[feature] Report Masto version in /api/v1/instance (#1977)

internal/typeutils/internaltofrontend.go

@@ -45,6 +45,7 @@ const (
 	instanceAccountsMaxFeaturedTags             = 10
 	instanceAccountsMaxProfileFields            = 6 // FIXME: https://github.com/superseriousbusiness/gotosocial/issues/1876
 	instanceSourceURL                           = "https://github.com/superseriousbusiness/gotosocial"
+	instanceMastodonVersion                     = "3.5.3"
 )
 
 var instanceStatusesSupportedMimeTypes = []string{
@@ -52,6 +53,10 @@ var instanceStatusesSupportedMimeTypes = []string{
 	string(apimodel.StatusContentTypeMarkdown),
 }
 
+func toMastodonVersion(in string) string {
+	return instanceMastodonVersion + "+" + strings.ReplaceAll(in, " ", "-")
+}
+
 func (c *converter) AccountToAPIAccountSensitive(ctx context.Context, a *gtsmodel.Account) (*apimodel.Account, error) {
 	// we can build this sensitive account easily by first getting the public account....
 	apiAccount, err := c.AccountToAPIAccountPublic(ctx, a)
@@ -740,6 +745,10 @@ func (c *converter) InstanceToAPIV1Instance(ctx context.Context, i *gtsmodel.Ins
 		MaxTootChars:     uint(config.GetStatusesMaxChars()),
 	}
 
+	if config.GetInstanceInjectMastodonVersion() {
+		instance.Version = toMastodonVersion(instance.Version)
+	}
+
 	// configuration
 	instance.Configuration.Statuses.MaxCharacters = config.GetStatusesMaxChars()
 	instance.Configuration.Statuses.MaxMediaAttachments = config.GetStatusesMediaMaxFiles()
@@ -839,6 +848,10 @@ func (c *converter) InstanceToAPIV2Instance(ctx context.Context, i *gtsmodel.Ins
 		Rules:         []interface{}{},            // todo: not implemented
 	}
 
+	if config.GetInstanceInjectMastodonVersion() {
+		instance.Version = toMastodonVersion(instance.Version)
+	}
+
 	// thumbnail
 	thumbnail := apimodel.InstanceV2Thumbnail{}