TSIOBufferReader

Traffic Server IO buffer reader API.

Synopsis

#include <ts/ts.h>

TSIOBufferReader TSIOBufferReaderAlloc(TSIOBuffer bufp)
TSIOBufferReader TSIOBufferReaderClone(TSIOBufferReader readerp)
void TSIOBufferReaderFree(TSIOBufferReader readerp)
void TSIOBufferReaderConsume(TSIOBufferReader readerp, int64_t nbytes)
TSIOBufferBlock TSIOBufferReaderStart(TSIOBufferReader readerp)
int64_t TSIOBufferReaderAvail(TSIOBufferReader readerp)
bool TSIOBufferReaderIsAvailAtLeast(TSIOBufferReader, int64_t nbytes)
int64_t TSIOBufferReaderRead(TSIOBufferReader reader, const void * buf, int64_t length)
bool TSIOBufferReaderIterate(TSIOBufferReader reader, TSIOBufferBlockFunc* func, void* context)
TSIOBufferBlockFunc

bool (*TSIOBufferBlockFunc)(void const* data, int64_t nbytes, void* context)

data is the data in the TSIOBufferBlock and is nbytes long. context is opaque data provided to the API call along with this function and passed on to the function. This function should return true to continue iteration or false to terminate iteration.

Description

TSIOBufferReader is an read accessor for TSIOBuffer. It represents a location in the contents of the buffer. A buffer can have multiple readers and each reader consumes data in the buffer independently. Data which for which there are no readers is discarded from the buffer. This has two very important consequences –

  • Data for which there are no readers and no writer will be discarded. In effect this means without
    any readers only the current write buffer block will be maintained, older buffer blocks will disappear.
  • Conversely keeping a reader around unused will pin the buffer data in memory. This can be useful or harmful.

A buffer has a fixed amount of possible readers (currently 5) which is determined at compile time. Reader allocation is fast and cheap until this maxium is reached at which point it fails.

TSIOBufferReaderAlloc() allocates a reader for the IO buffer bufp. This should only be
called on a newly allocated buffer. If not the location of the reader in the buffer will be indeterminate. Use TSIOBufferReaderClone() to get another reader if the buffer is already in use.

TSIOBufferReaderClone() allocates a reader and sets its position in the buffer to be the same as reader.

TSIOBufferReaderFree() de-allocates the reader. Any data referenced only by this reader is
discarded from the buffer.
TSIOBufferReaderConsume() advances the position of reader in its IO buffer by the
the smaller of nbytes and the maximum available in the buffer.

TSIOBufferReaderStart() returns the IO buffer block containing the position of reader.

Note

The byte at the position of reader is in the block but is not necessarily the first byte of the block.

TSIOBufferReaderAvail() returns the number of bytes which reader could consume. That is
the number of bytes in the IO buffer starting at the current position of reader.
TSIOBufferReaderIsAvailAtLeast() return true if the available number of bytes for
reader is at least nbytes, false if not. This can be more efficient than TSIOBufferReaderAvail() because the latter must walk all the IO buffer blocks in the IO buffer. This function returns as soon as the return value can be determined. In particular a value of 1 for nbytes means only the first buffer block will be checked.
TSIOBufferReaderRead() reads data from reader. This first copies data from the IO
buffer for reader to the target buffer bufp, starting at reader`s position, and then advances (as with :func:`TSIOBufferReaderConsume) reader`s position past the copied data. The amount of data read in this fashion is the smaller of the amount of data available in the IO buffer for :arg:`reader and the size of the target buffer (length).

TSIOBufferReaderIterate() iterates over the blocks for reader. For each block func is called with with the data for the block and context. The context is an opaque type to this function and is passed unchanged to func. It is intended to be used as context for func. If func returns false the iteration terminates. If func returns true the block is consumed. The return value for TSIOBufferReaderIterate() is the return value from the last call to func.

Note

If it would be a problem for the iteration to consume the data (especially in cases where false might be returned) the reader can be cloned via TSIOBufferReaderClone() to keep the data in the IO buffer and available. If not needed the reader can be destroyed or if needed the original reader can be destroyed and replaced by the clone.

Note

Destroying a TSIOBuffer will de-allocate and destroy all readers for that buffer.

See also

TSIOBufferCreate(3ts)