signalViewer.kt

src/jvmMain/kotlin/afield/app/server/signalViewer.kt · 57 lines

package afield.app.server

import afield.ui.visualization.SignalViewer
import io.ktor.http.ContentType
import io.ktor.http.HttpStatusCode
import io.ktor.server.response.respondText
import io.ktor.server.routing.Route
import io.ktor.server.routing.get
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.ensureActive
import kotlinx.coroutines.withContext
import kotlinx.coroutines.withTimeout
import kotlin.coroutines.coroutineContext

The HTTP side of the frontend signal viewer: one route that answers range queries over a SignalViewer a box is currently showing.

GET /signal-viewer/{id} takes a start, an end and a points count and returns that much of the signal as JSON, which is how the plot zooms and pans without the box running again. The id names an entry in the viewer's weak registry, so once a box replaces its output the viewer it was showing becomes collectable and the route answers 410 Gone rather than resampling a signal whose evaluators have been released.

Sampling is confined to two threads and abandoned after twelve seconds, and the window call is handed a check that throws once the client has gone, so an abandoned zoom stops between sample batches instead of finishing a query nobody will read.

fun Route.installSignalViewerRoutes()

Read-only, opaque source IDs; never accepts or compiles code from a browser request.

fun Route.installSignalViewerRoutes() {
    val sampling = Dispatchers.Default.limitedParallelism(2)
    get("/signal-viewer/{id}") {
        val source = SignalViewer.find(call.parameters["id"].orEmpty())
        if (source == null) {
            call.respondText("Signal expired. Run the source box again.", status = HttpStatusCode.Gone)
            return@get
        }
        try {
            val q = call.request.queryParameters
            val from = q["start"]?.toDoubleOrNull() ?: throw IllegalArgumentException("Missing start")
            val to = q["end"]?.toDoubleOrNull() ?: throw IllegalArgumentException("Missing end")
            val points = q["points"]?.toIntOrNull() ?: throw IllegalArgumentException("Missing points")
            val result = withContext(sampling) {
                withTimeout(12_000) {
                    val context = coroutineContext
                    source.window(from, to, points) { context.ensureActive() }
                }
            }
            call.response.headers.append("Cache-Control", "no-store")
            call.respondText(result.toJson(), ContentType.Application.Json)
        } catch (e: IllegalArgumentException) {
            call.respondText(e.message ?: "Invalid signal window", status = HttpStatusCode.BadRequest)
        }
    }
}