readlline.c

[詳解]

/*++
/* NAME
/*  readlline 3
/* SUMMARY
/*  read logical line
/* SYNOPSIS
/*  #include <readlline.h>
/*
/*  VSTRING *readllines(buf, fp, lineno, first_line)
/*  VSTRING *buf;
/*  VSTREAM *fp;
/*  int *lineno;
/*  int *first_line;
/*
/*  VSTRING *readlline(buf, fp, lineno)
/*  VSTRING *buf;
/*  VSTREAM *fp;
/*  int *lineno;
/* DESCRIPTION
/*  readllines() reads one logical line from the named stream.
/* .IP "blank lines and comments"
/*  Empty lines and whitespace-only lines are ignored, as
/*  are lines whose first non-whitespace character is a `#'.
/* .IP "multi-line text"
/*  A logical line starts with non-whitespace text. A line that
/*  starts with whitespace continues a logical line.
/* .PP
/*  The result value is the input buffer argument or a null pointer
/*  when no input is found.
/*
/*  readlline() is a backwards-compatibility wrapper.
/*
/*  Arguments:
/* .IP buf
/*  A variable-length buffer for input. The result is null terminated.
/* .IP fp
/*  Handle to an open stream.
/* .IP lineno
/*  A null pointer, or a pointer to an integer that is incremented
/*  after reading a physical line.
/* .IP first_line
/*  A null pointer, or a pointer to an integer that will contain
/*  the line number of the first non-blank, non-comment line
/*  in the result logical line.
/* DIAGNOSTICS
/*  Warning: a continuation line that does not continue preceding text.
/*  The invalid input is ignored, to avoid complicating caller code.
/* SECURITY
/* .ad
/* .fi
/*  readlline() imposes no logical line length limit therefore it
/*  should be used for reading trusted information only.
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

/* System library. */

#include <sys_defs.h>
#include <ctype.h>

/* Utility library. */

#include "msg.h"
#include "vstream.h"
#include "vstring.h"
#include "readlline.h"

#define STR(x) vstring_str(x)
#define LEN(x) VSTRING_LEN(x)
#define END(x) vstring_end(x)

/* readllines - read one logical line */

VSTRING *readllines(VSTRING *buf, VSTREAM *fp, int *lineno, int *first_line)
{
    int     ch;
    int     next;
    ssize_t start;
    char   *cp;

    VSTRING_RESET(buf);

    /*
     * Ignore comment lines, all whitespace lines, and empty lines. Terminate
     * at EOF or at the beginning of the next logical line.
     */
    for (;;) {
    /* Read one line, possibly not newline terminated. */
    start = LEN(buf);
    while ((ch = VSTREAM_GETC(fp)) != VSTREAM_EOF && ch != '\n')
        VSTRING_ADDCH(buf, ch);
    if (lineno != 0 && (ch == '\n' || LEN(buf) > start))
        *lineno += 1;
    /* Ignore comment line, all whitespace line, or empty line. */
    for (cp = STR(buf) + start; cp < END(buf) && ISSPACE(*cp); cp++)
         /* void */ ;
    if (cp == END(buf) || *cp == '#')
        vstring_truncate(buf, start);
    else if (start == 0 && lineno != 0 && first_line != 0)
        *first_line = *lineno;
    /* Terminate at EOF or at the beginning of the next logical line. */
    if (ch == VSTREAM_EOF)
        break;
    if (LEN(buf) > 0) {
        if ((next = VSTREAM_GETC(fp)) != VSTREAM_EOF)
        vstream_ungetc(fp, next);
        if (next != '#' && !ISSPACE(next))
        break;
    }
    }
    VSTRING_TERMINATE(buf);

    /*
     * Invalid input: continuing text without preceding text. Allowing this
     * would complicate "postconf -e", which implements its own multi-line
     * parsing routine. Do not abort, just warn, so that critical programs
     * like postmap do not leave behind a truncated table.
     */
    if (LEN(buf) > 0 && ISSPACE(*STR(buf))) {
    msg_warn("%s: logical line must not start with whitespace: \"%.30s%s\"",
         VSTREAM_PATH(fp), STR(buf),
         LEN(buf) > 30 ? "..." : "");
    return (readllines(buf, fp, lineno, first_line));
    }

    /*
     * Done.
     */
    return (LEN(buf) > 0 ? buf : 0);
}