How do I upload a file with metadata using a REST web service

Question

I have a REST web service that currently exposes this URL   http   server data media  where users can POST the following JSON          Name    Test        Latitude   12 59817       Longitude   52 12873     in order to create a new Media metadata   Now I need the ability to upload a file at the same time as the media metadata  What s the best way of going about this  I could introduce a new property called file and base64 encode the file  but I was wondering if there was a better way   There s also using multipart form-data like what a HTML form would send over  but I m using a REST web service and I want to stick to using JSON if at all possible

User · Accepted Answer

I agree with Greg that a two phase approach is a reasonable solution, however I would do it the other way around. I would do:

POST http://server/data/media
body:
{
    "Name": "Test",
    "Latitude": 12.59817,
    "Longitude": 52.12873
}

To create the metadata entry and return a response like:

201 Created
Location: http://server/data/media/21323
{
    "Name": "Test",
    "Latitude": 12.59817,
    "Longitude": 52.12873,
    "ContentUrl": "http://server/data/media/21323/content"
}

The client can then use this ContentUrl and do a PUT with the file data.

The nice thing about this approach is when your server starts get weighed down with immense volumes of data, the url that you return can just point to some other server with more space/capacity. Or you could implement some kind of round robin approach if bandwidth is an issue.

User · Answer

One way to approach the problem is to make the upload a two phase process  First  you would upload the file itself using a POST  where the server returns some identifier back to the client  an identifier might be the SHA1 of the file contents   Then  a second request associates the metadata with the file data          Name    Test        Latitude   12 59817       Longitude   52 12873       ContentID    7a788f56fa49ae0ba5ebde780efe4d6a89b5db47      Including the file data base64 encoded into the JSON request itself will increase the size of the data transferred by 33   This may or may not be important depending on the overall size of the file   Another approach might be to use a POST of the raw file data  but include any metadata in the HTTP request header  However  this falls a bit outside basic REST operations and may be more awkward for some HTTP client libraries

User · Answer

To build on ccleve s answer  if you are using superagent   express   multer  on the front end side build your multipart request doing something like this  superagent      post url       accept  application json        field  myVeryRelevantJsonData   JSON stringify   peep   Peep Peep              attach  myFile   file    cf https   visionmedia github io superagent  multipart-requests  On the express side  whatever was passed as field will end up in req body after doing  app use express json   limit   3MB        Your route would include something like this  const multerMemStorage   multer memoryStorage    const multerUploadToMem   multer     storage  multerMemStorage       Also specify fileFilter  limits         router post   myUploads     multerUploadToMem single  myFile      async  req  res  next    gt           Find back myVeryRelevantJsonData       logger verbose  Uploaded req body   JSON stringify req body              If your file is text      const newFileText   req file buffer toString        logger verbose  Uploaded text   newFileText         return next                One thing to keep in mind though is this note from the multer doc  concerning disk storage   Note that req body might not have been fully populated yet  It depends on the order that the client transmits fields and files to the server   I guess this means it would be unreliable to  say  compute the target dir filename based on json metadata passed along the file

User · Answer

Just because you re not wrapping the entire request body in JSON  doesn t meant it s not RESTful to use multipart form-data to post both the JSON and the file s  in a single request  curl -F  quot metadata  lt metadata json quot  -F  quot file  my-file tar gz quot  http   example com add-file  on the server side   class AddFileResource Resource       def render POST self  request           metadata   json loads request args  metadata   0           file body   request args  file   0               to upload multiple files  it s possible to either use separate  quot form fields quot  for each  curl -F  quot metadata  lt metadata json quot  -F  quot file1  some-file tar gz quot  -F  quot file2  some-other-file tar gz quot  http   example com add-file     in which case the server code will have request args  file1   0  and request args  file2   0  or reuse the same one for many  curl -F  quot metadata  lt metadata json quot  -F  quot files  some-file tar gz quot  -F  quot files  some-other-file tar gz quot  http   example com add-file     in which case request args  files   will simply be a list of length 2  or pass multiple files through a single field  curl -F  quot metadata  lt metadata json quot  -F  quot files  some-file tar gz some-other-file tar gz quot  http   example com add-file     in which case request args  files   will be a string containing all the files  which you ll have to parse yourself     not sure how to do it  but I m sure it s not difficult  or better just use the previous approaches  The difference between   and  lt  is that   causes the file to get attached as a file upload  whereas  lt  attaches the contents of the file as a text field  P S  Just because I m using curl as a way to generate the POST requests doesn t mean the exact same HTTP requests couldn t be sent from a programming language such as Python or using any sufficiently capable tool

User · Answer

I don t understand why  over the course of eight years  no one has posted the easy answer  Rather than encode the file as base64  encode the json as a string  Then just decode the json on the server side   In Javascript   let formData   new FormData    formData append  file   myfile   formData append  myjson   JSON stringify myJsonObject      POST it using Content-Type  multipart form-data  On the server side  retrieve the file normally  and retrieve the json as a string  Convert the string to an object  which is usually one line of code no matter what programming language you use    Yes  it works great  Doing it in one of my apps

User · Answer

If your file and its metadata creating one resource  its perfectly fine to upload them both in one request  Sample request would be    POST https   target com myresources resourcename HTTP 1 1  Accept  application json  Content-Type  multipart form-data    boundary -----------------------------28947758029299  Host  target com  -------------------------------28947758029299  Content-Disposition  form-data  name  application json     markers                            point  new GLatLng 40 266044 -74 718479                 homeTeam   Lawrence Library                awayTeam   LUGip                markerImage   images red png                information    Linux users group meets second Wednesday of each month                 fixture   Wednesday 7pm                capacity                   previousScore                                       point  new GLatLng 40 211600 -74 695702                homeTeam   Hamilton Library                awayTeam   LUGip HW SIG                markerImage   images white png                information    Linux users can meet the first Tuesday of the month to work out harward and configuration issues                 fixture   Tuesday 7pm                capacity                   tv                                       point  new GLatLng 40 294535 -74 682012                homeTeam   Applebees                awayTeam   After LUPip Mtg Spot                markerImage   images newcastle png                information    Some of us go there after the main LUGip meeting  drink brews  and talk                 fixture   Wednesday whenever                capacity   2 to 4 pints                tv                     -------------------------------28947758029299  Content-Disposition  form-data  name  name   filename  myfilename pdf   Content-Type  application octet-stream   PDF-1 4   2 0 obj  lt  lt  Length 57 Filter FlateDecode gt  gt stream x r 26S00SI2P0Qn F  i     Y0i  k   endstream endobj 4 0 obj  lt  lt  Type Page MediaBox 0 0 595 842  Resources lt  lt  Font lt  lt  F1 1 0 R gt  gt  gt  gt  Contents 2 0 R Parent 3 0 R gt  gt  endobj 1 0 obj  lt  lt  Type Font Subtype Type1 BaseFont Helvetica Encoding WinAnsiEncoding gt  gt  endobj 3 0 obj  lt  lt  Type Pages Count 1 Kids 4 0 R  gt  gt  endobj 5 0 obj  lt  lt  Type Catalog Pages 3 0 R gt  gt  endobj 6 0 obj  lt  lt  Producer iTextSharp 5 5 11 2000-2017 iText Group NV   AGPL-version    CreationDate D 20170630120636 02 00   ModDate D 20170630120636 02 00   gt  gt  endobj xref 0 7 0000000000 65535 f  0000000250 00000 n  0000000015 00000 n  0000000338 00000 n  0000000138 00000 n  0000000389 00000 n  0000000434 00000 n  trailer  lt  lt  Size 7 Root 5 0 R Info 6 0 R ID   lt c7c34272c2e618698de73f4e1a65a1b5 gt  lt c7c34272c2e618698de73f4e1a65a1b5 gt   gt  gt   iText-5 5 11 startxref 597   EOF  -------------------------------28947758029299--

User · Answer

I realize this is a very old question  but hopefully this will help someone else out as I came upon this post looking for the same thing   I had a similar issue  just that my metadata was a Guid and int   The solution is the same though   You can just make the needed metadata part of the URL   POST accepting method in your  Controller  class   public Task lt HttpResponseMessage gt  PostFile string name  float latitude  float longitude          See http   stackoverflow com a 10327789 431906 for how to accept a file     return null      Then in whatever you re registering routes  WebApiConfig Register HttpConfiguration config  for me in this case   config Routes MapHttpRoute      name   FooController       routeTemplate   api  controller   name   latitude   longitude        defaults  new

[web-services] How do I upload a file with metadata using a REST web service?

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