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106 lines
4.0 KiB
Go
106 lines
4.0 KiB
Go
// When Go is encoding a particular type to JSON,
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// it looks to see if the type has a MarshalJSON()
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// method implemented on it. If it has, then Go will
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// call this method to determine how to encode it.
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package main
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import (
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"encoding/json"
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"errors"
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"fmt"
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"io"
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"net/http"
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)
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type envelope map[string]any
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// This was the original function signature without enveloping
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// func (app *application) writeJSON(w http.ResponseWriter, status int, data any, headers http.Header) error {
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func (app *application) writeJSON(w http.ResponseWriter, status int, data envelope, headers http.Header) error {
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// TODO set a flag for wether to indent or not. Indenting cost CPU time, more memory, and more allocs
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// approximately 65% more time 30% more mem.
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//js, err := json.Marshal(data)
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// Use the json.MarshalIndent() function so that whitespace is added to the encoded
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// JSON. Here we use no line prefix ("") and tab indents ("\t") for each element.
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js, err := json.MarshalIndent(data, "", "\t")
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if err != nil {
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return err
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}
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js = append(js, '\n')
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// At this point, we know that we won't encounter any more errors before writing the
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// response, so it's safe to add any headers that we want to include. We loop
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// through the header map and add each header to the http.ResponseWriter header map.
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// Note that it's OK if the provided header map is nil. Go doesn't throw an error
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// if you try to range over (or generally, read from) a nil map.
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for key, value := range headers {
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w.Header()[key] = value
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}
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// Add the "Content-Type: application/json" header, then write the status code and
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// JSON response.
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w.Header().Set("Content-Type", "application/json")
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w.WriteHeader(status)
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w.Write(js)
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return nil
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}
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func (app *application) readJSON(w http.ResponseWriter, r *http.Request, dst any) error {
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// Decode the request body into the target destination.
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err := json.NewDecoder(r.Body).Decode(dst)
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if err != nil {
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// If there is an error during decoding, start the triage...
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var syntaxError *json.SyntaxError
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var unmarshalTypeError *json.UnmarshalTypeError
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var invalidUnmarshalError *json.InvalidUnmarshalError
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switch {
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// Use the errors.As() function to check whether the error has the type
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// *json.SyntaxError. If it does, then return a plain-english error message
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// which includes the location of the problem.
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case errors.As(err, &syntaxError):
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return fmt.Errorf("body contains badly-formed JSON (at character %d)", syntaxError.Offset)
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// In some circumstances Decode() may also return an io.ErrUnexpectedEOF error
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// for syntax errors in the JSON. So we check for this using errors.Is() and
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// return a generic error message. There is an open issue regarding this at
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// https://github.com/golang/go/issues/25956.
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case errors.Is(err, io.ErrUnexpectedEOF):
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return errors.New("body contains badly-formed JSON")
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// Likewise, catch any *json.UnmarshalTypeError errors. These occur when the
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// JSON value is the wrong type for the target destination. If the error relates
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// to a specific field, then we include that in our error message to make it
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// easier for the client to debug.
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case errors.As(err, &unmarshalTypeError):
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if unmarshalTypeError.Field != "" {
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return fmt.Errorf("body contains incorrect JSON type for field %q", unmarshalTypeError.Field)
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}
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return fmt.Errorf("body contains incorrect JSON type (at character %d)", unmarshalTypeError.Offset)
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// An io.EOF error will be returned by Decode() if the request body is empty. We
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// check for this with errors.Is() and return a plain-english error message
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// instead.
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case errors.Is(err, io.EOF):
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return errors.New("body must not be empty")
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// A json.InvalidUnmarshalError error will be returned if we pass something
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// that is not a non-nil pointer to Decode(). We catch this and panic,
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// rather than returning an error to our handler.
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case errors.As(err, &invalidUnmarshalError):
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panic(err)
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// For anything else, return the error message as-is.
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default:
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return err
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}
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}
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return nil
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}
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