form - form.go

  // Package form provides an easy to use way to parse form values from an HTTP
  // request into a struct.
  package form // import "vimagination.zapto.org/form"
  
  import (
  	"net/http"
  	"reflect"
  	"strings"
  	"sync"
  )
  
  var interType = reflect.TypeOf((*formParser)(nil)).Elem()
  
  type processorDetails struct {
  	processor
  	Post, Required bool
  	Index          []int
  }
  
  type typeMap map[string]processorDetails
  
  var (
  	tmMu     sync.RWMutex
  	typeMaps = make(map[reflect.Type]typeMap)
  )
  
  func getTypeMap(t reflect.Type) typeMap {
  	tmMu.RLock()
  	defer tmMu.RUnlock()
  
  	tm, ok := typeMaps[t]
  
  	if !ok {
  		tm = createTypeMap(t)
  	}
  
  	return tm
  }
  
  func basicTypeProcessor(t reflect.Type, tag reflect.StructTag) processor {
  	switch t.Kind() {
  	case reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Int:
  		return newInum(tag, t.Bits())
  	case reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uint:
  		return newUnum(tag, t.Bits())
  	case reflect.Float32, reflect.Float64:
  		return newFloat(tag, t.Bits())
  	case reflect.String:
  		return newString(tag)
  	case reflect.Bool:
  		return boolean{}
  	}
  
  	return nil
  }
  
  func createTypeMap(t reflect.Type) typeMap {
  	tm, ok := typeMaps[t]
  	if ok {
  		return tm
  	}
  
  	tm = make(typeMap)
  
  	for i := 0; i < t.NumField(); i++ {
  		f := t.Field(i)
  		if f.PkgPath != "" {
  			continue
  		}
  
  		name, required, post, ignore := parseTag(f.Name, f.Tag.Get("form"))
  		if ignore {
  			continue
  		}
  
  		p := createProcessor(f, tm, i)
  		if p == nil {
  			continue
  		}
  
  		tm[name] = processorDetails{
  			processor: p,
  			Required:  required,
  			Post:      post,
  			Index:     []int{i},
  		}
  	}
  
  	typeMaps[t] = tm
  
  	return tm
  }
  
  func parseTag(name, tag string) (string, bool, bool, bool) {
  	var required, post bool
  
  	if tag == "-" {
  		return "", false, false, true
  	} else if tag != "" {
  		if p := strings.IndexByte(tag, ','); p >= 0 {
  			if p > 0 {
  				name = tag[:p]
  			}
  
  			rest := tag[p:]
  			required = strings.Contains(rest, ",required,") || strings.HasSuffix(rest, ",required")
  			post = strings.Contains(rest, ",post,") || strings.HasSuffix(rest, ",post")
  		} else {
  			name = tag
  		}
  	}
  
  	return name, required, post, false
  }
  
  func createProcessor(f reflect.StructField, tm typeMap, i int) processor {
  	if f.Type.Implements(interType) {
  		return inter(false)
  	} else if reflect.PointerTo(f.Type).Implements(interType) {
  		return inter(true)
  	} else if k := f.Type.Kind(); k == reflect.Slice || k == reflect.Pointer {
  		return createSlicePtrProcessor(f, k)
  	} else if k == reflect.Struct && f.Anonymous {
  		return createMapProcessor(f, tm, i)
  	}
  
  	return basicTypeProcessor(f.Type, f.Tag)
  }
  
  func createSlicePtrProcessor(f reflect.StructField, k reflect.Kind) processor {
  	et := f.Type.Elem()
  
  	s := basicTypeProcessor(et, f.Tag)
  	if s == nil {
  		return nil
  	}
  
  	if k == reflect.Slice {
  		return slice{
  			processor: s,
  			typ:       reflect.SliceOf(et),
  		}
  	}
  
  	return pointer{
  		processor: s,
  		typ:       et,
  	}
  }
  
  func createMapProcessor(f reflect.StructField, tm typeMap, i int) processor {
  	for n, p := range createTypeMap(f.Type) {
  		if _, ok := tm[n]; !ok {
  			tm[n] = processorDetails{
  				processor: p.processor,
  				Required:  p.Required,
  				Post:      p.Post,
  				Index:     append(append(make([]int, 0, len(p.Index)+1), i), p.Index...),
  			}
  		}
  	}
  
  	return nil
  }
  
  // Process parses the form data from the request into the passed value, which
  // must be a pointer to a struct.
  //
  // Form keys are assumed to be the field names unless a 'form' tag is provided
  // with an alternate name, for example, in the following struct, the int is
  // parse with key 'A' and the bool is parsed with key 'C'.
  //
  //	type Example struct {
  //		A int
  //		B bool `form:"C"`
  //	}
  //
  // Two options can be added to the form tag to modify the processing. The
  // 'post' option forces the processor to parse a value from the PostForm field
  // of the Request, and the 'required' option will have an error thrown if the
  // key in not set.
  //
  // Number types can also have minimums and maximums checked during processing
  // by setting the 'min' and 'max' tags accordingly.
  //
  // In a similar vein, string types can utilise the 'regex' tag to set a
  // regular expression to be matched against.
  //
  // Anonymous structs are traversed, but will not override more local fields.
  //
  // Slices of basic types can be processed, and errors returned from any such
  // processing will be of the Errors type, which each indexed entry
  // corresponding to the index of the processed data.
  //
  // Pointers to basic types can also be processed, with the type being allocated
  // even if an error occurs.
  //
  // Lastly, a custom data processor can be specified by attaching a method to
  // the field type with the following specification:
  //
  // ParseForm([]string) error.
  func Process(r *http.Request, fv any) error {
  	v := reflect.ValueOf(fv)
  	if v.Kind() != reflect.Pointer {
  		return ErrNeedPointer
  	}
  
  	for v.Kind() == reflect.Pointer {
  		v = v.Elem()
  	}
  
  	if v.Kind() != reflect.Struct {
  		return ErrNeedStruct
  	}
  
  	tm := getTypeMap(v.Type())
  
  	if err := r.ParseForm(); err != nil {
  		return err
  	}
  
  	return processForm(r, v, tm)
  }
  
  func processForm(r *http.Request, v reflect.Value, tm typeMap) error {
  	var errors ErrorMap
  
  	for key, pd := range tm {
  		var (
  			val []string
  			ok  bool
  		)
  
  		if pd.Post {
  			val, ok = r.PostForm[key]
  		} else {
  			val, ok = r.Form[key]
  		}
  
  		if ok {
  			if err := pd.processor.process(v.FieldByIndex(pd.Index), val); err != nil {
  				if errors == nil {
  					errors = make(ErrorMap)
  				}
  
  				errors[key] = err
  			}
  		} else if pd.Required {
  			if errors == nil {
  				errors = make(ErrorMap)
  			}
  
  			errors[key] = ErrRequiredMissing
  		}
  	}
  
  	if len(errors) > 0 {
  		return errors
  	}
  
  	return nil
  }