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@node Reference
@chapter Reference
@menu
* Headers for HTTP 402:: Headers for the 402 status code and their effect on the user agent's operation
* JavaScript API:: JavaScript API to communicate with the wallet
* Stylesheet-based presence detection:: Presence detection using CSS style sheets and no JavaScript
@end menu
@node Headers for HTTP 402
@section Headers for HTTP 402
The HTTP status code @code{402 Payment Required} can be used by the merchant
frontend to trigger operations related to payments in the user agent. The user
agent associates at most one proposal with every URL via the proposal's
@code{fulfillment_url} field. The associated proposal is either missing (in
case it doesn't exist), paid (in case the payment for it was successfully sent
to the merchant) or unpaid. If the associated proposal is unpaid, @code{402
Payment Required} will cause the user agent to pay for the associated proposal.
The following headers for @code{402 Payment Required} are recognized by Taler and further influence the processing:
@table @code
@item X-Taler-Refund-Url
If this header present, the value of this header must be a URL that the user agent can use to request and process refunds.
@item X-Taler-Contract-Url
If there is no associated proposal, the user agent will fetch a proposal from
this URL and process it. This typically prompts the user to agree to pay.
@item X-Taler-Offer-Url
If there is no associated proposal and @code{X-Taler-Contract-Url} is not
specified, the browser will navigate to this URL.
@item X-Taler-User-Tipping-Url
If this header present, the value of this header must be a URL that the user agent can use to obtain tips (small, non-binding
financial rewards) payed from the merchant to the user's wallet. If this field is present, @code{X-Taler-User-Tipping-Exchange}
and @code{X-Taler-User-Tipping-Amount} must also be present.
@item X-Taler-User-Tipping-Exchange
Exchange base URL for the exchange that the merchant helps withdrawing the tip from.
@item X-Taler-User-Tipping-Amount
Amount of tip that the user is receiving, in the standard amount format (CURR:X.Y).
@end table
@node JavaScript API
@section JavaScript API
The following functions are defined in the @code{taler} namespace of the @code{taler-wallet-lib} helper library
available at @url{https://git.taler.net/web-common.git/tree/taler-wallet-lib.js}.
@table @code
@item onPresent(callback: () => void)
Add a callback to be called when support for Taler payments is detected.
@item onAbsent(callback: () => void)
Add a callback to be called when support for Taler payments is disabled.
@item pay(@{contract_url: string, offer_url: string@})
Results in the same action as a @code{402 Payment Required} with @code{contract_url} in
the @code{X-Taler-Contract-Url} header and @code{offer_url} in the @code{X-Taler-Payment-Url} header.
@item refund(refund_url: string)
Results in the same action as a @code{402 Payment Required} with @code{refund_url} in
the @code{X-Taler-Refund-Url} header.
@end table
@node Stylesheet-based presence detection
@section Stylesheet-based presence detection
Stylesheet-based presence detection will be applied on all pages that have the
@code{data-taler-nojs} attribute of the @code{html} element set @code{true}.
The default/fallback stylesheet, that will be taken over by the wallet once
installed, must be included with the id @code{taler-presence-stylesheet}, like
this:
The following CSS classes can be used:
@table @code
@item taler-installed-hide
A CSS rule will set the @code{display} property for this class to @code{none} once the Taler wallet is installed and enabled.
If the wallet is not installed, @code{display} will be @code{inherit}.
@item taler-installed-show
A CSS rule will set the @code{display} property for this class to @code{inherit} once the Taler wallet is installed and enabled.
If the wallet is not installed, @code{display} will be @code{none}.
@end table
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