How To Pass Multiple Parameters In A URL To Plug
Solution 1
The URL structure you want to use is not really well-formed. And therefore your issue is framework-agnostic, because almost all frameworks/libraries will have a problem to parse the URL in your intended way.
/uid=ToddFlanders&pwd=MyTestPword
is treated as a path without any query parameters.
PATH: /uid=ToddFlanders&pwd=MyTestPword
QUERY STRING: (empty/unset)
QUERY PARAMS: [ ]
I guess you really want to have something like /?uid=ToddFlanders&pwd=MyTestPword
.
PATH: /
QUERY STRING: uid=ToddFlanders&pwd=MyTestPword
QUERY PARAMS: [ uid: "ToddFlanders", pwd: "MyTestPword" ]
Furthermore Plug.Conn.Utils.params/1
is intended to parse header parameters. Use Plug.Conn.Query.decode/1
for query parameters instead.
So, in your example I would suggest to adjust the application code as following:
defmodule Sci do
import Plug.Conn
use Plug.Router
@userid "uid"
@password "pwd"
plug :match
plug :dispatch
get "/" do
conn = fetch_params(conn) # populates conn.params
%{ @userid => usr, @password => pass } = conn.params
send_resp(conn, 200, "Hello #{usr}. Your password is #{pass}")
end
match _ do
send_resp(conn, 404, "oops")
end
def start do
Plug.Adapters.Cowboy.http Sci, [], port: 4000
end
def stop do
Plug.Adapters.Cowboy.shutdown Sci.HTTP
end
end
And then you can successfully try http://localhost:4000/?uid=ToddFlanders&pwd=MyTestPword
.
(Also it should not hit the match(_)
function, because /
should always match if you do the request to this path properly.
Solution 2
I'm not versatile with Plug, but for a demo code, I used fetch_params/1 and then conn.params["foo"]
, conn.params["bar"]
and so on, and this definitely worked.
Update: since Plug 0.12.0, fetch_query_params/2 should be used
Solution 3
You should use fetch_query_params
now.
https://hexdocs.pm/plug/Plug.Conn.html#fetch_query_params/2
Onorio Catenacci
I've been writing software for 25+ years now. I pursue ornithology as an avocation. If you want to contact me, contact me via my blog. http://onor.io av00M52Kg330gF5G
Updated on June 04, 2022Comments
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Onorio Catenacci almost 2 years
So I'm trying to pass multiple parameters in a URL to plug. This is the URL I'm using for testing:
http://localhost:4000/uid=ToddFlanders&pwd=MyTestPword
And this is the code:
defmodule Sci do @userid "uid" @password "pwd" import Plug.Conn import Plug.Conn.Utils use Plug.Router plug :match plug :dispatch get "/:args" do %{@userid => usr} = params(args) %{@password => pass} = params(args) send_resp(conn, 200, "Hello #{usr}. Your password is #{pass}") end match _ do send_resp(conn, 404, "oops") end def start do Plug.Adapters.Cowboy.http Sci, [], port: 4000 end def stop do Plug.Adapters.Cowboy.shutdown Sci.HTTP end end
If I pass just one argument (either uid or pwd) it matches fine. If I remove the
?
at the front of the query string it fails--throws an exception.I also tried this:
get "/:args" do %{@userid => usr, @password => pass} = params(args)
Also didn't work. So two questions:
1.) Is that the right way to pass multiple parameters in a URL?
2.) Is there some trick to get plug to see both parameters?
Any thoughts or insights would be welcome--even a suggestion of a better way to do this.
Elixir v0.15.1 and Plug v0.5.1
EDIT:
Adding a stacktrace per Jose's comment:
iex(2)> 07:46:56.499 [error] Error in process <0.232.0> with exit value: {[{reason,{badmatch,#{}}},{mfa,{'Elixir.Plug.Adapters.Cowboy.Handler',init,3}},{stacktrace,[{'Elixir.Sci','-do_match/2-fun-0-',2,[{file,"lib/sci.ex"},{line,18}]},{'Eli xir.Sci',call,2,[{file,"lib/sci.ex"},{line,1}]},{'Elixir.Plug.Adapters.Cowboy.Handler'... iex(2)> 07:46:56.510 [error] Ranch listener Sci.HTTP had connection process started with :cowboy_protocol:start_link/4 at #PID<0.232.0> exit with reason: {[reason: {:badmatch, %{}}, mfa: {Plug.Adapters.Cowboy.Handler, :init, 3}, stacktrace: [{Sci, :"-do_match/2-fun-0-", 2, [file: 'lib/sci.ex', line: 18]}, {Sci, :call, 2, [file: 'lib/sci.ex', line: 1]}, {Plug.Adapters.Cowboy.Handler, :init, 3, [file: 'lib/plug/adapters/cowboy/handler.ex', line: 7]}, {:cowboy_handler, :handler_ init, 4, [file: 'src/cowboy_handler.erl', line: 64]}, {:cowboy_protocol, :execute, 4, [file: 'src/cowboy_protocol.erl', line: 435]}], req: [socket: #Port<0.5168>, transport: :ranch_tcp, connection: :keepalive, pid: #PID<0.232.0>, method: "G ET", version: :"HTTP/1.1", peer: {{127, 0, 0, 1}, 63880}, host: "localhost", host_info: :undefined, port: 4000, path: "/uid=ToddFlanders&pwd=MyTestPassword", path_info: :undefined, qs: "", qs_vals: :undefined, bindings: [], headers: [{"host ", "localhost:4000"}, {"connection", "keep-alive"}, {"cache-control", "max-age=0"}, {"accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8"}, {"user-agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/53 7.36 (KHTML, like Gecko) Chrome/35.0.1916.153 Safari/537.36"}, {"accept-encoding", "gzip,deflate,sdch"}, {"accept-language", "en-US,en;q=0.8"}], p_headers: [{"connection", ["keep-alive"]}], cookies: :undefined, meta: [], body_state: :waitin g, buffer: "", multipart: :undefined, resp_compress: false, resp_state: :waiting, resp_headers: [], resp_body: "", onresponse: :undefined], opts: {Sci, []}], [{:cowboy_protocol, :execute, 4, [file: 'src/cowboy_protocol.erl', line: 435]}]} iex(2)> 07:46:56.969 [error] Error in process <0.233.0> with exit value: {[{reason,{badmatch,#{}}},{mfa,{'Elixir.Plug.Adapters.Cowboy.Handler',init,3}},{stacktrace,[{'Elixir.Sci','-do_match/2-fun-0-',2,[{file,"lib/sci.ex"},{line,18}]},{'Eli xir.Sci',call,2,[{file,"lib/sci.ex"},{line,1}]},{'Elixir.Plug.Adapters.Cowboy.Handler'... iex(2)> 07:46:56.971 [error] Ranch listener Sci.HTTP had connection process started with :cowboy_protocol:start_link/4 at #PID<0.233.0> exit with reason: {[reason: {:badmatch, %{}}, mfa: {Plug.Adapters.Cowboy.Handler, :init, 3}, stacktrace: [{Sci, :"-do_match/2-fun-0-", 2, [file: 'lib/sci.ex', line: 18]}, {Sci, :call, 2, [file: 'lib/sci.ex', line: 1]}, {Plug.Adapters.Cowboy.Handler, :init, 3, [file: 'lib/plug/adapters/cowboy/handler.ex', line: 7]}, {:cowboy_handler, :handler_ init, 4, [file: 'src/cowboy_handler.erl', line: 64]}, {:cowboy_protocol, :execute, 4, [file: 'src/cowboy_protocol.erl', line: 435]}], req: [socket: #Port<0.5174>, transport: :ranch_tcp, connection: :keepalive, pid: #PID<0.233.0>, method: "G ET", version: :"HTTP/1.1", peer: {{127, 0, 0, 1}, 63881}, host: "localhost", host_info: :undefined, port: 4000, path: "/favicon.ico", path_info: :undefined, qs: "", qs_vals: :undefined, bindings: [], headers: [{"host", "localhost:4000"}, {" connection", "keep-alive"}, {"accept", "*/*"}, {"user-agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/35.0.1916.153 Safari/537.36"}, {"accept-encoding", "gzip,deflate,sdch"}, {"accept-language", "e n-US,en;q=0.8"}], p_headers: [{"connection", ["keep-alive"]}], cookies: :undefined, meta: [], body_state: :waiting, buffer: "", multipart: :undefined, resp_compress: false, resp_state: :waiting, resp_headers: [], resp_body: "", onresponse: :undefined], opts: {Sci, []}], [{:cowboy_protocol, :execute, 4, [file: 'src/cowboy_protocol.erl', line: 435]}]}
EDIT 2: I had jotted down the wrong URL above; that's now corrected. Also to add to the question, if I make the URL this:
http://localhost:4000/?uid=ToddFlanders&pwd=MyTestPword
, the code jumps down to thematch _ do
clause -
Onorio Catenacci over 9 yearsIt's a good suggestion but it still doesn't seem to be working. Could you point me to your demo code?
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sasajuric over 9 yearsI don't have it online, but here's a sketch: gist.github.com/sasa1977/99cc0526f5b4dd903e21
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Onorio Catenacci over 9 yearsThat doesn't seem to do it either Sasa. I'd paste the stacktrace up here but I get the feeling that I'm missing something very obvious.
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sasajuric over 9 yearsHere's the working demo: gist.github.com/sasa1977/1917609ecd6127f736e6. I've just tried with Elixir 0.15.0 and Plug 0.6. Include it in your mix project, make sure you call Web.start_server from somewhere, and try it out. I can't see your code, so a blind guess - are you threading connection while handling a request? This is crucial, because every operation (such as fetch_params) returns a modified conn struct. If you run fetch_params, but then look into the previous version of conn struct, you won't find those params there. You have to use the result of fetch_params (new conn).
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Onorio Catenacci over 9 yearsI'll take a look at the working demo when I get a chance; thanks for your assistance Sasa!
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Onorio Catenacci over 9 yearsOk, I have to admit the difference between header parameters and query parameters wasn't clear to me but after having read your response (among those others) I see that I was mixing up the two ideas.
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CoderDennis about 8 yearsThe docs link in this answer now leads to a 404 and I'm getting
(UndefinedFunctionError) undefined function Plug.Conn.fetch_params/1
. Was this function replaced by something else? (P.S. I'm enjoying your book!) -
CoderDennis about 8 years
fetch_query_params
looks like the actual function name. -
sasajuric about 8 years@CoderDennis Yes, this happened at 0.12.0, see github.com/elixir-lang/plug/blob/…. I'll update the answer, thanks for pointing this out. (P.S. glad you like the book :-) )