $sbPath $fileId
CkRest_AddQueryParam $rest "alt" "media"

# To download to memory, we'll send the request in one call, then receive
# the response header, and then the response body.
# If the response header indicates failure or an unexpected response, then the
# body is not the data we desire.

# First send the HTTP request.
set success [CkRest_SendReqNoBody $rest "GET" [CkStringBuilder_getAsString $sbPath]]
if {$success != 1} then {
    puts [CkRest_lastErrorText $rest]
    delete_CkAuthGoogle $gAuth
    delete_CkRest $rest
    delete_CkCache $gdCache
    delete_CkStringBuilder $sbPath
    exit
}

# Get the response header.
set statusCode [CkRest_ReadResponseHeader $rest]
if {$statusCode != 200} then {
    puts "response status code = [CkRest_get_ResponseStatusCode $rest]"
    puts "response status text = [CkRest_responseStatusText $rest]"
    puts "response header: [CkRest_responseHeader $rest]"

    # Read the response body (which should be error text or HTML)
    set errResponseBody [CkRest_readRespBodyString $rest]
    if {[CkRest_get_LastMethodSuccess $rest] == 1} then {
        puts "response body: $errResponseBody"
    }

    delete_CkAuthGoogle $gAuth
    delete_CkRest $rest
    delete_CkCache $gdCache
    delete_CkStringBuilder $sbPath
    exit
}

# Read the response body, which should contain the file data.
set jpgBytes [new_CkByteData]

set success [CkRest_ReadRespBodyBinary $rest $jpgBytes]
if {[CkRest_get_LastMethodSuccess $rest] != 1} then {
    puts [CkRest_lastErrorText $rest]
    delete_CkAuthGoogle $gAuth
    delete_CkRest $rest
    delete_CkCache $gdCache
    delete_CkStringBuilder $sbPath
    delete_CkByteData $jpgBytes
    exit
}

# Save jpgBytes to a file so we can examine the file to verify that it worked.
set fac [new_CkFileAccess]

CkFileAccess_WriteEntireFile $fac "qa_output/penguins_out.jpg" $jpgBytes

puts "File downloaded."

delete_CkAuthGoogle $gAuth
delete_CkRest $rest
delete_CkCache $gdCache
delete_CkStringBuilder $sbPath
delete_CkByteData $jpgBytes
delete_CkFileAccess $fac