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Per-client codepage detection and handling

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Matthew R. Wilson committed 2025-11-25 16:31:09 -08:00
1 parent 1859568369
commit 7b7d375e91
14 files changed
+349 -109
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telnet.go
+152 -46
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@@ -33,6 +33,14 @@ type DevInfo interface {
// from AltDimensions().
TerminalType() string
// Codepage is the Codepage interface that implements the EBCDIC
// translation for the detected code page for the terminal, if supported.
// This may be nil if the client code page is unknown. Whenever calling
// the screen functions, always pass the value returned by this Codepage()
// function in the ScreenOpts (nil is allowed to default to the global
// default codepage).
Codepage() Codepage
// Private version of AltDimensions() so callers can't fake us out; only
// real implementations returned by NegotiateTelnet() will work.
altDimensions() (rows, cols int)
@@ -284,32 +292,42 @@ func getTerminalType(conn net.Conn) (string, error) {
var modelRegex = regexp.MustCompile(`^IBM-\d{4}-([2-5])`)
func makeDeviceInfo(conn net.Conn, termtype string) (DevInfo, error) {
var rows, cols, cpid int
var codepage Codepage
var isx3270 bool
// tn3270e restricts to a small list of valid models, but since we're
// not doing tn3270e, we are seeing a variety of model numbers. We'll
// generically handle anything claiming to be a -2, -3, -4, or -5 type.
//
// We'll default to known terminal sizes in case we don't get the
// structured field query response later.
modelresult := modelRegex.FindStringSubmatch(termtype)
if len(modelresult) == 2 {
switch modelresult[1] {
case "2":
return &deviceInfo{24, 80, termtype}, nil
rows = 24
cols = 80
case "3":
return &deviceInfo{32, 80, termtype}, nil
rows = 32
cols = 80
case "4":
return &deviceInfo{43, 80, termtype}, nil
rows = 43
cols = 80
case "5":
return &deviceInfo{27, 132, termtype}, nil
rows = 27
cols = 132
}
} else if termtype != "IBM-DYNAMIC" {
// If it's not a fixed-size type, it should be IBM-DYNAMIC. If it
// isn't, we don't know how to deal with it. We'll just fall back on a
// simple 24x80 assumption.
rows = 24
cols = 80
termtype = "unknown (" + termtype + ")"
}
// If it's not a fixed-size type, it should be IBM-DYNAMIC. If it isn't,
// we don't know how to deal with it. We'll just fall back on a simple
// 24x80 assumption.
if termtype != "IBM-DYNAMIC" {
return &deviceInfo{24, 80, "unknown (" + termtype + ")"}, nil
}
// For IBM-DYNAMIC, we need to discover the alternate screen size with
// a structured field query.
// Now we'll discover the terminal size and character set.
// First, we perform an ERASE / WRITE ALTERNATE to clear the screen
// and put it in alternate screen mode. (EWA, reset WCC, telnet EOR)
@@ -320,7 +338,8 @@ func makeDeviceInfo(conn net.Conn, termtype string) (DevInfo, error) {
// Now we need to send the Write Structured Field command (0xf3) with the
// "Read Partition - Query" structured field. Note that we're
// telnet-escaping the 0xff in the data, but the subfield length is the
// *unescaped* length (5).
// *unescaped* length, including the 2 length bytes but excluding the
// telnet EOR (5).
if _, err := conn.Write([]byte{0xf3, 0, 5, 0x01, 0xff, 0xff, 0x02,
0xff, 0xef}); err != nil {
return nil, err
@@ -334,9 +353,9 @@ func makeDeviceInfo(conn net.Conn, termtype string) (DevInfo, error) {
conn.SetReadDeadline(time.Time{})
if err != nil && errors.Is(err, os.ErrDeadlineExceeded) {
// Timeout. In this case, we'll assume it's because the client didn't
// reply to our query command. In that case, we'll fall back to
// treating the terminal as a 24x80.
return &deviceInfo{24, 80, termtype}, nil
// reply to our query command. In that case, we'll return whatever
// we're already assuming.
return &deviceInfo{24, 80, termtype, nil}, nil
} else if err != nil {
return nil, err
}
@@ -344,11 +363,10 @@ func makeDeviceInfo(conn net.Conn, termtype string) (DevInfo, error) {
return nil, ErrTelnetError
}
var rows, cols int
// There are an arbitrary number of query reply structured fields. We
// are only interested in the "Usable Area" SFID=0x81 QCODE=0x81 field,
// so we'll just consume any others. Consume all data until the EOR is
// received.
// There are an arbitrary number of query reply structured fields. We are
// only interested in the "Usable Area" SFID=0x81 QCODE=0x81 field and
// "Character Sets" QCODE=0x85 field so we'll just consume any others.
// Consume all data until the EOR is received.
for {
// Two bytes are big-endian length.
buf, err := telnetReadN(conn, 2)
@@ -371,42 +389,125 @@ func makeDeviceInfo(conn net.Conn, termtype string) (DevInfo, error) {
return nil, ErrTelnetError
}
// Note that because length isn't at the beginning, offsets in buf
// are 2 less than in the 3270 datastream documentation.
if !(buf[0] == 0x81 && buf[1] == 0x81) {
// Not 'Usable Area' query reply
// Note that because length isn't at the beginning, offsets in buf are
// 2 less than in the 3270 data stream documentation.
if buf[0] == 0x81 && buf[1] == 0x81 {
// Usable Area
rows, cols, err = getUsableArea(buf)
if err != nil {
return nil, err
}
} else if buf[0] == 0x81 && buf[1] == 0x85 {
// Character Sets
cpid = getCodepageID(buf)
} else if buf[0] == 0x81 && buf[1] == 0xA1 {
// RPQ Names. We use this to determine if the client is x3270
// family.
isx3270 = getRPQNames(buf)
} else {
// Not a field we're interested in
continue
}
// A valid Usable Area reply will always include at least 18 (20 with
// length) bytes.
if l < 18 {
return nil, ErrTelnetError
}
// big-endian two byte values
cols = int(buf[4])<<8 + int(buf[5])
rows = int(buf[6])<<8 + int(buf[7])
}
switch cpid {
case 37:
// If x3270 family, assume that this is really the default "bracket"
// codepage, which reports as 37, not true CP37.
if isx3270 {
codepage = CodepageBracket()
} else {
codepage = Codepage037()
}
case 924:
codepage = Codepage924()
case 1047:
codepage = Codepage1047()
case 1140:
codepage = Codepage1140()
default:
// nil codepage will be accepted in ScreenOpts to default to the
// global default codepage.
codepage = nil
}
return &deviceInfo{rows, cols, termtype, codepage}, nil
}
// getUsableArea processes the "Query Reply (Usable Area)" response to return
// the rows and columns count of the terminal. The byte slice passed in to buf
// must begin with {0x81, 0x81}.
func getUsableArea(buf []byte) (rows, cols int, err error) {
// A valid Usable Area reply will always include at least 18 (20 with
// length) bytes.
if len(buf) < 18 || buf[0] != 0x81 || buf[1] != 0x81 {
return 0, 0, ErrTelnetError
}
// big-endian two byte values
cols = int(buf[4])<<8 + int(buf[5])
rows = int(buf[6])<<8 + int(buf[7])
if rows == 0 || cols == 0 {
// We got an IBM-DYNAMIC device type, but it didn't include a
// Usable Area query response.
return nil, ErrUnknownTerminal
// Got a Usable Area response but the values are 0?
return 0, 0, ErrUnknownTerminal
}
// We support 12- and 14-bit addressing. Using 16-bit addressing would
// require a mode change and the current API design doesn't support
// tracking the state necessary for that.
// We support 12- and 14-bit addressing. Using 16-bit addressing
// would require a mode change and the current API design doesn't
// support tracking the state necessary for that.
//
// We'll limit the reported screen size to what fits in 14-bit addressing
// by removing rows if necessary.
// We'll limit the reported screen size to what fits in 14-bit
// addressing by removing rows if necessary.
for rows*cols >= 1<<14 {
rows--
}
return &deviceInfo{rows, cols, termtype}, nil
return rows, cols, nil
}
// getCodepageID processes the "Query Reply (Character Sets)" response to
// return the integer code page number if present. If unable, returns 0. The
// byte slice passed in to buf must begin with {0x81, 0x85}.
func getCodepageID(buf []byte) int {
// Initial validity check.
if len(buf) < 11 || buf[0] != 0x81 || buf[1] != 0x85 {
return 0
}
// If the GF bit is not set, no point in continuing.
if buf[2]&(1<<1) != 1<<1 {
return 0
}
// Descriptor length -- and do we have at least one descriptor?
dl := int(buf[10])
if len(buf) < 11+dl {
return 0
}
// No matter how long the descriptor is, the code page will 2-byte big
// endian integer in the last two bytes.
cpid := int(buf[11+dl-2])<<8 + int(buf[11+dl-1])
return cpid
}
// getRPGNames checks the "Query Reply (RPQ NAMES)" response to see if the
// client is in the x3270 family. The byte slice passed in to buf must begin
// with {0x81, 0xA1}.
func getRPQNames(buf []byte) bool {
if len(buf) < 16 {
return false
}
// "x3270" in EBCDIC
if buf[11] == 0xa7 && buf[12] == 0xf3 && buf[13] == 0xf2 &&
buf[14] == 0xf7 && buf[15] == 0xf0 {
return true
}
return false
}
// UnNegotiateTelnet will naively (e.g. not checking client responses) attempt
@@ -543,6 +644,7 @@ func telnetReadN(conn net.Conn, n int) ([]byte, error) {
type deviceInfo struct {
rows, cols int
termtype string
codepage Codepage
}
func (d *deviceInfo) AltDimensions() (rows, cols int) {
@@ -556,3 +658,7 @@ func (d *deviceInfo) TerminalType() string {
func (d *deviceInfo) altDimensions() (rows, cols int) {
return d.rows, d.cols
}
func (d *deviceInfo) Codepage() Codepage {
return d.codepage
}