GuzzlePromiseAdapter::then() breaks promise chaining by returning $this

I believe this is a bug; ran across while poking around at other matters.

OC\Http\Client\GuzzlePromiseAdapter::then() calls the underlying Guzzle promise’s then(...), but discards the returned promise and returns $this instead.

This breaks normal promise chaining semantics.

server/lib/private/Http/Client/GuzzlePromiseAdapter.php

Lines 34 to 66 in 2a5e57d

    
           	/** 
        
           	 * Appends fulfillment and rejection handlers to the promise, and returns 
        
           	 * a new promise resolving to the return value of the called handler. 
        
           	 * 
        
           	 * @param ?callable(IResponse): void $onFulfilled Invoked when the promise fulfills. Gets an \OCP\Http\Client\IResponse passed in as argument 
        
           	 * @param ?callable(Exception): void $onRejected Invoked when the promise is rejected. Gets an \Exception passed in as argument 
        
           	 * 
        
           	 * @return IPromise 
        
           	 * @since 28.0.0 
        
           	 */ 
        
           	public function then( 
        
           		?callable $onFulfilled = null, 
        
           		?callable $onRejected = null, 
        
           	): IPromise { 
        
           		if ($onFulfilled !== null) { 
        
           			$wrappedOnFulfilled = static function (ResponseInterface $response) use ($onFulfilled): void { 
        
           				$onFulfilled(new Response($response)); 
        
           			}; 
        
           		} else { 
        
           			$wrappedOnFulfilled = null; 
        
           		} 
        
           		if ($onRejected !== null) { 
        
           			$wrappedOnRejected = static function (RequestException $e) use ($onRejected): void { 
        
           				$onRejected($e); 
        
           			}; 
        
           		} else { 
        
           			$wrappedOnRejected = null; 
        
           		} 
        
           		$this->promise->then($wrappedOnFulfilled, $wrappedOnRejected); 
        
           		return $this; 
        
           	}

The current implementation also contradicts the IPromise::then() docs, which say it returns a new promise resolving to the handler’s return value.

For what it's worth, app_api is currently a consumer...

https://github.com/nextcloud/app_api/blob/c9364a51c2491c0aadc2d200b50d40e4f5c3a037/lib/Service/AppAPIService.php#L131-L149

Also could use some unit tests for async contract behavior...

Something for the backend experts 🤔

@artonge

@artonge something for your team maybe it seems otherwise @DaphneMuller team will run into problem with this sooner or later (app api)

@oleksandr-nc

@oleksandr-nc @julien-nc @marcelklehr @kyteinsky FYI

OC\Http\Client\GuzzlePromiseAdapter::then() calls the underlying Guzzle promise’s then(...), but discards the returned promise and returns $this instead.

This breaks normal promise chaining semantics.

Without much knowledge of the guzzle stuff, I suppose it's done that way to use the wrapper callbacks, and returns its own $this so this wrapped method can be chained.
The promise from guzzle isn't discarded, the object protected PromiseInterface $promise, is used again on subsequent calls of this method, which is essentially chaining in PromiseInterface's context.

The current implementation also contradicts the IPromise::then() docs, which say it returns a new promise resolving to the handler’s return value.

yeah the doc is a bit misleading.

Navigation Menu

Repository navigation

`GuzzlePromiseAdapter::then()` breaks promise chaining by returning `$this` #59178

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

	/**
	* Appends fulfillment and rejection handlers to the promise, and returns
	* a new promise resolving to the return value of the called handler.
	*
	* @param ?callable(IResponse): void $onFulfilled Invoked when the promise fulfills. Gets an \OCP\Http\Client\IResponse passed in as argument
	* @param ?callable(Exception): void $onRejected Invoked when the promise is rejected. Gets an \Exception passed in as argument
	*
	* @return IPromise
	* @since 28.0.0
	*/
	public function then(
	?callable $onFulfilled = null,
	?callable $onRejected = null,
	): IPromise {
	if ($onFulfilled !== null) {
	$wrappedOnFulfilled = static function (ResponseInterface $response) use ($onFulfilled): void {
	$onFulfilled(new Response($response));
	};
	} else {
	$wrappedOnFulfilled = null;
	}

	if ($onRejected !== null) {
	$wrappedOnRejected = static function (RequestException $e) use ($onRejected): void {
	$onRejected($e);
	};
	} else {
	$wrappedOnRejected = null;
	}

	$this->promise->then($wrappedOnFulfilled, $wrappedOnRejected);
	return $this;
	}

GuzzlePromiseAdapter::then() breaks promise chaining by returning $this #59178

Description

Activity

skjnldsv commented on Mar 26, 2026

susnux commented on Mar 27, 2026

DaphneMuller commented on Mar 30, 2026

kyteinsky commented on Mar 30, 2026

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

`GuzzlePromiseAdapter::then()` breaks promise chaining by returning `$this` #59178