Gmail REST api batch support for getting messages - gmail

Question

We need to switch from google client library to Gmail REST api in our project, and I've encountered a problem with batch() because it is not available in REST api - you can only get list of ids of messages and then get each message one by one using it's id.
If we use that gmail library everything seems to be clear. We create a batch object and then queue each GET request inside of it. We don't have to care how it's implemented inside.
At the moment I'm trying to do some POC and I'm testing these suggestions https://developers.google.com/gmail/api/guides/batch
with Postman but with no luck..
I'm getting 400 bad request.
How should a proper request body look like in Postman (or other application)?
The next step will be implementing multipart request in Java and sending POST using RestTemplate but I need to present some POC in Postman first.
I'm setting it like on this screenshot ->
Postman
What am I doing wrong?:)

Answer 1

You are close. Here is a working example:
Request
POST https://www.googleapis.com/batch
Content-Type: multipart/mixed; boundary="foo_bar"
Authorization: Bearer {ACCESS_TOKEN}
--foo_bar
Content-Type: application/http
GET /gmail/v1/users/me/messages/152d10540c21bd07
--foo_bar
Content-Type: application/http
GET /gmail/v1/users/me/messages/152d1050d666d7ad
--foo_bar--
Response
--batch_7Xp52oGIwpA_AAEAc7ERnGU
Content-Type: application/http
HTTP/1.1 200 OK
ETag: "A-DdBGA6g-wV4rIZCu5Hcm3JQpY/w2hzEg9kqXFH7AEJ-oSc-y10HNQ"
Content-Type: application/json; charset=UTF-8
Date: Thu, 11 Feb 2016 16:02:06 GMT
Expires: Thu, 11 Feb 2016 16:02:06 GMT
Cache-Control: private, max-age=0
Content-Length: 2809
{
"id": "152d10540c21bd07",
"threadId": "152d1050d666d7ad",
"labelIds": [
"SENT",
"INBOX",
"IMPORTANT"
],
"snippet": "Likewise buddy.", ...
}
--batch_7Xp52oGIwpA_AAEAc7ERnGU
Content-Type: application/http
HTTP/1.1 200 OK
ETag: "A-DdBGA6g-wV4rIZCu5Hcm3JQpY/7v2nqQFBDmEHVvEQoboiwSidilE"
Content-Type: application/json; charset=UTF-8
Date: Thu, 11 Feb 2016 16:02:06 GMT
Expires: Thu, 11 Feb 2016 16:02:06 GMT
Cache-Control: private, max-age=0
Content-Length: 1752
{
"id": "152d1050d666d7ad",
"threadId": "152d1050d666d7ad",
"labelIds": [
"SENT",
"INBOX",
"IMPORTANT"
],
"snippet": "Nice to meet you.", ...
}
--batch_7Xp52oGIwpA_AAEAc7ERnGU--
You don't have to specify the host in each part of the batch, and giving the access token in the Authorization header is enough. You don't have to specify the Content-Length yourself, and don't forget to wrap you boundary string with ".
Then you just have to parse the JSON of each part and you are done.

Answer 2

You need to include gmail/v1 on the POST URL and on each request.
Don't forget about the " around your boundary on the Content-Type header.
See original batch gmail requests documentation: https://developers.google.com/gmail/api/guides/batch
The following worked for me:
POST /batch/gmail/v1 HTTP/1.1
Host: www.googleapis.com
Authorization: Bearer {YOUR_ACCESS_TOKEN}
Content-Type: multipart/mixed; boundary="foo_bar"
--foo_bar
Content-Type: application/http
GET /gmail/v1/users/me/messages/1732ebdcb9b8cccf
--foo_bar
Content-Type: application/http
GET /gmail/v1/users/me/messages/1732ecadae4907e2
--foo_bar--
Creating request with Postman - body screenshot
Creating request with Postman - headers screenshot

Answer 3

Just wanted to say that Lucila's answer is now the correct one - the global (https://www.googleapis.com/batch) endpoint is now deprecated, and you must make a post request to your request-specific endpoint (https://www.googleapis.com/batch/gmail/v1 for gmail, for instance).
See this link for additional context.
Apologies for making a new answer for this, I don't have enough reputation to leave a comment.