opSys-shell/scanner.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>
#include <stdbool.h>

#include "scanner.h"

//TODO: handle EOF more completely (currently only EOF at the start of the line is handled)
/**
 * Reads an inputline from stdin.
 * @return a string containing the inputline.
 */
char *readInputLine() {
    int strLen = INITIAL_STRING_SIZE;
    int c = getchar();
    int i = 0;

    // part of EOF handling; return NULL when EOF is encountered at the start of input.
    // this is further handled in main(). 
    if (c == -1) {
      return NULL;
    }

    char *s = malloc((strLen + 1) * sizeof(*s));
    assert(s != NULL);

    bool quoteStarted = false;
    while (c != '\n' || quoteStarted) { // Ensure that newlines in strings are accepted
        if (c == '\"') {
            quoteStarted = !quoteStarted;
        }
        s[i++] = c;

        if (i >= strLen) { // Resize the string if necessary
            strLen = 2 * strLen;
            s = realloc(s, (strLen + 1) * sizeof(*s));
            assert(s != NULL);
        }
        c = getchar();
    }
    s[i] = '\0';
    return s;
}

/**
 * The function isOperatorCharacter checks whether the input paramater \param c is an operator.
 * @param c input character.
 * @return a bool denoting whether \param c is an operator.
 */
bool _isOperatorCharacter(char c) {
    return c == '&' || c == '|' || c == ';' || c == '<' || c == '>';
}

/**
 * Reads an identifier in string \param s starting at index \param start.
 * @param s input string.
 * @param start starting index in string \param s.
 * @return a pointer to the start of the identifier string
 */
char *_matchIdentifier(char *s, int *start) {
    int strLen = INITIAL_STRING_SIZE;
    int pos = 0, offset = 0;

    char *ident = malloc((strLen + 1) * sizeof(*ident));
    assert(ident != NULL);

    bool quoteStarted = false;
    size_t lenS = strlen(s);
    while ((*start + offset <= lenS && !isspace(s[*start + offset]) && !_isOperatorCharacter(s[*start + offset])) || quoteStarted) { // Ensure that whitespace in strings is accepted
        if (s[*start + offset] == '\"') { // Strip the quotes from the input before storing in the identifier
            quoteStarted = !quoteStarted;
            offset++;
            continue;
        }
        ident[pos++] = s[*start + offset++];
        if (pos >= strLen) { // Resize the string if necessary
            strLen = 2 * strLen;
            ident = realloc(ident, (strLen + 1) * sizeof(*ident));
            assert(ident != NULL);
        }
    }
    ident[pos] = '\0';
    *start = *start + offset;
    return ident;
}

/**
 * The function newNode makes a new node for the token list and fills it with the token that
 * has been read. Precondition: !isspace(a[*ip]).
 * @param s input string.
 * @param start starting index in string \param s.
 * @return a list node that contains the current token.
 */
List _newNode(char *s, int *start) {
    List node = malloc(sizeof(*node));
    assert(node != NULL);
    node->next = NULL;
    node->t = _matchIdentifier(s, start);
    return node;
}

/**
 * Reads an operator in string \param s starting at index \param start.
 * @param s input string.
 * @param start starting index in string \param s.
 * @return a pointer to the start of the operator string.
 */
char *_matchOperator(char *s, int *start) {
    int strLen = 2; // the operator consists of *at most* 2 characters
    int pos = 0, offset = 0;

    char *op = malloc((strLen + 1) * sizeof(*op));
    assert(op != NULL);

    while (_isOperatorCharacter(s[*start + offset])) {
        op[pos++] = s[*start + offset++];
    }
    op[pos] = '\0';
    *start = *start + offset;
    return op;
}

/**
 * The function newOperatorNode makes a new operator node for the token list and fills it with the token that
 * has been read. Precondition: !isspace(a[*ip]).
 * @param s input string.
 * @param start starting index in string \param s.
 * @return a list node that contains the current token.
 */
List _newOperatorNode(char *s, int *start) {
    List node = malloc(sizeof(*node));
    assert(node != NULL);
    node->next = NULL;
    node->t = _matchOperator(s, start);
    return node;
}

/**
 * The function tokenList reads an array and puts the tokens that are read in a list.
 * @param s input string.
 * @return a pointer to the beginning of the list.
 */
List getTokenList(char *s) {
    List lastNode = NULL;
    List node = NULL;
    List tl = NULL;
    int i = 0;
    int length = strlen(s);
    while (i < length) {
        if (isspace(s[i])) { // spaces are skipped
            i++;
        }else {
            node = _isOperatorCharacter(s[i]) ? _newOperatorNode(s, &i) : _newNode(s, &i);
            if (lastNode == NULL) { // there is no list yet
                tl = node;
            } else { // a list already exists; add current node at the end
                (lastNode)->next = node;
            }
            lastNode = node;
        }
    }
    return tl;
}

/**
 * Checks whether list \param l is empty.
 * @param l input list.
 * @return a bool denoting whether \param l is empty.
 */
bool isEmpty(List l) {
    return l == NULL;
}

/**
 * The function printList prints the tokens in a token list, separated by commas.
 * @param li the input list to be printed.
 */
void printList(List li) {
    if (li == NULL) return;
    printf("(\"%s\", \"%d\")", li->t, li->type);
    li = li->next;
    while (li != NULL) {
        printf("(\"%s\", \"%d\")", li->t, li->type);
        li = li->next;
    }
    printf("\n");
}

/**
 * The function freeTokenlist frees the memory of the nodes of the list, and of the strings
 * in the nodes.
 * @param li the starting node of a list.
 */
void freeTokenList(List li) {
    if (li == NULL) {
        return;
    }
    free(li->t);
    freeTokenList(li->next);
    free(li);
}