Function ssb_validate::message::validate_message_hash_chain

pub fn validate_message_hash_chain<T: AsRef<[u8]>, U: AsRef<[u8]>>(
    message_bytes: T, 
    previous_msg_bytes: Option<U>
) -> Result<()>

Check that a message is a valid message relative to the previous message.

It expects the messages to be the JSON encoded message of shape: {key: "", value: {...}}

This checks that:

• the sequence starts at one if it’s the first message
• the previous is correctly set to null if it’s the first message
• the sequence increments correctly
• the author has not changed
• the feed is not forked
• the actual hash matches the hash claimed in key

This does not check:

• the signature. See ssb-verify-signatures which lets you to batch verification of signatures.

previous_msg_bytes will be None only when message_bytes is the first message by that author.

Example

use ssb_validate::message::validate_message_hash_chain;
let valid_message_1 = r##"{
  "key": "%/v5mCnV/kmnVtnF3zXtD4tbzoEQo4kRq/0d/bgxP1WI=.sha256",
  "value": {
    "previous": null,
    "author": "@U5GvOKP/YUza9k53DSXxT0mk3PIrnyAmessvNfZl5E0=.ed25519",
    "sequence": 1,
    "timestamp": 1470186877575,
    "hash": "sha256",
    "content": {
      "type": "about",
      "about": "@U5GvOKP/YUza9k53DSXxT0mk3PIrnyAmessvNfZl5E0=.ed25519",
      "name": "Piet"
    },
    "signature": "QJKWui3oyK6r5dH13xHkEVFhfMZDTXfK2tW21nyfheFClSf69yYK77Itj1BGcOimZ16pj9u3tMArLUCGSscqCQ==.sig.ed25519"
  },
  "timestamp": 1571140551481
}"##;
let valid_message_2 = r##"{
  "key": "%kLWDux4wCG+OdQWAHnpBGzGlCehqMLfgLbzlKCvgesU=.sha256",
  "value": {
    "previous": "%/v5mCnV/kmnVtnF3zXtD4tbzoEQo4kRq/0d/bgxP1WI=.sha256",
    "author": "@U5GvOKP/YUza9k53DSXxT0mk3PIrnyAmessvNfZl5E0=.ed25519",
    "sequence": 2,
    "timestamp": 1470187292812,
    "hash": "sha256",
    "content": {
      "type": "about",
      "about": "@U5GvOKP/YUza9k53DSXxT0mk3PIrnyAmessvNfZl5E0=.ed25519",
      "image": {
        "link": "&MxwsfZoq7X6oqnEX/TWIlAqd6S+jsUA6T1hqZYdl7RM=.sha256",
        "size": 642763,
        "type": "image/png",
        "width": 512,
        "height": 512
      }
    },
    "signature": "j3C7Us3JDnSUseF4ycRB0dTMs0xC6NAriAFtJWvx2uyz0K4zSj6XL8YA4BVqv+AHgo08+HxXGrpJlZ3ADwNnDw==.sig.ed25519"
  },
  "timestamp": 1571140551485
}"##;
 let result = validate_message_hash_chain(valid_message_2.as_bytes(), Some(valid_message_1));
 assert!(result.is_ok());