Struct CodexAppServerClient 

pub struct CodexAppServerClient { /* private fields */ }

Async client for the Codex app-server v2 JSON-RPC protocol.

Cheap to Clone; every clone shares the same underlying connection and pending-request table. Construct one with Self::spawn (launches codex app-server as a child process, the common case), Self::connect_streams (bring your own duplex byte stream), or Self::connect_unix (a Unix socket to an already-running codex app-server daemon).

You must complete the initialize / initialized handshake before calling any other method - the app-server rejects everything else on a fresh connection with a "Not initialized" error. See Self::initialize and Self::send_initialized.

Implementations

impl CodexAppServerClient

pub fn spawn( command: &str, extra_args: &[String], ) -> Result<(Self, EventStream)>

Spawns command app-server (default command = "codex") with stdio piped and connects to it over the stdio JSONL transport.

extra_args are appended after app-server, e.g. ["--enable".into(), "some_feature".into()] or ["-c".into(), r#"model="gpt-5.4""#.into()].

The child process is killed (kill_on_drop) once every clone of the returned client has been dropped - dropping the last clone always terminates the child, whether or not it’s currently mid-write. It’s also reaped promptly and automatically the moment the connection is otherwise known to be dead: a transport read error, clean EOF (e.g. the child crashed or exited), or a write that exceeds the internal stall timeout - none of these require the caller to drop the client or issue another call first.

pub fn spawn_with_events_capacity( command: &str, extra_args: &[String], events_capacity: usize, ) -> Result<(Self, EventStream)>

Same as Self::spawn, but with an explicit capacity for the internal event channel instead of DEFAULT_EVENTS_CHANNEL_CAPACITY. See EventStream’s doc comment for what this bounds and the drop policy once it fills up.

Errors

Returns Error::Io if events_capacity is 0 - tokio::sync::mpsc::channel panics on a zero capacity, and that panic’s message doesn’t mention which knob caused it (useful context this crate has and a bare unwrap deep inside tokio wouldn’t surface), so it’s rejected here instead with a message that does.

pub fn connect_streams<R, W>(reader: R, writer: W) -> (Self, EventStream)

where R: AsyncBufRead + Unpin + Send + 'static, W: AsyncWrite + Unpin + Send + 'static,

Connects to an already-open duplex stream (e.g. any AsyncBufRead + AsyncWrite pair) speaking the same NDJSON JSON-RPC protocol. See also Self::connect_unix for the common case of a codex app-server daemon’s Unix domain socket.

pub fn connect_streams_with_events_capacity<R, W>( reader: R, writer: W, events_capacity: usize, ) -> Result<(Self, EventStream)>

where R: AsyncBufRead + Unpin + Send + 'static, W: AsyncWrite + Unpin + Send + 'static,

Same as Self::connect_streams, but with an explicit capacity for the internal event channel instead of DEFAULT_EVENTS_CHANNEL_CAPACITY. See Self::spawn_with_events_capacity for the zero-capacity error case (identical here).

pub async fn connect_unix(path: impl AsRef<Path>) -> Result<(Self, EventStream)>

Connects to a codex app-server (or codex app-server daemon) listening on a Unix domain socket (--listen unix://PATH).

pub async fn connect_unix_with_events_capacity( path: impl AsRef<Path>, events_capacity: usize, ) -> Result<(Self, EventStream)>

Same as Self::connect_unix, but with an explicit capacity for the internal event channel instead of DEFAULT_EVENTS_CHANNEL_CAPACITY. See Self::spawn_with_events_capacity for the zero-capacity error case (identical here).

pub fn with_call_timeout(self, timeout: Duration) -> Self

Returns a client that applies timeout to every request/response call instead of DEFAULT_CALL_TIMEOUT. Cloning preserves the timeout; mixing timeouts across clones of the same connection is fine (it’s a per-call setting checked in Self::call_request, not a property of the shared connection state).

pub async fn call_raw_method( &self, method: impl Into<String>, params: Value, ) -> Result<Value>

Issues one raw JSON-RPC method call and returns its raw result value.

This is the escape hatch for bridges and generated surfaces that need to call app-server methods dynamically. Prefer the typed generated wrappers when the method is known at compile time.

pub fn send_initialized(&self) -> Result<()>

Sends the initialized notification. Call this exactly once, immediately after Self::initialize succeeds - the app-server rejects every other method until it’s received.

impl CodexAppServerClient

pub async fn initialize( &self, params: InitializeParams, ) -> Result<InitializeResponse>

Calls the initialize app-server method.

pub async fn thread_start( &self, params: ThreadStartParams, ) -> Result<ThreadStartResponse>

Calls the thread/start app-server method.

pub async fn thread_resume( &self, params: ThreadResumeParams, ) -> Result<ThreadResumeResponse>

Calls the thread/resume app-server method.

pub async fn thread_fork( &self, params: ThreadForkParams, ) -> Result<ThreadForkResponse>

Calls the thread/fork app-server method.

pub async fn thread_archive( &self, params: ThreadArchiveParams, ) -> Result<ThreadArchiveResponse>

Calls the thread/archive app-server method.

pub async fn thread_delete( &self, params: ThreadDeleteParams, ) -> Result<ThreadDeleteResponse>

Calls the thread/delete app-server method.

pub async fn thread_unsubscribe( &self, params: ThreadUnsubscribeParams, ) -> Result<ThreadUnsubscribeResponse>

Calls the thread/unsubscribe app-server method.

pub async fn thread_increment_elicitation( &self, params: ThreadIncrementElicitationParams, ) -> Result<ThreadIncrementElicitationResponse>

Calls the thread/increment_elicitation app-server method.

pub async fn thread_decrement_elicitation( &self, params: ThreadDecrementElicitationParams, ) -> Result<ThreadDecrementElicitationResponse>

Calls the thread/decrement_elicitation app-server method.

pub async fn thread_name_set( &self, params: ThreadSetNameParams, ) -> Result<ThreadSetNameResponse>

Calls the thread/name/set app-server method.

pub async fn thread_goal_set( &self, params: ThreadGoalSetParams, ) -> Result<ThreadGoalSetResponse>

Calls the thread/goal/set app-server method.

pub async fn thread_goal_get( &self, params: ThreadGoalGetParams, ) -> Result<ThreadGoalGetResponse>

Calls the thread/goal/get app-server method.

pub async fn thread_goal_clear( &self, params: ThreadGoalClearParams, ) -> Result<ThreadGoalClearResponse>

Calls the thread/goal/clear app-server method.

pub async fn thread_metadata_update( &self, params: ThreadMetadataUpdateParams, ) -> Result<ThreadMetadataUpdateResponse>

Calls the thread/metadata/update app-server method.

pub async fn thread_settings_update( &self, params: ThreadSettingsUpdateParams, ) -> Result<ThreadSettingsUpdateResponse>

Calls the thread/settings/update app-server method.

pub async fn thread_memory_mode_set( &self, params: ThreadMemoryModeSetParams, ) -> Result<ThreadMemoryModeSetResponse>

Calls the thread/memoryMode/set app-server method.

pub async fn memory_reset(&self) -> Result<MemoryResetResponse>

Calls the memory/reset app-server method.

pub async fn thread_unarchive( &self, params: ThreadUnarchiveParams, ) -> Result<ThreadUnarchiveResponse>

Calls the thread/unarchive app-server method.

pub async fn thread_compact_start( &self, params: ThreadCompactStartParams, ) -> Result<ThreadCompactStartResponse>

Calls the thread/compact/start app-server method.

pub async fn thread_shell_command( &self, params: ThreadShellCommandParams, ) -> Result<ThreadShellCommandResponse>

Calls the thread/shellCommand app-server method.

pub async fn thread_approve_guardian_denied_action( &self, params: ThreadApproveGuardianDeniedActionParams, ) -> Result<ThreadApproveGuardianDeniedActionResponse>

Calls the thread/approveGuardianDeniedAction app-server method.

pub async fn thread_background_terminals_clean( &self, params: ThreadBackgroundTerminalsCleanParams, ) -> Result<ThreadBackgroundTerminalsCleanResponse>

Calls the thread/backgroundTerminals/clean app-server method.

pub async fn thread_background_terminals_list( &self, params: ThreadBackgroundTerminalsListParams, ) -> Result<ThreadBackgroundTerminalsListResponse>

Calls the thread/backgroundTerminals/list app-server method.

pub async fn thread_background_terminals_terminate( &self, params: ThreadBackgroundTerminalsTerminateParams, ) -> Result<ThreadBackgroundTerminalsTerminateResponse>

Calls the thread/backgroundTerminals/terminate app-server method.

pub async fn thread_rollback( &self, params: ThreadRollbackParams, ) -> Result<ThreadRollbackResponse>

Calls the thread/rollback app-server method.

pub async fn thread_list( &self, params: ThreadListParams, ) -> Result<ThreadListResponse>

Calls the thread/list app-server method.

pub async fn thread_search( &self, params: ThreadSearchParams, ) -> Result<ThreadSearchResponse>

Calls the thread/search app-server method.

pub async fn thread_loaded_list( &self, params: ThreadLoadedListParams, ) -> Result<ThreadLoadedListResponse>

Calls the thread/loaded/list app-server method.

pub async fn thread_read( &self, params: ThreadReadParams, ) -> Result<ThreadReadResponse>

Calls the thread/read app-server method.

pub async fn thread_turns_list( &self, params: ThreadTurnsListParams, ) -> Result<ThreadTurnsListResponse>

Calls the thread/turns/list app-server method.

pub async fn thread_items_list( &self, params: ThreadItemsListParams, ) -> Result<ThreadItemsListResponse>

Calls the thread/items/list app-server method.

pub async fn thread_inject_items( &self, params: ThreadInjectItemsParams, ) -> Result<ThreadInjectItemsResponse>

Calls the thread/inject_items app-server method.

pub async fn skills_list( &self, params: SkillsListParams, ) -> Result<SkillsListResponse>

Calls the skills/list app-server method.

pub async fn skills_extra_roots_set( &self, params: SkillsExtraRootsSetParams, ) -> Result<SkillsExtraRootsSetResponse>

Calls the skills/extraRoots/set app-server method.

pub async fn hooks_list( &self, params: HooksListParams, ) -> Result<HooksListResponse>

Calls the hooks/list app-server method.

pub async fn marketplace_add( &self, params: MarketplaceAddParams, ) -> Result<MarketplaceAddResponse>

Calls the marketplace/add app-server method.

pub async fn marketplace_remove( &self, params: MarketplaceRemoveParams, ) -> Result<MarketplaceRemoveResponse>

Calls the marketplace/remove app-server method.

pub async fn marketplace_upgrade( &self, params: MarketplaceUpgradeParams, ) -> Result<MarketplaceUpgradeResponse>

Calls the marketplace/upgrade app-server method.

pub async fn plugin_list( &self, params: PluginListParams, ) -> Result<PluginListResponse>

Calls the plugin/list app-server method.

pub async fn plugin_installed( &self, params: PluginInstalledParams, ) -> Result<PluginInstalledResponse>

Calls the plugin/installed app-server method.

pub async fn plugin_read( &self, params: PluginReadParams, ) -> Result<PluginReadResponse>

Calls the plugin/read app-server method.

pub async fn plugin_skill_read( &self, params: PluginSkillReadParams, ) -> Result<PluginSkillReadResponse>

Calls the plugin/skill/read app-server method.

pub async fn plugin_share_save( &self, params: PluginShareSaveParams, ) -> Result<PluginShareSaveResponse>

Calls the plugin/share/save app-server method.

pub async fn plugin_share_update_targets( &self, params: PluginShareUpdateTargetsParams, ) -> Result<PluginShareUpdateTargetsResponse>

Calls the plugin/share/updateTargets app-server method.

pub async fn plugin_share_list( &self, params: PluginShareListParams, ) -> Result<PluginShareListResponse>

Calls the plugin/share/list app-server method.

pub async fn plugin_share_checkout( &self, params: PluginShareCheckoutParams, ) -> Result<PluginShareCheckoutResponse>

Calls the plugin/share/checkout app-server method.

pub async fn plugin_share_delete( &self, params: PluginShareDeleteParams, ) -> Result<PluginShareDeleteResponse>

Calls the plugin/share/delete app-server method.

pub async fn app_list(&self, params: AppsListParams) -> Result<AppsListResponse>

Calls the app/list app-server method.

pub async fn fs_read_file( &self, params: FsReadFileParams, ) -> Result<FsReadFileResponse>

Calls the fs/readFile app-server method.

pub async fn fs_write_file( &self, params: FsWriteFileParams, ) -> Result<FsWriteFileResponse>

Calls the fs/writeFile app-server method.

pub async fn fs_create_directory( &self, params: FsCreateDirectoryParams, ) -> Result<FsCreateDirectoryResponse>

Calls the fs/createDirectory app-server method.

pub async fn fs_get_metadata( &self, params: FsGetMetadataParams, ) -> Result<FsGetMetadataResponse>

Calls the fs/getMetadata app-server method.

pub async fn fs_read_directory( &self, params: FsReadDirectoryParams, ) -> Result<FsReadDirectoryResponse>

Calls the fs/readDirectory app-server method.

pub async fn fs_remove( &self, params: FsRemoveParams, ) -> Result<FsRemoveResponse>

Calls the fs/remove app-server method.

pub async fn fs_copy(&self, params: FsCopyParams) -> Result<FsCopyResponse>

Calls the fs/copy app-server method.

pub async fn fs_watch(&self, params: FsWatchParams) -> Result<FsWatchResponse>

Calls the fs/watch app-server method.

pub async fn fs_unwatch( &self, params: FsUnwatchParams, ) -> Result<FsUnwatchResponse>

Calls the fs/unwatch app-server method.

pub async fn skills_config_write( &self, params: SkillsConfigWriteParams, ) -> Result<SkillsConfigWriteResponse>

Calls the skills/config/write app-server method.

pub async fn plugin_install( &self, params: PluginInstallParams, ) -> Result<PluginInstallResponse>

Calls the plugin/install app-server method.

pub async fn plugin_uninstall( &self, params: PluginUninstallParams, ) -> Result<PluginUninstallResponse>

Calls the plugin/uninstall app-server method.

pub async fn turn_start( &self, params: TurnStartParams, ) -> Result<TurnStartResponse>

Calls the turn/start app-server method.

pub async fn turn_steer( &self, params: TurnSteerParams, ) -> Result<TurnSteerResponse>

Calls the turn/steer app-server method.

pub async fn turn_interrupt( &self, params: TurnInterruptParams, ) -> Result<TurnInterruptResponse>

Calls the turn/interrupt app-server method.

pub async fn thread_realtime_start( &self, params: ThreadRealtimeStartParams, ) -> Result<ThreadRealtimeStartResponse>

Calls the thread/realtime/start app-server method.

pub async fn thread_realtime_append_audio( &self, params: ThreadRealtimeAppendAudioParams, ) -> Result<ThreadRealtimeAppendAudioResponse>

Calls the thread/realtime/appendAudio app-server method.

pub async fn thread_realtime_append_text( &self, params: ThreadRealtimeAppendTextParams, ) -> Result<ThreadRealtimeAppendTextResponse>

Calls the thread/realtime/appendText app-server method.

pub async fn thread_realtime_append_speech( &self, params: ThreadRealtimeAppendSpeechParams, ) -> Result<ThreadRealtimeAppendSpeechResponse>

Calls the thread/realtime/appendSpeech app-server method.

pub async fn thread_realtime_stop( &self, params: ThreadRealtimeStopParams, ) -> Result<ThreadRealtimeStopResponse>

Calls the thread/realtime/stop app-server method.

pub async fn thread_realtime_list_voices( &self, params: ThreadRealtimeListVoicesParams, ) -> Result<ThreadRealtimeListVoicesResponse>

Calls the thread/realtime/listVoices app-server method.

pub async fn review_start( &self, params: ReviewStartParams, ) -> Result<ReviewStartResponse>

Calls the review/start app-server method.

pub async fn model_list( &self, params: ModelListParams, ) -> Result<ModelListResponse>

Calls the model/list app-server method.

pub async fn model_provider_capabilities_read( &self, params: ModelProviderCapabilitiesReadParams, ) -> Result<ModelProviderCapabilitiesReadResponse>

Calls the modelProvider/capabilities/read app-server method.

pub async fn experimental_feature_list( &self, params: ExperimentalFeatureListParams, ) -> Result<ExperimentalFeatureListResponse>

Calls the experimentalFeature/list app-server method.

pub async fn permission_profile_list( &self, params: PermissionProfileListParams, ) -> Result<PermissionProfileListResponse>

Calls the permissionProfile/list app-server method.

pub async fn experimental_feature_enablement_set( &self, params: ExperimentalFeatureEnablementSetParams, ) -> Result<ExperimentalFeatureEnablementSetResponse>

Calls the experimentalFeature/enablement/set app-server method.

pub async fn remote_control_enable( &self, params: Option<RemoteControlEnableParams>, ) -> Result<RemoteControlEnableResponse>

Calls the remoteControl/enable app-server method.

pub async fn remote_control_disable( &self, params: Option<RemoteControlDisableParams>, ) -> Result<RemoteControlDisableResponse>

Calls the remoteControl/disable app-server method.

pub async fn remote_control_status_read( &self, ) -> Result<RemoteControlStatusReadResponse>

Calls the remoteControl/status/read app-server method.

pub async fn remote_control_pairing_start( &self, params: RemoteControlPairingStartParams, ) -> Result<RemoteControlPairingStartResponse>

Calls the remoteControl/pairing/start app-server method.

pub async fn remote_control_pairing_status( &self, params: RemoteControlPairingStatusParams, ) -> Result<RemoteControlPairingStatusResponse>

Calls the remoteControl/pairing/status app-server method.

pub async fn remote_control_client_list( &self, params: RemoteControlClientsListParams, ) -> Result<RemoteControlClientsListResponse>

Calls the remoteControl/client/list app-server method.

pub async fn remote_control_client_revoke( &self, params: RemoteControlClientsRevokeParams, ) -> Result<RemoteControlClientsRevokeResponse>

Calls the remoteControl/client/revoke app-server method.

pub async fn collaboration_mode_list( &self, params: CollaborationModeListParams, ) -> Result<CollaborationModeListResponse>

Calls the collaborationMode/list app-server method.

pub async fn mock_experimental_method( &self, params: MockExperimentalMethodParams, ) -> Result<MockExperimentalMethodResponse>

Calls the mock/experimentalMethod app-server method.

pub async fn environment_add( &self, params: EnvironmentAddParams, ) -> Result<EnvironmentAddResponse>

Calls the environment/add app-server method.

pub async fn environment_info( &self, params: EnvironmentInfoParams, ) -> Result<EnvironmentInfoResponse>

Calls the environment/info app-server method.

pub async fn mcp_server_oauth_login( &self, params: McpServerOauthLoginParams, ) -> Result<McpServerOauthLoginResponse>

Calls the mcpServer/oauth/login app-server method.

pub async fn config_mcp_server_reload(&self) -> Result<()>

Calls the config/mcpServer/reload app-server method.

pub async fn mcp_server_status_list( &self, params: ListMcpServerStatusParams, ) -> Result<ListMcpServerStatusResponse>

Calls the mcpServerStatus/list app-server method.

pub async fn mcp_server_resource_read( &self, params: McpResourceReadParams, ) -> Result<McpResourceReadResponse>

Calls the mcpServer/resource/read app-server method.

pub async fn mcp_server_tool_call( &self, params: McpServerToolCallParams, ) -> Result<McpServerToolCallResponse>

Calls the mcpServer/tool/call app-server method.

pub async fn windows_sandbox_setup_start( &self, params: WindowsSandboxSetupStartParams, ) -> Result<WindowsSandboxSetupStartResponse>

Calls the windowsSandbox/setupStart app-server method.

pub async fn windows_sandbox_readiness( &self, ) -> Result<WindowsSandboxReadinessResponse>

Calls the windowsSandbox/readiness app-server method.

pub async fn account_login_start( &self, params: LoginAccountParams, ) -> Result<LoginAccountResponse>

Calls the account/login/start app-server method.

pub async fn account_login_cancel( &self, params: CancelLoginAccountParams, ) -> Result<CancelLoginAccountResponse>

Calls the account/login/cancel app-server method.

pub async fn account_logout(&self) -> Result<LogoutAccountResponse>

Calls the account/logout app-server method.

pub async fn account_rate_limits_read( &self, ) -> Result<GetAccountRateLimitsResponse>

Calls the account/rateLimits/read app-server method.

pub async fn account_rate_limit_reset_credit_consume( &self, params: ConsumeAccountRateLimitResetCreditParams, ) -> Result<ConsumeAccountRateLimitResetCreditResponse>

Calls the account/rateLimitResetCredit/consume app-server method.

pub async fn account_usage_read(&self) -> Result<GetAccountTokenUsageResponse>

Calls the account/usage/read app-server method.

pub async fn account_workspace_messages_read( &self, ) -> Result<GetWorkspaceMessagesResponse>

Calls the account/workspaceMessages/read app-server method.

pub async fn account_send_add_credits_nudge_email( &self, params: SendAddCreditsNudgeEmailParams, ) -> Result<SendAddCreditsNudgeEmailResponse>

Calls the account/sendAddCreditsNudgeEmail app-server method.

pub async fn feedback_upload( &self, params: FeedbackUploadParams, ) -> Result<FeedbackUploadResponse>

Calls the feedback/upload app-server method.

pub async fn command_exec( &self, params: CommandExecParams, ) -> Result<CommandExecResponse>

Calls the command/exec app-server method.

pub async fn command_exec_write( &self, params: CommandExecWriteParams, ) -> Result<CommandExecWriteResponse>

Calls the command/exec/write app-server method.

pub async fn command_exec_terminate( &self, params: CommandExecTerminateParams, ) -> Result<CommandExecTerminateResponse>

Calls the command/exec/terminate app-server method.

pub async fn command_exec_resize( &self, params: CommandExecResizeParams, ) -> Result<CommandExecResizeResponse>

Calls the command/exec/resize app-server method.

pub async fn process_spawn( &self, params: ProcessSpawnParams, ) -> Result<ProcessSpawnResponse>

Calls the process/spawn app-server method.

pub async fn process_write_stdin( &self, params: ProcessWriteStdinParams, ) -> Result<ProcessWriteStdinResponse>

Calls the process/writeStdin app-server method.

pub async fn process_kill( &self, params: ProcessKillParams, ) -> Result<ProcessKillResponse>

Calls the process/kill app-server method.

pub async fn process_resize_pty( &self, params: ProcessResizePtyParams, ) -> Result<ProcessResizePtyResponse>

Calls the process/resizePty app-server method.

pub async fn config_read( &self, params: ConfigReadParams, ) -> Result<ConfigReadResponse>

Calls the config/read app-server method.

pub async fn external_agent_config_detect( &self, params: ExternalAgentConfigDetectParams, ) -> Result<ExternalAgentConfigDetectResponse>

Calls the externalAgentConfig/detect app-server method.

pub async fn external_agent_config_import( &self, params: ExternalAgentConfigImportParams, ) -> Result<ExternalAgentConfigImportResponse>

Calls the externalAgentConfig/import app-server method.

pub async fn external_agent_config_import_read_histories( &self, ) -> Result<ExternalAgentConfigImportHistoriesReadResponse>

Calls the externalAgentConfig/import/readHistories app-server method.

pub async fn config_value_write( &self, params: ConfigValueWriteParams, ) -> Result<ConfigWriteResponse>

Calls the config/value/write app-server method.

pub async fn config_batch_write( &self, params: ConfigBatchWriteParams, ) -> Result<ConfigWriteResponse>

Calls the config/batchWrite app-server method.

pub async fn config_requirements_read( &self, ) -> Result<ConfigRequirementsReadResponse>

Calls the configRequirements/read app-server method.

pub async fn account_read( &self, params: GetAccountParams, ) -> Result<GetAccountResponse>

Calls the account/read app-server method.

pub async fn fuzzy_file_search( &self, params: FuzzyFileSearchParams, ) -> Result<FuzzyFileSearchResponse>

Calls the fuzzyFileSearch app-server method.

pub async fn fuzzy_file_search_session_start( &self, params: FuzzyFileSearchSessionStartParams, ) -> Result<FuzzyFileSearchSessionStartResponse>

Calls the fuzzyFileSearch/sessionStart app-server method.

pub async fn fuzzy_file_search_session_update( &self, params: FuzzyFileSearchSessionUpdateParams, ) -> Result<FuzzyFileSearchSessionUpdateResponse>

Calls the fuzzyFileSearch/sessionUpdate app-server method.

pub async fn fuzzy_file_search_session_stop( &self, params: FuzzyFileSearchSessionStopParams, ) -> Result<FuzzyFileSearchSessionStopResponse>

Calls the fuzzyFileSearch/sessionStop app-server method.

Trait Implementations

impl Clone for CodexAppServerClient

fn clone(&self) -> CodexAppServerClient

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.