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helpers.go
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/
helpers.go
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package main
import (
"encoding/json"
"errors"
"fmt"
"io"
"net/http"
"strings"
"qvidahl.no/thomas/comicbot/header"
)
type malformedRequest struct {
status int
msg string
}
func (mr *malformedRequest) Error() string {
return mr.msg
}
func decodeJSONBody(w http.ResponseWriter, r *http.Request, dst interface{}) error {
if r.Header.Get("Content-Type") != "" {
value, _ := header.ParseValueAndParams(r.Header, "Content-Type")
if value != "application/json" {
msg := "Content-Type header is not application/json"
return &malformedRequest{status: http.StatusUnsupportedMediaType, msg: msg}
}
}
r.Body = http.MaxBytesReader(w, r.Body, 1048576)
dec := json.NewDecoder(r.Body)
dec.DisallowUnknownFields()
err := dec.Decode(&dst)
if err != nil {
var syntaxError *json.SyntaxError
var unmarshalTypeError *json.UnmarshalTypeError
switch {
case errors.As(err, &syntaxError):
msg := fmt.Sprintf("Request body contains badly-formed JSON (at position %d)", syntaxError.Offset)
return &malformedRequest{status: http.StatusBadRequest, msg: msg}
case errors.Is(err, io.ErrUnexpectedEOF):
msg := fmt.Sprintf("Request body contains badly-formed JSON")
return &malformedRequest{status: http.StatusBadRequest, msg: msg}
case errors.As(err, &unmarshalTypeError):
msg := fmt.Sprintf("Request body continas an invalid value for the %q field ( at position %d)", unmarshalTypeError.Field, unmarshalTypeError.Offset)
return &malformedRequest{status: http.StatusBadRequest, msg: msg}
case strings.HasPrefix(err.Error(), "json: unknown field "):
fieldName := strings.TrimPrefix(err.Error(), "json: unknown field ")
msg := fmt.Sprintf("Request body contains unknown field %s", fieldName)
return &malformedRequest{status: http.StatusBadRequest, msg: msg}
case errors.Is(err, io.EOF):
msg := "Request body must not be empty"
return &malformedRequest{status: http.StatusBadRequest, msg: msg}
case err.Error() == "http: request body too large":
msg := "Request body must not be larger than 1MB"
return &malformedRequest{status: http.StatusRequestEntityTooLarge, msg: msg}
default:
return err
}
}
err = dec.Decode(&struct{}{})
if err != io.EOF {
msg := "Request body must only contain a single JSON object"
return &malformedRequest{status: http.StatusBadRequest, msg: msg}
}
return nil
}