struc2frm

README

struc2frm

Golang Struct to HTML Form

• Package struc2frm converts or transforms a
  golang struct into an HTML input form.

• Tired of the boilerplate?
  All your admin and backend forms generated directly from golang structs.

• Field info is taken from the json struct tag.

• Additional attributes are taken from the form struct tag

• Package does not provide parsing request forms into a struct type.
  For this, we recommend github.com/go-playground/form
  since it accepts json tags despite containing ,omitempty.

• github.com/go-playground/form also tolerates superfluous request fields -
  thus the submit button does not cause an error.

Example

type entryForm struct {
    Department  string `json:"department,omitempty"    form:"subtype='select',accesskey='p',onchange='true',title='loading items'"`
    Separator01 string `json:"separator01,omitempty"   form:"subtype='separator'"`
    HashKey     string `json:"hashkey,omitempty"       form:"maxlength='16',size='16',suffix='changes randomness'"`
    Groups      int    `json:"groups,omitempty"        form:"min=1,max='100',maxlength='3',size='3'"`
    Items       string `json:"items,omitempty"         form:"subtype='textarea',cols='22',rows='12',maxlength='4000',title='add times - delimited by newline (enter)'"`
    Group01     string `json:"group01,omitempty"       form:"subtype='fieldset'"`
    Date        string `json:"date,omitempty"          form:"subtype='date',nobreak=true,min='1989-10-29',max='2030-10-29'"`
    Time        string `json:"time,omitempty"          form:"subtype='time',maxlength='12',size='12'"`
    Group02     string `json:"group02,omitempty"       form:"subtype='fieldset'"`
    DateLayout  string `json:"date_layout,omitempty"   form:"accesskey='t',maxlength='16',size='16',pattern='[0-9\\.\\-/]{10}',placeholder='2006/01/02 15:04'"` // 2006-01-02 15:04
    CheckThis   bool   `json:"checkthis,omitempty"     form:"suffix='without consequence'"`

    // Requires distinct way of form parsing
    // Upload     []byte `json:"upload,omitempty"       form:"accesskey='u',accept='.xlsx'"`
}

// getting a converter
s2f := struc2frm.New()
s2f.ShowHeadline = true
s2f.AddOptions("department", []string{"ub", "fm"}, []string{"UB", "FM"})

// init values
frm := entryForm{
    HashKey: time.Now().Format("2006-01-02"),
    Groups:  4,
    Date:    time.Now().Format("2006-01-02"),
    Time:    time.Now().Format("15:04"),
}

// pulling in values from http request
dec := form.NewDecoder()
dec.SetTagName("json") // recognizes and ignores ,omitempty
err = dec.Decode(&frm, req.Form)
if err != nil {
    fmt.Fprintf(w, "Could not decode form: %v <br>\n", err)
}

// render to HTML
fmt.Fprint(w, s2f.HTML(frm))

Fully functional example code in directory systemtest

Select / dropdown inputs

• Use string field with subtype select

• Use size=1 or size=5 to determine the height

• Use AddOptions() to fill input[select] elements

• Use onchange='true'

Other field specifics

• Use float64 or int to create number inputs - with attributes min=1,max=100,step=2.
  Notice that step=2 defines maximum precision; uneven numbers become invalid.
  This is an HTML5 restriction.

• string, textarea, float64 and int fields have the attributes maxlength='16',size='16'

• string supports attributes placeholder='2006/01/02 15:04',pattern='[0-9\\.\\-/]{10}'
  to show a pattern to the user (placeholder)
  and to restrict the entry to a regular expression

• Use string field with subtype textarea and attributes cols='32',rows='22'

• Use string field with subtype date and attributes min='1989-10-29' or max=...

• Use string field with subtype time

• Use bool to create a checkbox

• Every string field with subtype separator is rendered into a horizontal line

• Every string field with subtype fieldset is rendered into grouping box with label

General

• Every field can have an attribute suffix=...

• Every field can have an attribute title=...
  for mouse-over tooltips

• Values of suffix=..., title=..., pattern=... need , instead of ,

• Every field can have an attribute accesskey='t'
  Accesskeys are not put into the label, but into the input tag

• Every field can have an attribute nobreak='true'
  so that the next input remains on the same line

File upload

• input[file] must have golang type []byte

• input[file] should be named upload
  and requires ParseMultipartForm() instead of ParseForm()

• ParseMultipartForm() and ExtractUploadedFile() are helper funcs
  to extract file upload data

Example

err := ParseMultipartForm(req)
if err != nil {
    fmt.Fprintf(w, "Cannot parse multi part form: %v<br>\n", err)
    return
}

type entryForm struct {
    TextField string `json:"text_field,omitempty"   form:"maxlength='16',size='16'"`
    // Requires distinct way of form parsing
    Upload []byte `json:"upload,omitempty"          form:"accesskey='u',accept='.txt',suffix='*.txt files'"`
}

s2f := New()
s2f.ShowHeadline = true
s2f.Indent = 80

// init values
frm := entryForm{
    TextField: "some-init-text",
}

dec := form.NewDecoder()
dec.SetTagName("json") // recognizes and ignores ,omitempty
err = dec.Decode(&frm, req.Form)
if err != nil {
    fmt.Fprintf(w, "Could not decode form: %v <br>\n", err)
}

bts, excelFileName, err := ExtractUploadedFile(req)
if err != nil {
    fmt.Fprintf(w, "Cannot extract file from POST form: %v<br>\n", err)
}

fileMsg := ""
if len(bts) > 0 && excelFileName != "" {
    fileMsg = fmt.Sprintf("%v bytes read from excel file -%v- <br>\n", len(bts), excelFileName)
    fileMsg = fmt.Sprintf("%vFile content is --%v-- <br>\n", fileMsg, string(bts))
} else {
    fileMsg = "No upload filename - or empty file<br>\n"

}

fmt.Fprintf(
    w,
    defaultHTML,
    s2f.HTML(frm),
    fileMsg,
)

See handler-file-upload_test.go on how to programmatically POST a file and key-values.

CSS Styling

Styling is done via CSS selectors
and can be customized
by changing or appending struc2frm.New().CSS

div.struc2frm {
    padding: 4px;
}
div.struc2frm  input {
    margin:  4px;
}

The media query CSS block in default struc2frm.New().CSS
can be used to change the label width depending on screen width.

Label width can also be changed by setting
via struc2frm.New().Indent and struc2frm.New().IndentAddenum to none-zero values.

div.struc2frm-34323168 H3 {
    margin-left: 116px; /* programmatically set via s3f.Indent for each form */
}

/* change specific inputs */
div.struc2frm label[for="time"] {
    min-width: 20px;
}
div.struc2frm select[name="department"] {
    background-color: darkkhaki;
}

Submit button

If your form only has select inputs with onchange='this.form.submit()'
then no submit button is shown.

This can be overridden by setting struc2frm.New().ShowSubmit to true.

Technical stuff

Language	files	blank	comment	code
Go	5	123	68	672
Markdown	1	61	0	150
CSS	1	26	8	120
HTML	1	6	1	30

• Default CSS is init-loaded from an in-package file default.css,
  mostly to have syntax highlighting while editing it.

TODO

• Low Prio: Add field type option group
  meanwhile use select / dropdown

Documentation

Overview

Package struc2frm creates an HTML input form for a given struct type; see README.md for details.

Index

• func Decode(r *http.Request, ptr2Struct interface{}) error
• func ExtractUploadedFile(r *http.Request, names ...string) (bts []byte, fname string, err error)
• func FileUploadH(w http.ResponseWriter, req *http.Request)
• func FormH(w http.ResponseWriter, req *http.Request)
• func HTML(intf interface{}) template.HTML
• func New() *s2FT
• func ParseMultipartForm(r *http.Request) error

Functions

func Decode

func Decode(r *http.Request, ptr2Struct interface{}) error

Decode decodes the form into an instance of stuct and checks the

func ExtractUploadedFile

func ExtractUploadedFile(r *http.Request, names ...string) (bts []byte, fname string, err error)

ExtractUploadedFile extracts a file from an HTTP POST request. It needs the request form to be prepared with ParseMultipartForm.

func FileUploadH

func FileUploadH(w http.ResponseWriter, req *http.Request)

FileUploadH is an http handler func for file upload

func FormH

func FormH(w http.ResponseWriter, req *http.Request)

FormH is an example http handler func

func HTML

func HTML(intf interface{}) template.HTML

HTML takes a struct instance and uses the default formatter to turns it into an HTML form.

func New

func New() *s2FT

New converter

func ParseMultipartForm

func ParseMultipartForm(r *http.Request) error

ParseMultipartForm parses an HTTP request form with file attachments