gmaildecode.php

function decodeBody($body) {
    $rawData = $body;
    $sanitizedData = strtr($rawData,'-_', '+/');
    $decodedMessage = base64_decode($sanitizedData);
    if(!$decodedMessage){
        $decodedMessage = FALSE;
    }
    return $decodedMessage;
}

$client = getClient();
$gmail = new Google_Service_Gmail($client);

$list = $gmail->users_messages->listUsersMessages('me', ['maxResults' => 1000]);

try{
    while ($list->getMessages() != null) {

        foreach ($list->getMessages() as $mlist) {

            $message_id = $mlist->id;
            $optParamsGet2['format'] = 'full';
            $single_message = $gmail->users_messages->get('me', $message_id, $optParamsGet2);
            $payload = $single_message->getPayload();
            $parts = $payload->getParts();
            // With no attachment, the payload might be directly in the body, encoded.
            $body = $payload->getBody();
            $FOUND_BODY = FALSE;
            // If we didn't find a body, let's look for the parts
            if(!$FOUND_BODY) {
                foreach ($parts  as $part) {
                    if($part['parts'] && !$FOUND_BODY) {
                        foreach ($part['parts'] as $p) {
                            if($p['parts'] && count($p['parts']) > 0){
                                foreach ($p['parts'] as $y) {
                                    if(($y['mimeType'] === 'text/html') && $y['body']) {
                                        $FOUND_BODY = decodeBody($y['body']->data);
                                        break;
                                    }
                                }
                            } else if(($p['mimeType'] === 'text/html') && $p['body']) {
                                $FOUND_BODY = decodeBody($p['body']->data);
                                break;
                            }
                        }
                    }
                    if($FOUND_BODY) {
                        break;
                    }
                }
            }
            // let's save all the images linked to the mail's body:
            if($FOUND_BODY && count($parts) > 1){
                $images_linked = array();
                foreach ($parts  as $part) {
                    if($part['filename']){
                        array_push($images_linked, $part);
                    } else{
                        if($part['parts']) {
                            foreach ($part['parts'] as $p) {
                                if($p['parts'] && count($p['parts']) > 0){
                                    foreach ($p['parts'] as $y) {
                                        if(($y['mimeType'] === 'text/html') && $y['body']) {
                                            array_push($images_linked, $y);
                                        }
                                    }
                                } else if(($p['mimeType'] !== 'text/html') && $p['body']) {
                                    array_push($images_linked, $p);
                                }
                            }
                        }
                    }
                }
                // special case for the wdcid...
                preg_match_all('/wdcid(.*)"/Uims', $FOUND_BODY, $wdmatches);
                if(count($wdmatches)) {
                    $z = 0;
                    foreach($wdmatches[0] as $match) {
                        $z++;
                        if($z > 9){
                            $FOUND_BODY = str_replace($match, 'image0' . $z . '@', $FOUND_BODY);
                        } else {
                            $FOUND_BODY = str_replace($match, 'image00' . $z . '@', $FOUND_BODY);
                        }
                    }
                }
                preg_match_all('/src="cid:(.*)"/Uims', $FOUND_BODY, $matches);
                if(count($matches)) {
                    $search = array();
                    $replace = array();
                    // let's trasnform the CIDs as base64 attachements 
                    foreach($matches[1] as $match) {
                        foreach($images_linked as $img_linked) {
                            foreach($img_linked['headers'] as $img_lnk) {
                                if( $img_lnk['name'] === 'Content-ID' || $img_lnk['name'] === 'Content-Id' || $img_lnk['name'] === 'X-Attachment-Id'){
                                    if ($match === str_replace('>', '', str_replace('<', '', $img_lnk->value)) 
                                            || explode("@", $match)[0] === explode(".", $img_linked->filename)[0]
                                            || explode("@", $match)[0] === $img_linked->filename){
                                        $search = "src=\"cid:$match\"";
                                        $mimetype = $img_linked->mimeType;
                                        $attachment = $gmail->users_messages_attachments->get('me', $mlist->id, $img_linked['body']->attachmentId);
                                        $data64 = strtr($attachment->getData(), array('-' => '+', '_' => '/'));
                                        $replace = "src=\"data:" . $mimetype . ";base64," . $data64 . "\"";
                                        $FOUND_BODY = str_replace($search, $replace, $FOUND_BODY);
                                    }
                                }
                            }
                        }
                    }
                }
            }
            // If we didn't find the body in the last parts, 
            // let's loop for the first parts (text-html only)
            if(!$FOUND_BODY) {
                foreach ($parts  as $part) {
                    if($part['body'] && $part['mimeType'] === 'text/html') {
                        $FOUND_BODY = decodeBody($part['body']->data);
                        break;
                    }
                }
            }
            // With no attachment, the payload might be directly in the body, encoded.
            if(!$FOUND_BODY) {
                $FOUND_BODY = decodeBody($body['data']);
            }
            // Last try: if we didn't find the body in the last parts, 
            // let's loop for the first parts (text-plain only)
            if(!$FOUND_BODY) {
                foreach ($parts  as $part) {
                    if($part['body']) {
                        $FOUND_BODY = decodeBody($part['body']->data);
                        break;
                    }
                }
            }
            if(!$FOUND_BODY) {
                $FOUND_BODY = '(No message)';
            }
            // Finally, print the message ID and the body
            print_r($message_id . ": " . $FOUND_BODY);
        }

        if ($list->getNextPageToken() != null) {
            $pageToken = $list->getNextPageToken();
            $list = $gmail->users_messages->listUsersMessages('me', ['pageToken' => $pageToken, 'maxResults' => 1000]);
        } else {
            break;
        }
    }
} catch (Exception $e) {
    echo $e->getMessage();
}