Serializer that stores and pulls a generic configuration object from the HttpHeader instance so as to configure an interceptor on a per-request basis

interceptor-request-config-serializer.ts

import { HttpHeaders, HttpRequest } from '@angular/common/http';
import { isNullOrUndefined } from '../../util/misc-util';
import { HttpClientHeaders, HttpClientOptions } from './http-client-options';

/**
 * Unfortunately Angular does not provide a way to pass metadata/configs into interceptors so
 * we have to do it ourselves.
 *
 * https://github.com/angular/angular/issues/18155
 */

export interface PullInterceptorConfigResult<T> {
  request: HttpRequest<any>; // NOSONAR
  config: T | undefined;
}

export class InterceptorRequestConfigSerializer {
  static pullConfig<T>(req: HttpRequest<any>, configName: string): PullInterceptorConfigResult<T> { // NOSONAR
    return InterceptorRequestHeaderConfigSerializer.pullConfig(req, configName);
  }

  static setConfig(options: HttpClientOptions, configName: string, config: object): HttpClientOptions | undefined {
    return InterceptorRequestHeaderConfigSerializer.setConfig(options, configName, config);
  }

}

class InterceptorRequestHeaderConfigSerializer {
  private static readonly INTERCEPTOR_HEADER_PROPERTY_PREFIX = '__interceptor-config__';

  static pullConfig<T>(req: HttpRequest<any>, configName: string): PullInterceptorConfigResult<T> { // NOSONAR
    if (!(req.headers instanceof HttpHeaders)) {
      // Not an instance of HttpHeaders -> no config set
      return { request: req, config: undefined };
    }

    const headersInst: HttpHeaders = req.headers;
    const headerProperty: string = this.getHeaderProperty(configName);
    const config: T = headersInst[headerProperty];
    return { request: req, config };
  }

  static setConfig(options: HttpClientOptions, configName: string, config: object): HttpClientOptions | undefined {
    if (isNullOrUndefined(options)) {
      return undefined;
    }

    const headersInst: HttpHeaders = this.getHeadersInstance(options.headers);
    const headerProperty: string = this.getHeaderProperty(configName);
    headersInst[headerProperty] = config;

    return {
      ...options,
      headers: headersInst
    };
  }

  private static getHeadersInstance(inputHeaders: HttpClientHeaders): HttpHeaders {
    if (inputHeaders instanceof HttpHeaders) {
      return inputHeaders;
    }
    if (isNullOrUndefined(inputHeaders)) {
      return new HttpHeaders();
    }
    return new HttpHeaders(inputHeaders);
  }

  private static getHeaderProperty(configName: string): string {
    return `${this.INTERCEPTOR_HEADER_PROPERTY_PREFIX}${configName}`;
  }

}

// Backup class in case the above class doesn't work
// eslint-disable-next-line @typescript-eslint/no-unused-vars
class InterceptorRequestHeaderConfigSerializer2 {
  private static readonly INTERCEPTOR_HEADER_PREFIX = 'X-Interceptor-Headers-';

  /**
   * Gets the interceptor header and removes it
   */
  static pullConfig<T>(req: HttpRequest<any>, configName: string): PullInterceptorConfigResult<T> { // NOSONAR
    let headerValue: T;
    const headersInst: HttpHeaders = this.getHeadersInstance(req.headers);
    const headerKey: string = this.getHeaderKey(configName);
    const headerValueStr: string = headersInst.get(headerKey);
    if (!isNullOrUndefined(headerValueStr)) {
      headerValue = JSON.parse(headerValueStr);
      req = req.clone({
        headers: req.headers.delete(headerKey)
      });
    }

    return { request: req, config: headerValue };
  }

  static setConfig(options: HttpClientOptions, configName: string, config: object): HttpClientOptions | undefined {
    if (isNullOrUndefined(options)) {
      return undefined;
    }

    const headersInst: HttpHeaders = this.getHeadersInstance(options.headers);
    const headerKey: string = this.getHeaderKey(configName);
    const headerValueStr: string = JSON.stringify(config);
    const newHeadersInst: HttpHeaders = headersInst.set(headerKey, headerValueStr);

    return {
      ...options,
      headers: newHeadersInst
    };
  }

  private static getHeadersInstance(inputHeaders: HttpClientHeaders): HttpHeaders {
    if (inputHeaders instanceof HttpHeaders) {
      return inputHeaders;
    }
    if (isNullOrUndefined(inputHeaders)) {
      return new HttpHeaders();
    }
    return new HttpHeaders(inputHeaders);
  }

  private static getHeaderKey(configName: string): string {
    return `${this.INTERCEPTOR_HEADER_PREFIX}${configName}`;
  }

}