party/cmd/api/helpers.go

package main

import (
	"net/http"
	"encoding/json"
	"strings"
	"errors"
	"fmt"
	"io"
	"net/url"
	"strconv"
	"party.at/party/internal/validator"
	"github.com/julienschmidt/httprouter"
	
)

type envelope map[string]interface{}

func (app *application) readString(qs url.Values, key string, defaultValue string) string {
	// Extract the value for a given key from the query string. If no key exists this
	// will return the empty string "".
	s := qs.Get(key)
	// If no key exists (or the value is empty) then return the default value.
	if s == "" {
		return defaultValue
	}

	// Otherwise return the string.
	return s
}

func (app *application) readCSV(qs url.Values, key string, defaultValue []string) []string {
	// Extract the value from the query string.
	csv := qs.Get(key)

	// If no key exists (or the value is empty) then return the default value.
	if csv == "" {
		return defaultValue
	}

	// Otherwise parse the value into a []string slice and return it.
	return strings.Split(csv, ",")
}

func (app *application) readInt(qs url.Values, key string, defaultValue int, v *validator.Validator) int {
	// Extract the value from the query string.
	s := qs.Get(key)

	// If no key exists (or the value is empty) then return the default value.
	if s == "" {
		return defaultValue
	}

	// Try to convert the value to an int. If this fails, add an error message to the
	// validator instance and return the default value.
	i, err := strconv.Atoi(s)
	if err != nil {
		v.AddError(key, "must be an integer value")
		return defaultValue
	}

	// Otherwise, return the converted integer value.
	return i
}

func (app *application) readIDParam(r *http.Request) (int64, error) {
	params := httprouter.ParamsFromContext(r.Context())

	id, err := strconv.ParseInt(params.ByName("id"), 10, 64)
	if err != nil || id < 1 {
		return 0, errors.New("invalid id parameter")
	}

	return id, nil
}

func (app *application) writeJSON(w http.ResponseWriter, status int, data envelope, headers http.Header) error {
	// Encode the data to JSON, returning the error if there was one.
	js, err := json.MarshalIndent(data, "", "\t")
	if err != nil {
		return err
	}


	// Append a newline to make it easier to view in terminal applications.
	js = append(js, '\n')


	// At this point, we know that we won't encounter any more errors before writing the
	// response, so it's safe to add any headers that we want to include. We loop
	// through the header map and add each header to the http.ResponseWriter header map.
	// Note that it's OK if the provided header map is nil. Go doesn't throw an error
	// if you try to range over (or generally, read from) a nil map.
	for key, value := range headers {
		w.Header()[key] = value
	}


	// Add the "Content-Type: application/json" header, then write the status code and
	// JSON response.
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	w.Write(js)
	
	return nil
}

func (app *application) readJSON(w http.ResponseWriter, r *http.Request, dst interface{}) error {
	maxBytes := 1048576

	r.Body = http.MaxBytesReader(w, r.Body, int64(maxBytes))

	// Initialize the json.Decoder, and call the DisallowUnknownFields() method on it
	// before decoding. This means that if the JSON from the client now includes any
	// field which cannot be mapped to the target destination, the decoder will return
	// an error instead of just ignoring the field.
	dec := json.NewDecoder(r.Body)
	dec.DisallowUnknownFields()
	// Decode the request body to the destination.
	err := dec.Decode(dst)
	if err != nil {
		var syntaxError *json.SyntaxError
		var unmarshalTypeError *json.UnmarshalTypeError
		var invalidUnmarshalError *json.InvalidUnmarshalError
		
		switch {
			case errors.As(err, &syntaxError):
				return fmt.Errorf("body contains badly-formed JSON (at character %d)", syntaxError.Offset)
		
			case errors.Is(err, io.ErrUnexpectedEOF):
				return errors.New("body contains badly-formed JSON")

			case errors.As(err, &unmarshalTypeError):
				if unmarshalTypeError.Field != "" {
					return fmt.Errorf("body contains incorrect JSON type for field %q", unmarshalTypeError.Field)
				}
	
				return fmt.Errorf("body contains incorrect JSON type (at character %d)", unmarshalTypeError.Offset)

			case errors.Is(err, io.EOF):
				return errors.New("body must not be empty")

			// If the JSON contains a field which cannot be mapped to the target destination
			// then Decode() will now return an error message in the format "json: unknown
			// field "<name>"". We check for this, extract the field name from the error,
			// and interpolate it into our custom error message. Note that there's an open
			// issue at https://github.com/golang/go/issues/29035 regarding turning this
			// into a distinct error type in the future.
			case strings.HasPrefix(err.Error(), "json: unknown field "):
				fieldName := strings.TrimPrefix(err.Error(), "json: unknown field ")
				return fmt.Errorf("body contains unknown key %s", fieldName)

				
			// If the request body exceeds 1MB in size the decode will now fail with the
			// error "http: request body too large". There is an open issue about turning
			// this into a distinct error type at https://github.com/golang/go/issues/30715.
			case err.Error() == "http: request body too large":
				return fmt.Errorf("body must not be larger than %d bytes", maxBytes)
	
			case errors.As(err, &invalidUnmarshalError):
				panic(err)
			
			default:
				return err
		}
	}

	// Call Decode() again, using a pointer to an empty anonymous struct as the
	// destination. If the request body only contained a single JSON value this will
	// return an io.EOF error. So if we get anything else, we know that there is
	// additional data in the request body and we return our own custom error message.
	err = dec.Decode(&struct{}{})
	if err != io.EOF {
		return errors.New("body must only contain a single JSON value")
	}

	return nil
}

func (app *application) background(fn func()) {
	// Launch a background goroutine.
	go func() {
		// Recover any panic.
		defer func() {
			if err := recover(); err != nil {
				app.logger.PrintError(fmt.Errorf("%s", err), nil)
			}
		}()

		// Execute the arbitrary function that we passed as the parameter.
		fn()
	}()
}