`ChainRpc` asks a node what a public address holds and what has happened to it.
The node is trusted with nothing: it never sees a key and cannot move money.
What it CAN do is lie about a balance or withhold a history, so nothing here
treats an answer as authoritative beyond "this is what that node said".
🔴 A JSON-RPC error arrives with HTTP 200. The transport succeeded; the node
said no. A client that checks only the status code carries on with a body that
has no `result`, fails somewhere less obvious, and throws away the node's own
explanation on the way — the difference between "insufficient funds for rent
exemption" on screen and a parse error nobody can act on. Both cases are
tested, including an error carrying no message.
🔴 A FAILED transaction still appears in an address's history, and is shown as
failed. Not doing that is the worst kind of wrong: somebody would believe a
payment went through. `err` is an OBJECT for one class of failure and an ARRAY
for another, so the check is "not null" rather than a shape — testing for an
object alone would pass one whole class of failure off as a success. Both
shapes tested.
⚠️ A body with neither result nor error is malformed, never a balance of zero.
Reading a missing result as zero would show somebody an empty wallet that is
not empty.
⚠️ Lamports as a Long throughout, and to the edge of the UI. Five SOL already
exceeds Int.MAX_VALUE, and converting to a fractional unit early means carrying
rounding through code that compares and subtracts — a rounding error in a
balance is money.
⚠️ A transaction the node has not dated yet reports no time rather than 1970.
It has the transaction and has not assigned a block time; "just now" is the
truth and the epoch is not.
⚠️ Which node somebody points at is a privacy decision the app has to state:
asking a public RPC endpoint for an address's balance ties that address to this
device's IP in somebody else's logs. Running your own node is the only answer
that removes it; the default exists so the wallet works at all, not because it
is private.
15 tests, against a MockWebServer. App builds, every JVM suite green.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
