129 lines
5.3 KiB
Go
129 lines
5.3 KiB
Go
package main
|
|
|
|
import (
|
|
"encoding/json"
|
|
"errors"
|
|
"fmt"
|
|
"github.com/julienschmidt/httprouter"
|
|
"io"
|
|
"net/http"
|
|
"strconv"
|
|
)
|
|
|
|
/*
|
|
Note: The readIDParam() method doesn't use any dependencies from our
|
|
application struct so it could just be a regular function, rather than a method on
|
|
application. But in general, I suggest setting up all your application-specific handlers
|
|
and helpers so that they are methods on application. It helps maintain consistency in
|
|
your code structure, and also future-proofs your code for when those handlers and
|
|
helpers change later, and they do need access to dependency.
|
|
|
|
Retrieve the "id" URL parameter from the current request context, then convert it to
|
|
an integer and return it. If the operation isn't successful, return 0 and an error.
|
|
*/
|
|
func (app *application) readIDParam(r *http.Request) (int64, error) {
|
|
/*
|
|
When httprouter is parsing a request, any interpolated URL parameters will be
|
|
stored in the request context. We can use the ParamsFromContext() function to
|
|
retrieve a slice containing these parameter names and values.
|
|
*/
|
|
params := httprouter.ParamsFromContext(r.Context())
|
|
|
|
/*
|
|
We can then use the ByName() method to get the value of the "id" parameter from
|
|
the slice. In our project all movies will have a unique positive integer ID, but
|
|
the value returned by ByName() is always a string. So we try to convert it to a
|
|
base 10 integer (with a bit size of 64). If the parameter couldn't be converted,
|
|
or is less than 1, we know the ID is invalid so we use the http.NotFound()
|
|
func to return a 404 Not Found Response.
|
|
*/
|
|
id, err := strconv.ParseInt(params.ByName("id"), 10, 64)
|
|
if err != nil || id < 1 {
|
|
return 0, errors.New("invalid id parameter")
|
|
}
|
|
|
|
return id, nil
|
|
}
|
|
|
|
type envelope map[string]any
|
|
|
|
/*
|
|
Define a writeJSON() helper for sending responses. This takes the destination
|
|
http.ResponseWriter, the HTTP status code to send, the data to encode to JSON, and a
|
|
header map containing any additional HTTP headers we want to include in the response.
|
|
*/
|
|
func (app *application) writeJSON(w http.ResponseWriter, status int, data envelope, headers http.Header) error {
|
|
/*
|
|
Use the json.MarshalIndent() function so that whitespace is added to
|
|
the encoded JSON. Here we use no line prefix ("") and tab indents ("\t") for each element.
|
|
*/
|
|
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
|
|
}
|
|
|
|
// And 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 any) error {
|
|
// Initialize a new json.Decoder instance which reads from the request body, and then use the Decode() method to decode the body contents into the input struct.
|
|
err := json.NewDecoder(r.Body).Decode(dst)
|
|
if err != nil {
|
|
// If there is an error during decoding, start the triage...
|
|
var syntaxError *json.SyntaxError
|
|
var unmarshalTypeError *json.UnmarshalTypeError
|
|
var invalidUnmarshalError *json.InvalidUnmarshalError
|
|
|
|
switch {
|
|
// Use the errors.As() function to check whether the error has the type *json.SyntaxError. If it does, then return a plain-english error message which includes the location problem.
|
|
case errors.As(err, &syntaxError):
|
|
return fmt.Errorf("body contains badly-formed JSON (at character %d)", syntaxError.Offset)
|
|
|
|
// In some circumstances Decode() may also return an io.ErrUnexpectedEOF error for syntax errors in the JSON. So we check for this using errors.Is() and return a generic error message.
|
|
case errors.Is(err, io.ErrUnexpectedEOF):
|
|
return errors.New("body contains badly-formed JSON")
|
|
|
|
// Likewise, catch any *json.UnmarshalTypeError errors. These occur when the JSON value is the wrong type for the target destination. If the error relates to a specific field, then we include that in our error message to make it easier for the client to debug.
|
|
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)
|
|
|
|
// An io.EOF error will be returned by Decode() if the request body is empty. We check for this with errors.Is() and return a plain-english error message instead.
|
|
case errors.Is(err, io.EOF):
|
|
return errors.New("body must not be empty")
|
|
|
|
// A json.InvalidUnmarshalError error will be returned if we pass something that is not a non-nil pointer to Decode(). We catch this and panic, rather than returning an error to our handler.
|
|
case errors.As(err, &invalidUnmarshalError):
|
|
panic(err)
|
|
|
|
// For anything else, return the error mesasge as-is.
|
|
default:
|
|
return err
|
|
}
|
|
}
|
|
|
|
return nil
|
|
}
|