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Zotero Web API File Uploads

In addition to providing ways to read and write online library data, the Zotero Web API allows you to upload attachment files.

The exact process depends on whether you are adding a new attachment file or modifying an existing one and whether you are performing a full upload or uploading a binary diff.

1a) Create a new attachment

i. Get attachment item template

GET /items/new?itemType=attachment&linkMode={imported_file,imported_url,linked_file,linked_url}
{
  "itemType": "attachment",
  "linkMode": "imported_url",
  "title": "",
  "accessDate": "",
  "url": "",
  "note": "",
  "tags": [],
  "relations": {},
  "contentType": "",
  "charset": "",
  "filename": "",
  "md5": null,
  "mtime": null
}

ii. Create child attachment item

POST /users/<userID>/items
Content-Type: application/json
Zotero-Write-Token: <token>
[
  {
    "itemType": "attachment",
    "parentItem": "ABCD2345",
    "linkMode": "imported_url",
    "title": "My Document",
    "accessDate": "2012-03-14T17:45:54Z",
    "url": "http://example.com/doc.pdf",
    "note": "",
    "tags": [],
    "relations": {},
    "contentType": "application/pdf",
    "charset": "",
    "filename": "doc.pdf",
    "md5": null,
    "mtime": null
  }
]

md5 and mtime can be edited directly in personal libraries for WebDAV-based file syncing. They cannot be edited directly in group libraries and should not be edited directly in personal libraries using Zotero File Storage, which provides an atomic method (detailed below) for setting the properties along with the corresponding file.

Top-level attachments can be created by excluding the parentItem property or setting it to false. Though the API allows all attachments to be made top-level items for backward-compatibility, it is recommended that only file attachments (imported_file/linked_file) and PDF imported web attachments (imported_url with content type application/pdf) be allowed as top-level items, as in the Zotero client.

1b) Modify an existing attachment

i. Retrieve the attachment information

GET /users/<userID>/items/<itemKey>
{
  "key": "ABCD2345",
  "version": 124,
  "library": { ... },
  ...
  "data": {
    "key": "ABCD2345",
    "version": 124,
    "itemType": "attachment",
    "linkMode": "imported_file",
    "title": "My Document",
    "note": "",
    "tags": [],
    "relations": {},
    "contentType": "text/plain",
    "charset": "utf-8",
    "filename": "doc.txt",
    "md5": "4fa38e3f2c360ca181e633d02bab91f5",
    "mtime": "1331171741767"
  }
}

ii. Download the existing file

GET /users/<userID>/items/<itemKey>/file

Check the ETag header of the response to make sure it matches the attachment item's md5 value. If it doesn't, check the attachment item again. If the attachment item still has a different hash, the latest version of the file may be available only via WebDAV, not via Zotero File Storage, and it is up to the client how to proceed.

Save the file as filename and set the modification time to the mtime provided in the attachment item.

iii. Make changes to the file

Note that to perform a faster partial upload using a binary diff, you must save a copy of the file before changes are made.

2) Get upload authorization

POST /users/<userID>/items/<itemKey>/file
Content-Type: application/x-www-form-urlencoded
If-None-Match: *
md5=<hash>&filename=<filename>&filesize=<bytes>&mtime=<milliseconds>

For existing attachments, use If-Match: <hash> in place of If-None-Match: *, where <hash> is the previous MD5 hash of the file (as provided in the ETag header when downloading it).

Note that mtime must be provided in milliseconds, not seconds.

A successful 200 response returns one of two possible JSON objects:

{
  "url": ...,
  "contentType": ...,
  "prefix": ...,
  "suffix": ...,
  "uploadKey": ...
}

or

{ "exists": 1 }

In the latter case, the file already exists on the server and was successfully associated with the specified item. No further action is necessary.

Common responses
200 OK The upload was authorized or the file already exists.
403 Forbidden File editing is denied.
409 Conflict The target library is locked.
412 Precondition Failed The file has changed remotely since retrieval (i.e., the provided ETag no longer matches). Conflict resolution is left to the client.
413 Request Entity Too Large The upload would exceed the storage quota of the library owner.
428 Precondition Required If-Match or If-None-Match was not provided.
429 Too Many Requests Too many unfinished uploads. Try again after the number of seconds specified in the Retry-After header.

3a) Full upload

i. POST file

Concatenate prefix, the file contents, and suffix and POST to url with the Content-Type header set to contentType.

prefix and suffix are strings containing multipart/form-data. In some environments, it may be easier to work directly with the form parameters. Add params=1 to the upload authorization request above to retrieve the individual parameters in a params array, which will replace contentType, prefix, and suffix.

Common responses
201 Created The file was successfully uploaded.

ii. Register upload

POST /users/<userID>/items/<itemKey>/file
Content-Type: application/x-www-form-urlencoded
If-None-Match: *
upload=<uploadKey>

For existing attachments, use If-Match: <hash>, where <hash> is the previous MD5 hash of the file, provided as the md5 property in the attachment item.

Common responses
204 No Content The upload was successfully registered.
412 Precondition Failed The file has changed remotely since retrieval (i.e., the provided ETag no longer matches).

After the upload has been registered, the attachment item will reflect the new metadata.

3b) Partial upload

PATCH /users/<userID>/items/<itemKey>/file?algorithm={xdelta,vcdiff,bsdiff}&upload=<uploadKey>
If-Match: <previous-value-of-md5-property>
<Binary diff of old and new versions>

For best results, we recommend using Xdelta version 3 with the “-9 -S djw” flags. bsdiff takes significantly longer to generate diffs. 'vcdiff' is an alias for 'xdelta', as Xdelta3 can process diffs in VCDIFF format.

Clients may wish to automatically fall back to a full upload — possibly with some form of warning — if HTTP PATCH is not supported by a user's proxy server (indicated, in theory, by a 405 Method Not Allowed).

After the upload has finished, the attachment item will reflect the new metadata.

Common responses
204 No Content The patch was successfully applied.
409 Conflict The target library is locked; the patched file does not match the provided MD5 hash or file size
428 Precondition Required If-Match or If-None-Match was not provided.
429 Too Many Requests Too many unfinished uploads. Try again after the number of seconds specified in the Retry-After header.