## libvirt-stream

libvirt-stream - APIs for management of streams

Provides APIs for the management of streams Copyright (C) 2006-2014 Red Hat, Inc. This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library. If not, see <http://www.gnu.org/licenses/>.

## Synopsis

    typedef enum virStreamEventType;
    typedef enum virStreamFlags;
    typedef enum virStreamRecvFlagsValues;
    int	virStreamAbort			(virStreamPtr stream);
    int	virStreamEventAddCallback	(virStreamPtr stream,
    					 int events,
    					 virStreamEventCallback cb,
    					 void * opaque,
    					 virFreeCallback ff);
    typedef void virStreamEventCallback		(virStreamPtr stream,
    					 int events,
    					 void * opaque);
    int	virStreamEventRemoveCallback	(virStreamPtr stream);
    int	virStreamEventUpdateCallback	(virStreamPtr stream,
    					 int events);
    int	virStreamFinish			(virStreamPtr stream);
    int	virStreamFree			(virStreamPtr stream);
    virStreamPtr	virStreamNew		(virConnectPtr conn,
    					 unsigned int flags);
    int	virStreamRecv			(virStreamPtr stream,
    					 char * data,
    					 size_t nbytes);
    int	virStreamRecvAll		(virStreamPtr stream,
    					 virStreamSinkFunc handler,
    					 void * opaque);
    int	virStreamRecvFlags		(virStreamPtr stream,
    					 char * data,
    					 size_t nbytes,
    					 unsigned int flags);
    int	virStreamRecvHole		(virStreamPtr stream,
    					 long long * length,
    					 unsigned int flags);
    int	virStreamRef			(virStreamPtr stream);
    int	virStreamSend			(virStreamPtr stream,
    					 const char * data,
    					 size_t nbytes);
    int	virStreamSendAll		(virStreamPtr stream,
    					 virStreamSourceFunc handler,
    					 void * opaque);
    int	virStreamSendHole		(virStreamPtr stream,
    					 long long length,
    					 unsigned int flags);
    typedef int virStreamSinkFunc		(virStreamPtr st,
    					 const char * data,
    					 size_t nbytes,
    					 void * opaque);
    typedef int virStreamSinkHoleFunc		(virStreamPtr st,
    					 long long length,
    					 void * opaque);
    typedef int virStreamSourceFunc		(virStreamPtr st,
    					 char * data,
    					 size_t nbytes,
    					 void * opaque);
    typedef int virStreamSourceHoleFunc		(virStreamPtr st,
    					 int * inData,
    					 long long * length,
    					 void * opaque);
    typedef int virStreamSourceSkipFunc		(virStreamPtr st,
    					 long long length,
    					 void * opaque);
    int	virStreamSparseRecvAll		(virStreamPtr stream,
    					 virStreamSinkFunc handler,
    					 virStreamSinkHoleFunc holeHandler,
    					 void * opaque);
    int	virStreamSparseSendAll		(virStreamPtr stream,
    					 virStreamSourceFunc handler,
    					 virStreamSourceHoleFunc holeHandler,
    					 virStreamSourceSkipFunc skipHandler,
    					 void * opaque);

## Description

## Details

### Enum virStreamEventType

    enum virStreamEventType {
        VIR_STREAM_EVENT_READABLE = 1
        VIR_STREAM_EVENT_WRITABLE = 2
        VIR_STREAM_EVENT_ERROR = 4
        VIR_STREAM_EVENT_HANGUP = 8
    };

### Enum virStreamFlags

    enum virStreamFlags {
        VIR_STREAM_NONBLOCK = 1
    };

### Enum virStreamRecvFlagsValues

    enum virStreamRecvFlagsValues {
        VIR_STREAM_RECV_STOP_AT_HOLE = 1
    };

### Function type virStreamEventCallback

    void	virStreamEventCallback		(virStreamPtr stream,
    					 int events,
    					 void * opaque)

Callback for receiving stream events. The callback will be invoked once for each event which is pending.

`stream`: | stream on which the event occurred
`events`: | bitset of events from virEventHandleType constants
`opaque`: | user data registered with handle

### Function type virStreamSinkFunc

    int	virStreamSinkFunc		(virStreamPtr st,
    					 const char * data,
    					 size_t nbytes,
    					 void * opaque)

The virStreamSinkFunc callback is used together with the virStreamRecvAll or virStreamSparseRecvAll functions for libvirt to provide the data that has been received. The callback will be invoked multiple times, providing data in small chunks. The application should consume up 'nbytes' from the 'data' array of data and then return the number actual number of bytes consumed. The callback will continue to be invoked until it indicates the end of the stream has been reached. A return value of -1 at any time will abort the receive operation Please note that for more accurate error reporting the callback should set appropriate errno on failure.

`st`: | the stream object
`data`: | preallocated array to be filled with data
`nbytes`: | size of the data array
`opaque`: | optional application provided data
`Returns`: | the number of bytes consumed or -1 upon error

### Function type virStreamSinkHoleFunc

    int	virStreamSinkHoleFunc		(virStreamPtr st,
    					 long long length,
    					 void * opaque)

This callback is used together with the virStreamSparseRecvAll function for libvirt to provide the size of a hole that occurred in the stream. The callback may be invoked multiple times as holes are found during processing a stream. The application should create the hole in the stream target and then return. A return value of -1 at any time will abort the receive operation. Please note that for more accurate error reporting the callback should set appropriate errno on failure.

`st`: | the stream object
`length`: | stream hole size
`opaque`: | optional application provided data
`Returns`: | 0 on success, -1 upon error

### Function type virStreamSourceFunc

    int	virStreamSourceFunc		(virStreamPtr st,
    					 char * data,
    					 size_t nbytes,
    					 void * opaque)

The virStreamSourceFunc callback is used together with the virStreamSendAll and virStreamSparseSendAll functions for libvirt to obtain the data that is to be sent. The callback will be invoked multiple times, fetching data in small chunks. The application should fill the 'data' array with up to 'nbytes' of data and then return the number actual number of bytes. The callback will continue to be invoked until it indicates the end of the source has been reached by returning 0. A return value of -1 at any time will abort the send operation. Please note that for more accurate error reporting the callback should set appropriate errno on failure.

`st`: | the stream object
`data`: | preallocated array to be filled with data
`nbytes`: | size of the data array
`opaque`: | optional application provided data
`Returns`: | the number of bytes filled, 0 upon end of file, or -1 upon error

### Function type virStreamSourceHoleFunc

    int	virStreamSourceHoleFunc		(virStreamPtr st,
    					 int * inData,
    					 long long * length,
    					 void * opaque)

The virStreamSourceHoleFunc callback is used together with the virStreamSparseSendAll function for libvirt to obtain the length of section stream is currently in. Moreover, upon successful return, @length should be updated with how many bytes are left until the current section ends (either data section or hole section). Also the stream is currently in data section, @inData should be set to a non-zero value and vice versa. NB: there's an implicit hole at the end of each file. If that's the case, @inData and @length should be both set to 0. This function should not adjust the current position within the file. Please note that for more accurate error reporting the callback should set appropriate errno on failure.

`st`: | the stream object
`inData`: | are we in data section
`length`: | how long is the section we are currently in
`opaque`: | optional application provided data
`Returns`: | 0 on success, -1 upon error

### Function type virStreamSourceSkipFunc

    int	virStreamSourceSkipFunc		(virStreamPtr st,
    					 long long length,
    					 void * opaque)

This callback is used together with the virStreamSparseSendAll to skip holes in the underlying file as reported by virStreamSourceHoleFunc. The callback may be invoked multiple times as holes are found during processing a stream. The application should skip processing the hole in the stream source and then return. A return value of -1 at any time will abort the send operation. Please note that for more accurate error reporting the callback should set appropriate errno on failure.

`st`: | the stream object
`length`: | stream hole size
`opaque`: | optional application provided data
`Returns`: | 0 on success, -1 upon error.

### virStreamAbort ()

    int	virStreamAbort			(virStreamPtr stream)

Request that the in progress data transfer be cancelled abnormally before the end of the stream has been reached. For output streams this can be used to inform the driver that the stream is being terminated early. For input streams this can be used to inform the driver that it should stop sending data. If the stream is non-blocking, any callback must be removed beforehand.

`stream`: | pointer to the stream object
`Returns`: | 0 on success, -1 upon error

### virStreamEventAddCallback ()

    int	virStreamEventAddCallback	(virStreamPtr stream,
    					 int events,
    					 virStreamEventCallback cb,
    					 void * opaque,
    					 virFreeCallback ff)

Register a callback to be notified when a stream becomes writable, or readable. This is most commonly used in conjunction with non-blocking data streams to integrate into an event loop

`stream`: | pointer to the stream object
`events`: | set of events to monitor
`cb`: | callback to invoke when an event occurs
`opaque`: | application defined data
`ff`: | callback to free @opaque data
`Returns`: | 0 on success, -1 upon error

### virStreamEventRemoveCallback ()

    int	virStreamEventRemoveCallback	(virStreamPtr stream)

Remove an event callback from the stream

`stream`: | pointer to the stream object
`Returns`: | 0 on success, -1 on error

### virStreamEventUpdateCallback ()

    int	virStreamEventUpdateCallback	(virStreamPtr stream,
    					 int events)

Changes the set of events to monitor for a stream. This allows for event notification to be changed without having to unregister & register the callback completely. This method is guaranteed to succeed if a callback is already registered

`stream`: | pointer to the stream object
`events`: | set of events to monitor
`Returns`: | 0 on success, -1 if no callback is registered

### virStreamFinish ()

    int	virStreamFinish			(virStreamPtr stream)

Indicate that there is no further data to be transmitted on the stream. For output streams this should be called once all data has been written. For input streams this should be called once virStreamRecv returns end-of-file. This method is a synchronization point for all asynchronous errors, so if this returns a success code the application can be sure that all data has been successfully processed. If the stream is non-blocking, any callback must be removed beforehand.

`stream`: | pointer to the stream object
`Returns`: | 0 on success, -1 upon error

### virStreamFree ()

    int	virStreamFree			(virStreamPtr stream)

Decrement the reference count on a stream, releasing the stream object if the reference count has hit zero. There must not be an active data transfer in progress when releasing the stream. If a stream needs to be disposed of prior to end of stream being reached, then the virStreamAbort function should be called first.

`stream`: | pointer to the stream object
`Returns`: | 0 upon success, or -1 on error

### virStreamNew ()

    virStreamPtr	virStreamNew		(virConnectPtr conn,
    					 unsigned int flags)

Creates a new stream object which can be used to perform streamed I/O with other public API function. When no longer needed, a stream object must be released with virStreamFree. If a data stream has been used, then the application must call virStreamFinish or virStreamAbort before free'ing to, in order to notify the driver of termination. If a non-blocking data stream is required passed VIR_STREAM_NONBLOCK for flags, otherwise pass 0.

`conn`: | pointer to the connection
`flags`: | bitwise-OR of virStreamFlags
`Returns`: | the new stream, or NULL upon error

### virStreamRecv ()

    int	virStreamRecv			(virStreamPtr stream,
    					 char * data,
    					 size_t nbytes)

Reads a series of bytes from the stream. This method may block the calling application for an arbitrary amount of time. Errors are not guaranteed to be reported synchronously with the call, but may instead be delayed until a subsequent call. An example using this with a hypothetical file download API looks like virStreamPtr st = virStreamNew(conn, 0); int fd = open("demo.iso", O_WRONLY, 0600); virConnectDownloadFile(conn, "demo.iso", st); while (1) { char buf[1024]; int got = virStreamRecv(st, buf, 1024); if (got < 0) { virStreamAbort(st); break; } if (got == 0) { virStreamFinish(st); break; } int offset = 0; while (offset < got) { int sent = write(fd, buf + offset, got - offset); if (sent < 0) { virStreamAbort(st); goto done; } offset += sent; } } if (virStreamFinish(st) < 0) ... report an error .... done: virStreamFree(st); close(fd);

`stream`: | pointer to the stream object
`data`: | buffer to read into from stream
`nbytes`: | size of @data buffer
`Returns`: | the number of bytes read, which may be less than requested. Returns 0 when the end of the stream is reached, at which time the caller should invoke virStreamFinish() to get confirmation of stream completion. Returns -1 upon error, at which time the stream will be marked as aborted, and the caller should now release the stream with virStreamFree. Returns -2 if there is no data pending to be read & the stream is marked as non-blocking.

### virStreamRecvAll ()

    int	virStreamRecvAll		(virStreamPtr stream,
    					 virStreamSinkFunc handler,
    					 void * opaque)

Receive the entire data stream, sending the data to the requested data sink. This is simply a convenient alternative to virStreamRecv, for apps that do blocking-I/O. An example using this with a hypothetical file download API looks like int mysink(virStreamPtr st, const char *buf, int nbytes, void *opaque) { int *fd = opaque; return write(*fd, buf, nbytes); } virStreamPtr st = virStreamNew(conn, 0); int fd = open("demo.iso", O_WRONLY); virConnectUploadFile(conn, st); if (virStreamRecvAll(st, mysink, &fd) < 0) { ...report an error ... goto done; } if (virStreamFinish(st) < 0) ...report an error... virStreamFree(st); close(fd);

`stream`: | pointer to the stream object
`handler`: | sink callback for writing data to application
`opaque`: | application defined data
`Returns`: | 0 if all the data was successfully received. The caller should invoke virStreamFinish(st) to flush the stream upon success and then virStreamFree Returns -1 upon any error, with virStreamAbort() already having been called, so the caller need only call virStreamFree()

### virStreamRecvFlags ()

    int	virStreamRecvFlags		(virStreamPtr stream,
    					 char * data,
    					 size_t nbytes,
    					 unsigned int flags)

Reads a series of bytes from the stream. This method may block the calling application for an arbitrary amount of time. This is just like virStreamRecv except this one has extra @flags. Calling this function with no @flags set (equal to zero) is equivalent to calling virStreamRecv(stream, data, nbytes). If flag VIR_STREAM_RECV_STOP_AT_HOLE is set, this function will stop reading from stream if it has reached a hole. In that case, -3 is returned and virStreamRecvHole() should be called to get the hole size. An example using this flag might look like this: while (1) { char buf[4096]; int ret = virStreamRecvFlags(st, buf, len, VIR_STREAM_STOP_AT_HOLE); if (ret < 0) { if (ret == -3) { long long len; ret = virStreamRecvHole(st, &len, 0); if (ret < 0) { ...error.. } else { ...seek len bytes in target... } } else { return -1; } } else { ...write buf to target... } }

`stream`: | pointer to the stream object
`data`: | buffer to read into from stream
`nbytes`: | size of @data buffer
`flags`: | bitwise-OR of virStreamRecvFlagsValues
`Returns`: | 0 when the end of the stream is reached, at which time the caller should invoke virStreamFinish() to get confirmation of stream completion. Returns -1 upon error, at which time the stream will be marked as aborted, and the caller should now release the stream with virStreamFree. Returns -2 if there is no data pending to be read & the stream is marked as non-blocking. Returns -3 if there is a hole in stream and caller requested to stop at a hole.

### virStreamRecvHole ()

    int	virStreamRecvHole		(virStreamPtr stream,
    					 long long * length,
    					 unsigned int flags)

This API is used to determine the @length in bytes of the empty space to be created in a @stream's target file when uploading or downloading sparsely populated files. This is the counterpart to virStreamSendHole().

`stream`: | pointer to the stream object
`length`: | number of bytes to skip
`flags`: | extra flags; not used yet, so callers should always pass 0
`Returns`: | 0 on success, -1 on error or when there's currently no hole in the stream

### virStreamRef ()

    int	virStreamRef			(virStreamPtr stream)

Increment the reference count on the stream. For each additional call to this method, there shall be a corresponding call to virStreamFree to release the reference count, once the caller no longer needs the reference to this object.

`stream`: | pointer to the stream
`Returns`: | 0 in case of success, -1 in case of failure

### virStreamSend ()

    int	virStreamSend			(virStreamPtr stream,
    					 const char * data,
    					 size_t nbytes)

Write a series of bytes to the stream. This method may block the calling application for an arbitrary amount of time. Once an application has finished sending data it should call virStreamFinish to wait for successful confirmation from the driver, or detect any error. This method may not be used if a stream source has been registered. Errors are not guaranteed to be reported synchronously with the call, but may instead be delayed until a subsequent call. An example using this with a hypothetical file upload API looks like virStreamPtr st = virStreamNew(conn, 0); int fd = open("demo.iso", O_RDONLY); virConnectUploadFile(conn, "demo.iso", st); while (1) { char buf[1024]; int got = read(fd, buf, 1024); if (got < 0) { virStreamAbort(st); break; } if (got == 0) { virStreamFinish(st); break; } int offset = 0; while (offset < got) { int sent = virStreamSend(st, buf+offset, got-offset); if (sent < 0) { virStreamAbort(st); goto done; } offset += sent; } } if (virStreamFinish(st) < 0) ... report an error .... done: virStreamFree(st); close(fd);

`stream`: | pointer to the stream object
`data`: | buffer to write to stream
`nbytes`: | size of @data buffer
`Returns`: | the number of bytes written, which may be less than requested. Returns -1 upon error, at which time the stream will be marked as aborted, and the caller should now release the stream with virStreamFree. Returns -2 if the outgoing transmit buffers are full & the stream is marked as non-blocking.

### virStreamSendAll ()

    int	virStreamSendAll		(virStreamPtr stream,
    					 virStreamSourceFunc handler,
    					 void * opaque)

Send the entire data stream, reading the data from the requested data source. This is simply a convenient alternative to virStreamSend, for apps that do blocking-I/O. An example using this with a hypothetical file upload API looks like int mysource(virStreamPtr st, char *buf, int nbytes, void *opaque) { int *fd = opaque; return read(*fd, buf, nbytes); } virStreamPtr st = virStreamNew(conn, 0); int fd = open("demo.iso", O_RDONLY); virConnectUploadFile(conn, st); if (virStreamSendAll(st, mysource, &fd) < 0) { ...report an error ... goto done; } if (virStreamFinish(st) < 0) ...report an error... virStreamFree(st); close(fd);

`stream`: | pointer to the stream object
`handler`: | source callback for reading data from application
`opaque`: | application defined data
`Returns`: | 0 if all the data was successfully sent. The caller should invoke virStreamFinish(st) to flush the stream upon success and then virStreamFree Returns -1 upon any error, with virStreamAbort() already having been called, so the caller need only call virStreamFree().

### virStreamSendHole ()

    int	virStreamSendHole		(virStreamPtr stream,
    					 long long length,
    					 unsigned int flags)

Rather than transmitting empty file space, this API directs the @stream target to create @length bytes of empty space. This API would be used when uploading or downloading sparsely populated files to avoid the needless copy of empty file space. An example using this with a hypothetical file upload API looks like: virStream st; while (1) { char buf[4096]; size_t len; if (..in hole...) { ..get hole size... virStreamSendHole(st, len, 0); } else { ...read len bytes... virStreamSend(st, buf, len); } }

`stream`: | pointer to the stream object
`length`: | number of bytes to skip
`flags`: | extra flags; not used yet, so callers should always pass 0
`Returns`: | 0 on success, -1 error

### virStreamSparseRecvAll ()

    int	virStreamSparseRecvAll		(virStreamPtr stream,
    					 virStreamSinkFunc handler,
    					 virStreamSinkHoleFunc holeHandler,
    					 void * opaque)

Receive the entire data stream, sending the data to the requested data sink @handler and calling the skip @holeHandler to generate holes for sparse stream targets. This is simply a convenient alternative to virStreamRecvFlags, for apps that do blocking-I/O. An example using this with a hypothetical file download API looks like: int mysink(virStreamPtr st, const char *buf, int nbytes, void *opaque) { int *fd = opaque; return write(*fd, buf, nbytes); } int myskip(virStreamPtr st, long long offset, void *opaque) { int *fd = opaque; return lseek(*fd, offset, SEEK_CUR) == (off_t) -1 ? -1 : 0; } virStreamPtr st = virStreamNew(conn, 0); int fd = open("demo.iso", O_WRONLY); virConnectDownloadSparseFile(conn, st); if (virStreamSparseRecvAll(st, mysink, myskip, &fd) < 0) { ...report an error ... goto done; } if (virStreamFinish(st) < 0) ...report an error... virStreamFree(st); close(fd); Note that @opaque data is shared between both @handler and @holeHandler callbacks.

`stream`: | pointer to the stream object
`handler`: | sink callback for writing data to application
`holeHandler`: | stream hole callback for skipping holes
`opaque`: | application defined data
`Returns`: | 0 if all the data was successfully received. The caller should invoke virStreamFinish(st) to flush the stream upon success and then virStreamFree(st). Returns -1 upon any error, with virStreamAbort() already having been called, so the caller need only call virStreamFree().

### virStreamSparseSendAll ()

    int	virStreamSparseSendAll		(virStreamPtr stream,
    					 virStreamSourceFunc handler,
    					 virStreamSourceHoleFunc holeHandler,
    					 virStreamSourceSkipFunc skipHandler,
    					 void * opaque)

Send the entire data stream, reading the data from the requested data source. This is simply a convenient alternative to virStreamSend, for apps that do blocking-I/O. An example using this with a hypothetical file upload API looks like int mysource(virStreamPtr st, char *buf, int nbytes, void *opaque) { int *fd = opaque; return read(*fd, buf, nbytes); } int myskip(virStreamPtr st, long long offset, void *opaque) { int *fd = opaque; return lseek(*fd, offset, SEEK_CUR) == (off_t) -1 ? -1 : 0; } int myindata(virStreamPtr st, int *inData, long long *offset, void *opaque) { int *fd = opaque; if (@fd in hole) { *inData = 0; *offset = holeSize; } else { *inData = 1; *offset = dataSize; } return 0; } virStreamPtr st = virStreamNew(conn, 0); int fd = open("demo.iso", O_RDONLY); virConnectUploadSparseFile(conn, st); if (virStreamSparseSendAll(st, mysource, myindata, myskip, &fd) < 0) { ...report an error ... goto done; } if (virStreamFinish(st) < 0) ...report an error... virStreamFree(st); close(fd); Note that @opaque data are shared between @handler, @holeHandler and @skipHandler.

`stream`: | pointer to the stream object
`handler`: | source callback for reading data from application
`holeHandler`: | source callback for determining holes
`skipHandler`: | skip holes as reported by @holeHandler
`opaque`: | application defined data
`Returns`: | 0 if all the data was successfully sent. The caller should invoke virStreamFinish(st) to flush the stream upon success and then virStreamFree. Returns -1 upon any error, with virStreamAbort() already having been called, so the caller need only call virStreamFree().