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authorFlorian Dold <florian.dold@gmail.com>2020-04-09 14:27:36 +0530
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wallet exchange management
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+Design Doc 002: Wallet Exchange Management
+##########################################
+
+.. note::
+
+ This design document is currently a draft, it
+ does not reflect any implementation decisions yet.
+
+Summary
+=======
+
+This document presents the requirements and proposed interface for an API that
+wallet-core exposes (to clients such as the CLI, WebExtension, Android Wallet)
+to manage exchanges known to and used by the wallet.
+
+
+Motivation
+==========
+
+There currently is no documented API for this functionality. The API that the
+WebExtension API uses doesn't support all required functionality and exposes
+the internal DB storage format.
+
+
+Background and Requirements
+===========================
+
+The wallet maintains a list of known exchanges. For each exchange in this
+list, the wallet regularly makes network queries to fetch updated information
+about the exchange's cryptographic key material and fee structure.
+
+Additionally, the wallet maintains a list of *trusted auditors*. Auditors
+certify that they audit a (sub)set of denominations offered by the exchange.
+
+When an exchange is marked as *directly trusted*, the wallet can use it
+for withdrawals independent of how the exchange is audited. Otherwise,
+a withdrawal can only proceed if an adequate set of denominations is
+audited by a trusted auditor.
+
+An exchange might only be known the wallet temporarily. For example,
+the wallet UI may allow the user to review the fee structure of an
+exchange before the wallet is permanently added to the wallet.
+Once a an exchange is either (a) marked as trusted or (b) used for a
+withdrawal operation, it is marked as permanent.
+
+Exchanges that are not permanent will be automatically be removed
+("garbage-collected") by the wallet after some time.
+
+Exchanges also expose their terms of service (ToS) document.
+Before withdrawing, the wallet must ensure that the user
+has reviewed and accepted the current version of this ToS document.
+
+Exchange Management During Withdrawal
+-------------------------------------
+
+The functions to list / view exchanges can either be used in the context of
+some exchange management activity or in the context of a withdrawal. In the
+context of a withdrawal, additional filtering must be applied, as not every
+exchange is compatible with every withdrawal process. Additionally, the list
+of exchanges might contain additional details pertaining to this particular
+withdrawal process.
+
+An exchange is considered *compatible* if it accepts wire transfers with a wire
+method that matches the one of the withdrawal *and* the current exchange
+protocol version of the exchange is compatible with the exchange protocol
+version of the wallet.
+
+During the withdrawal process, the bank can also suggest an exchange. Unless
+the exchange is already known to the wallet, this exchange will be added
+non-permanently to the wallet. The bank-suggested will only be selected by
+default if no other trusted exchange compatible with the withdrawal process is
+known to the wallet.
+
+Otherwise, the exchange selected by default will be the exchange that has most
+recently been used for a withdrawal and is compatible with the current withdrawal.
+
+
+Open Questions
+--------------
+
+If the user reviews a **new** exchange during withdrawal
+but then does not decide to use it, will this exchange be permanent?
+
+Pro:
+
+* Staying permanently in the list might help when comparing multiple exchanges
+
+Con:
+
+* It clutters the list of exchanges, especially as we're not planning
+ to have a mechanism to remove exchanges.
+
+=> Maybe non-permanent exchanges can be "sticky" to some particular
+withdrawal session?
+
+
+Proposed Solution
+=================
+
+We will add the following functions (invoked over IPC with wallet-core).
+
+queryExchangeInfo
+-----------------
+
+This function will query information about an exchange based on the base URL
+of the exchange. If the exchange is not known yet to the wallet, it will be
+added non-permanently.
+
+Request:
+
+.. code:: ts
+
+ interface QueryExchangeInfoRequest {
+ // If given, return error description if the exchange is
+ // not compatible with this withdrawal operation.
+ talerWithdrawUri?: string;
+
+ // Exchange base URL to use for the query.
+ exchangeBaseUrl: string;
+
+ // If true, the query already returns a result even if
+ // /wire and denomination signatures weren't processed yet
+ partial: boolean;
+ }
+
+Response:
+
+.. code:: ts
+
+ interface QueryExchangeInfoResponse {
+ exchangeBaseUrl: string;
+
+ // Master public key
+ exchangePub: string;
+
+ trustedDirectly: boolean;
+
+ // The "reasonable-ness" of the exchange's fees.
+ feeStructureSummary: FeeStructureSummary | undefined;
+
+ // Detailled info for each individual denomination
+ denominations: ExchangeDenomination[];
+
+ // Currency of the exchange.
+ currency: string;
+
+ // Last observed protocol version range of the exchange
+ protocolVersionRange: string;
+
+ // Is this exchange either trusted directly or in use?
+ permanent: boolean;
+
+ // Only present if the last exchange information update
+ // failed. Same error as the corresponding pending operation.
+ lastError?: OperationError;
+
+ wireInfo: ExchangeWireInfo;
+
+ // Auditing state for each auditor.
+ auditingState: ExchangeAuditingState[];
+
+ // Do we trust an auditor that sufficiently audits
+ // this exchange's denominations?
+ trustedViaAuditor: boolean;
+
+ currentTosVersion: string;
+ acceptedTosVersion: string;
+
+ withdrawalRelatedInfo?: {
+ // Can the user accept the withdrawal directly?
+ // This field is redundant and derivable from other fields.
+ acceptable: boolean;
+
+ recommendedByBank: boolean;
+
+ // Is this exchange the default exchange for this withdrawal?
+ isDefault: boolean;
+
+ // The "reasonable-ness" of the exchange's fees, in context
+ // of the withdrawn amount.
+ feeStructureSummaryForAmount: FeeStructureSummaryForAmount;
+ };
+ }
+
+ export interface ExchangeWireInfo {
+ feesForType: { [wireMethod: string]: WireFee[] };
+ accounts: { paytoUri: string }[];
+ }
+
+ interface ExchangeAuditingState {
+ auditorName: string;
+ auditorBaseUrl: string;
+ auditorPub: string;
+
+ // Is the auditor already trusted by the wallet?
+ trustedByWallet: boolean;
+
+ // Does the auditor audit some reasonable set of
+ // denominations of the exchange?
+ // If this is false, at least some warning should be shown.
+ auditedDenominationsReasonable: boolean;
+ }
+
+
+ interface FeeStructureSummary {
+ // Does the fee structure fulfill our basic reasonableness
+ // requirements?
+ reasonable: boolean;
+
+ // Lower range of amounts that this exchange can
+ // deal with efficiently.
+ smallAmount: Amount;
+
+ // Upper range of amounts that this exchange can deal
+ // with efficiently.
+ bigAmount: Amount;
+
+ // Rest to be specified later
+ // [ ... ]
+ }
+
+
+getExchangeTos
+--------------
+
+Request:
+
+.. code:: ts
+
+ interface GetExchangeTosRequest {
+ exchangeBaseUrl: string;
+ }
+
+
+Response:
+
+.. code:: ts
+
+ interface GetTosResponse {
+ // Version of the exchange ToS (corresponds to tos ETag)
+ version: string;
+
+ // Text of the exchange ToS, with (optional) markdown markup.
+ tosMarkdownText: string;
+ }
+
+listExchanges
+-------------
+
+List exchanges known to the wallet. Either lists all exchanges, or exchanges
+related to a withdrawal process.
+
+Request:
+
+.. code:: ts
+
+ interface ExchangeListRequest {
+ // If given, only return exchanges that
+ // match the currency of this withdrawal
+ // process.
+ talerWithdrawUri?: string;
+ }
+
+Response:
+
+.. code:: ts
+
+ interface ExchangeListRespose {
+ // Only returned in the context of withdrawals.
+ // The base URL of the exchange that should
+ // be considered the default for the withdrawal.
+ withdrawalDefaultExchangeBaseUrl?: string;
+
+ exchanges: {
+ exchangeBaseUrl: string;
+
+ // Incompatible exchanges are also returned,
+ // as otherwise users might wonder why their expected
+ // exchange is not there.
+ compatibility: "compatible" |
+ "incompatible-version" | "incompatible-wire";
+
+ // Currency of the exchange.
+ currency: string;
+
+ // Does the wallet directly trust this exchange?
+ trustedDirectly: boolean;
+
+ // Is this exchange either trusted directly or in use?
+ permanent: boolean;
+
+ // This information is only returned if it's
+ // already available to us, as the list query
+ // must be fast!
+ trustedViaAuditor: boolean | undefined;
+
+ // The "reasonable-ness" of the exchange's fees.
+ // Only provided if available (if we've already queried
+ // and checked this exchange before).
+ feeStructureSummary: FeeStructureSummary | undefined;
+
+ // Did the user accept the current version of the exchange's ToS?
+ currentTosAccepted: boolean;
+
+ withdrawalRelatedInfo?: {
+ // Can the user accept the withdrawal directly?
+ // This field is redundant and derivable from other fields.
+ acceptable: boolean;
+
+ recommendedByBank: boolean;
+
+ // Is this exchange the default exchange for this withdrawal?
+ isDefault: boolean;
+
+ // The "reasonable-ness" of the exchange's fees, in context
+ // of the withdrawn amount.
+ // Only provided if available (if we've already queried
+ // and checked this exchange before).
+ feeStructureSummaryForAmount: FeeStructureSummaryForAmount | undefined;
+ };
+ }[];
+ }
+
+
+setExchangeTrust
+----------------
+
+Request:
+
+.. code:: ts
+
+ interface SetExchangeTrustRequest {
+ exchangeBaseUrl: string;
+
+ trusted: boolean;
+ }
+
+The response is an empty object or an error response.
+
+setExchangeTosAccepted
+----------------------
+
+Request:
+
+.. code:: ts
+
+ interface SetExchangeTosAccepted {
+ exchangeBaseUrl: string;
+ }
+
+The response is an empty object or an error response.
+
+
+Alternatives
+============
+
+* The UI could directly access the wallet's DB for more flexible access to the
+ required data. But this would make the UI less robust against changes in wallet-core.
+