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fix(PaymentSession): find minSendAmount independent of rate #1048

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Merged
sidvishnoi merged 1 commit into from
May 2, 2025
Merged

fix(PaymentSession): find minSendAmount independent of rate #1048

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75 changes: 33 additions & 42 deletions src/background/services/paymentSession.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -84,56 +84,46 @@ export class PaymentSession {
Object.assign(this, this.deps);
}

#adjustAmountLastRate: AmountValue;
#adjustAmountController = new AbortController();
#adjustAmountPromise: null | Promise<void> = null;
adjustAmount(rate: AmountValue): Promise<void> {
if (this.#adjustAmountLastRate && rate !== this.#adjustAmountLastRate) {
this.#adjustAmountController.abort(
new DOMException(
`Aborting existing probing for rate=${this.#adjustAmountLastRate}`,
'AbortError',
),
);
this.#adjustAmountController = new AbortController();
this.#adjustAmountPromise = null;
}

this.#adjustAmountLastRate = rate;
this.#adjustAmountPromise ??= this._adjustAmount(
rate,
this.#adjustAmountController.signal,
);

return this.#adjustAmountPromise;
// We keep setting #minSendAmount to non-zero values as we probe. Instead of
// checking #minSendAmount > 0, use this boolean to know if probing completed.
#minSendAmountFound = false;
#minSendAmount = 0n;
#minSendAmountPromise: ReturnType<typeof this._findMinSendAmount>;

findMinSendAmount(): Promise<void> {
this.#minSendAmountPromise ??= this._findMinSendAmount();
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@sidvishnoi sidvishnoi May 2, 2025

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This ensures we call _findMinSendAmount() only once per PaymentSession instance.

return this.#minSendAmountPromise;
}

private async _adjustAmount(
rate: AmountValue,
signal: AbortSignal,
): Promise<void> {
this.rate = rate;
get minSendAmount(): bigint {
if (!this.#minSendAmountFound) {
throw new Error('minSendAmount not figured out yet');
}
return this.#minSendAmount;
}

async adjustAmount(hourlyRate: AmountValue) {
this.rate = hourlyRate;
// The amount that needs to be sent every second.
// In senders asset scale already.
let amountToSend = BigInt(this.rate) / 3600n;
await this.findMinSendAmount();
if (this.rate !== hourlyRate) {
throw new DOMException(
`Aborting existing probing for rate=${hourlyRate}`,
'AbortError',
);
}
const amount = BigInt(this.rate) / 3600n;
this.setAmount(bigIntMax(amount, this.#minSendAmount));
}

private async _findMinSendAmount(signal?: AbortSignal): Promise<void> {
let amountToSend = bigIntMax(this.#minSendAmount, MIN_SEND_AMOUNT);
const senderAssetScale = this.sender.assetScale;
const receiverAssetScale = this.receiver.assetScale;
const isCrossCurrency = this.sender.assetCode !== this.receiver.assetCode;

if (!isCrossCurrency) {
if (amountToSend <= MIN_SEND_AMOUNT) {
// We need to add another unit when using a debit amount, since
// @interledger/pay subtracts one unit.
if (senderAssetScale <= receiverAssetScale) {
amountToSend = MIN_SEND_AMOUNT + 1n;
} else if (senderAssetScale > receiverAssetScale) {
// If the sender scale is greater than the receiver scale, the unit
// issue will not be present.
amountToSend = MIN_SEND_AMOUNT;
}
}

// If the sender can facilitate the rate, but the amount can not be
// represented in the receiver's scale we need to send the minimum amount
// for the receiver (1 unit, but in the sender's asset scale)
Expand Down Expand Up @@ -165,14 +155,15 @@ export class PaymentSession {

amountToSend = BigInt(amountIter.next().value);
while (true) {
signal.throwIfAborted();
signal?.throwIfAborted();
this.#minSendAmount = amountToSend;
try {
await this.createPaymentQuote(
amountToSend.toString(),
this.incomingPaymentUrl,
this.sender,
);
this.setAmount(amountToSend);
this.#minSendAmountFound = true;
break;
} catch (e) {
if (isTokenExpiredError(e)) {
Expand Down
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