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phish_unpack() function

phish_datum() function

C syntax:

int phish_unpack(char **buf, int32_t *len)
int phish_datum(int flag) 

C examples:

#include "phish.h"
char *buf;
int len;
int type = phish_unpack(&buf,&len);
int iport = phish_datum(1); 

C++ syntax:

int unpack(char **buf, int32_t *len)
int datum(int flag) 

C++ examples:

#include "phish.hpp"
char *buf;
int len;
int type = phish::unpack(&buf,&len);
int iport = phish::datum(1); 

Python syntax:

def unpack()
def datum(flag) 

Python examples:

import phish
type,value,len = phish.unpack()
iport = phish.datum(1) 


These are PHISH library functions which can be called from a minnow application. In PHISH lingo, a "minnow" is a stand-alone application which makes calls to the PHISH library.

These functions are used to unpack a datum after it has been received from another minnow or query other info about the datum.

As discussed in this section of the PHISH Library doc page, datums sent and recived by the PHISH library contain one or more fields. A field is a fundamental data type, such as an "32-bit integer" or "vector of doubles" or a NULL-terminated character string. These fields are packed into a contiguous byte string when then are sent, using integer flags to indicate what type and length of data comes next. These unpack functions allow the minnow to extract data from the datum, one field at a time.

Note that these functions return pointers to the internal buffer holding the datum within the PHISH library. The buffer will be overwritten when the minnow returns control to the PHISH library and the next datum is received. Typically this occurs when a callback function in the minnow returns. This means that if you want the data to persist within the minnow, you must make a copy. It is OK to unpack several fields from the same datum before making copies of the fields. It is also OK to pack one or more received fields for sending and wait to send it until after another datum is received. This is because calls to "phish_pack" functions copy data into a separate send buffer.

The phish_unpack() function returns the next field and its length, from the most recently received datum. Note that len is typed as a pointer to int32_t which is a 32-bit integer. In C or C++, the minnow can simply declare len to be a pointer to "int" and the function will work as expected. The only case where this will fail (with a compile-time error) is if the native "int" on a machine is not a 32-bit int.

Phish_unpack returns an integer flag set to one of these values (defined in src/phish.h):

PHISH_CHAR, PHISH_INT*, PHISH_UINT*, PHISH_FLOAT, and PHISH_DOUBLE are a single character, a signed integer (of length 8,16,32,64 bits), an unsigned integer (of length 8,16,32,64 bits), a float (typically 4 bytes), and a double (typically 8 bytes).

PHISH_RAW is a string of raw bytes which can store whatever the sending minnow put into its send buffer, e.g. a C data structure containing a collection of various C primitive data types.

PHISH_RAW is a string of raw bytes which minnows can format in any manner, e.g. a C data structure containing a collection of various C primitive data types. PHISH_STRING is a standard C-style NULL-terminated C-string. The NULL is included in the field.

The ARRAY types are contiguous sequences of int*, uint*, float, or double values, packed one after the other.

PHISH_PICKLE is an option available when using the Python wrapper on the PHISH library to encode arbitrary Python objects in pickled form as a string of bytes. It should not normally be used in a minnow written in C or C++.

Phish_unpack also returns buf and len. Buf is a char pointer to where the field starts. You will need to cast this to the appropriate data type before accessing the data if it is not a character string. Len is the length of the field, with the following meanings:

The phish_datum() function returns information about the most recently received datum.

If flag is set to 0, phish_datum returns the number of fields in the datum. This value is also passed as an argument to the callback function invovked by the phish_loop and phish_probe functions, so a minnow typically does not need to use phish_datum to retrieve this info.

If flag is set to 1, phish_datum returns the input port the datum was received on. See the phish_port functions for a discussion of ports.

The phish_datum() function does not conflict with the phish_unpack() function. Phish_datum() can be called before or after or in between a series of phish_unpack() calls.

Restrictions: none

Related commands:

phish_recv, phish_pack