Storing and retrieving photo files from riak through nitrogen using riak-erlang-client

Question

I am running a riak cluster of 5 nodes which i connect to through a protocol buffer client riak-erlang-client. I installed riak-erlang-client as a nitrogen plugin as i suggested at this stackoverflow link. I know how to upload files through the nitrogen web-framework after then i try to store them in the riak database and later i retrieve them.

I have looked at this highlight shown at Basho resources

curl -XPUT http://localhost:10018/buckets/images/keys/<image_name>.jpg -H 'Content-Type: image/jpeg' --data-binary @<image_name>.jpg

But it is not meeting my needs at all since it does not even use the client i am using!!

I have ever used the file libraries of Erlang/OTP to read photo files from the ./scratch directory of nitrogen so as to save the photo files a binary streams in the riak database but i failed to retrieve them to my nitrogen driven web application.

Any help is welcomed.

What code have you written so far? How does it fail? Do you get an error message? — legoscia, Jan 22 '15 at 16:09
When you stored them via the protocol buffer client, did you add a content type to the metadata so the web app knows how to handle them? — Joe, Jan 22 '15 at 20:18
@legoscia @Joe I use `{ok, Binary} = file:read_file(Filename)` to read the photo file as a binary stream, then i use `Obj = riakc_obj:new(<<"images">>,<<"Filename">>,Binary)`. I have used these functions `Obj2 = riakc_obj:update_content_type(Obj,<<"image/jpeg">>)` and finally `riakc_pb_socket:put(Pid,Obj2)`. Now retrieving and deserialize the object: `{ok, Obj3} = riakc_pb_socket:get(Pid, <<"images">>, <<"Filename">>),Val = binary_to_term(riakc_obj:get_value(Obj3)), CT = riakc_obj:get_content_type(Obj3)`. How do i use `#image{}`,Val, CT to render the image in the nitrogen page? — Vianney Sserwanga, Jan 23 '15 at 03:41
`binary_to_term(riakc_obj:get_value(Obj3))` doesn't seem right - you should get back exactly what you put it, i.e. binary image data, not a binary-encoded erlang term. — Joe, Jan 23 '15 at 15:00

Vianney Sserwanga · Answer 1 · 2018-11-04T14:05:35.613

First add the riak-erlang-client to Nitrogen as a Plugin using rebar. Add a dependency like the one below to the rebar.config in your project. Basho resource

{deps, [
    {riakc, "1.4.1",
      {git, "git://github.com/basho/riak-erlang-client", 
         {tag, "1.4.1"}}}
   ]}.

Then run make in your application

cd ../../myapp
make

Upload the file using for example this Nitrogen upload example. The source code if found here.

In the finish_upload_event section capture the LocalFileName file path in the scratch folder. Use the file path to read the file.

event(_) -> ok.

start_upload_event(Tag) ->
    wf:flash(wf:f("Upload started with tag (~p)", [Tag])).

finish_upload_event(_Tag, undefined, _, _) -> 
   wf:flash("Please select a file."), ok;

finish_upload_event(_Tag, _FileName, LocalFileName, _Node) ->
   {ok, Binary_image} = file:read_file(LocalFileName),

   %% Open a connection to the Riak database
   {ok, Pid} = riakc_pb_socket:start(DBNode,PORT,{connect_timeout,TIMEOUT},auto_reconnect, false}])).

   %% If the bucket where you save your images is called my_images, create the riak object
   Obj = riakc_obj:new(term_to_binary(my_images),term_to_binary(My_key),Binary_image),

   %% Save to the database
   ok = riakc_pb_socket:put(Pid, Obj,[]).

To read the image from the database and display it in the web browser

-module(image).
-include_lib("nitrogen_core/include/wf.hrl").
-compile(export_all).   

main() -> 
   %% Set the content-type of the image
   wf:content_type("image/png"),
   {ok, Pid} = riakc_pb_socket:start(DBNode,PORT,{connect_timeout,TIMEOUT},auto_reconnect, false}])).

   %% Read the image data from the database
   {ok, Fetched} = riakc_pb_socket:get(Pid,     term_to_binary(my_images),term_to_binary(My_key),[]),

   %% Record the image record
   Binary_image = binary_to_term(riakc_obj:get_value(Fetched)),
   Binary_image.        

event(_) -> ok.

In the browser structure your URL to the image file like http://example.com/image

Where image is the module rendering the image file.

Storing and retrieving photo files from riak through nitrogen using riak-erlang-client

1 Answers1