How can I decode/recreate Google Flights Search URLs? - base64

Question

The Problem
On Google Flights, search information is encoded in a URL parameter, presumably so users can share flight searches with each other easily.
The URL format looks like this:
https://www.google.com/travel/flights/search?tfs=CBwQAhoeagcIARIDSE5MEgoyMDIxLTA5LTEzcgcIARIDU0ZPGh5qBwgBEgNTRk8SCjIwMjEtMDktMTdyBwgBEgNITkxwAYIBCwj___________8BQAFIAZgBAQ
I am trying to write a program that can generate flight search URLs given flight information (origin, destination, flight dates, passengers, etc). To do this I need know how the information is encoded in the URL so I can recreate it.
What I've tried
I know that the flight info is encoded in base64 or some variant of it (I've been using base64decode.org for testing). For a round-trip flight from HNL-SFO on 2021-09-13 - 2021-09-17, Google Flights has this URL:
https://www.google.com/travel/flights/search?tfs=CBwQAhoeagcIARIDSE5MEgoyMDIxLTA5LTEzcgcIARIDU0ZPGh5qBwgBEgNTRk8SCjIwMjEtMDktMTdyBwgBEgNITkxwAYIBCwj___________8BQAFIAZgBAQ
The part of the tfs query parameter before the underscores decodes to
jHNL
2021-09-13rSFOjSFO
2021-09-17rHNLp
which contains some (but not all) recognizable flight info. What I don't understand is the whitespace between the recognizable information. Using this site, I learned that the whitespace is a mix of characters:
U+0008 : <control> BACKSPACE [BS]
U+001C : <control> INFORMATION SEPARATOR FOUR {file separator (FS)}
U+0010 : <control> DATA LINK ESCAPE [DLE]
U+0002 : <control> START OF TEXT [STX]
U+001A : <control> SUBSTITUTE [SUB]
U+001E : <control> INFORMATION SEPARATOR TWO {record separator (RS)}
U+006A : LATIN SMALL LETTER J
U+0007 : <control> BELL [BEL]
U+0008 : <control> BACKSPACE [BS]
U+0001 : <control> START OF HEADING [SOH]
U+0012 : <control> DEVICE CONTROL TWO [DC2]
U+0003 : <control> END OF TEXT [ETX]
U+0048 : LATIN CAPITAL LETTER H
U+004E : LATIN CAPITAL LETTER N
U+004C : LATIN CAPITAL LETTER L
...
This suggests that I'm not decoding the data properly. I've tried some other variants of base64, but haven't had any luck.
Does anyone know how this info is encoded? Another thing I haven't been able to figure out is how the information after the underscores (8BQAFIAZgBAQ) is encoded. Based on the behavior of the Google Flights site, I think it encodes passenger information, but it base64 decodes to only whitespace characters.
Additional Context
Two years ago I made a working version of the program which produced URLs like
https://www.google.com/flights?hl=en#flt=ORD.MCO.2021-07-16*MCO.ORD.2021-07-19;c:USD;e:1;px:2,2,0,0;sd:1;t:f
Several months ago Google changed the format they use from the above to the encoded version. I want to figure out how to recreate the encoded URLs so I can update my program instead of retiring it.

Answer 1

You can have your program output flight URLs in query format using the q URL param. No need to encode/decode the URL.
For example:
https://www.google.com/travel/flights?q=Flights%20to%20SFO%20from%20HNL%20on%202022-09-13%20through%202022-09-17
Which leads to the results page: HNL <> SFO Flight Results

Answer 2

I miss having the ability to encode a query and have the same question. Nice work with finding out it's in base64.
I think reverse engineering is the only way to find out how things are encoded. For example, the stuff after the underlines is most likely binary-encoded.
See the below for economy:
11101111 10111111 10111101 00010100 00000000 00010100 11101111 10111111 10111101 00011001 11101111 10111111 10111101 00010000 00010000
And the same query but for for business class
11101111 10111111 10111101 00010100 00000000 00010100 11101111 10111111 10111101 00101001 11101111 10111111 10111101 00010000 00010000
As you can see the 10th byte goes from 00011001 to 10111101