feat(Send Email Node): Add content-id for email attachments

[pemontto]

✨ Feature

This PR adds Content-IDs (CIDs) for email attachments based on their property name. Using CIDs is the most widely supported way to include inline images in HTML emails.

Using the workflow below you can send HTML emails with inline images from the attached files

View sample workflow

{
  "nodes": [
    {
      "parameters": {
        "functionCode": "items[0].json = [\n  {\n    name: '200'\n  },\n  {\n    name: '300'\n  },\n  {\n    name: '300'\n  },\n  {\n    name: '300'\n  },\n];\nreturn items;"
      },
      "name": "Mock Data",
      "type": "n8n-nodes-base.function",
      "typeVersion": 1,
      "position": [
        -220,
        -120
      ]
    },
    {
      "parameters": {
        "url": "=https://picsum.photos/{{$json[\"name\"]}}",
        "responseFormat": "file",
        "options": {}
      },
      "name": "HTTP Request",
      "type": "n8n-nodes-base.httpRequest",
      "typeVersion": 1,
      "position": [
        180,
        -120
      ]
    },
    {
      "parameters": {
        "functionCode": "return items[0].json.map(item => {\n  return {\n    json: item\n  }\n});\n"
      },
      "name": "Split into Items",
      "type": "n8n-nodes-base.function",
      "typeVersion": 1,
      "position": [
        -20,
        -120
      ]
    },
    {
      "parameters": {
        "functionCode": "const binaryProperties = {};\nlet bodyHTML = '';\nfor (let i=0;i<items.length;i++) {\n  let item = items[i];\n  binaryProperties[`data${i}`] = item.binary.data;\n  bodyHTML += `\\n<h4>img cid:data${i}</h4><img src=\"cid:data${i}\">`\n}\n\n\n\nreturn [\n  {\n    json: {\n      binaryProperties: Object.keys(binaryProperties).join(','),\n      bodyHTML\n    },\n    binary: binaryProperties,\n  }\n]\n"
      },
      "name": "Merge into one item",
      "type": "n8n-nodes-base.function",
      "typeVersion": 1,
      "position": [
        380,
        -120
      ]
    },
    {
      "parameters": {
        "fromEmail": "me@example.com",
        "toEmail": "joe@example.com",
        "subject": "Test CID Embedded Images",
        "text": "Images",
        "html": "=<h1>Images</h1>\n{{ $json.bodyHTML }}",
        "attachments": "={{$json[\"binaryProperties\"]}}",
        "options": {
          "allowUnauthorizedCerts": true
        }
      },
      "name": "Send Email",
      "type": "n8n-nodes-base.emailSend",
      "typeVersion": 1,
      "position": [
        580,
        -120
      ],
      "credentials": {
        "smtp": {
          "id": "47",
          "name": "SMTP account"
        }
      }
    }
  ],
  "connections": {
    "Mock Data": {
      "main": [
        [
          {
            "node": "Split into Items",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "HTTP Request": {
      "main": [
        [
          {
            "node": "Merge into one item",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Split into Items": {
      "main": [
        [
          {
            "node": "HTTP Request",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Merge into one item": {
      "main": [
        [
          {
            "node": "Send Email",
            "type": "main",
            "index": 0
          }
        ]
      ]
    }
  }
}

🐛 Bug

This also fixes an issues where the error object has a circular reference with certificate errors which makes things very hard to debug, particularly in large workflows. Instead of seeing this:

The error now looks like this:

[Joffcom]

NODE-541

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01 ⚠️

Comparison is base (e88b9d8) 27.69% compared to head (39913e8) 27.69%.

❗ Current head 39913e8 differs from pull request most recent head 1b091d4. Consider uploading reports for the commit 1b091d4 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3632      +/-   ##
==========================================
- Coverage   27.69%   27.69%   -0.01%     
==========================================
  Files        2948     2948              
  Lines      180869   180871       +2     
  Branches    19635    19635              
==========================================
  Hits        50090    50090              
- Misses     130034   130036       +2     
  Partials      745      745              

Impacted Files	Coverage Δ
...es/nodes-base/nodes/EmailSend/v2/send.operation.ts	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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[Joffcom]

Thanks for the PR @pemontto 🙌

[janober]

Got released with n8n@0.230.1