# Call HTTP endpoints during Assemblies

Robot: `/http/request`

🤖/http/request calls your application during an Assembly and emits returned input file references.

Calls an HTTP endpoint during the Assembly and expects optional JSON describing zero or more input
files or result-file URLs to emit from this Step.

Your endpoint must return a 2xx response. An empty body, `[]`, or `{ "files": [] }` means this
Step emits no files. You can also return one file object, an array of file objects, or
`{ "files": [...] }` / `{ "files": { "name": {...} } }`. Returned file objects must include
either a `path` that matches one of the input file paths sent to your endpoint, or an HTTP(S)
`url` that Transloadit downloads and emits as a new result file.

Stage: alpha

## Usage example

Ask your application which input files should continue:

```json
{
  "steps": {
    "request": {
      "robot": "/http/request",
      "method": "POST",
      "payload": "metadata",
      "url": "https://example.com/transloadit/files",
      "use": []
    }
  }
}
```

## Parameters

* `interpolate`: Controls whether Assembly Variables are interpolated for individual instruction fields.

  By default, most Robot instruction fields interpolate Assembly Variables. Set this to `false` to treat every instruction field as literal text, or set an individual field path to `false` to treat only that field as literal text. For Robot-specific fields that are literal by default, set this to `true` or set that field path to `true` to opt back into interpolation.

  Use field names such as `path`, or dotted paths such as `ffmpeg.vf` for nested objects.

* `output_meta`: Allows you to specify a set of metadata that is more expensive on CPU power to calculate, and thus is disabled by default to keep your Assemblies processing fast.

  For images, you can add `"has_transparency": true` in this object to extract if the image contains transparent parts and `"dominant_colors": true` to extract an array of hexadecimal color codes from the image.

  For images, you can also add `"blurhash": true` to extract a [BlurHash](https://blurha.sh) string — a compact representation of a placeholder for the image, useful for showing a blurred preview while the full image loads.

  For videos, you can add the `"colorspace": true` parameter to extract the colorspace of the output video.

  For videos, you can also add `"interlaced": true` to detect whether the video is interlaced. This combines the cheap ffprobe `field_order` flag with a bounded `idet` sampling pass over the first frames of the source, exposing `interlaced`, `field_order`, and a diagnostic `interlace_detection` object under `file.meta`. This is computationally expensive and billed accordingly.

  For audio, you can add `"mean_volume": true` to get a single value representing the mean average volume of the audio file.

  You can also set this to `false` to skip metadata extraction and speed up transcoding.

* `user_meta`: Adds custom metadata to each file emitted by this Robot without modifying the file’s contents.

  The values are merged with any existing `user_meta` carried by the input file. If both objects contain the same key, this Robot’s value takes precedence. Assembly Variables are supported, for example `{ "internal_file_id": "${file.id}" }`.

* `result`: Whether the results of this Step should be present in the Assembly Status JSON

* `queue`: Setting the queue to 'batch', manually downgrades the priority of jobs for this step to avoid consuming Priority job slots for jobs that don't need zero queue waiting times

* `force_accept`: Force a Robot to accept a file type it would have ignored.

  By default, Robots ignore files they are not familiar with.
  [🤖/video/encode](/docs/robots/video-encode.md), for
  example, will happily ignore input images.

  With the `force_accept` parameter set to `true`, you can force Robots to accept all files thrown at them.
  This will typically lead to errors and should only be used for debugging or combatting edge cases.

* `ignore_errors`: Ignore errors during specific phases of processing.

  Setting this to `["meta"]` will cause the Robot to ignore errors during metadata extraction.

  Setting this to `["execute"]` will cause the Robot to ignore errors during the main execution phase.

  Setting this to `true` is equivalent to `["meta", "execute"]` and will ignore errors in both phases.

* `use`: Specifies which Step(s) to use as input.

  * You can pick any names for Steps except `":original"` (reserved for user uploads handled by Transloadit)
  * You can provide several Steps as input with arrays:
    ```json
    {
      "use": [
        ":original",
        "encoded",
        "resized"
      ]
    }
    ```
  * You can also tag input Steps with `as` to pass semantic intent to robots:
    ```json
    {
      "use": [
        {
          "name": ":original",
          "as": "image"
        },
        {
          "name": ":original",
          "as": "mask"
        }
      ]
    }
    ```

  > [!Tip]
  > That's likely all you need to know about `use`, but you can view [Advanced use cases](/docs/topics/use-parameter.md).

* `url`: The HTTP or HTTPS endpoint to call.

* `method`: HTTP method to use for the request.

* `payload`: Controls what is sent to your endpoint.

  * `none`: Send no request body.
  * `metadata`: Send a JSON body with Assembly metadata, fields, the previous Step, and file metadata.
  * `file`: Send multipart form data with a `payload` JSON field and the first input file as a
    `file` part.
  * `files`: Send multipart form data with a `payload` JSON field and all input files as repeated
    `files[]` parts. Useful with `bundle_steps`.

  The `payload` JSON object contains `assembly`, `fields`, `previous_step`, `file`, and
  `files`. `file` is the first input file’s metadata or `null`; `files` is an array of input
  file metadata.

* `headers`: Custom request headers.

  Headers can be specified as an array of strings in the format `"Header-Name: value"`, an array
  of objects, an object map, or a JSON string that will be parsed into an object/array.

* `timeout`: Maximum number of seconds to wait for the HTTP request.

  The effective timeout is the lower of this value and Transloadit’s server-side cap. The cap is 30
  seconds plus 1 second per MiB sent to your endpoint.

* `max_response_size`: Maximum accepted response size in bytes. The response should normally be a small JSON document.

* `max_result_files`: Maximum number of files that the endpoint may return.

* `max_result_file_size`: Maximum allowed size in bytes for each result file returned by URL. If the remote server reports a
  larger file size, the result download is rejected before it starts. If the remote server does not
  report a size upfront, the download is aborted once this limit is exceeded.

* `result_download_timeout`: Maximum number of seconds to spend downloading each result file returned by URL.