ErrorHandlerBase classes

When an error handler needs services (a logger, metrics), extend ErrorHandlerBase and register with host.http.error(Cls). Class handlers do not take an options object; declare static deps on the class instead.

import {
  ErrorHandlerBase,
  FlareError,
  FlareHost,
  FlareResponse,
  Logger,
} from "@flare-ts/core";
import type { HttpErrorContext, ResponseLike } from "@flare-ts/core";
import { node } from "@flare-ts/core/node";

class HttpErrors extends ErrorHandlerBase {
  public static override deps = [Logger];
  readonly #log = this.inject(Logger);

  override handle(
    err: FlareError | Error,
    context: HttpErrorContext,
  ): ResponseLike | void {
    this.#log.error(err, "request failed", {
      stage: context.stage ?? null,
      target: context.target ?? null,
    });
    if (err instanceof FlareError && err.category === "conflict") {
      return new FlareResponse(409, { error: err.name });
    }
  }
}

const host = new FlareHost(node);
host.http.error(HttpErrors);

const app = host.build();
app.run();

Required static members

Member	Required?	Purpose
static deps	Yes	Services via this.inject() ([] if none)
static config	Optional	Config via this.config()

Registration throws at call time if static deps is missing.

handle()

Override handle(err, context) and return a ResponseLike to override the response, or return nothing to defer. The second argument is HttpErrorContext, not FlareHttpContext.

There is no static state on error handlers. They’re not part of the request-state graph.

Group registration

host.http.group("/api", (g) => {
  g.error(HttpErrors);
  g.get("/items", () => new FlareResponse(200, { ok: true }));
  return g.register();
});

Arc-level handlers run first, then group handlers.

Related

• Inline error handlers
• Register a custom handler