refactoring, support for storing feature photos

* errors put into separate package
* added table to store feature photos
* added API endpoints for serving photos
* POST /data extended to accept photos using a multipart/form-data body

errs/errors.go

@@ -0,0 +1,63 @@
+package errs
+
+import "fmt"
+
+type ConstError string
+
+func (e ConstError) Error() string {
+	return string(e)
+}
+
+const (
+	ErrUserNotExists               = ConstError("user does not exist")
+	ErrUserAlreadyExists           = ConstError("user already exists")
+	ErrPhotoNotExists              = ConstError("photo does not exist (for the given feature)")
+	ErrAttemptedSystemUser         = ConstError("attempted to associate with system user")
+	ErrUnsupportedImageFormat      = ConstError("unsupported image format")
+	ErrUnsupportedImageContentType = ConstError("unsupported image content type")
+	ErrNonUniqueCreatedFeatureIDs  = ConstError("created features do not have unique IDs")
+)
+
+type EErrPhotoNotProvided *ErrPhotoNotProvided
+
+type ErrPhotoNotProvided struct {
+	Reference string
+}
+
+func NewErrPhotoNotProvided(reference string) *ErrPhotoNotProvided {
+	return &ErrPhotoNotProvided{
+		Reference: reference,
+	}
+}
+
+func (e *ErrPhotoNotProvided) Error() string {
+	return fmt.Sprintf("referenced photo %s which was not provided", e.Reference)
+}
+
+type ErrFeatureForPhotoNotExists struct {
+	PhotoFeatureReference int64
+}
+
+func NewErrFeatureForPhotoNotExists(reference int64) *ErrFeatureForPhotoNotExists {
+	return &ErrFeatureForPhotoNotExists{
+		PhotoFeatureReference: reference,
+	}
+}
+
+func (e *ErrFeatureForPhotoNotExists) Error() string {
+	return fmt.Sprintf("photos were referenced for feature with local ID %d which does not exist in posted created features", e.PhotoFeatureReference)
+}
+
+type ErrUnsupportedContentType struct {
+	Reference string
+}
+
+func NewErrUnsupportedContentType(reference string) *ErrUnsupportedContentType {
+	return &ErrUnsupportedContentType{
+		Reference: reference,
+	}
+}
+
+func (e *ErrUnsupportedContentType) Error() string {
+	return fmt.Sprintf("photo %s has an unsupported Content-Type", e.Reference)
+}