datastar/sdk

Architecture Decision Record: Datastar SDK

Summary

Datastar has had a few helper tools in the past for different languages. The SDK effort is to unify around the tooling needed for Hypermedia On Whatever your Like (HOWL) based UIs. Although Datastar the library can use any plugins, the default bundle includes robust Server Sent Event (SSE) base approach. Most current languages and backend don't have great tooling around the style of delivering content to the frontend.

Decision

Provide an SDK in a language agnostic way, to that end

1. Keep SDK as minimal as possible
2. Allow per language/framework extended features to live in an SDK sugar version

Details

Assumptions

The core mechanics of Datastar’s SSE support is

1. Data gets sent to browser as SSE events.
2. Data comes in via JSON from browser under a datastar namespace.

Library

[!WARNING] All naming conventions are shown using Go as the standard. Things may vary per language norms but please keep as close as possible.

ServerSentEventGenerator

There must be a ServerSentEventGenerator namespace. In Go this is implemented as a struct, but could be a class or even namespace in languages such as C.

Construction / Initialization

1. There must be a way to create a new instance of this object based on the incoming HTTP Request and Response objects.
2. The ServerSentEventGenerator must use a response controller that has the following response headers set by default
   1. Cache-Control = nocache
   2. Content-Type = text/event-stream
   3. Connection = keep-alive only if a HTTP/1.1 connection is used (see spec)
3. Then the created response should flush immediately to avoid timeouts while 0-♾️ events are created
4. Multiple calls using ServerSentEventGenerator should be single threaded to guarantee order. The Go implementation uses a mutex to facilitate this behavior but might not be needed in a some environments

ServerSentEventGenerator.send

ServerSentEventGenerator.send(
    eventType: EventType,
    dataLines: string[],
    options?: {
        eventId?: string,
        retryDuration?: durationInMilliseconds
    }
)

All top level ServerSentEventGenerator should use a unified sending function. This method should be private/protected

Args

EventType

An enum of Datastar supported events. Will be a string over the wire. Currently valid values are

Event	Description
datastar-merge-fragments	Merges HTML fragments into the DOM
datastar-merge-signals	Merges signals into the signals
datastar-remove-fragments	Removes HTML fragments from the DOM
datastar-remove-signals	Removes signals from the signals
datastar-execute-script	Executes JavaScript in the browser

Options

• eventId (string) Each event may include an eventId. This can be used by the backend to replay events. This is part of the SSE spec and is used to tell the browser how to handle the event. For more details see https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#id
• retryDuration (duration) Each event may include a retryDuration value. If one is not provided the SDK must default to 1000 milliseconds. This is part of the SSE spec and is used to tell the browser how long to wait before reconnecting if the connection is lost. For more details see https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#retry

Logic

When called the function must write to the response buffer the following in specified order. If any part of this process fails you must return/throw an error depending on language norms.

1. Must write event: EVENT_TYPE\n where EVENT_TYPE is EventType.
2. If a user defined event ID is provided, the function must write id: EVENT_ID\n where EVENT_ID is the event ID.
3. Must write retry: RETRY_DURATION\n where RETRY_DURATION is the provided retry duration, unless the value is the default of 1000 milliseconds.
4. For each string in the provided dataLines, you must write data: DATA\n where DATA is the provided string.
5. Must write a \n\n to complete the event per the SSE spec.
6. Afterward the writer should immediately flush. This can be confounded by other middlewares such as compression layers.

ServerSentEventGenerator.MergeFragments

ServerSentEventGenerator.MergeFragments(
    fragments: string,
    options?: {
        selector?: string,
        mergeMode?: FragmentMergeMode,
        useViewTransition?: boolean,
        eventId?: string,
        retryDuration?: durationInMilliseconds
     }
 )

Example Output

Minimal:

event: datastar-merge-fragments
data: fragments <div id="feed">
data: fragments     <span>1</span>
data: fragments </div>

Maximal:

event: datastar-merge-fragments
id: 123
retry: 2000
data: selector #feed
data: useViewTransition true
data: fragments <div id="feed">
data: fragments     <span>1</span>
data: fragments </div>

MergeFragments is a helper function to send HTML fragments to the browser to be merged into the DOM.

Args

FragmentMergeMode

An enum of Datastar supported fragment merge modes. Will be a string over the wire Valid values should match the FragmentMergeMode and currently include

Mode	Description
morph	Use Idiomorph to merge the fragment into the DOM
inner	Replace the innerHTML of the selector with the fragment
outer	Replace the outerHTML of the selector with the fragment
prepend	Prepend the fragment to the selector
append	Append the fragment to the selector
before	Insert the fragment before the selector
after	Insert the fragment after the selector
upsertAttributes	Update the attributes of the selector with the fragment

Options

• selector (string) The CSS selector to use to insert the fragments. If not provided or empty, Datastar will default to using the id attribute of the fragment.
• mergeMode (FragmentMergeMode) The mode to use when merging the fragment into the DOM. If not provided the Datastar client side will default to morph.
• useViewTransition Whether to use view transitions, if not provided the Datastar client side will default to false.

Logic

When called the function must call ServerSentEventGenerator.send with the datastar-merge-fragments event type.

1. If selector is provided, the function must include the selector in the event data in the format selector SELECTOR\n, unless the selector is empty.
2. If mergeMode is provided, the function must include the merge mode in the event data in the format merge MERGE_MODE\n, unless the value is the default of morph.
3. If useViewTransition is provided, the function must include the view transition in the event data in the format useViewTransition USE_VIEW_TRANSITION\n, unless the value is the default of false. USE_VIEW_TRANSITION should be true or false (string), depending on the value of the useViewTransition option.
4. The function must include the fragments in the event data, with each line prefixed with fragments . This should be output after all other event data.

ServerSentEventGenerator.RemoveFragments

ServerSentEventGenerator.RemoveFragments(
    selector: string,
    options?: {
        useViewTransition?: boolean,
        eventId?: string,
        retryDuration?: durationInMilliseconds
    }
)

Example Output

Minimal:

event: datastar-remove-fragments
data: selector #target

Maximal:

event: datastar-remove-fragments
id: 123
retry: 2000
data: selector #target
data: useViewTransition true

RemoveFragments is a helper function to send a selector to the browser to remove HTML fragments from the DOM.

Args

selector is a CSS selector that represents the fragments to be removed from the DOM. The selector must be a valid CSS selector. The Datastar client side will use this selector to remove the fragment from the DOM.

Options

• useViewTransition Whether to use view transitions, if not provided the Datastar client side will default to false.

Logic

1. When called the function must call ServerSentEventGenerator.send with the datastar-remove-fragments event type.
2. The function must include the selector in the event data in the format selector SELECTOR\n.
3. If useViewTransition is provided, the function must include the view transition in the event data in the format useViewTransition USE_VIEW_TRANSITION\n, unless the value is the default of false. USE_VIEW_TRANSITION should be true or false (string), depending on the value of the useViewTransition option.

ServerSentEventGenerator.MergeSignals

ServerSentEventGenerator.MergeSignals(
    signals: string,
    options ?: {
        onlyIfMissing?: boolean,
        eventId?: string,
        retryDuration?: durationInMilliseconds
     }
 )

Example Output

Minimal:

event: datastar-merge-signals
data: signals {"output":"Patched Output Test","show":true,"input":"Test","user":{"name":"","email":""}}

Maximal:

event: datastar-merge-signals
id: 123
retry: 2000
data: onlyIfMissing true
data: signals {"output":"Patched Output Test","show":true,"input":"Test","user":{"name":"","email":""}}

MergeSignals is a helper function to send one or more signals to the browser to be merged into the signals.

Args

Data is a JavaScript object or JSON string that will be sent to the browser to update signals in the signals. The data must evaluate to a valid JavaScript. It will be converted to signals by the Datastar client side.

Options

• onlyIfMissing (boolean) Whether to merge the signal only if it does not already exist. If not provided, the Datastar client side will default to false, which will cause the data to be merged into the signals.

Logic

When called the function must call ServerSentEventGenerator.send with the datastar-merge-signals event type.

1. If onlyIfMissing is provided, the function must include it in the event data in the format onlyIfMissing ONLY_IF_MISSING\n, unless the value is the default of false. ONLY_IF_MISSING should be true or false (string), depending on the value of the onlyIfMissing option.
2. The function must include the signals in the event data, with each line prefixed with signals . This should be output after all other event data.

ServerSentEventGenerator.RemoveSignals

ServerSentEventGenerator.RemoveSignals(
    paths: string[],
    options?: {
        eventId?: string,
        retryDuration?: durationInMilliseconds
    }
)

Example Output

Minimal:

event: datastar-remove-signals
data: paths user.name
data: paths user.email

Maximal:

event: datastar-remove-signals
id: 123
retry: 2000
data: paths user.name
data: paths user.email

RemoveSignals is a helper function to send signals to the browser to be removed from the signals.

Args

paths is a list of strings that represent the signal paths to be removed from the signals. The paths must be valid . delimited paths to signals within the signals. The Datastar client side will use these paths to remove the data from the signals.

Logic

When called the function must call ServerSentEventGenerator.send with the datastar-remove-signals event type.

1. The function must include the paths in the event data, with each line prefixed with paths . Space-separated paths such as paths foo.bar baz.qux.hello world should be allowed.

ServerSentEventGenerator.ExecuteScript

ServerSentEventGenerator.ExecuteScript(
    script: string,
    options?: {
        autoRemove?: boolean,
        attributes?: string,
        eventId?: string,
        retryDuration?: durationInMilliseconds
    }
)

Example Output

Minimal:

event: datastar-execute-script
data: script window.location = "https://data-star.dev"

Maximal:

event: datastar-execute-script
id: 123
retry: 2000
data: autoRemove false
data: attributes type text/javascript
data: script window.location = "https://data-star.dev"

Args

script is a string that represents the JavaScript to be executed by the browser.

Options

• autoRemove Whether to remove the script after execution, if not provided the Datastar client side will default to true.
• attributes A line separated list of attributes to add to the script element, if not provided the Datastar client side will default to type module. Each item in the array should be a string in the format key value.

Logic

When called the function must call ServerSentEventGenerator.send with the datastar-execute-script event type.

1. If autoRemove is provided, the function must include the auto remove script value in the event data in the format autoRemove AUTO_REMOVE\n, unless the value is the default of true.
2. If attributes is provided, the function must include the attributes in the event data, with each line prefixed with attributes , unless the attributes value is the default of type module.
3. The function must include the script in the event data, with each line prefixed with script . This should be output after all other event data.

ReadSignals(r *http.Request, signals any) error

ReadSignals is a helper function to parse incoming data from the browser. It should take the incoming request and convert into an object that can be used by the backend.

Args

• r (http.Request) The incoming request object from the browser. This object must be a valid Request object per the language specifics.
• signals (any) The signals object that the incoming data will be extracted into. The exact function signature will depend on the language specifics.

Logic

1. The function must parse the incoming HTTP request
   1. If the incoming method is GET, the function must parse the query string's datastar key and treat it as a URL encoded JSON string.
   2. Otherwise, the function must parse the body of the request as a JSON encoded string.
   3. If the incoming data is not valid JSON, the function must return an error.