automata-programming.md

Constructional Design using State Machines

Author: Pavl G.

This document establishes a constructional design for a low-level IO API that operates on filesystems of all types; the constructional design is completely based on the computational automata theory, that focuses particularly on designing machines that automate algorithms with {predefined set of states $$Q$$, initial state $$q$$, transitioning function $$\delta$$, set of input symbols $$\Sigma$$, set of final accepting states $$F$$}. Conceptually, a language $$L$$ could be accepted from these set of final accepting states (e.g., on_eof_reached and on_error_encountered); the language $$L_M$$ is a set of all strings that could be recognized by its machine $$M$$; whose alphabets are the $$\Sigma$$.

Note

In this API; the language could be all the available strings for read/write IO operations from and to a filesystem. In which, the start string (or char depending on the implementation of the state machines) is the

The following is the an example for the implementation of the file_read algorithm that utilizes a dynamic way of determining the number of bytes to read using the file stat attributes:

/**
 * @brief A tech=demo for the implementation of the file reading algorithm that provides a dynamic algorithm of determining the number of bytes to read out of a file using the file stat attributes from the Unix Standard library by requesting a call to the file status utility.
 * @author pavl_g.
 * @date 10-2025
 */
#include <electrostatic/electronetsoft/util/filesystem/file_operations.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>

static inline void update_file_postprocessor(file_mem *mem) {
    if (NULL == mem || mem->fd < 0) {
        return;
    }
    if (mem->n_bytes <= 0) {
        mem->n_bytes = 1;
    }
    fprintf(stdout, "Size of memory buffer (in bytes) = %zd\n",
            mem->n_bytes);
    mem->buffer = calloc(mem->n_bytes, sizeof (char));

    if (NULL == mem->buffer) {
        return;
    }
}

static inline void on_read_bytes(file_mem *mem, ssize_t bytes) {
    fprintf(stdout, "Read Bytes: %s", mem->buffer);
}

static inline void on_eof_reached(file_mem *mem) {
    fprintf(stdout, "Read Bytes after EOF: %s\n", mem->buffer);
    fprintf(stdout, "EOF Reached!\n");
    // deallocates memory here!
    if (NULL != mem->buffer) {
        free(mem->buffer);
        mem->buffer = NULL;
    }
}

int main() {
    fprintf(stdout, "Hello Fle Read Automata!\n");

    int fd = open("/home/pavl-g/Desktop/Glossary_for_AI", O_RDWR);

    if (fd < 0) {
        fprintf(stderr, "Error Encountered: %s\n", strerror(errno));
        exit(errno);
    }

    file_mem _file_mem = {
            .fd = fd,
            .trailing = '9',
            .buffer = NULL,
            .n_bytes = -1,
            .file_size = -1,
            .file_pos = -1
    };

    file_op_processor __processor = {
        .update_file_postprocessor = &update_file_postprocessor,
        .on_read_bytes = &on_read_bytes,
        .on_eof_reached = &on_eof_reached
    };

    status_code __status = read_into_mem(&_file_mem, &__processor);

    if (PASS != __status) {
        fprintf(stderr, "Error Encountered: %s\n", strerror(__status));
        exit(__status);
    }

    return 0;
}

[file_read.c]

#include <electrostatic/electronetsoft/util/filesystem/file_operations.h>
#include <electrostatic/electronetsoft/util/filesystem/file_status.h>

status_code read_into_mem(file_mem *mem, file_op_processor *processor) {
    // pre-processing automata -- Input validation
    if (mem->fd < 0) {
        return EUNDEFINEDBUFFER;
    }

    if (NULL != mem->buffer) {
        return -1;
    }

    // pre-processing automata -- Calculating the file size, current position,
                                // and the number of bytes to read
    status_code ___status = update_file_attrs(mem, processor);
    if (PASS != ___status) {
        return ___status;
    }

    if (NULL == mem->buffer) {
        return EUNDEFINEDBUFFER;
    }

    // processing automata -- Reading n_bytes into heap buffer
    //                        starting from the current file position
    while (1) {
        ssize_t read_bytes = 0;
        read_bytes = read(mem->fd, (mem->buffer + read_bytes), (mem->n_bytes - 1));
        // post processing automata
        if (-1 == read_bytes) {
            // terminated with error; report error!
            if (NULL != processor && NULL != processor->on_error_encountered) {
                processor->on_error_encountered(mem, errno);
            }
            return errno;
        } else if (0 == read_bytes) {
            // EOF terminate!
            mem->buffer[mem->n_bytes - 1] = mem->trailing; /* add a null-terminating character */
            if (NULL != processor && NULL != processor->on_eof_reached) {
                processor->on_eof_reached(mem);
            }
            return PASS;
        } else if (read_bytes > 0) {
            // execute on_read
            if (NULL != processor && NULL != processor->on_read_bytes) {
                processor->on_read_bytes(mem, read_bytes);
            }
        }
    }
    return ASSERTION_FAILURE;
}

file_read.dot

digraph FileReadingFSM {
    rankdir=LR;
    node [shape=circle, style=filled, fillcolor="#e6f2ff"];

    // States
    S0 [label="S0\nStart"];
    S1 [label="S1\nfd < 0?"];
    S2 [label="S2\nbuffer != NULL?"];
    S3 [label="S3\nupdate_file_attrs"];
    S4 [label="S4\nPASS?"];
    S5 [label="S5\nbuffer == NULL?"];
    S6 [label="S6\nRead Loop"];
    S7 [label="S7\nread == -1"];
    S8 [label="S8\nread == 0"];
    S9 [label="S9\nread > 0"];
    S10 [label="S10\nError Terminate", shape=doublecircle, fillcolor="#ffe6e6"];
    S11 [label="S11\nEOF Terminate", shape=doublecircle, fillcolor="#e6ffe6"];
    S12 [label="S12\nRead Callback"];
    S13 [label="S13\nFinal", shape=doublecircle, fillcolor="#ffe6e6"];

    // Transitions (pre-processing)
    S0 -> S1 [label="entry"];
    S1 -> S10 [label="fd < 0"];
    S1 -> S2 [label="fd >= 0"];
    S2 -> S10 [label="buffer != NULL"];
    S2 -> S3 [label="buffer == NULL"];
    S3 -> S4 [label="call update_file_attrs"];
    S4 -> S10 [label="PASS != status"];
    S4 -> S5 [label="PASS == status"];
    S5 -> S10 [label="buffer == NULL"];
    S5 -> S6 [label="buffer != NULL"];

    // Read loop transitions
    S6 -> S7 [label="read == -1"];
    S6 -> S8 [label="read == 0"];
    S6 -> S9 [label="read > 0"];
    S7 -> S10 [label="on_error_encountered"];
    S8 -> S11 [label="on_eof_reached"];
    S9 -> S12 [label="on_read_bytes"];
    S12 -> S6 [label="loop"];

    // Termination
    S10 -> S13 [label="return error"];
    S11 -> S13 [label="return PASS"];
    S6 -> S13 [label="ASSERTION_FAILURE (unreachable)"];

    // Final state
    S13 [shape=doublecircle, fillcolor="#ffe6e6"];
}

graphviz.svg

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<title>FileReadingFSM</title>
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<g id="node1" class="node">
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<text xml:space="preserve" text-anchor="middle" x="30.01" y="-26.84" font-family="Times,serif" font-size="14.00">Start</text>
</g>
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<title>S1</title>
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<text xml:space="preserve" text-anchor="middle" x="164.22" y="-26.84" font-family="Times,serif" font-size="14.00">fd &lt; 0?</text>
</g>
<!-- S0&#45;&gt;S1 -->
<g id="edge1" class="edge">
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</g>
<!-- S1&#45;&gt;S2 -->
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<text xml:space="preserve" text-anchor="middle" x="2060.58" y="-207.84" font-family="Times,serif" font-size="14.00">Error Terminate</text>
</g>
<!-- S1&#45;&gt;S10 -->
<g id="edge2" class="edge">
<title>S1-&gt;S10</title>
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</g>
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</g>
<!-- S2&#45;&gt;S3 -->
<g id="edge5" class="edge">
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</g>
<!-- S2&#45;&gt;S10 -->
<g id="edge4" class="edge">
<title>S2-&gt;S10</title>
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</g>
<!-- S4 -->
<g id="node5" class="node">
<title>S4</title>
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<text xml:space="preserve" text-anchor="middle" x="920.48" y="-173.84" font-family="Times,serif" font-size="14.00">PASS?</text>
</g>
<!-- S3&#45;&gt;S4 -->
<g id="edge6" class="edge">
<title>S3-&gt;S4</title>
<path fill="none" stroke="black" d="M727.57,-182.16C773.21,-183.17 829.71,-184.43 869.55,-185.32"/>
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<text xml:space="preserve" text-anchor="middle" x="804.22" y="-189.34" font-family="Times,serif" font-size="14.00">call update_file_attrs</text>
</g>
<!-- S5 -->
<g id="node6" class="node">
<title>S5</title>
<ellipse fill="#e6f2ff" stroke="black" cx="1166.4" cy="-186.44" rx="82.4" ry="82.4"/>
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<text xml:space="preserve" text-anchor="middle" x="1166.4" y="-173.84" font-family="Times,serif" font-size="14.00">buffer == NULL?</text>
</g>
<!-- S4&#45;&gt;S5 -->
<g id="edge8" class="edge">
<title>S4-&gt;S5</title>
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</g>
<!-- S4&#45;&gt;S10 -->
<g id="edge7" class="edge">
<title>S4-&gt;S10</title>
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</g>
<!-- S5&#45;&gt;S6 -->
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<title>S7</title>
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<title>S6-&gt;S7</title>
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<title>S8-&gt;S11</title>
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<polygon fill="black" stroke="black" points="1971.96,-582.79 1981.71,-578.63 1971.5,-575.81 1971.96,-582.79"/>
<text xml:space="preserve" text-anchor="middle" x="1851.45" y="-598.66" font-family="Times,serif" font-size="14.00">on_eof_reached</text>
</g>
<!-- S12 -->
<g id="node13" class="node">
<title>S12</title>
<ellipse fill="#e6f2ff" stroke="black" cx="2060.58" cy="-409.44" rx="69.31" ry="69.31"/>
<text xml:space="preserve" text-anchor="middle" x="2060.58" y="-413.64" font-family="Times,serif" font-size="14.00">S12</text>
<text xml:space="preserve" text-anchor="middle" x="2060.58" y="-396.84" font-family="Times,serif" font-size="14.00">Read Callback</text>
</g>
<!-- S9&#45;&gt;S12 -->
<g id="edge16" class="edge">
<title>S9-&gt;S12</title>
<path fill="none" stroke="black" d="M1712.4,-479.83C1776.73,-466.79 1899.99,-441.8 1980.99,-425.37"/>
<polygon fill="black" stroke="black" points="1981.54,-428.83 1990.65,-423.41 1980.15,-421.97 1981.54,-428.83"/>
<text xml:space="preserve" text-anchor="middle" x="1851.45" y="-477.52" font-family="Times,serif" font-size="14.00">on_read_bytes</text>
</g>
<!-- S10&#45;&gt;S13 -->
<g id="edge18" class="edge">
<title>S10-&gt;S13</title>
<path fill="none" stroke="black" d="M2108.12,-284.35C2118.83,-299.61 2129.99,-315.96 2139.93,-331.44 2184.36,-400.57 2231.6,-483.87 2258.58,-532.52"/>
<polygon fill="black" stroke="black" points="2255.38,-533.98 2263.29,-541.04 2261.51,-530.59 2255.38,-533.98"/>
<text xml:space="preserve" text-anchor="middle" x="2193.13" y="-478.31" font-family="Times,serif" font-size="14.00">return error</text>
</g>
<!-- S11&#45;&gt;S13 -->
<g id="edge19" class="edge">
<title>S11-&gt;S13</title>
<path fill="none" stroke="black" d="M2138.01,-573.44C2170.15,-573.44 2206.5,-573.44 2234.51,-573.44"/>
<polygon fill="black" stroke="black" points="2234.45,-576.94 2244.45,-573.44 2234.45,-569.94 2234.45,-576.94"/>
<text xml:space="preserve" text-anchor="middle" x="2193.13" y="-577.64" font-family="Times,serif" font-size="14.00">return PASS</text>
</g>
<!-- S12&#45;&gt;S6 -->
<g id="edge17" class="edge">
<title>S12-&gt;S6</title>
<path fill="none" stroke="black" d="M1990.78,-409.14C1903.56,-409.17 1748.61,-410.53 1616.25,-418.64 1576.55,-421.07 1532.21,-425.54 1496.96,-429.51"/>
<polygon fill="black" stroke="black" points="1496.9,-425.99 1487.36,-430.6 1497.69,-432.94 1496.9,-425.99"/>
<text xml:space="preserve" text-anchor="middle" x="1668.96" y="-422.84" font-family="Times,serif" font-size="14.00">loop</text>
</g>
</g>
</svg>