MethodError when creating form request without headers

[Octogonapus]

This works fine (note the header):

HTTP.request(
    "POST",
    "http://localhost:8081",
    Dict("Authorization" => "Bearer as7das876das"),
    HTTP.Form(["files" => open("/dev/random", "r")]),
    response_stream=devnull,
)

However this throws a MethodError:

HTTP.request(
    "POST",
    "http://localhost:8081",
    HTTP.Form(["files" => open("/dev/random", "r")]),
    response_stream=devnull,
)

ERROR: MethodError: no method matching iterate(::HTTP.Forms.Form)

Closest candidates are:
  iterate(::Union{LinRange, StepRangeLen})
   @ Base range.jl:880
  iterate(::Union{LinRange, StepRangeLen}, ::Integer)
   @ Base range.jl:880
  iterate(::T) where T<:Union{Base.KeySet{<:Any, <:Dict}, Base.ValueIterator{<:Dict}}
   @ Base dict.jl:698
  ...

Stacktrace:
  [1] iterate
    @ ./iterators.jl:202 [inlined]
  [2] iterate
    @ ./iterators.jl:201 [inlined]
  [3] mkheaders(h::HTTP.Forms.Form, headers::Vector{Pair{SubString{String}, SubString{String}}})
    @ HTTP.Messages ~/.julia/packages/HTTP/SN7VW/src/Messages.jl:209
  [4] mkheaders(h::HTTP.Forms.Form)
    @ HTTP.Messages ~/.julia/packages/HTTP/SN7VW/src/Messages.jl:209
  [5] mkreqheaders(h::HTTP.Forms.Form, ch::Bool)
    @ HTTP.MessageRequest ~/.julia/packages/HTTP/SN7VW/src/clientlayers/MessageRequest.jl:15
  [6] (::HTTP.MessageRequest.var"#makerequest#3"{HTTP.MessageRequest.var"#makerequest#1#4"{HTTP.RedirectRequest.var"#redirects#3"{HTTP.RedirectRequest.var"#redirects#1#4"{HTTP.HeadersRequest.var"#defaultheaders#2"{HTTP.HeadersRequest.var"#defaultheaders#1#3"{HTTP.CookieRequest.var"#managecookies#4"{HTTP.CookieRequest.var"#managecookies#1#5"{HTTP.RetryRequest.var"#manageretries#3"{HTTP.RetryRequest.var"#manageretries#1#4"{HTTP.ConnectionRequest.var"#connections#4"{HTTP.ConnectionRequest.var"#connections#1#5"{HTTP.TimeoutRequest.var"#timeouts#3"{HTTP.TimeoutRequest.var"#timeouts#1#4"{HTTP.ExceptionRequest.var"#exceptions#2"{HTTP.ExceptionRequest.var"#exceptions#1#3"{typeof(HTTP.StreamRequest.streamlayer)}}}}}}}}}}}}}}}})(method::String, url::URIs.URI, headers::HTTP.Forms.Form, body::Vector{UInt8}; copyheaders::Bool, response_stream::Base.DevNull, http_version::HTTP.Strings.HTTPVersion, verbose::Int64, kw::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
    @ HTTP.MessageRequest ~/.julia/packages/HTTP/SN7VW/src/clientlayers/MessageRequest.jl:25
  [7] request(stack::HTTP.MessageRequest.var"#makerequest#3"{HTTP.MessageRequest.var"#makerequest#1#4"{HTTP.RedirectRequest.var"#redirects#3"{HTTP.RedirectRequest.var"#redirects#1#4"{HTTP.HeadersRequest.var"#defaultheaders#2"{HTTP.HeadersRequest.var"#defaultheaders#1#3"{HTTP.CookieRequest.var"#managecookies#4"{HTTP.CookieRequest.var"#managecookies#1#5"{HTTP.RetryRequest.var"#manageretries#3"{HTTP.RetryRequest.var"#manageretries#1#4"{HTTP.ConnectionRequest.var"#connections#4"{HTTP.ConnectionRequest.var"#connections#1#5"{HTTP.TimeoutRequest.var"#timeouts#3"{HTTP.TimeoutRequest.var"#timeouts#1#4"{HTTP.ExceptionRequest.var"#exceptions#2"{HTTP.ExceptionRequest.var"#exceptions#1#3"{typeof(HTTP.StreamRequest.streamlayer)}}}}}}}}}}}}}}}}, method::String, url::String, h::HTTP.Forms.Form, b::Vector{UInt8}, q::Nothing; headers::HTTP.Forms.Form, body::Vector{UInt8}, query::Nothing, kw::Base.Pairs{Symbol, Base.DevNull, Tuple{Symbol}, NamedTuple{(:response_stream,), Tuple{Base.DevNull}}})
    @ HTTP ~/.julia/packages/HTTP/SN7VW/src/HTTP.jl:457
  [8] #request#20
    @ ~/.julia/packages/HTTP/SN7VW/src/HTTP.jl:315 [inlined]
  [9] request
    @ ~/.julia/packages/HTTP/SN7VW/src/HTTP.jl:313 [inlined]

The docs seem to indicate this should be okay to do.

• Julia v1.9.4
• HTTP.jl v1.10.0
• MbelTLS.jl v1.1.8

[fredrikekre]

What in the docs do you refer to? To me it looks like headers is passed everywhere.

[Octogonapus]

Ah you're right, I missed it in the docs. So this is just meant to be a user error? The exception is confusing, maybe that could be improved?

[fredrikekre]

Yea I think it is just a victim of duck typing -- headers are allowed to be anything that iterates key-value pairs IIRC, and it isn't really possible to put a type restriction on it. Probably possible to make the error message better though.