feat(spanner): make affinity keys configurable via spanner_grpc_confi…

[alkatrivedi]

No description provided.

[gemini-code-assist]

Code Review

This pull request implements multiplexed session affinity for Spanner by generating unique UUID-based affinity keys for transactions and snapshots. It updates the gRPC configuration to support metadata-based affinity and modifies the Snapshot and Transaction classes to inject these keys into request headers, as well as handling the unbinding of keys during commit or rollback operations. Feedback is provided regarding the potential risks of bypassing the grpcGcp.createGcpApiConfig helper, performance inefficiencies caused by repeated linear searches in the configuration, and the need to avoid direct mutation of request configuration objects to prevent side effects.

[surbhigarg92]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces support for multiplexed session affinity keys in Spanner transactions and snapshots. It generates a unique affinity key for multiplexed sessions, injects it into request options, and ensures it is unbound when the transaction ends, commits, or rolls back. Unit tests have been added to verify this behavior. The reviewer feedback suggests avoiding mutation of the config object in request and requestStream by shallow copying it, and using optional chaining when accessing nested parent properties to prevent potential runtime TypeErrors.

[gemini-code-assist]

Mutating the config object passed to this.request and this.requestStream can lead to unexpected side effects if the caller reuses the configuration object (e.g., during retries or multiple sequential requests). It is safer to shallow copy the config object before modifying its gaxOpts property.

    this.request = (config: any, callback: Function) => {
      if (this._affinityKey) {
        let gaxOpts;
        if (!config.gaxOpts || Object.keys(config.gaxOpts).length === 0) {
          gaxOpts = this._bindGaxOpts as any;
        } else {
          gaxOpts = injectGaxOpt(
            config.gaxOpts,
            'affinityKey',
            this._affinityKey,
          );
        }
        config = Object.assign({}, config, {gaxOpts});
      }
      return session.request(config, callback);
    };

    this.requestStream = (config: any) => {
      if (this._affinityKey) {
        let gaxOpts;
        if (!config.gaxOpts || Object.keys(config.gaxOpts).length === 0) {
          gaxOpts = this._bindGaxOpts as any;
        } else {
          gaxOpts = injectGaxOpt(
            config.gaxOpts,
            'affinityKey',
            this._affinityKey,
          );
        }
        config = Object.assign({}, config, {gaxOpts});
      }
      return session.requestStream(config);
    };

[gemini-code-assist]

Accessing nested properties like this.session.parent and database.parent.parent without optional chaining can cause a TypeError at runtime if any of these parent references are undefined (e.g., in lightweight test environments or mocked sessions). Using optional chaining ensures defensive programming and avoids potential crashes.

Suggested change

	const database = this.session.parent as Database;
	const spanner = database.parent.parent as Spanner;
	const client = spanner.clients_.get('SpannerClient') as any;
	const database = this.session?.parent as Database;
	const spanner = database?.parent?.parent as Spanner;
	const client = spanner?.clients_?.get('SpannerClient') as any;

[alkatrivedi]

/gcbrun