Buffers

Usage

use Buffers;

Support for buffers - regions of memory without a particular interpretation.

This module provides bytes and buffer types which can be used to manage memory regions.

These types should be safe to use in a multi-locale context. These types should free their memory after the last user of that memory goes out of scope. They are currently reference counted but that may not always be the case.

Bytes Type

A bytes is a contiguous memory region - really a data structure containing a pointer, length, and also the information necessary to free the memory region when it is no longer used.

Buffers

A buffer consists of a sequence of views into bytes objects. A bytes object might be shared by several buffer objects. It is efficient to go to a particular offset in a buffer, and to push or pop bytes objects from the beginning or end of a buffer.

record bytes

This type represents a contiguous sequence of bytes. This sequence of bytes is represented with a C pointer and length and is currently reference counted. Note that this record contains private fields in addition to the home field.

var home: locale

The home locale storing the data

proc bytes.init()

Construct an empty bytes object

proc bytes.init(len: int(64), out error: syserr)

Construct a bytes object by allocating zero-filled memory.

Arguments:
  • len -- the number of bytes to allocate
  • error -- (optional) capture an error that was encountered instead of halting on error
proc bytes.ptr(): c_void_ptr

Note

The pointer returned by this method is only valid for the lifetime of the bytes object and will be invalid if this memory is freed.

Returns:a c_void_ptr to the internal byte array
proc bytes.len: int(64)
Returns:the number of bytes stored in a bytes object
record buffer_iterator

This type represents a particular location with a buffer. Use buffer methods like buffer.start and buffer.advance to create and manipulate buffer_iterator s. Note that this record contains private fields in addition to the home field.

var home: locale

The home locale storing the data

record buffer_range

A region within a buffer (indicated by two buffer_iterator s )

var start: buffer_iterator
var end: buffer_iterator
proc buffer_range.len: int(64)
Returns:the number of bytes stored in a buffer_range
record buffer

A buffer which can contain multiple memory regions (that is, multiple regions of bytes objects). Note that this record contains private fields in addition to the home field.

var home: locale

The home locale storing the data

proc buffer.init(out error: syserr)

Create an empty buffer.

Arguments:error -- (optional) capture an error that was encountered instead of halting on error
proc buffer.flatten(range: buffer_range, out error: syserr)

Flatten a buffer. Create a new bytes object and copy the buffer into it. This function should work even if buffer is remote.

Arguments:
  • range -- the region of the buffer to copy, for example buffer.all()
  • error -- (optional) capture an error that was encountered instead of halting on error
Returns:

a newly constructed bytes object on the current locale
proc buffer.len
Returns:the number of bytes stored in a buffer object
proc buffer.append(b: bytes, skip_bytes: int(64) = 0, len_bytes: int(64) = b.len, out error: syserr)

Append a bytes object to a buffer. This function might store the passed bytes object by reference instead of copying it. The current implementation will always do so and will always increase the reference count of the bytes object. The version of this function called without the error argument will halt if an error is encountered.

Arguments:
  • b -- the bytes object to append
  • skip_bytes -- how many bytes at the front of b to skip
  • len_bytes -- how many bytes to append to the buffer
  • error -- (optional) capture an error that was encountered instead of halting on error
proc buffer.append(buf: buffer, part: buffer_range = AppendExpr.Call08, out error: syserr)

Append a buffer object to a buffer. This function might store a pointers to the bytes objects contained in buf instead of copying them. If that happens, the current implementation will increase their reference counts. The version of this function called without the error argument will halt if an error is encountered.

Arguments:
  • buf -- the buffer object to append
  • part -- a buffer_range indicating which section of the buffer to copy. Defaults to all of the buffer.
  • error -- (optional) capture an error that was encountered instead of halting on error
proc buffer.prepend(b: bytes, skip_bytes: int(64) = 0, len_bytes: int(64) = b.len, out error: syserr)

Prepend a bytes object to a buffer. This function might store the passed bytes object by reference instead of copying it. The current implementation will always do so and will always increase the reference count of the bytes object. The version of this function called without the error argument will halt if an error is encountered.

Arguments:
  • b -- the bytes object to prepend
  • skip_bytes -- how many bytes at the front of b to skip
  • len_bytes -- how many bytes to append to the buffer
  • error -- (optional) capture an error that was encountered instead of halting on error
proc buffer.start(): buffer_iterator
Returns:a buffer_iterator to the start of a buffer
proc buffer.end(): buffer_iterator
Returns:a buffer_iterator to the end of a buffer
proc buffer.all(): buffer_range
Returns:a buffer_range for the entirety of a buffer
proc buffer.next_part(ref it: buffer_iterator)

Advance a buffer_iterator to the next contiguous memory region stored therein

Arguments:it -- the buffer iterator to advance
proc buffer.prev_part(ref it: buffer_iterator)

Advance a buffer_iterator to the previous contiguous memory region stored therein

Arguments:it -- the buffer iterator to advance
proc buffer.advance(ref it: buffer_iterator, amount: int(64))

Advance a buffer_iterator by a particular number of bytes.

Arguments:
  • it -- the buffer iterator to advance
  • amount -- the number of bytes to advance
proc buffer.copyout(it: buffer_iterator, out value: ?T, out error: syserr): buffer_iterator

Read a basic type (integral or floating point value) or string from a buffer. For basic types, this method reads the value by copying from memory - so it reads a binary value in native endianness. For strings, this method reads a string encoded as the string length (as int) followed by that number of bytes (as uint(8)).

Arguments:
  • it -- a buffer_iterator where reading will start
  • value -- a basic type or string
  • error -- (optional) capture an error that was encountered instead of halting on error
Returns:

a buffer iterator storing the position immediately after the read value.
proc buffer.copyin(it: buffer_iterator, value: ?T, out error: syserr): buffer_iterator

Write a basic type (integral or floating point value) or string to a buffer. For basic types, this method writes the value by copying to memory - so it writes a binary value in native endianness. For strings, this method writes a string encoded as the string length (as int) followed by that number of bytes (as uint(8)).

Arguments:
  • it -- a buffer_iterator where reading will start
  • value -- a basic type or string
  • error -- (optional) capture an error that was encountered instead of halting on error
Returns:

a buffer iterator storing the position immediately after the written value.