65 lines
2.7 KiB
Go
65 lines
2.7 KiB
Go
package data
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import (
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"errors"
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"fmt"
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"strconv"
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"strings"
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)
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// ErrInvalidRuntimeFormat : Define an error that our UnmarshalJSON() method can return if we're unable to parse or convert the JSON string successfully
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var ErrInvalidRuntimeFormat = errors.New("invalid runtime format")
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// Runtime
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/*
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Declare a custom Runtime type, which has the underlying type int32
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(the same as our Movie struct field)
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*/
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type Runtime int32
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// MarshalJSON
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/*
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Implement a MarshalJSON() method on the Runtime type so that it satisfies the json.Marshaler interface. This should return the JSON-encoded value for the movie runtime (in our case, it will return string in the format "<runtime> mins").
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*/
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func (r Runtime) MarshalJSON() ([]byte, error) {
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// Generate a string containing the movie runtime in the required format.
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jsonValue := fmt.Sprintf("%d mins", r)
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// Use the strconv.Quote() function on the string to wrap it in double
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// quotes. It needs to be surrounded by double quotes in order to be
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// a valid *JSON string*.
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quotedJSONValue := strconv.Quote(jsonValue)
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// Convert the quoted string value to a byte slice and return it.
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return []byte(quotedJSONValue), nil
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}
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// UnmarshalJSON
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// Implement a UnmarshalJSON() method on the Runtime type so that it satisfies the json.Unmarshaler interface. IMPORTANT: Because UnmarshalJSON() needs to modify the receiver (our Runtime type), we must use a pointer receiver for this to work correctly. Otherwise, we will only be modifying a copy (which is then discarded when this method returns).
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func (r *Runtime) UnmarshalJSON(jsonValue []byte) error {
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// We expect that the incoming JSON value will be a string in the format "<runtimes> mins", and the first thing we need to do is remove the surrounding double-quotes from this string. If we can't unquote it, then we return the ErrInvalidRuntimeFormat error.
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unquotedJSONValue, err := strconv.Unquote(string(jsonValue))
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if err != nil {
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return ErrInvalidRuntimeFormat
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}
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// Split the string to isolate the part containing the number.
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parts := strings.Split(unquotedJSONValue, " ")
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// Sanity check the parts of the string to make sure it was in the expected format. If it isn't, we return the ErrInvalidRuntimeFormat error again.
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if len(parts) != 2 || parts[1] != "mins" {
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return ErrInvalidRuntimeFormat
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}
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// Otherwise, parse the string containing the number into an int32. Again, if this fails, return the ErrInvalidRuntimeFormat error.
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i, err := strconv.ParseInt(parts[0], 10, 32)
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if err != nil {
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return ErrInvalidRuntimeFormat
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}
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// Convert the int32 to a Runtime type and assign this to the receiver. Note that we use the * operator to deference the receiver (which is a pointer to a Runtime type) in order to set the underlying value of the pointer.
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*r = Runtime(i)
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return nil
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}
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