When referencing content hosted outside of the repository, you can create an empty binary to act as a placeholder for the external content, specifying the URL of the external content.
Instead of supplying the binary in the body of the request, you provide a Link header which uses the rel="http://fedora.info/definitions/fcrepo#ExternalContent" and specifies where to get the resource and how to handle it.
Link: <http://example.org/some/content>; rel="http://fedora.info/definitions/fcrepo#ExternalContent"; handling="proxy"; type="image/tiff" Link: <http://example.org/some/content>; rel="http://fedora.info/definitions/fcrepo#ExternalContent"; handling="proxy"; type="image/tiff"
The Fedora API specifies 3 methods of handling external content, all of which are supported.
- copy - Copy the binary from the provided URI and then treat it as a normal internal LDP-NR.
- redirect - On requests for the LDP-NR provide a redirect (302 Found or 307 Temporary Redirect) to the external URI.
- proxy - On requests for the LDP-NR proxy the request through the Fedora server the client with the same interaction as an internally stored LDP-NR.
If you provide a type= parameter to the Link header this content type will be used, however if type= is omitted, then the server attempts to determine the Content-Type.
If the external URI has a file prefix (ie. local disk storage) then application/octet-stream is returned.
If the external URI has a http prefix then a HEAD request is made to the URI provided in the Link header to retrieve the Content-type header, if this header is not returned the resource cannot be added to the repository.
Examples:
Proxying a file on the local server.
Creating the proxy LDP-NR
> curl -i -H"Link: <file:///local/file/storage/wonderful.tiff>; rel=\"http://fedora.info/definitions/fcrepo#ExternalContent\"; handling=\"proxy\"; type=\"image/tiff\"" -XPUT -ufedoraAdmin:fedoraAdmin http://localhost:8080/rest/test_proxy_local_file HTTP/1.1 201 Created Date: Fri, 29 Jun 2018 14:15:54 GMT Set-Cookie: JSESSIONID=aedg7ilmx9zxugi8x9em7l8h;Path=/ Expires: Thu, 01 Jan 1970 00:00:00 GMT Set-Cookie: rememberMe=deleteMe; Path=/; Max-Age=0; Expires=Thu, 28-Jun-2018 14:15:54 GMT ETag: "0e409de61b53a864ad3a87f4faf884d88cf041ff" Last-Modified: Fri, 29 Jun 2018 14:15:55 GMT Link: <http://localhost:8080/rest/test_proxy_local_file/fcr:metadata>; rel="describedby"; anchor="http://localhost:8080/rest/test_proxy_local_file" Link: <http://localhost:8080/static/constraints/NonRDFSourceConstraints.rdf>; rel="http://www.w3.org/ns/ldp#constrainedBy" Content-Location: file:/local/file/storage/wonderful.tiff Link: <http://localhost:8080/rest/test_proxy_local_file/fcr:acl>; rel="acl" Location: http://localhost:8080/rest/test_proxy_local_file Content-Type: text/plain Content-Length: 48 Server: Jetty(9.3.1.v20150714) http://localhost:8080/rest/test_proxy_local_file
Results of a request
> curl -i http://localhost:8080/rest/test_proxy_local_file -ufedoraAdmin:fedoraAdmin HTTP/1.1 200 OK Date: Fri, 29 Jun 2018 16:40:48 GMT Set-Cookie: JSESSIONID=zhy7150ie8vo1bsc9ycb1ghu1;Path=/ Expires: Thu, 01 Jan 1970 00:00:00 GMT Set-Cookie: rememberMe=deleteMe; Path=/; Max-Age=0; Expires=Thu, 28-Jun-2018 16:40:48 GMT ETag: "0e409de61b53a864ad3a87f4faf884d88cf041ff" Last-Modified: Fri, 29 Jun 2018 14:15:55 GMT Content-Type: image/tiff Accept-Ranges: bytes Content-Disposition: attachment; filename=""; creation-date="Fri, 29 Jun 2018 14:15:55 GMT"; modification-date="Fri, 29 Jun 2018 14:15:55 GMT"; size=14761236 Link: <http://www.w3.org/ns/ldp#Resource>;rel="type" Link: <http://www.w3.org/ns/ldp#NonRDFSource>;rel="type" Link: <http://localhost:8080/rest/test_proxy_local_file/fcr:acl>; rel="acl" Content-Location: file:/Users/whikloj/Desktop/wonderful.tiff Link: <http://localhost:8080/rest/test_proxy_local_file/fcr:metadata>; rel="describedby" Link: <http://localhost:8080/static/constraints/NonRDFSourceConstraints.rdf>; rel="http://www.w3.org/ns/ldp#constrainedBy" Accept-External-Content-Handling: copy,redirect,proxy Allow: DELETE,HEAD,GET,PUT,OPTIONS Cache-Control: no-transform, must-revalidate, max-age=0 Content-Length: 14761236 Server: Jetty(9.3.1.v20150714) ...<BODY CONTENT>...
Redirect to an external URI
Creating the redirect LDP-NR
> curl -i -H"Link: <http://localhost:8111/wonderful.jp2>; rel=\"http://fedora.info/definitions/fcrepo#ExternalContent\"; handling=\"redirect\"; type=\"image/jp2\"" -XPUT -ufedoraAdmin:fedoraAdmin http://localhost:8080/rest/test_redirect_remote_file HTTP/1.1 201 Created Date: Fri, 29 Jun 2018 16:11:16 GMT Set-Cookie: JSESSIONID=1rv3ytcylpb093ra1mhznx9dp;Path=/ Expires: Thu, 01 Jan 1970 00:00:00 GMT Set-Cookie: rememberMe=deleteMe; Path=/; Max-Age=0; Expires=Thu, 28-Jun-2018 16:11:16 GMT ETag: "009b79832d68313dd45ca6aab0528b34f9054713" Last-Modified: Fri, 29 Jun 2018 16:11:16 GMT Link: <http://localhost:8080/rest/test_redirect_remote_file/fcr:metadata>; rel="describedby"; anchor="http://localhost:8080/rest/test_redirect_remote_file" Link: <http://localhost:8080/static/constraints/NonRDFSourceConstraints.rdf>; rel="http://www.w3.org/ns/ldp#constrainedBy" Content-Location: http://localhost:8111/wonderful.jp2 Link: <http://localhost:8080/rest/test_redirect_remote_file/fcr:acl>; rel="acl" Location: http://localhost:8080/rest/test_redirect_remote_file Content-Type: text/plain Content-Length: 52 Server: Jetty(9.3.1.v20150714) http://localhost:8080/rest/test_redirect_remote_file
Results of a request
> curl -i http://localhost:8080/rest/test_redirect_remote_file -ufedoraAdmin:fedoraAdmin -L HTTP/1.1 307 Temporary Redirect Date: Fri, 29 Jun 2018 16:11:59 GMT Set-Cookie: JSESSIONID=cg9yt3o4whnmmxe9vllwerdz;Path=/ Expires: Thu, 01 Jan 1970 00:00:00 GMT Set-Cookie: rememberMe=deleteMe; Path=/; Max-Age=0; Expires=Thu, 28-Jun-2018 16:11:59 GMT ETag: "009b79832d68313dd45ca6aab0528b34f9054713" Last-Modified: Fri, 29 Jun 2018 16:11:16 GMT Content-Type: image/jp2 Accept-Ranges: bytes Content-Disposition: attachment; filename=""; creation-date="Fri, 29 Jun 2018 16:11:16 GMT"; modification-date="Fri, 29 Jun 2018 16:11:16 GMT"; size=305517 Link: <http://www.w3.org/ns/ldp#Resource>;rel="type" Link: <http://www.w3.org/ns/ldp#NonRDFSource>;rel="type" Link: <http://localhost:8080/rest/test_redirect_remote_file/fcr:acl>; rel="acl" Content-Location: http://localhost:8111/wonderful.jp2 Link: <http://localhost:8080/rest/test_redirect_remote_file/fcr:metadata>; rel="describedby" Link: <http://localhost:8080/static/constraints/NonRDFSourceConstraints.rdf>; rel="http://www.w3.org/ns/ldp#constrainedBy" Accept-External-Content-Handling: copy,redirect,proxy Allow: DELETE,HEAD,GET,PUT,OPTIONS Location: http://localhost:8111/wonderful.jp2 Content-Length: 305517 Server: Jetty(9.3.1.v20150714) HTTP/1.1 200 OK Date: Fri, 29 Jun 2018 16:12:59 GMT Server: Apache/2.4.29 (Unix) PHP/7.2.4 Last-Modified: Fri, 29 Jun 2018 16:09:29 GMT ETag: "4a96d-56fca128f2040" Accept-Ranges: bytes Content-Length: 305517 ...<BODY CONTENT>...
Copy a remote resource
Create the LDP-NR using external content
> curl -i -H"Link: <http://localhost:8111/wonderful.jp2>; rel=\"http://fedora.info/definitions/fcrepo#ExternalContent\"; handling=\"copy\"; type=\"image/jp2\"" -XPUT -ufedoraAdmin:fedoraAdmin http://localhost:8080/rest/test_copy_remote_file HTTP/1.1 201 Created Date: Fri, 29 Jun 2018 16:19:45 GMT Set-Cookie: JSESSIONID=1hmga57f6q5hh1td785dghsjfh;Path=/ Expires: Thu, 01 Jan 1970 00:00:00 GMT Set-Cookie: rememberMe=deleteMe; Path=/; Max-Age=0; Expires=Thu, 28-Jun-2018 16:19:45 GMT ETag: "d9cc4f3b266a19f0c225356a5caabb9080d680b4" Last-Modified: Fri, 29 Jun 2018 16:19:45 GMT Link: <http://localhost:8080/rest/test_copy_remote_file/fcr:metadata>; rel="describedby"; anchor="http://localhost:8080/rest/test_copy_remote_file" Link: <http://localhost:8080/static/constraints/NonRDFSourceConstraints.rdf>; rel="http://www.w3.org/ns/ldp#constrainedBy" Link: <http://localhost:8080/rest/test_copy_remote_file/fcr:acl>; rel="acl" Location: http://localhost:8080/rest/test_copy_remote_file Content-Type: text/plain Content-Length: 48 Server: Jetty(9.3.1.v20150714) http://localhost:8080/rest/test_copy_remote_file
Results of a request
> curl -i http://localhost:8080/rest/test_copy_remote_file -ufedoraAdmin:fedoraAdmin HTTP/1.1 200 OK Date: Fri, 29 Jun 2018 16:39:56 GMT Set-Cookie: JSESSIONID=h0ywas10h63p1340ajakqp1vy;Path=/ Expires: Thu, 01 Jan 1970 00:00:00 GMT Set-Cookie: rememberMe=deleteMe; Path=/; Max-Age=0; Expires=Thu, 28-Jun-2018 16:39:56 GMT ETag: "d9cc4f3b266a19f0c225356a5caabb9080d680b4" Last-Modified: Fri, 29 Jun 2018 16:19:45 GMT Content-Type: image/jp2 Accept-Ranges: bytes Content-Disposition: attachment; filename=""; creation-date="Fri, 29 Jun 2018 16:19:45 GMT"; modification-date="Fri, 29 Jun 2018 16:19:45 GMT"; size=305517 Link: <http://www.w3.org/ns/ldp#Resource>;rel="type" Link: <http://www.w3.org/ns/ldp#NonRDFSource>;rel="type" Link: <http://localhost:8080/rest/test_copy_remote_file/fcr:acl>; rel="acl" Link: <http://localhost:8080/rest/test_copy_remote_file/fcr:metadata>; rel="describedby" Link: <http://localhost:8080/static/constraints/NonRDFSourceConstraints.rdf>; rel="http://www.w3.org/ns/ldp#constrainedBy" Accept-External-Content-Handling: copy,redirect,proxy Allow: DELETE,HEAD,GET,PUT,OPTIONS Cache-Control: no-transform, must-revalidate, max-age=0 Content-Length: 305517 Server: Jetty(9.3.1.v20150714) ...<BODY CONTENT>...
