`PolygonRestClient.fetchResult` closes `HttpClient` too early, causing `JobCancellationException`

[lakshya-linamani]

Hi 👋

We’ve run into a reproducible problem using PolygonRestClient with Ktor. The issue comes from the way the library currently manages its HttpClient.

Problem

In PolygonRestClient, the helper methods are implemented like this:

private inline fun <R> withHttpClient(codeBlock: (client: HttpClient) -> R) =
    httpClientProvider.buildClient().use(codeBlock)

internal suspend inline fun <reified T> fetchResult(
    urlBuilderBlock: URLBuilder.() -> Unit,
    vararg options: PolygonRestOption
): T {
    val url = baseUrlBuilder.apply(urlBuilderBlock).build()
    return withHttpClient { httpClient ->
        httpClient.get(url) {
            options.forEach { this.it() }
            headers["User-Agent"] = Version.userAgent
        }
    }.body()
}

This combination causes two problems:

1. withHttpClient wraps the client in .use { … }, so the client is closed immediately after the lambda returns.
2. .body() is called after the client has already been closed.

As a result, deserialization frequently fails with:

kotlinx.coroutines.JobCancellationException: Parent job is Completed; job=SupervisorJobImpl{Completed}@...

Why this happens

• HttpClient.get() is suspendable. The request pipeline is not finished when the block returns.
• Because .use { … } closes the client right away, the pipeline is cancelled.
• Then .body() tries to deserialize from a closed client → cancellation exception.

Suggested Fix

• Remove .use { … } and let the client live across calls.

  • HttpClient is designed to be a long-lived, reusable instance.
  • Close it once when the application shuts down, not per request.

• Move .body() inside the withHttpClient block, so the response is fully materialized before the client is closed (if you insist on keeping .use).

For example:

private inline fun <R> withHttpClient(codeBlock: (client: HttpClient) -> R): R =
    codeBlock(httpClientProvider.buildClient())

internal suspend inline fun <reified T> fetchResult(
    urlBuilderBlock: URLBuilder.() -> Unit,
    vararg options: PolygonRestOption
): T {
    val url = baseUrlBuilder.apply(urlBuilderBlock).build()
    return withHttpClient { httpClient ->
        httpClient.get(url) {
            options.forEach { opt -> opt(this) }
            header(HttpHeaders.UserAgent, Version.userAgent)
        }.body()
    }
}

Impact

This makes all REST calls brittle — in a Ktor server context, almost every call to PolygonRestClient eventually fails with JobCancellationException.

Workarounds

The only workaround today is to bypass PolygonRestClient.fetchResult entirely and re-implement REST calls with your own HttpClient. But this defeats the purpose of using the official SDK.

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Environment:

• Ktor 2.3.x
• Kotlin 1.9/2.0
• polygon-io/client-jvm (latest release)
• JDK 17

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Would you be open to a PR to fix this? I can draft one if you agree with the proposed change.

Thanks!