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I always like to check my form fields to see if their values are convertible to needed types and if not then inform the user about invalid fields. form produces *errors.errorString and this is not useful when generating error responses for this purpose.

What about defining a new error type such as below to give more control over them

e.g.

type Error []Field

func (e Error) Error() string {
  return "todo"
}

type Field struct {
  Name string // tag name e.g. time from form:"time"
  Message string // original error message 
  Type reflect.Type // point out the expected type so we can generate even more graceful error messages by checking this e.g. "time must be a UTC date"
  SliceIndex int // point out the index if an invalid Type placed in a slice except []byte
}

A dummy usage:

type Post struct {
  Time time.Time `form:"time"`
}

var p Post
err := form.DecodeValues(&p, url.Values{"time", []string{"AnInvalidDate"}})
if (err.(form.Error))[0].Type == form.TimeType {
 // so I can response a nice error message to user like:
 // HTTP 400
 // {"message": "Invalid Form Data", fields: {"time": "must be UTC formatted"}}
}

I'd like to implement this if you'll consider accepting the PR

Is possible parse anonimous fields without prefix if it's tag ommited or empty string (like json)?

Example:

package main

import (
	"encoding/json"
	"fmt"

	"github.com/ajg/form"
)

type T1 struct {
	X int `json:"x,omitempty" form:"x,omitempty"`
	Y int `json:"y,omitempty" form:"y,omitempty"`
}

type T2 struct {
	*T1 `json:"" form:""`
	A   int `json:"a,omitempty" form:"a,omitempty"`
	B   int `json:"b,omitempty" form:"b,omitempty"`
}

type T3 struct {
	*T1 `json:"t1" form:"t1"`
	A   int `json:"a,omitempty" form:"a,omitempty"`
	B   int `json:"b,omitempty" form:"b,omitempty"`
}

func main() {
	x := T2{&T1{1, 2}, 3, 4}
	s, _ := json.Marshal(x)
	s2, _ := form.EncodeToString(x)
	fmt.Println(string(s), s2)

	x2 := T3{&T1{1, 2}, 3, 4}
	s, _ = json.Marshal(x2)
	s2, _ = form.EncodeToString(x2)
	fmt.Println(string(s), s2)
}

Output:

{"x":1,"y":2,"a":3,"b":4} T1.x=1&T1.y=2&a=3&b=4
{"t1":{"x":1,"y":2},"a":3,"b":4} a=3&b=4&t1.x=1&t1.y=2

Second result is ok, but in first best result is "x=1&y=2&a=3&b=4"

Hi,
I have this:
type Film struct {
Genres []string
Topics []string
}

I am obliged to indicate the index of slice in the input form:

Is possible NOT indicate the index and only leave "Topics"? With gorilla/schema it is possible, but gorilla/schema, in general, is much more limited...

Thanks!

Best,
Emilio

It would be nice to have the ability to encode files in the form data.

For example, we could have a special struct tag that indicates this field represents a file path.

Hi!
In the app that I created found a problem. I use a lot of this library, it allow so much fields but not anonymous fields. For example, i have in my project a two structs:

type Length struct {
    Title        map[string]string `json:"title"`
    Release  map[string]string `json:"release,omitempty"`
    Genres   Genre                  `json:"genres"`
    Topics    []string                 `json:"genres"`
}

type FilmBasedEpisodes struct {
    Length
    Channel  Channel
    Seasons  []Season
}

But when I want do this:

....
r.ParseMultipartForm(maxMemory)
dataFormHTML := r.Form
film := FilmBasedEpisodes{}
err := form.DecodeValues(&film, dataFormHTML)
....

The content of dataFormHTML is, for example, like this:

"Title.US":"Six Feet Under", "Title.ES": "A dos metros bajo tierra", "Channel.Original":"HBO"

The error from ajg.form in go compiler is : Title doesn't exist in struct main.FilmBasedEpisodes

I understand that the library not is compatible with anonymous fields, right? If I wrong, then, how I do it?

Best,
Emilio

A particular third-party API I wish to contact used periods in the key names. I have the keys in my structs labelled as such:

type whatever struct {
CleanupReturnCleaned bool form:"cleanup.returnCleaned"
}

but when I run form.EncodeToString() I get:
cleanup%5C.returnCleaned=true

I've read the documentation in the Readme and have tried escaping the period with a back slash but that doesnt seem to have the desired effect. Am I misreading the readme, or is this not possible using ajg/form?

Cheers!

http://semver.org/
https://dave.cheney.net/2016/06/24/gophers-please-tag-your-releases

Due to the intentional special casing of periods within form, any API which uses periods in a form field cannot be interacted with without some hacks. For example, the fastly API utilizes periods in their form fields: https://docs.fastly.com/api/config#settings_9740ff4ac0c1777f455274c4850ece23

The go-fastly library attempted to work around this by manually ripping out the generated escapes, but that leads to other things being unintentionally ripped out, as noted in this case: fastly/go-fastly#11

Is there any workaround for interacting with forms which have periods in their form keys?

The implementation of isEmptyValue makes encoding certain structs a bit non-intuitive. Similar to the discussion here, I am trying to encode a 0 in a request.

I would expect the following code to result in "num=0&name=test" but instead I end up with "num=&name=test" even though my value does "exist".

package main

import (
    "bytes"
    "github.com/ajg/form"
    "log"
)

type Thing struct {
    String  string `form:"name,omitempty"`
    Integer *uint  `form:"num,omitempty"`
}

func main() {

    a_num := uint(0)
    u := Thing{"test", &a_num}
    buf := new(bytes.Buffer)
    if err := form.NewEncoder(buf).DelimitWith('|').Encode(u); err != nil {
        log.Printf("[ERR] %s", err)
    }
    body := buf.String()
    log.Printf("[DEBUG] %s", body)

}

The library fails to decode a struct if field is missing.

E.g. I do have a struct

type TokenExchange struct {
  Type string `form:"grant_type"`
  Code string `form:"code"`
}

The input string to parse

grant_type=authorization_code&code=xxx&client_id=xxx

The library fails to decode string with an error

client_id doesn't exist in main.TokenExchange

I would expect that library skips client_id.

It looks like the tests are failing on Go 1.17 and up around parsing semicolons.

There are a couple ways to resolve - one of them is using the Go handler: https://pkg.go.dev/net/http#AllowQuerySemicolons

Other suggestions: https://golangshowcase.com/question/invalid-semicolon-separator-in-query-after-go-1-17

➜  form git:(master) ✗ go test ./...
--- FAIL: TestDecodeString (0.00s)
    decode_test.go:17: DecodeString(";C=42%2B6.6i;A.0=x;M.Bar=8;F=6.6;A.1=y;R=8734;A.2=z;Zs.0.Qp=33_44;B=true;M.Foo=7;T=2013-10-01T07:05:34.000000088Z;E.Bytes1=%00%01%02;Bytes2=%03%04%05;Zs.0.Q=11_22;Zs.0.Z=2006-12-01;M.Qux=9;life=42;S=Hello,+there.;P\\.D\\\\Q\\.B.A=P/D;P\\.D\\\\Q\\.B.B=Q-B;U=http%3A%2F%2Fexample.org%2Ffoo%23bar;"): invalid semicolon separator in query
    decode_test.go:17: DecodeString(";C=42%2B6.6i;A.0=x;M.Bar=8;F=6.6;A.1=y;R=8734;A.2=z;Zs.0.Qp=33_44;B=true;M.Foo=7;T=2013-10-01T07:05:34.000000088Z;E.Bytes1=%00%01%02;Bytes2=%03%04%05;Zs.0.Q=11_22;Zs.0.Z=2006-12-01;M.Qux=9;life=42;S=Hello,+there.;P\\.D\\\\Q\\.B.A=P/D;P\\.D\\\\Q\\.B.B=Q-B;U=http%3A%2F%2Fexample.org%2Ffoo%23bar;"): invalid semicolon separator in query
    decode_test.go:17: DecodeString(";C=42%2B6.6i;A.0=x;M.Bar=8;F=6.6;A.1=y;R=8734;A.2=z;Zs.0.Qp=33_44;B=true;M.Foo=7;T=2013-10-01T07:05:34.000000088Z;E.Bytes1=%00%01%02;Bytes2=%03%04%05;Zs.0.Q=11_22;Zs.0.Z=2006-12-01;M.Qux=9;life=42;S=Hello,+there.;P\\.D\\\\Q\\.B.A=P/D;P\\.D\\\\Q\\.B.B=Q-B;U=http%3A%2F%2Fexample.org%2Ffoo%23bar;"): invalid semicolon separator in query
--- FAIL: TestDecodeValues (0.00s)
panic: invalid semicolon separator in query [recovered]
        panic: invalid semicolon separator in query
FAIL

It would be useful for my use case if both the encoder and decoder structs exposed a Reset method which allowed changing the underlying io.Writer or io.Reader without having to create new instances. This makes it possible to use sync.Pool for example to manage a set of instances. The implementation would be trivial given that they don't have state other than the writer or reader. Would you consider a PR that added these? I'm thinking something like:

in decode.go:

func (d *decoder) Reset(r io.Reader) {
    d.r = r
}

in encode.go

func (e *encoder) Reset(w io.Writer) {
    e.w = w
}

👋🏻 I have an API that expects data to be sent like so:

services[]=A&services[]=B

How can I achieve this?

Currently the default behaviour appears to number each element within the slice.

I see there's a DelimitWith method but that doesn't quite achieve what I need (e.g. DelimitWith('|')):

services|0=A&services|1=B

Is there a custom unmarshal method I can define that might help encode the data how I need it?

Thanks!

Please tag commit 9aeb3cf with v1.5.2. It simplify the lib usage with go mod and unlocks the latest.