Sending Files

When a channel template (Template) has a field of type file or image_upload, the file data is passed to the pipeline in base64 format. To send files, the $$ prefix of the templating language is used, which unpacks an array of files into a repeating structure.

File data structure

Each file in the array contains the following fields:

Field	Description
content	File data in base64
name	File name
mime	MIME type of the file (for example, image/png, application/pdf)
size	File size in bytes

Syntax in Pack

To unpack an array of files in the Pack pipe, the following construct is used:

$$template.<shortname>[<array_name>]

Where:

• <shortname> — shortname of the file field in Template (for example, file_field)
• <array_name> — key name in the resulting JSON (for example, array, files, attachments)

Example: single file

If Template has a single file field file_field, the Pack pipe will look like this:

{
  "id": 1,
  "type": "pack",
  "params": {
    "type": "JSON",
    "template": {
      "message": "$template.message",
      "subid": "$subscription.subid",
      "$$template.file_field[files]": {
        "content": "[$]content",
        "filename": "[$]name",
        "type": "[$]mime",
        "size": "[$]size"
      },
      "campaignId": "$in.c_id"
    }
  },
  "outs": {
    "success": 2,
    "error": 3
  }
}

Result in $in.body (with one file):

{
  "message": "Hello",
  "subid": "sub_123",
  "files": [
    {
      "content": "base64encodeddata...",
      "filename": "document.pdf",
      "type": "application/pdf",
      "size": "45000"
    }
  ],
  "campaignId": "101"
}

Example: multiple files

If the user uploaded multiple files, each will be added to the files array:

{
  "message": "Hello",
  "subid": "sub_123",
  "files": [
    {
      "content": "base64data1...",
      "filename": "image1.png",
      "type": "image/png",
      "size": "12000"
    },
    {
      "content": "base64data2...",
      "filename": "image2.png",
      "type": "image/png",
      "size": "8000"
    }
  ],
  "campaignId": "101"
}

Full pipeline example with a file

[
  {
    "id": 1,
    "type": "pack",
    "params": {
      "type": "JSON",
      "template": {
        "message": "$template.message",
        "subid": "$subscription.subid",
        "$$template.file_field[files]": {
          "content": "[$]content",
          "filename": "[$]name"
        },
        "campaignId": "$in.c_id"
      }
    },
    "outs": {
      "success": 2,
      "error": 3
    }
  },
  {
    "id": 2,
    "type": "http_request",
    "params": {
      "method": "POST",
      "timeout": 30,
      "content_type": "json",
      "url": "https://api.example.com/send",
      "success_codes": [200]
    },
    "outs": {
      "success": 4,
      "error": 3
    }
  },
  {
    "id": 4,
    "type": "event",
    "params": {
      "channel_id": 10001,
      "action_type": 100001,
      "event": {
        "send_message_id": "$origin.send_message_id"
      }
    }
  },
  {
    "id": 3,
    "type": "event",
    "params": {
      "channel_id": 10001,
      "action_type": 100003,
      "event": {
        "send_message_id": "$origin.send_message_id",
        "message": "$error.code $error.message"
      }
    }
  }
]

tip

Note the HTTP request timeout: when sending files, it is recommended to increase timeout (for example, to 30 seconds), since base64 data increases the request body size.

caution

A channel is not designed to send attachments larger than 1 MB per communication. It is recommended not to exceed 500 KB. For more details, see technical limitations.