#!/usr/bin/awk -f
# gopher-validate.awk Version 4
#
# Validate gopher directory or text
#
# Relevant RFCs:
# gopher://gopher.fnord.one/0/Mirrors/RFC/rfc1436.txt
# gopher://gopher.fnord.one/0/Mirrors/RFC/rfc8962.txt
#
# See also:
# https://tildegit.org/sloum/mapcheck/src/branch/master/mapcheck
# https://codemadness.org/git/gopher-validator/file/gopher-validator.c.html
#
# This script requires:
# - /bin/sh
# - curl
# - iconv
# - /usr/bin/awk
# - /usr/bin/mktemp

function mktemp() {
    cmd = "/usr/bin/mktemp"
    while ((cmd | getline) > 0) {
        retval = $0
    }
    result = close(cmd)
    if (result != 0) {
        print "Error: mktemp failed exit status: " result
        exit
    }
    if (length(retval) == 0) {
        print "Error: mktemp failed, no tmpfile"
        exit
    }
    return retval
}

function unlink(name) {
    system("rm " name)
    return
}

function validate_encoding(iconv, encoding, file) {
    cmd = sprintf("%s -f %s -t %s <%s >/dev/null 2>/dev/null",
        iconv, encoding, encoding, file)
    result = system(cmd)
    if (result == 0) {
        retval = 1
    } else {
        retval = 0
    }
    return retval
}

function validate_gophermap(file) {
    # valid gopher item types
    types["0"] = 0
    types["1"] = 0
    types["2"] = 0
    types["3"] = 0
    types["4"] = 0
    types["5"] = 0
    types["6"] = 0
    types["7"] = 0
    types["8"] = 0
    types["9"] = 0
    types["I"] = 0
    types["M"] = 0
    types["P"] = 0
    types["T"] = 0
    types["c"] = 0
    types["e"] = 0
    types["g"] = 0
    types["h"] = 0
    types["i"] = 0
    types["s"] = 0
    types["v"] = 0
    types["+"] = 0
    types[";"] = 0
    types["!"] = 0
    types["."] = 0

    FS = "\t"
    ilines = 0
    iline_warning_seen = 0
    lineno = 0
    seen_end = 0
    retval = 1
    while (getline <file) {
        lineno++
        if (/\r$/) {
            $0 = substr($0, 0, length($0) - 1)
        } else {
            printf "Error: Missing CR character on line %d\n\n", lineno
            print "RFC1436 Section 2:"
            print "    A CR LF denotes the end of the item."
            retval = 0
            break
        }
        if (seen_end) {
            print "Error: Unexpected trailing text after end of gophermap.\n"
            print "RFC1436 Introduction:"
            print "    The server responds with a block of text terminated"
            print "    by a period on a line by itself and closes the"
            print "    connection."
            retval = 0
            break
        }
        if (NF == 1 && $0 == ".") {
            seen_end = 1
            continue
        }
        if (NF == 4 || (NF == 5 && $5 == "+")) {
            # items with 4 fields are normal
            # gopher+ items are ignored
        } else {
            printf "Error: %d fields on line %d, expected 4\n\n", NF, lineno
            print "RFC1436 Introduction:"
            print "    Each item in a directory is identified by a"
            print "    [1] type... [and] user-visible name..."
            print "    [2] an opaque selector string..."
            print "    [3] a host name..."
            print "    [4] and an IP portnumber..."
            retval = 0
            break
        }
        if (length($1) > 71) {
            msg = "Error"
            if (warn_longlines) {
                msg = "Warning"
            }
            printf "%s: Long user display string on line %d\n\n", msg, lineno
            print "RFC1436 Section 3.9:"
            print "    ... user display string should be kept"
            print "    under 70 characters in length.\n"
            if (!warn_longlines) {
                retval = 0
                break
            }
        }
        Item_Type = substr($1, 1, 1)
        if (!(Item_Type in types)) {
            printf "Warning: Non-standard gophertype \"%s\" on line %d\n\n",
                Item_Type, lineno
            print "RFC1436 Section 3.8:"
            print "A list of defined item-type characters follows:"
            print "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, +, T, g, I"
            print "UMN gopher object/GSgopherobj.h:"
            print "M, P, c, e, h, i, s, v, ;, !, .\n"
        }
        User_Name = substr($1, 2)
        if (length(User_Name) > 0 && User_Name !~ /^[[:print:]]+$/) {
            printf "Error: Non-printable characters on line %d\n\n", lineno
            print "RFC1436 Appendix:"
            print "    It is *highly* recommended that the User_Name field"
            print "    contain only printable characters, since many"
            print "    different clients will be using it."
            retval = 0
            break
        }
        if (/^i/) {
            ilines++
        } else {
            ilines = 0
        }
        if (ilines > 20 && !iline_warning_seen) {
            print "Warning: Over 20 consecutive info-lines"
            print "Gophermap may contain content rather than navigation."
            print "See:"
            print "gopher://gopher.icu/phlog/Computing/The-state-of-gopher.md"
            print ""
            iline_warning_seen = 1
        }
    }
    close(file)
    return retval
}

function validate_text(curl, iconv, uri) {
    # use curl to fetch gopher directory or text
    curlcfg = mktemp()
    curlout = mktemp()
    print "--max-filesize 256K"      > curlcfg
    print "--max-redirs 0"          >> curlcfg
    print "--output " curlout       >> curlcfg
    print "--proto =gopher,gophers" >> curlcfg
    print "--silent"                >> curlcfg
    print "--url " uri              >> curlcfg
    fflush(curlcfg)
    result = system(curl " -K " curlcfg)
    unlink(curlcfg)
    if (result != 0) {
        unlink(curlout)
        print "Error: Curl couldn't fetch URI"
        exit 1
    }

    # use iconv to validate the result character encoding
    valid_encodings[0] = "ASCII"
    valid_encodings[1] = "UTF-8"

    # All 8-bit characters represent valid ISO-8859-1 (Latin)
    # encoding so checking for invalid encoding is meaningless.
    # valid_encodings[2] = "ISO-8859-1"

    is_valid = 0
    for (i = 0; i < 2; i++) {
        encoding = valid_encodings[i]
        result = validate_encoding(iconv, encoding, curlout)
        if (result) {
            is_valid = 1
            break
        }
    }
    if (!is_valid) {
        print "Error: Invalid character encoding."
        print "Expected ASCII or UTF-8.\n"
        print "RFC1436 Section 4(b):"
        print "    The well-tempered server ought to send \"text\"..."
        unlink(curlout)
        exit 1
    }

    # validate gophermap if it is a directory
    if (type == "1") {
        result = validate_gophermap(curlout)
        if (result == 0) {
            unlink(curlout)
            exit 1
        }
    }

    print "Valid"
    unlink(curlout)
    exit 0
}

function validate_uri(uri) {
    if (uri !~ /^gophers?:\/\//) {
        print "Error: expected gopher: protocol URI"
        exit 1
    }
    result = match(uri, /^gophers?:\/\/[^\/]*\/(.)\//)
    if (result == 0) {
        type = ""
    } else {
        type = substr(uri, RLENGTH - 1, 1)
    }
    if (length(type) != 1) {
        print "Error: couldn't find item type in URI"
        exit 1
    }
    if (type != "0" && type != "1") {
       print "Error: Expected item type 0 or 1 in URI"
       exit 1
    }
    return type
}

BEGIN {
    if (ARGC < 2) {
        print "Usage: gopher-validate.awk -- [options] URI"
        print ""
        print "Options:"
        print "--warn-longlines  Warn instead of error on long lines"
        print ""
        exit 1
    } 
    uri = ""
    warn_longlines = 0
    for (i = 1; i < ARGC; i++) {
        arg = ARGV[i]
        if (arg == "--warn-longlines") {
             warn_longlines = 1
        } else {
             if (length(uri) > 0) {
                 print "Error: Unrecognized argument: " arg
                 exit 1
             } else {
                 uri = arg
             }
        }
    }
    type = validate_uri(uri)
    curl = "curl"
    result = system("command -v " curl " >/dev/null")
    if (result) {
        print "Error: Couldn't find command: " curl
        exit 1
    }
    iconv = "iconv"
    result = system("command -v " iconv " >/dev/null")
    if (result) {
        print "Error: Couldn't find command: " iconv
        exit 1
    }
    validate_text(curl, iconv, uri)
}