SRT API Functions

  • [Library Initialization](#Library-Initialization) * [srt_startup](#srt_startup) * [srt_cleanup](#srt_cleanup)

  • [Creating and configuring sockets](#Creating-and-configuring-sockets) * [srt_socket](#srt_socket) * [srt_bind](#srt_bind) * [srt_create_socket](#srt_create_socket) * [srt_bind_peerof](#srt_bind-peerof) * [srt_getsockstate](#srt_getsockstate) * [srt_getsndbuffer](#srt_getsndbuffer) * [srt_close](#srt_close)

  • [Connecting](#Connecting) * [srt_listen](#srt_listen) * [srt_accept](#srt_accept) * [srt_listen_callback](#srt_listen_callback) * [srt_connect](#srt_connect) * [srt_connect_debug](#srt_connect_debug) * [srt_rendezvous](#srt_rendezvous)

  • [Options and properties](#Options-and-properties) * [srt_getpeername](#srt_getpeername) * [srt_getsockname](#srt_getsockname) * [srt_getsockopt, srt_getsockflag](#srt_getsockopt-srt_getsockflag) * [srt_setsockopt, srt_setsockflag](#srt_setsockopt-srt_setsockflag)

  • [Helper data types for transmission](#Helper-data-types-for-transmission) * [SRT_MSGCTRL](#SRT_MSGCTRL)

  • [Transmission](#Transmission) * [srt_send, srt_sendmsg, srt_sendmsg2](#srt_send-srt_sendmsg-srt_sendmsg2) * [srt_recv, srt_recvmsg, srt_recvmsg2](#srt_recv-srt_recvmsg-srt_recvmsg2) * [srt_sendfile, srt_recvfile](#srt_sendfile-srt_recvfile)

  • [Diagnostics](#Diagnostics) * [srt_getlasterror_str](#srt_getlasterror_str) * [srt_getlasterror](#srt_getlasterror) * [srt_strerror](#srt_strerror) * [srt_clearlasterror](#srt_clearlasterror)

  • [Performance tracking](#Performance-tracking) * [srt_bstats, srt_bistats](#srt_bstats-srt_bistats)

  • [Asynchronous operations (epoll)](#Asynchronous-operations-epoll) * [srt_epoll_create](#srt_epoll_create) * [srt_epoll_add_usock, srt_epoll_add_ssock, srt_epoll_update_usock, srt_epoll_update_ssock](#srt_epoll_add_usock-srt_epoll_add_ssock-srt_epoll_update_usock-srt_epoll_update_ssock) * [srt_epoll_remove_usock, srt_epoll_remove_ssock](#srt_epoll_remove_usock-srt_epoll_remove_ssock) * [srt_epoll_wait](#srt_epoll_wait) * [srt_epoll_uwait](#srt_epoll_uwait) * [srt_epoll_set](#srt_epoll_set) * [srt_epoll_release](#srt_epoll_release)

  • [Logging control](#Logging-control) * [srt_setloglevel](#srt_setloglevel) * [srt_addlogfa, srt_dellogfa, srt_resetlogfa](#srt_addlogfa-srt_dellogfa-srt_resetlogfa) * [srt_setloghandler](#srt_setloghandler) * [srt_setlogflags](#srt_setlogflags)

Library initialization

### srt_startup ` int srt_startup(void); `

This function shall be called at the start of an application that uses the SRT library. It provides all necessary platform-specific initializations, sets up global data, and starts the SRT GC thread. If this function isn’t explicitly called, it will be called automatically when creating the first socket. However, relying on this behavior is strongly discouraged.

  • Returns:

    • 0 = successfully run, or already started

    • 1 = this is the first startup, but the GC thread is already running

    • -1 = failed

  • Errors:

    • SRT_ECONNSETUP (with error code set): Reported when required system

resource(s) failed to initialize. This is currently used only on Windows to report a failure from WSAStartup.

### srt_cleanup ` int srt_cleanup(void); `

This function cleans up all global SRT resources and shall be called just before exiting the application that uses the SRT library. This cleanup function will still be called from the C++ global destructor, if not called by the application, although relying on this behavior is stronly discouraged.

  • Returns:

    • 0 (A possibility to return other values is reserved for future use)

IMPORTANT: Note that the startup/cleanup calls have an instance counter. This means that if you call srt_startup multiple times, you need to call the srt_cleanup function exactly the same number of times.

Creating and configuring sockets

### srt_socket ` SRTSOCKET srt_socket(int af, int type, int protocol); `

Creates an SRT socket:

  • af: family (either AF_INET or AF_INET6)

  • type, protocol: ignored

NOTE: The UDT library uses the type parameter to specify file or message mode by specifying that SOCK_STREAM corresponds to a TCP-like file transmission mode, and SOCK_DGRAM corresponds to an SCTP-like message transmission mode. SRT still supports these modes. However, this is controlled by the SRTO_MESSAGEAPI socket option when the transmission type is file (SRTO_TRANSTYPE set to SRTT_FILE) and the only reasonable value for the type parameter here is SOCK_DGRAM.

  • Returns:

    • a valid socket ID on success

    • INVALID_SOCKET (-1) on error

  • Errors:

    • SRT_ENOTBUF: not enough memory to allocate required resources

NOTE: This is probably a design flaw (BUG?). Usually underlying system errors are reported by SRT_ECONNSETUP.

### srt_create_socket ` SRTSOCKET srt_create_socket(); `

Creates a socket in AF_INET family only.

NOTE: In future the address family may be removed from initial socket configuration, which will free the user from specifying it in srt_socket. The srt_create_socket function will be used for all families. The family will be specified only with the first srt_bind or srt_connect, and in this case SRT_EINVPARAM will not be used (see [srt_bind](#srt_bind) below).

### srt_bind ` int srt_bind(SRTSOCKET u, const struct sockaddr* name, int namelen); `

Binds a socket to a local address and port. Binding specifies the local network interface and the UDP port number to be used for the socket. When the local address is a form of INADDR_ANY, then it’s bound to all interfaces. When the port number is 0, then the port number will be system-allocated if necessary.

This call is obligatory for a listening socket before calling srt_listen and for rendezvous mode before calling srt_connect, otherwise it’s optional. For a listening socket it defines the network interface and the port where the listener should expect a call request. In case of rendezvous mode (when the socket has set SRTO_RENDEZVOUS to true, in this mode both parties connect to one another) it defines the network interface and port from which packets will be sent to the peer and to which the peer is expected to send packets.

For a connecting socket this call can set up the outgoing port to be used in the communication. It is allowed that multiple SRT sockets share one local outgoing port, as long as SRTO_REUSEADDR is set to true (default). Without this call the port will be automatically selected by the system.

See **NOTE* below under* [srt_create_socket](#srt_create_socket).

  • Returns:

    • SRT_ERROR (-1) on error, otherwise 0

  • Errors:

    • SRT_EINVSOCK: Socket passed as u designates no valid socket

    • SRT_EINVOP: Socket already bound

    • SRT_EINVPARAM: Address family in name is not one set for srt_socket

    • SRT_ECONNSETUP: Internal creation of a UDP socket failed

    • SRT_ESOCKFAIL: Internal configuration of a UDP socket (bind, setsockopt) failed

NOTE: SRT_EINVPARAM will not be the case in future, when the family is removed from the initial socket configuration, see [srt_create_socket](#srt_create_socket) above.

### srt_bind_peerof

` int srt_bind_peerof(SRTSOCKET u, UDPSOCKET udpsock); `

A version of srt_bind that acquires a given UDP socket instead of creating one.

### srt_getsockstate

` SRT_SOCKSTATUS srt_getsockstate(SRTSOCKET u); `

Gets the current status of the socket. Possible states are:

  • SRTS_INIT: Created, but not bound

  • SRTS_OPENED: Created and bound, but not in use yet.

  • SRTS_LISTENING: Socket is in listening state

  • SRTS_CONNECTING: The connect operation was initiated, but not yet

finished. This may also mean that it has timed out; you can only know that after getting a socket error report from srt_epoll_wait. In blocking mode it’s not possible because srt_connect does not return until the socket is connected or failed due to timeout or interrupted call. * SRTS_CONNECTED: The socket is connected and ready for transmission. * SRTS_BROKEN: The socket was connected, but the connection was broken * SRTS_CLOSING: The socket may still be open and active, but closing is requested, so no further operations will be accepted (active operations will be completed before closing) * SRTS_CLOSED: The socket has been closed, but not yet removed by the GC thread * SRTS_NONEXIST: The specified number does not correspond to a valid socket.

### srt_getsndbuffer

` int srt_getsndbuffer(SRTSOCKET sock, size_t* blocks, size_t* bytes); `

Retrieves information about the sender buffer.

  • sock: Socket to test

  • blocks: Written information about buffer blocks in use

  • bytes: Written information about bytes in use

This function can be used for diagnostics. It is especially useful when the socket needs to be closed asynchronously.

### srt_close

` int srt_close(SRTSOCKET u); `

Closes the socket and frees all used resources. Note that underlying UDP sockets may be shared between sockets, so these are freed only with the last user closed.

  • Returns:

    • SRT_ERROR (-1) in case of error, otherwise 0

  • Errors:

    • SRT_EINVSOCK: Socket u indicates no valid socket ID

Connecting

### srt_listen ` int srt_listen(SRTSOCKET u, int backlog); `

This sets up the listening state on a socket with a backlog setting that defines how many sockets may be allowed to wait until they are accepted (excessive connection requests are rejected in advance).

  • Returns:

    • SRT_ERROR (-1) in case of error, otherwise 0.

  • Errors:

    • SRT_EINVPARAM: Value of backlog is 0 or negative.

    • SRT_EINVSOCK: Socket u indicates no valid SRT socket.

    • SRT_EUNBOUNDSOCK: srt_bind has not yet been called on that socket.

    • SRT_ERDVNOSERV: SRTO_RENDEZVOUS flag is set to true on specified socket.

    • SRT_EINVOP: Internal error (should not happen when SRT_EUNBOUNDSOCK is reported).

    • SRT_ECONNSOCK: The socket is already connected.

    • SRT_EDUPLISTEN: The address used in srt_bind by this socket is already

occupied by another listening socket. Binding multiple sockets to one IP address and port is allowed, as long as SRTO_REUSEADDR is set to true, but only one of these sockets can be set up as a listener.

### srt_accept

` SRTSOCKET srt_accept(SRTSOCKET lsn, struct sockaddr* addr, int* addrlen); `

Accepts a pending connection and creates a new socket to handle it. The socket that is connected to a remote party is returned.

  • lsn: the listener socket previously configured by srt_listen

  • addr: the IP address and port specification for the remote party

  • addrlen: INPUT: size of addr pointed object. OUTPUT: real size of the

returned object

NOTE: addr is allowed to be NULL, in which case it’s understood that the application is not interested in the address from which the connection originated. Otherwise addr should specify an object into which the address will be written, and addrlen must also specify a variable to contain the object size.

  • Returns:

    • A valid socket ID for the connection, on success

    • SRT_ERROR (-1) on failure

  • Errors:

    • SRT_EINVPARAM: NULL specified as addrlen, when addr is not NULL

    • SRT_EINVSOCK: lsn designates no valid socket ID. Can also mean Internal

Error when an error occurred while creating an accepted socket (BUG?)

  • SRT_ENOLISTEN: lsn is not set up as a listener (srt_listen not called,

or the listener socket has already been closed)

  • SRT_ERDVNOSERV: Internal error (if no SRT_ENOLISTEN reported, it means

that the socket could not be set up as rendezvous because srt_listen does not allow it)

  • SRT_EASYNCRCV: No connection reported so far. This error is reported only

when the lsn listener socket was configured as non-blocking for reading (SRTO_RCVSYN set to false); otherwise the call blocks until a connection is reported or an error occurs

### srt_listen_callback

` int srt_listen_callback(SRTSOCKET lsn, srt_listen_callback_fn* hook_fn, void* hook_opaque); `

This call installs a callback hook, which will be executed on a socket that is automatically created to handle the incoming connection on the listeneing socket (and is about to be returned by srt_accept), but before the connection has been accepted.

  • lsn: Listening socket where you want to install the callback hook

  • hook_fn: The callback hook function pointer

  • hook_opaque: The pointer value that will be passed to the callback function

  • Returns:

    • 0, if successful

    • -1, on error

  • Errors:

    • SRT_EINVPARAM reported when hook_fn is a null pointer

The callback function has the signature as per this type definition: ``` typedef int srt_listen_callback_fn(void* opaque, SRTSOCKET ns, int hs_version

const struct sockaddr* peeraddr, const char* streamid);

```

The callback function gets the following parameters passed:

  • opaque: The pointer passed as hook_opaque when registering

  • ns: The freshly created socket to handle the incoming connection

  • hs_version: The handshake version (usually 5, pre-1.3 versions use 4)

  • peeraddr: The address of the incoming connection

  • streamid: The value set to SRTO_STREAMID option set on the peer side

(Note that versions that use handshake version 4 are incapable of using any extensions, such as streamid, however they do support encryption. Note also that the SRT version isn’t yet extracted, however you can prevent too old version connections using SRTO_MINVERSION option).

The callback function is given an opportunity to:

  • use the passed information (streamid and peer address) to decide what to do with this connection

  • alter any options on the socket, which could not be set properly before on the listening socket to be derived by the accepted socket, and won’t be allowed to be altered after the socket is returned by srt_accept

Note that the returned socket has already set all derived options from the listener socket, as it happens normally, and the moment when this callback is called is when the conclusion handshake has been already received from the caller party, but not yet interpreted (the streamid field is extracted from it prematurely). When you, for example, set a passphrase on the socket at this very moment, the Key Material processing will happen against this already set passphrase, after the callback function is finished.

The callback function shall return 0, if the connection is to be accepted. If you return -1, or if the function throws an exception, this will be understood as a request to reject the incoming connection - in which case the about-to-be-accepted socket will be silently deleted and srt_accept will not report it. Note that in case of non-blocking mode the epoll bits for read-ready on the listener socket will not be set if the connection is rejected, including when rejected from this user function.

IMPORTANT: This function is called in the receiver worker thread, which means that it must do its checks and operations as quickly as possible and keep the minimum possible time, as every delay you do in this function will burden the processing of the incoming data on the associated UDP socket, which in case of a listener socket means the listener socket itself and every socket accepted off this listener socket. Avoid any extensive search operations, best cache in memory whatever database you have to check against the data received in streamid or peeraddr.

### srt_connect

` int srt_connect(SRTSOCKET u, const struct sockaddr* name, int namelen); `

Connects a socket to a remote party with a specified address and port.

  • u: SRT socket. This must be a freshly created socket that has not yet been

used for anything except possibly srt_bind. * name: specification of the remote address and port * namelen: size of the object passed by name

NOTES: 1. See NOTE regarding family under [srt_create_socket](#srt_create_socket), and SRT_EINVPARAM error under [srt_bind](#srt_bind) above. 2. The socket used here may be bound from upside so that it uses a predefined network interface or local outgoing port. If not, it behaves as if it was bound to INADDR_ANY (which binds on all interfaces) and port 0 (which makes the system assign the port automatically).

  • Returns:

    • SRT_ERROR (-1) in case of error, otherwise 0

  • Errors:

    • SRT_EINVSOCK: Socket u indicates no valid socket ID

    • SRT_EINVPARAM: Address family in name is not one set for srt_socket

    • SRT_ERDVUNBOUND: Socket u has set SRTO_RENDEZVOUS to true, but srt_bind

hasn’t yet been called on it. The srt_connect function is also used to connect a rendezvous socket, but rendezvous sockets must be explicitly bound to a local interface prior to connecting. Non-rendezvous sockets (caller sockets) can be left without binding - the call to srt_connect will bind them automatically.

  • SRT_ECONNSOCK: Socket u is already connected

  • SRT_ECONNREJ: Connection has been rejected

In case when SRT_ECONNREJ error was reported, you can get the reason for a rejected connection from srt_getrejectreason.

### srt_connect_debug

` int srt_connect_debug(SRTSOCKET u, const struct sockaddr* name, int namelen, int forced_isn); `

This function is for developers only and can be used for testing. It does the same thing as [srt_connect](#srt_connect), with the exception that it allows specifying the Initial Sequence Number for data transmission. Normally this value is generated randomly.

### srt_rendezvous ``` int srt_rendezvous(SRTSOCKET u, const struct sockaddr* local_name, int local_namelen,

const struct sockaddr* remote_name, int remote_namelen);

``` Performs a rendezvous connection. This is a shortcut for doing bind locally, setting the SRTO_RENDEZVOUS option to true, and doing srt_connect.

  • u: socket to connect

  • local_name: specifies the local network interface and port to bind

  • remote_name: specifies the remote party’s IP address and port

NOTE: The port value shall be the same in local_name and remote_name.

Options and properties

### srt_getpeername ` int srt_getpeername(SRTSOCKET u, struct sockaddr* name, int* namelen); `

Retrieves the remote address to which the socket is connected.

  • Returns:

    • SRT_ERROR (-1) in case of error, otherwise 0

  • Errors:

    • SRT_EINVSOCK: Socket u indicates no valid socket ID

    • SRT_ENOCONN: Socket u isn’t connected, so there’s no remote address to return

### srt_getsockname ` int srt_getsockname(SRTSOCKET u, struct sockaddr* name, int* namelen); `

Extracts the address to which the socket was bound. Although you should know the address(es) that you have used for binding yourself, this function can be useful for extracting the local outgoing port number when it was specified as 0 with binding for system autoselection. With this function you can extract the port number after it has been autoselected.

  • Returns:

    • SRT_ERROR (-1) in case of error, otherwise 0

  • Errors:

    • SRT_EINVSOCK: Socket u indicates no valid socket ID

    • SRT_ENOCONN: Socket u isn’t bound, so there’s no local

address to return (BUG? It should rather be SRT_EUNBOUNDSOCK)

### srt_getsockopt, srt_getsockflag ` int srt_getsockopt(SRTSOCKET u, int level /*ignored*/, SRT_SOCKOPT opt, void* optval, int* optlen); int srt_getsockflag(SRTSOCKET u, SRT_SOCKOPT opt, void* optval, int* optlen); `

Gets the value of the given socket option. The first version (srt_getsockopt) respects the BSD socket API convention, although the “level” parameter is ignored. The second version (srt_getsockflag) omits the “level” parameter completely.

Options correspond to various data types, so you need to know what data type is assigned to a particular option, and to pass a variable of the appropriate data type. Specifications are provided in the apps/socketoptions.hpp file at the srt_options object declaration.

  • Returns:

    • SRT_ERROR (-1) in case of error, otherwise 0

  • Errors:

    • SRT_EINVSOCK: Socket u indicates no valid socket ID

    • SRT_EINVOP: Option opt indicates no valid option

### srt_setsockopt, srt_setsockflag

` int srt_setsockopt(SRTSOCKET u, int level /*ignored*/, SRT_SOCKOPT opt, const void* optval, int optlen); int srt_setsockflag(SRTSOCKET u, SRT_SOCKOPT opt, const void* optval, int optlen); `

Sets a value for a socket option. The first version (srt_setsockopt) respects the BSD socket API convention, although the “level” parameter is ignored. The second version (srt_setsockflag) omits the “level” parameter completely.

Options correspond to various data types, so you need to know what data type is assigned to a particular option, and to pass a variable of the appropriate data type with the option value to be set.

  • Returns:

    • SRT_ERROR (-1) in case of error, otherwise 0

-Errors:

  • SRT_EINVSOCK: Socket u indicates no valid socket ID

  • SRT_EINVOP: Option opt indicates no valid option

  • Various other errors that may result from problems when setting a specific

option (see option description for details).

Helper data types for transmission

### SRT_MSGCTRL

The SRT_MSGCTRL structure:

``` typedef struct SRT_MsgCtrl_ {

int flags; // Left for future int msgttl; // TTL for a message, default -1 (no TTL limitation) int inorder; // Whether a message is allowed to supersede partially lost one. Unused in stream and live mode. int boundary; //0:mid pkt, 1(01b):end of frame, 2(11b):complete frame, 3(10b): start of frame uint64_t srctime; // source timestamp (usec), 0: use internal time int32_t pktseq; // sequence number of the first packet in received message (unused for sending) int32_t msgno; // message number (output value for both sending and receiving)

} SRT_MSGCTRL; ```

The SRT_MSGCTRL structure is used in srt_sendmsg2 and srt_recvmsg2 calls and specifies some special extra parameters:

  • flags: [IN, OUT]. RESERVED FOR FUTURE USE (should be 0). This is

intended to specify some special options controlling the details of how the called function should work.

  • msgttl: [IN]. In message and live mode only, specifies the TTL for

sending messages (in [ms]). Not used for receiving messages. If this value is not negative, it defines the maximum time up to which this message should stay scheduled for sending for the sake of later retransmission. A message is always sent for the first time, but the UDP packet carrying it may be (also partially) lost, and if so, lacking packets will be retransmitted. If the message is not successfully resent before TTL expires, further retransmission is given up and the message is discarded.

  • inorder: [IN]. In message mode only, specifies that sent messages should

be extracted by the receiver in the order of sending. This can be meaningful if a packet loss has happened, and a particular message must wait for retransmission so that it can be reassembled and then delivered. When this flag is false, the message can be delivered even if there are any previous messages still waiting for completion.

  • boundary: RESERVED FOR FUTURE USE. Intended to be used in a special mode

when you are allowed to send or retrieve a part of the message.

  • srctime:

    • [IN] Sender only. Specifies the application-provided timestamp. If not used

(specified as 0), the current system time (absolute microseconds since epoch) is used.

  • [OUT] Receiver only. Specifies the time when the packet was intended to be

delivered to the receiver.

  • pktseq: Receiver only. Reports the sequence number for the packet carrying

out the payload being returned. If the payload is carried out by more than one UDP packet, only the sequence of the first one is reported. Note that in live mode there’s always one UDP packet per message.

  • msgno: Message number that can be sent by both sender and receiver,

although it is required that this value remain monotonic in subsequent send calls. Normally message numbers start with 1 and increase with every message sent.

Helpers for `SRT_MSGCTRL`:

` void srt_msgctrl_init(SRT_MSGCTRL* mctrl); const SRT_MSGCTRL srt_msgctrl_default; `

Helpers for getting an object of SRT_MSGCTRL type ready to use. The first is a function that fills the object with default values. The second is a constant object and can be used as a source for assignment. Note that you cannot pass this constant object into any of the API functions because they require it to be mutable, as they use some fields to output values.

Transmission

### srt_send, srt_sendmsg, srt_sendmsg2 ` int srt_send(SRTSOCKET u, const char* buf, int len); int srt_sendmsg(SRTSOCKET u, const char* buf, int len, int ttl/* = -1*/, int inorder/* = false*/); int srt_sendmsg2(SRTSOCKET u, const char* buf, int len, SRT_MSGCTRL *mctrl); `

Sends a payload to a remote party over a given socket.

  • u: Socket used to send. The socket must be connected for this operation.

  • buf: Points to the buffer containing the payload to send.

  • len: Size of the payload specified in buf.

  • ttl: Time (in [ms]) to wait for a successful delivery. See description of

the [SRT_MSGCTRL::msgttl](#SRT_MSGCTRL) field. * inorder: Required to be received in the order of sending. See [SRT_MSGCTRL::inorder](#SRT_MSGCTRL). * mctrl: An object of [SRT_MSGCTRL](#SRT_MSGCTRL) type that contains extra parameters, including ttl and inorder.

The way this function works is determined by the mode set in options, and it has specific requirements:

1. In file/stream mode, the payload is byte-based. You are not required to know the size of the data, although they are only guaranteed to be received in the same byte order.

2. In file/message mode, the payload that you send using this function is a single message that you intend to be received as a whole. In other words, a single call to this function determines a message’s boundaries.

3. In live mode, you are only allowed to send up to the length of SRTO_PAYLOADSIZE, which can’t be larger than 1456 bytes (1316 default).

  • Returns:

    • Size of the data sent, if successful. Note that in file/stream mode the

returned size may be less than len, which means that it didn’t send the whole contents of the buffer. You would need to call this function again with the rest of the buffer next time to send it completely. In both file/message and live mode the successful return is always equal to len

  • In case of error, SRT_ERROR (-1)

  • Errors:

    • SRT_ENOCONN: Socket u used when the operation is not connected.

    • SRT_ECONNLOST: Socket u used for the operation has lost its connection.

    • SRT_EINVALMSGAPI: Incorrect API usage in message mode: * live mode: trying to send more bytes at once than SRTO_PAYLOADSIZE

    • SRT_EINVALBUFFERAPI: Incorrect API usage in stream mode: * Reserved for future use. The congestion controller object

      used for this mode doesn’t use any restrictions on this call for now, but this may change in future.

    • SRT_ELARGEMSG: Message to be sent can’t fit in the sending buffer (that is,

it exceeds the current total space in the sending buffer in bytes). This means that the sender buffer is too small, or the application is trying to send a larger message than initially predicted.

  • SRT_EASYNCSND: There’s no free space currently in the buffer to schedule

the payload. This is only reported in non-blocking mode (SRTO_SNDSYN set to false); in blocking mode the call is blocked until enough free space in the sending buffer becomes available.

  • SRT_ETIMEOUT: The condition described above still persists and the timeout

has passed. This is only reported in blocking mode when SRTO_SNDTIMEO is set to a value other than -1.

  • SRT_EPEERERR: This is reported only in the case where, as a stream is being

received by a peer, the srt_recvfile function encounters an error during a write operation on a file. This is reported by a UMSG_PEERERROR message from the peer, and the agent sets the appropriate flag internally. This flag persists up to the moment when the connection is broken or closed.

### srt_recv, srt_recvmsg, srt_recvmsg2

` int srt_recv(SRTSOCKET u, char* buf, int len); int srt_recvmsg(SRTSOCKET u, char* buf, int len); int srt_recvmsg2(SRTSOCKET u, char *buf, int len, SRT_MSGCTRL *mctrl); `

Extracts the payload waiting to be received. Note that srt_recv and srt_recvmsg are identical functions, two different names being kept for historical reasons. In the UDT predecessor the application was required to use either the UDT::recv version for stream mode and UDT::recvmsg for message mode. In SRT this distinction is resolved internally by the SRTO_MESSAGEAPI flag.

  • u: Socket used to send. The socket must be connected for this operation.

  • buf: Points to the buffer to which the payload is copied

  • len: Size of the payload specified in buf

  • mctrl: An object of [SRT_MSGCTRL](#SRT_MSGCTRL) type that contains extra

parameters

The way this function works is determined by the mode set in options, and it has specific requirements:

1. In file/stream mode, as many bytes as possible are retrieved, that is, only so many bytes that fit in the buffer and are currently available. Any data that is available but not extracted this time will be available next time.

2. In file/message mode, exactly one message is retrieved, with the boundaries defined at the moment of sending. If some parts of the messages are already retrieved, but not the whole message, nothing will be received (the function blocks or returns SRT_EASYNCRCV). If the message to be returned does not fit in the buffer, nothing will be received and the error is reported.

3. In live mode, the function behaves as in file/message mode, although the number of bytes retrieved will be at most the size of SRTO_PAYLOADSIZE. In this mode, however, with default settings of SRTO_TSBPDMODE and SRTO_TLPKTDROP, the message will be received only when its time to play has come, and until then it will be kept in the receiver buffer; also, when the time to play has come for a message that is next to the currently lost one, it will be delivered and the lost one dropped.

  • Returns:

    • Size (>0) of the data received, if successful.

    • 0, if the connection has been closed

    • SRT_ERROR (-1) when an error occurs

  • Errors:

    • SRT_ENOCONN: Socket u used for the operation is not connected.

    • SRT_ECONNLOST: Socket u used for the operation has lost connection

(this is reported only if the connection was unexpectedly broken, not when it was closed by the foreign host).

  • SRT_EINVALMSGAPI: Incorrect API usage in message mode: * live mode: size of the buffer is less than SRTO_PAYLOADSIZE

  • SRT_EINVALBUFFERAPI: Incorrect API usage in stream mode: * Currently not in use. File congestion control used for stream mode

    does not restrict the parameters. ???

  • SRT_ELARGEMSG: Message to be sent can’t fit in the sending buffer (that is,

it exceeds the current total space in the sending buffer in bytes). This means that the sender buffer is too small, or the application is trying to send a larger message than initially intended.

  • SRT_EASYNCRCV: There are no data currently waiting for delivery. This

happens only in non-blocking mode (when SRTO_RCVSYN is set to false). In blocking mode the call is blocked until the data are ready. How this is defined, depends on the mode:

  • In live mode (with SRTO_TSBPDMODE on), at least one packet must

be present in the receiver buffer and its time to play be in the past * In file/message mode, one full message must be available,

  • the next one waiting if there are no messages with inorder = false, or

possibly the first message ready with inorder = false

  • In file/stream mode, it is expected to have at least one byte of data

still not extracted * SRT_ETIMEOUT: The readiness condition described above is still not achieved

and the timeout has passed. This is only reported in blocking mode when SRTO_RCVTIMEO is set to a value other than -1.

### srt_sendfile, srt_recvfile

` int64_t srt_sendfile(SRTSOCKET u, const char* path, int64_t* offset, int64_t size, int block); int64_t srt_recvfile(SRTSOCKET u, const char* path, int64_t* offset, int64_t size, int block); `

These are functions dedicated to sending and receiving a file. You need to call this function just once for the whole file, although you need to know the size of the file prior to sending and also define the size of a single block that should be internally retrieved and written into a file in a single step. This influences only the performance of the internal operations; from the application perspective you just have one call that exits only when the transmission is complete.

  • u: Socket used for transmission. The socket must be connected.

  • path: Path to the file that should be read or written.

  • offset: Needed to pass or retrieve the offset used to read or write to a file

  • size: Size of transfer (file size, if offset is at 0)

  • block: Size of the single block to read at once before writing it to a file

The following values are recommended for the block parameter:

` #define SRT_DEFAULT_SENDFILE_BLOCK 364000 #define SRT_DEFAULT_RECVFILE_BLOCK 7280000 `

You need to pass them to the srt_sendfile or srt_recvfile function if you don’t know what value to chose.

  • Returns:

    • Size (>0) of the transmitted data of a file. It may be less than size, if

    the size was greater than the free space in the buffer, in which case you have to send rest of the file next time. * -1 in case of error.

  • Errors:

    • SRT_ENOCONN: Socket u used for the operation is not connected.

    • SRT_ECONNLOST: Socket u used for the operation has lost its connection.

    • SRT_EINVALBUFFERAPI: When socket has SRTO_MESSAGEAPI = true or

    SRTO_TSBPDMODE = true.

(BUG?: Looxlike MESSAGEAPI isn’t checked)

  • SRT_EINVRDOFF: There is a mistake in offset or size parameters, which

should match the index availability and size of the bytes available since offset index. This is actually reported for srt_sendfile when the seekg or tellg operations resulted in error. * SRT_EINVWROFF: Like above, reported for srt_recvfile and seekp/tellp. * SRT_ERDPERM: The read from file operation has failed (srt_sendfile). * SRT_EWRPERM: The write to file operation has failed (srt_recvfile).

Diagnostics

General notes concerning the “getlasterror” diagnostic functions: when an API function ends up with error, this error information is stored in a thread-local storage. This means that you’ll get the error of the operation that was last performed as long as you call this diagnostic function just after the failed function has returned. In any other situation the information provided by the diagnostic function is undefined.

### srt_getlasterror

` int srt_getlasterror(int* errno_loc); `

Get the numeric code of the last error. Additionally, in the variable passed as errno_loc the system error value is returned, or 0 if there was no system error associated with the last error. The system error is:

  • On POSIX systems, the value from errno

  • On Windows, the result from GetLastError() call

### srt_strerror ` const char* srt_strerror(int code, int errnoval); `

Returns a string message that represents a given SRT error code and possibly the errno value, if not 0.

NOTE: This function isn’t thread safe. It uses a static variable to hold the error description. There’s no problem with using it in a multithreaded environment, as long as only one thread in the whole application calls this function at the moment

### srt_getlasterror_str ` const char* srt_getlasterror_str(void); `

Get the text message for the last error. It’s a shortcut to calling first srt_getlasterror and then passing the returned value into srt_strerror. Note that, in contradiction to srt_strerror, this function is thread safe.

### srt_clearlasterror

` void srt_clearlasterror(void); `

This function clears the last error. After this call, the srt_getlasterror will report a “successful” code.

### srt_getrejectreason

` enum SRT_REJECT_REASON srt_getrejectreason(SRTSOCKET sock); `

This function shall be called after a connecting function (such as srt_connect) has returned an error, which’s code was SRT_ECONNREJ. It allows to get a more detailed rejection reason. This function returns a numeric code, which can be translated into a message by srt_rejectreason_str. The following codes are currently reported:

#### SRT_REJ_UNKNOWN

A fallback value for cases when there was no connection rejected.

#### SRT_REJ_SYSTEM

One of system function reported a failure. Usually this means some system error or lack of system resources to complete the task.

#### SRT_REJ_PEER

The connection has been rejected by peer, but no further details are available. This usually means that the peer doesn’t support rejection reason reporting.

#### SRT_REJ_RESOURCE

A problem with resource allocation (usually memory).

#### SRT_REJ_ROGUE

The data sent by one party to another cannot be properly interpreted. This should not happen during normal usage, unless it’s a bug, or some weird events are happening on the network.

#### SRT_REJ_BACKLOG

The listener’s backlog has exceeded (there are many other callers waiting for the opportunity of being connected and wait in the queue, which has reached its limit).

#### SRT_REJ_IPE

Internal Program Error. This should not happen during normal usage and it usually means a bug in the software (although this can be reported by both local and foreign host).

#### SRT_REJ_CLOSE

The listener socket was able to receive your request, but at this moment it is being closed. It’s likely that your next attempt will result with timeout.

#### SRT_REJ_VERSION

Any party of the connection has set up minimum version that is required for that connection, and the other party didn’t satisfy this requirement.

#### SRT_REJ_RDVCOOKIE

Rendezvous cookie collision. This normally should never happen, or the probability that this will really happen is negligible. However this can be also a result of a misconfiguration that you are trying to make a rendezvous connection where both parties try to bind to the same IP address, or both are local addresses of the same host - in which case the sent handshake packets are returning to the same host as if they were sent by the peer, who is this party itself. When this happens, this reject reason will be reported by every attempt.

#### SRT_REJ_BADSECRET

Both parties have defined a passprhase for connection and they differ.

#### SRT_REJ_UNSECURE

Only one connection party has set up a password. See also SRTO_ENFORCEDENCRYPTION flag in API.md.

#### SRT_REJ_MESSAGEAPI

The value for SRTO_MESSAGEAPI flag is different on both connection parties.

#### SRT_REJ_CONGESTION

The SRTO_CONGESTION option has been set up differently on both connection parties.

#### SRT_REJ_FILTER

The SRTO_PACKETFILTER option has been set differently on both connection parties.

### srt_rejectreason_str

` const char* srt_rejectreason_str(enum SRT_REJECT_REASON id); `

Returns a constant string for the reason of the connection rejected, as per given code id. Alternatively you can use the srt_rejectreason_msg array. This function additionally handles the case for unknown id by reporting SRT_REJ_UNKNOWN in such case.

Performance tracking

General note concerning sequence numbers used in SRT: they are 32-bit “circular numbers” with the most significant bit not included. For example 0x7FFFFFFF shifted forward by 3 becomes 2. As far as any comparison is concerned, it can be thought of as a “distance” which is an integer value expressing an offset to be added to one sequence in order to get the second one. This distance is only valid as long as the threshold value isn’t exceeded, so it’s stated that all sequence numbers that are anywhere taken into account were systematically updated and they are kept in the range between 0 and half of the maximum 0x7FFFFFFF. Hence the distance counting procedure always assumes that the sequence number are in the required range already, so for a numbers like 0x7FFFFFF0 and 0x10, for which the “numeric difference” would be 0x7FFFFFE0, the “distance” is 0x20.

### srt_bstats, srt_bistats ``` // perfmon with Byte counters for better bitrate estimation. int srt_bstats(SRTSOCKET u, SRT_TRACEBSTATS * perf, int clear);

// permon with Byte counters and instantaneous stats instead of moving averages for Snd/Rcvbuffer sizes. int srt_bistats(SRTSOCKET u, SRT_TRACEBSTATS * perf, int clear, int instantaneous); ```

Reports the current statistics

  • u: Socket from which to get statistics

  • perf: Pointer to an object to be written with the statistics

  • clear: 1 if the statistics should be cleared after retrieval

  • instantaneous: 1 if the statistics should use instant data, not moving averages

SRT_TRACEBSTATS is an alias to struct CBytePerfMon. For a complete description of the fields please refer to the document [statistics.md](statistics.md).

Asynchronous operations (epoll)

The epoll system is currently the only method for using multiple sockets in one thread with having the blocking operation moved to epoll waiting so that it can block on multiple sockets at once. That is, instead of blocking a single reading or writing operation, as it’s in blocking mode, it blocks until at least one of the sockets subscribed for a single waiting call in given operation mode is ready to do this operation without blocking. It’s usually combined with setting the nonblocking mode on a socket, which in SRT is set separately for reading and writing (SRTO_RCVSYN and SRTO_SNDSYN respectively) in order to ensure that in case of some internal error in the application (or even possibly a bug in SRT that has reported a spurious readiness report) the operation will end up with error rather than cause blocking, which would be more dangerous for the application in this case (SRT_EASYNCRCV and SRT_EASYNCRCV respectively).

The epoll system, similar to the one on Linux, relies on eid objects managed internally in SRT, which can be subscribed to particular sockets and the readiness status of particular operations. The srt_epoll_wait function can then be used to block until any readiness status in the whole eid is set.

### srt_epoll_create ` int srt_epoll_create(void); `

Creates a new epoll container.

  • Returns:

    • valid EID on success

    • -1 on failure

  • Errors:

    • SRT_ECONNSETUP: System operation failed or not enough space to create a new epoll.

System error might happen on systems that use a special method for the system part of epoll (epoll_create(), kqueue()), and therefore associated resources, like epoll on Linux.

### srt_epoll_add_usock, srt_epoll_add_ssock, srt_epoll_update_usock, srt_epoll_update_ssock

` int srt_epoll_add_usock(int eid, SRTSOCKET u, const int* events); int srt_epoll_add_ssock(int eid, SYSSOCKET s, const int* events); int srt_epoll_update_usock(int eid, SRTSOCKET u, const int* events); int srt_epoll_update_ssock(int eid, SYSSOCKET s, const int* events); `

Adds a socket to a container, or updates an existing socket subscription.

The _usock suffix refers to a user socket (SRT socket). The _ssock suffix refers to a system socket.

The _add_ functions add new sockets. The _update_ functions act on a socket that is in the container already and just allow changes in the subscription details. For example, if you have already subscribed a socket with SRT_EPOLL_OUT to wait until it’s connected, to change it into poll for read-readiness, you use this function on that same socket with a variable set to SRT_EPOLL_IN. This will not only change the event type which is polled on the socket, but also remove any readiness status for flags that are no longer set. It is discouraged to perform socket removal and adding back (instead of using _update_) because this way you may miss an event that could happen in a short moment between these two calls.

  • eid: epoll container id

  • u: SRT socket

  • s: system socket

  • events: points to * a variable set to epoll flags (see below) to use only selected events * NULL if you want to subscribe a socket for all events in level-triggered mode

Possible epoll flags are the following:

  • SRT_EPOLL_IN: report readiness for reading or incoming connection on a listener socket

  • SRT_EPOLL_OUT: report readiness for writing or a successful connection

  • SRT_EPOLL_ERR: report errors on the socket

  • SRT_EPOLL_ET: the event will be edge-triggered

The readiness states reported in by default are level-triggered. If SRT_EPOLL_ET flag is specified, the reported states are edge-triggered. Note that at this time the edge-triggered mode is supported only for SRT sockets, not for system sockets.

In the edge-triggered mode the function will only return socket states that have changed since the last call. All events reported in particular call of the waiting function will be cleared in the internal flags and will not be reported until the internal signaling logic clears this state and raises it again.

In the level-triggered mode the function will always return the readiness state as long as it lasts, until the internal signaling logic clear it.

Note that when you use SRT_EPOLL_ET flag in one subscription call, it defines edge-triggered mode for all events passed together with it. However, if you want to have some events reported as edge-triggered and others as level-triggered, you can do two separate subscriptions for the same socket.

  • Returns:

    • 0 if successful, otherwise -1

  • Errors:

    • SRT_EINVPOLLID: eid parameter doesn’t refer to a valid epoll container

BUG?: for add_ssock the system error results in an empty CUDTException() call which actually results in SRT_SUCCESS. For cases like that the SRT_ECONNSETUP code is predicted.

### srt_epoll_remove_usock, srt_epoll_remove_ssock

` int srt_epoll_remove_usock(int eid, SRTSOCKET u); int srt_epoll_remove_ssock(int eid, SYSSOCKET s); `

Removes a specified socket from an epoll container and clears all readiness states recorded for that socket.

The _usock suffix refers to a user socket (SRT socket). The _ssock suffix refers to a system socket.

  • Returns:

    • 0 if successful, otherwise -1

  • Errors:

    • SRT_EINVPOLLID: eid parameter doesn’t refer to a valid epoll container

### srt_epoll_wait ``` int srt_epoll_wait(int eid, SRTSOCKET* readfds, int* rnum, SRTSOCKET* writefds, int* wnum, int64_t msTimeOut,

SYSSOCKET* lrfds, int* lrnum, SYSSOCKET* lwfds, int* lwnum);

```

Blocks the call until any readiness state occurs in the epoll container.

Readiness can be on a socket in the container for the event type as per subscription. Note that in case when particular event was subscribed with SRT_EPOLL_ET flag, this event, when once reported in this function, will be cleared internally.

The first readiness state causes this function to exit, but all ready sockets are reported. This function blocks until the timeout specified in msTimeOut parameter. If timeout is 0, it exits immediately after checking. If timeout is -1, it blocks indefinitely until a readiness state occurs.

  • eid: epoll container

  • readfds and rnum: A pointer and length of an array to write SRT sockets that are read-ready

  • writefds and wnum: A pointer and length of an array to write SRT sockets that are write-ready

  • msTimeOut: Timeout specified in milliseconds, or special values (0 or -1)

  • lwfds and lwnum:A pointer and length of an array to write system sockets that are read-ready

  • lwfds and lwnum:A pointer and length of an array to write system sockets that are write-ready

Note that there is no space here to report sockets for which it’s already known that the operation will end up with error (athough such a state is known internally). If an error occurred on a socket then that socket is reported in both read-ready and write-ready arrays, regardless of what event types it was subscribed for. Usually then you subscribe given socket for only read readiness, for example (SRT_EPOLL_IN), but pass both arrays for read and write readiness. This socket will not be reported in the write readiness array even if it’s write ready (because this isn’t what it was subscribed for), but it will be reported there, if the next operation on this socket is about to be erroneous. On such sockets you can still perform an operation, just you should expect that it will always report and error. On the other hand that’s the only way to know what kind of error has occurred on the socket.

  • Returns:

    • The number (>0) of ready sockets, of whatever kind (if any)

    • -1 in case of error

  • Errors:

    • SRT_EINVPOLLID: eid parameter doesn’t refer to a valid epoll container

    • SRT_ETIMEOUT: Up to msTimeOut no sockets subscribed in eid were ready.

This is reported only if msTimeOut was >=0, otherwise the function waits indefinitely.

### srt_epoll_uwait ` int srt_epoll_uwait(int eid, SRT_EPOLL_EVENT* fdsSet, int fdsSize, int64_t msTimeOut); `

This function blocks a call until any readiness state occurs in the epoll container. Unlike srt_epoll_wait, it can only be used with eid subscribed to user sockets (SRT sockets), not system sockets.

This function blocks until the timeout specified in msTimeOut parameter. If timeout is 0, it exits immediately after checking. If timeout is -1, it blocks indefinitely until a readiness state occurs.

  • eid: epoll container

  • fdsSet : A pointer to an array of SRT_EPOLL_EVENT

  • fdsSize : The size of the fdsSet array

  • msTimeOutTimeout specified in milliseconds, or special values (0 or -1):

    • 0: Don’t wait, return immediately (report any sockets currently ready)

    • -1: Wait indefinitely.

  • Returns:

    • The number of user socket (SRT socket) state changes that have been reported

in fdsSet, if this number isn’t greater than fdsSize

  • Otherwise the return value is fdsSize + 1. This means that there was not

enough space in the output array to report all events. For events subscribed with SRT_EPOLL_ET flag only those will be cleared that were reported. Others will wait for the next call.

  • If no readiness state was found on any socket and the timeout has passed, 0

is returned (this is not possible when waiting indefinitely)

  • -1 in case of error

  • Errors:

    • SRT_EINVPOLLID: eid parameter doesn’t refer to a valid epoll container

    • SRT_EINVPARAM: One of possible usage errors: * fdsSize is < 0 * fdsSize is > 0 and fdsSet is a null pointer * eid was subscribed to any system socket

(IMPORTANT: this function reports timeout by returning 0, not by SRT_ETIMEOUT error.)

The SRT_EPOLL_EVENT structure:

``` typedef struct SRT_EPOLL_EVENT_ {

SRTSOCKET fd; int events;

} SRT_EPOLL_EVENT; ```

  • fd : the user socket (SRT socket)

  • events : event flags that report readiness of this socket - a combination

of SRT_EPOLL_IN, SRT_EPOLL_OUT and SRT_EPOLL_ERR - see [srt_epoll_add_usock](#srt_epoll_add_usock) for details

Note that when the SRT_EPOLL_ERR is set, the underlying socket error can’t be retrieved with srt_getlasterror(). The socket will be automatically closed and its state can be verified with a call to srt_getsockstate.

### srt_epoll_set ` int32_t srt_epoll_set(int eid, int32_t flags); `

This function allows to set or retrieve flags that change the default behavior of the epoll functions. All default values for these flags are 0. The following flags are available:

  • SRT_EPOLL_ENABLE_EMPTY: allows the srt_epoll_wait and srt_epoll_uwait

functions to be called with the EID not subscribed to any socket. The default behavior of these function is to report error in this case.

  • SRT_EPOLL_ENABLE_OUTPUTCHECK: Forces the srt_epoll_wait and srt_epoll_uwait

functions to check if the output array is not empty. For srt_epoll_wait it is still allowed that either system or user array is empty, as long as EID isn’t subscribed to this type of socket/fd. srt_epoll_uwait only checks if the general output array is not empty.

  • Parameters:

    • eid: the epoll container id

    • flags: a nonzero set of the above flags, or special values:

      • 0: clear all flags (set all defaults)

      • -1: do not modify any flags

  • Returns:

This function returns the state of the flags at the time before the call, or a special value -1 in case when an error occurred.

  • Errors:

    • SRT_EINVPOLLID: eid parameter doesn’t refer to a valid epoll container

### srt_epoll_release ` int srt_epoll_release(int eid); `

Deletes the epoll container.

  • Returns:

    • The number (>0) of ready sockets, of whatever kind (if any)

    • -1 in case of error

  • Errors:

    • SRT_EINVPOLLID: eid parameter doesn’t refer to a valid epoll container

Logging control

SRT has a widely used system of logs, as this is usually the only way to determine how the internals are working, without changing the rules by the act of tracing. Logs are split into levels (5 levels out of those defined by syslog are in use) and additional filtering is possible on FA (functional area). By default only up to the Note log level are displayed and from all FAs.

Logging can only be manipulated globally, with no regard to a specific socket. This is because lots of operations in SRT are not dedicated to any particular socket, and some are shared between sockets.

### srt_setloglevel

` void srt_setloglevel(int ll); `

Sets the minimum severity for logging. A particular log entry is displayed only if it has a severity greater than or equal to the minimum. Setting this value to LOG_DEBUG turns on all levels.

The constants for this value are those from <sys/syslog.h> (for Windows, refer to common/win/syslog_defs.h). The only meaningful are:

  • LOG_DEBUG: Highly detailed and very frequent messages

  • LOG_NOTICE: Occasionally displayed information

  • LOG_WARNING: Unusual behavior

  • LOG_ERR: Abnormal behavior

  • LOG_CRIT: Error that makes the current socket unusable

### srt_addlogfa, srt_dellogfa, srt_resetlogfa

` void srt_addlogfa(int fa); void srt_dellogfa(int fa); void srt_resetlogfa(const int* fara, size_t fara_size); `

A functional area (FA) is an additional filtering mechanism for logging. You can set up logging to display logs only from selected FAs. The list of FAs is collected in srt.h file, as identified by the SRT_LOGFA_ prefix. They are not enumerated here because they may be changed very often.

All FAs are turned on by default, except potentially dangerous ones (such as SRT_LOGFA_HAICRYPT). The reaons is that they may display either some security information that shall remain in the memory only (so, only if strictly required for the development), or some duplicated information (so you may want to turn this FA on, while turning off the others).

### srt_setloghandler ` void srt_setloghandler(void* opaque, SRT_LOG_HANDLER_FN* handler); typedef void SRT_LOG_HANDLER_FN(void* opaque, int level, const char* file, int line, const char* area, const char* message); `

By default logs are printed to standard error stream. This function replaces the sending to a stream with a handler function that will receive them.

### srt_setlogflags ` void srt_setlogflags(int flags); `

When you set a log handler with srt_setloghandler, you may also want to configure which parts of the log information you do not wish to be passed in the log line (the message parameter). A user’s logging facility may, for example, not wish to get the current time or log level marker, as it will provide this information on its own.

The following flags are available, as collected in logging_api.h public header:

  • SRT_LOGF_DISABLE_TIME: Do not provide the time in the header

  • SRT_LOGF_DISABLE_THREADNAME: Do not provide the thread name in the header

  • SRT_LOGF_DISABLE_SEVERITY: Do not provide severity information in the header

  • SRT_LOGF_DISABLE_EOL: Do not add the end-of-line character to the log line

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