[feature] add configuration to `/api/v1/instance` response (#670)

* add configuration object to api instance model

* regenerate swagger docs

* add func to return all supported mimes for media

* add instance configuration to api serialization

* fix json tags

* update instance endpoint tests

* fix typeutils tests

* final regen of swagger docs

* omitempty instance configuration

2 files changed, 95 insertions, 4 deletions

diff --git a/internal/api/client/instance/instancepatch_test.go b/internal/api/client/instance/instancepatch_test.go
index 90464d009..0f80627de 100644
--- a/internal/api/client/instance/instancepatch_test.go
+++ b/internal/api/client/instance/instancepatch_test.go
@@ -63,7 +63,7 @@ func (suite *InstancePatchTestSuite) TestInstancePatch1() {
 	b, err := io.ReadAll(result.Body)
 	suite.NoError(err)
 
-	suite.Equal(`{"uri":"http://localhost:8080","title":"Example Instance","description":"","short_description":"","email":"someone@example.org","version":"","registrations":true,"approval_required":true,"invites_enabled":false,"urls":{"streaming_api":"wss://localhost:8080"},"stats":{"domain_count":2,"status_count":16,"user_count":4},"thumbnail":"","contact_account":{"id":"01F8MH17FWEB39HZJ76B6VXSKF","username":"admin","acct":"admin","display_name":"","locked":false,"bot":false,"created_at":"2022-05-17T13:10:59.000Z","note":"","url":"http://localhost:8080/@admin","avatar":"","avatar_static":"","header":"","header_static":"","followers_count":1,"following_count":1,"statuses_count":4,"last_status_at":"2021-10-20T10:41:37.000Z","emojis":[],"fields":[]},"max_toot_chars":5000}`, string(b))
+	suite.Equal(`{"uri":"http://localhost:8080","title":"Example Instance","description":"","short_description":"","email":"someone@example.org","version":"","registrations":true,"approval_required":true,"invites_enabled":false,"configuration":{"statuses":{"max_characters":5000,"max_media_attachments":6,"characters_reserved_per_url":999},"media_attachments":{"supported_mime_types":["image/jpeg","image/gif","image/png"],"image_size_limit":1048576,"image_matrix_limit":16777216,"video_size_limit":5242880,"video_frame_rate_limit":60,"video_matrix_limit":16777216},"polls":{"max_options":6,"max_characters_per_option":50,"min_expiration":300,"max_expiration":2629746}},"urls":{"streaming_api":"wss://localhost:8080"},"stats":{"domain_count":2,"status_count":16,"user_count":4},"thumbnail":"","contact_account":{"id":"01F8MH17FWEB39HZJ76B6VXSKF","username":"admin","acct":"admin","display_name":"","locked":false,"bot":false,"created_at":"2022-05-17T13:10:59.000Z","note":"","url":"http://localhost:8080/@admin","avatar":"","avatar_static":"","header":"","header_static":"","followers_count":1,"following_count":1,"statuses_count":4,"last_status_at":"2021-10-20T10:41:37.000Z","emojis":[],"fields":[]},"max_toot_chars":5000}`, string(b))
 }
 
 func (suite *InstancePatchTestSuite) TestInstancePatch2() {
@@ -93,7 +93,7 @@ func (suite *InstancePatchTestSuite) TestInstancePatch2() {
 	b, err := io.ReadAll(result.Body)
 	suite.NoError(err)
 
-	suite.Equal(`{"uri":"http://localhost:8080","title":"Geoff's Instance","description":"","short_description":"","email":"","version":"","registrations":true,"approval_required":true,"invites_enabled":false,"urls":{"streaming_api":"wss://localhost:8080"},"stats":{"domain_count":2,"status_count":16,"user_count":4},"thumbnail":"","max_toot_chars":5000}`, string(b))
+	suite.Equal(`{"uri":"http://localhost:8080","title":"Geoff's Instance","description":"","short_description":"","email":"","version":"","registrations":true,"approval_required":true,"invites_enabled":false,"configuration":{"statuses":{"max_characters":5000,"max_media_attachments":6,"characters_reserved_per_url":999},"media_attachments":{"supported_mime_types":["image/jpeg","image/gif","image/png"],"image_size_limit":1048576,"image_matrix_limit":16777216,"video_size_limit":5242880,"video_frame_rate_limit":60,"video_matrix_limit":16777216},"polls":{"max_options":6,"max_characters_per_option":50,"min_expiration":300,"max_expiration":2629746}},"urls":{"streaming_api":"wss://localhost:8080"},"stats":{"domain_count":2,"status_count":16,"user_count":4},"thumbnail":"","max_toot_chars":5000}`, string(b))
 }
 
 func (suite *InstancePatchTestSuite) TestInstancePatch3() {
@@ -123,7 +123,7 @@ func (suite *InstancePatchTestSuite) TestInstancePatch3() {
 	b, err := io.ReadAll(result.Body)
 	suite.NoError(err)
 
-	suite.Equal(`{"uri":"http://localhost:8080","title":"localhost:8080","description":"","short_description":"\u003cp\u003eThis is some html, which is \u003cem\u003eallowed\u003c/em\u003e in short descriptions.\u003c/p\u003e","email":"","version":"","registrations":true,"approval_required":true,"invites_enabled":false,"urls":{"streaming_api":"wss://localhost:8080"},"stats":{"domain_count":2,"status_count":16,"user_count":4},"thumbnail":"","max_toot_chars":5000}`, string(b))
+	suite.Equal(`{"uri":"http://localhost:8080","title":"localhost:8080","description":"","short_description":"\u003cp\u003eThis is some html, which is \u003cem\u003eallowed\u003c/em\u003e in short descriptions.\u003c/p\u003e","email":"","version":"","registrations":true,"approval_required":true,"invites_enabled":false,"configuration":{"statuses":{"max_characters":5000,"max_media_attachments":6,"characters_reserved_per_url":999},"media_attachments":{"supported_mime_types":["image/jpeg","image/gif","image/png"],"image_size_limit":1048576,"image_matrix_limit":16777216,"video_size_limit":5242880,"video_frame_rate_limit":60,"video_matrix_limit":16777216},"polls":{"max_options":6,"max_characters_per_option":50,"min_expiration":300,"max_expiration":2629746}},"urls":{"streaming_api":"wss://localhost:8080"},"stats":{"domain_count":2,"status_count":16,"user_count":4},"thumbnail":"","max_toot_chars":5000}`, string(b))
 }
 
 func (suite *InstancePatchTestSuite) TestInstancePatch4() {
@@ -214,7 +214,7 @@ func (suite *InstancePatchTestSuite) TestInstancePatch6() {
 	b, err := io.ReadAll(result.Body)
 	suite.NoError(err)
 
-	suite.Equal(`{"uri":"http://localhost:8080","title":"localhost:8080","description":"","short_description":"","email":"","version":"","registrations":true,"approval_required":true,"invites_enabled":false,"urls":{"streaming_api":"wss://localhost:8080"},"stats":{"domain_count":2,"status_count":16,"user_count":4},"thumbnail":"","max_toot_chars":5000}`, string(b))
+	suite.Equal(`{"uri":"http://localhost:8080","title":"localhost:8080","description":"","short_description":"","email":"","version":"","registrations":true,"approval_required":true,"invites_enabled":false,"configuration":{"statuses":{"max_characters":5000,"max_media_attachments":6,"characters_reserved_per_url":999},"media_attachments":{"supported_mime_types":["image/jpeg","image/gif","image/png"],"image_size_limit":1048576,"image_matrix_limit":16777216,"video_size_limit":5242880,"video_frame_rate_limit":60,"video_matrix_limit":16777216},"polls":{"max_options":6,"max_characters_per_option":50,"min_expiration":300,"max_expiration":2629746}},"urls":{"streaming_api":"wss://localhost:8080"},"stats":{"domain_count":2,"status_count":16,"user_count":4},"thumbnail":"","max_toot_chars":5000}`, string(b))
 }
 
 func (suite *InstancePatchTestSuite) TestInstancePatch7() {
diff --git a/internal/api/model/instance.go b/internal/api/model/instance.go
index f36713cdc..e01710e34 100644
--- a/internal/api/model/instance.go
+++ b/internal/api/model/instance.go
@@ -62,6 +62,9 @@ type Instance struct {
 	ApprovalRequired bool `json:"approval_required"`
 	// Invites are enabled on this instance.
 	InvitesEnabled bool `json:"invites_enabled"`
+	// Configuration object containing values about status limits etc.
+	// This key/value will be omitted for remote instances.
+	Configuration *InstanceConfiguration `json:"configuration,omitempty"`
 	// URLs of interest for client applications.
 	URLS *InstanceURLs `json:"urls,omitempty"`
 	// Statistics about the instance: number of posts, accounts, etc.
@@ -79,6 +82,94 @@ type Instance struct {
 	MaxTootChars uint `json:"max_toot_chars"`
 }
 
+// InstanceConfiguration models instance configuration parameters.
+//
+// swagger:model instanceConfiguration
+type InstanceConfiguration struct {
+	// Instance configuration pertaining to status limits.
+	Statuses *InstanceConfigurationStatuses `json:"statuses"`
+	// Instance configuration pertaining to media attachment types + size limits.
+	MediaAttachments *InstanceConfigurationMediaAttachments `json:"media_attachments"`
+	// Instance configuration pertaining to poll limits.
+	Polls *InstanceConfigurationPolls `json:"polls"`
+}
+
+// InstanceConfigurationStatuses models instance status config parameters.
+//
+// swagger:model instanceConfigurationStatuses
+type InstanceConfigurationStatuses struct {
+	// Maximum allowed length of a post on this instance, in characters.
+	//
+	// example: 5000
+	MaxCharacters int `json:"max_characters"`
+	// Max number of attachments allowed on a status.
+	//
+	// example: 4
+	MaxMediaAttachments int `json:"max_media_attachments"`
+	// Amount of characters that a URL will be compressed to.
+	//
+	// example: 999
+	CharactersReservedPerURL int `json:"characters_reserved_per_url"`
+}
+
+// InstanceConfigurationMediaAttachments models instance media attachment config parameters.
+//
+// swagger:model instanceConfigurationMediaAttachments
+type InstanceConfigurationMediaAttachments struct {
+	// List of mime types that it's possible to upload to this instance.
+	//
+	// example: ["image/jpeg","image/gif"]
+	SupportedMimeTypes []string `json:"supported_mime_types"`
+	// Max allowed image size in bytes
+	//
+	// example: 2097152
+	ImageSizeLimit int `json:"image_size_limit"`
+	// Max allowed image size in pixels as height*width.
+	//
+	// GtS doesn't set a limit on this, but for compatibility
+	// we give Mastodon's 4096x4096px value here.
+	//
+	// example: 16777216
+	ImageMatrixLimit int `json:"image_matrix_limit"`
+	// Max allowed video size in bytes
+	//
+	// example: 10485760
+	VideoSizeLimit int `json:"video_size_limit"`
+	// Max allowed video frame rate.
+	//
+	// example: 60
+	VideoFrameRateLimit int `json:"video_frame_rate_limit"`
+	// Max allowed video size in pixels as height*width.
+	//
+	// GtS doesn't set a limit on this, but for compatibility
+	// we give Mastodon's 4096x4096px value here.
+	//
+	// example: 16777216
+	VideoMatrixLimit int `json:"video_matrix_limit"`
+}
+
+// InstanceConfigurationPolls models instance poll config parameters.
+//
+// swagger:model instanceConfigurationPolls
+type InstanceConfigurationPolls struct {
+	// Number of options permitted in a poll on this instance.
+	//
+	// example: 4
+	MaxOptions int `json:"max_options"`
+	// Number of characters allowed per option in the poll.
+	//
+	// example: 50
+	MaxCharactersPerOption int `json:"max_characters_per_option"`
+	// Minimum expiration time of the poll in seconds.
+	//
+	// example: 300
+	MinExpiration int `json:"min_expiration"`
+	// Maximum expiration time of the poll in seconds.
+	//
+	// example: 2629746
+	MaxExpiration int `json:"max_expiration"`
+}
+
 // InstanceURLs models instance-relevant URLs for client application consumption.
 //
 // swagger:model instanceURLs