Get rid of protobufs in P3A pings

[iefremov]

For now, a P3A pings consists of a base64-encoded protobuf.

message RawP3AValue {
  fixed64 metric_id = 1;
  bytes p3a_info = 2;
}

given that pings are small we can get rid of protobuf and replace it with simple json.

{
  "metric_id" : "hex-encoded-metric-id-string",
  "p3a_info" : "p3a info string" 
}

It is suggested to keep p3a string as is, because the current plan is to resurrect prochlo soon, presumbaly prochlo will utilize this format (of everything packed into p3a_info) somehow.

[iefremov]

cc @aekeus @porteron

[porteron]

This will be great for us on the stats side. @iefremov once you have data writing in the new format to the bucket let us know so we can update our aggregator to no longer attempt to decode the data.

[iefremov]

since we removed PROCHLO, nothing stops us from killing the "ugly string" (aka p3a_info) and making a normal json. I'll update the description with more details.

[iefremov]

I'm not sure about release notes for this change, @mattmcalister what do you think?

[mattmcalister]

@iefremov just say what it is... Migrate ping data to json format or something like that

[iefremov]

@mattmcalister I mean, I'm not sure whether this is release-notes/include or /exclude

[mattmcalister]

@rebron ...up to you.

[LaurenWags]

@iefremov @rillian since this is QA/Yes, could we get a test plan for this one? Thanks! cc @GeetaSarvadnya

[rillian]

I've added a brief test plan to brave/brave-core#11600.

Sorry about that, and please let me know if you need more details.

[LaurenWags]

thanks @rillian! I'll defer to @GeetaSarvadnya to determine if more info is needed. This looks like a good starting point 👍🏻

[GeetaSarvadnya]

Verification PASSED on

Brave | 1.36.87 Chromium: 98.0.4758.87 (Official Build) beta (64-bit)
-- | --
Revision | e4cd00f135fb4d8edc64c8aa6ecbe7cc79ebb3b2-refs/branch-heads/4758@{#1002}
OS | Windows 10 Version 21H2 (Build 19044.1503)

• Verified the test plan from Introduce JSON P3A pings that duplicate the legacy pings. brave-core#11600
• Logged Follow up of #15967 - https://p2a.brave.com/ endpoints are not listed in any network traffic tools #20982
• P2A pings are verified in Follow up of #15967 - https://p2a.brave.com/ endpoints are not listed in any network traffic tools #20982 (comment)
• Confirmed packets to the https://p3a-json.brave.com/ endpoint are in json format

json format	json format

• Waited for ~15 mins and confirmed count of json transmitted values (28 metrics) are matching with the list of values/stats in brave://local-state under p3a.logs (28 metrics)

brave://local-state	json format transmitted values

• Waited for ~50 mins and confirmed count of json transmitted values (33 metrics) are matching with the list of values/stats in brave://local-state under p3a.logs (33 metrics)

brave://local-state	json format transmitted values

• Confirmed packets to the https://p3a.brave.com/ endpoint is similar to what was sent before the change, encoded as a binary protocol buffer.

encoded binary	encoded binary

---

Verification PASSED using

Brave	1.36.88 Chromium: 98.0.4758.87 (Official Build) dev (x86_64)
Revision	e4cd00f135fb4d8edc64c8aa6ecbe7cc79ebb3b2-refs/branch-heads/4758@{#1002}
OS	macOS Version 11.6.1 (Build 20G224)

• Verified the test plan from Introduce JSON P3A pings that duplicate the legacy pings. brave-core#11600
• Confirmed packets to the https://p3a-json.brave.com/ endpoint are in JSON format

json format	json format

NOTE: unable to confirm count of JSON-transmitted values (36 metrics) matches the list of values/stats in brave://local-state under p3a.logs (42 metrics), however, there are 6 p2a.brave.com entries, which might accommodate it.

brave://local-state	JSON-format transmitted values	p2a.brave.com

• Confirmed p3a.brave.com and p3a-json.brave.com endpoints have the same ping count (separate run from other verifications).

p3a.brave.com	p3a-json.brave.com

• Confirmed packets to the https://p3a.brave.com/ endpoint is similar to what was sent before the change, encoded as a binary protocol buffer.

encoded binary	encoded binary

• Confirmed packets to the p2a.brave.com endpoint are similar to what was sent before the change, encoded as a binary protocol buffer.

encoded binary	encoded binary

---

Verification PASSED using

Brave	1.36.107 Chromium: 99.0.4844.45 (Official Build) (64-bit)
Revision	edbc0b8343c7b10fddb0e1b4efb280b0f6e38cab-refs/branch-heads/4844@{#788}
OS	Ubuntu 18.04 LTS

• Verified the test plan from Introduce JSON P3A pings that duplicate the legacy pings. brave-core#11600
• Confirmed packets to the https://p3a-json.brave.com/ endpoint are in JSON format

• Confirmed p3a.brave.com and p3a-json.brave.com endpoints have the same ping count

• Confirmed packets to the https://p3a.brave.com/ endpoint is similar to what was sent before the change, encoded as a binary protocol buffer.

• Confirmed packets to the p2a.brave.com endpoint are similar to what was sent before the change, encoded as a binary protocol buffer.

[Uni-verse]

Verification Completed using 1.36.108 Chromium 99.0.4844.51
OS: Android ARM
Device: Samsung GS 21
Firmware: Android 12

PASSED - Confirm packets to the https://p3a-json.brave.com/ endpoint are in [json format]
PASSED - Transmitted values should match what's listed in brave://local-state under p3a.logs.
PASSED -Confirmed p3a.brave.com and p3a-json.brave.com endpoints have the same ping count
PASSED - Confirm packets to the https://p3a.brave.com/ and https://p2a.brave.com/ endpoints are similar to what sent before the change, encoded as a binary protocol buffer, instead of in a human-readable strings like the json endpoint receives.