Early response parsing work

response.go

@@ -0,0 +1,192 @@
+// This file is part of https://github.com/racingmars/go3270/
+// Copyright 2020 by Matthew R. Wilson, licensed under the MIT license. See
+// LICENSE in the project root for license information.
+
+package go3270
+
+import (
+	"bytes"
+	"net"
+)
+
+// Response encapsulates data received from a 3270 client in response to the
+// previously sent screen.
+type Response struct {
+	// Which Action ID key did the user press?
+	AID AID
+
+	// Row the cursor was on (0-based).
+	Row int
+
+	// Column the cursor was on (0-based).
+	Col int
+
+	// Field values.
+	Values map[string]string
+}
+
+// AID is an Action ID character.
+type AID byte
+
+const (
+	AIDNone  AID = 0x60
+	AIDEnter AID = 0x7D
+	AIDPF1   AID = 0xF1
+	AIDPF2   AID = 0xF2
+	AIDPF3   AID = 0xF3
+	AIDPF4   AID = 0xF4
+	AIDPF5   AID = 0xF5
+	AIDPF6   AID = 0xF6
+	AIDPF7   AID = 0xF7
+	AIDPF8   AID = 0xF8
+	AIDPF9   AID = 0xF9
+	AIDPF10  AID = 0x7A
+	AIDPF11  AID = 0x7B
+	AIDPF12  AID = 0x7C
+	AIDPF13  AID = 0xC1
+	AIDPF14  AID = 0xC2
+	AIDPF15  AID = 0xC3
+	AIDPF16  AID = 0xC4
+	AIDPF17  AID = 0xC5
+	AIDPF18  AID = 0xC6
+	AIDPF19  AID = 0xC7
+	AIDPF20  AID = 0xC8
+	AIDPF21  AID = 0xC9
+	AIDPF22  AID = 0x4A
+	AIDPF23  AID = 0x4B
+	AIDPF24  AID = 0x4C
+	AIDPA1   AID = 0x6C
+	AIDPA2   AID = 0x6E
+	AIDPA3   AID = 0x6B
+	AIDClear AID = 0x6D
+)
+
+func readResponse(c net.Conn) (Response, error) {
+	var r Response
+	aid, err := readAID(c)
+	if err != nil {
+		return r, err
+	}
+	r.AID = aid
+
+	row, col, _, err := readPosition(c)
+	if err != nil {
+		return r, err
+	}
+	r.Col = col
+	r.Row = row
+
+	if err = readFields(c); err != nil {
+		return r, err
+	}
+
+	return r, nil
+}
+
+func readAID(c net.Conn) (AID, error) {
+	buf := make([]byte, 1)
+	for {
+		_, err := c.Read(buf)
+		if err != nil {
+			return AIDNone, err
+		}
+		b := buf[0]
+		if (b == 0x60) || (b >= 0x6b && b <= 0x6e) ||
+			(b >= 0x7a && b <= 0x7d) || (b >= 0x4a && b <= 0x4c) ||
+			(b >= 0xf1 && b <= 0xf9) || (b >= 0xc1 && b <= 0xc9) {
+			// We found a valid AID
+			debugf("Got AID byte: %x\n", b)
+			return AID(b), nil
+		}
+		// Consume non-AID bytes continuing loop
+		debugf("Got non-AID byte: %x\n", b)
+	}
+}
+
+func readPosition(c net.Conn) (row, col, addr int, err error) {
+	buf := make([]byte, 1)
+	raw := make([]byte, 2)
+
+	// Read two bytes
+	for i := 0; i < 2; i++ {
+		if _, err := c.Read(buf); err != nil {
+			return 0, 0, 0, err
+		}
+		raw[i] = buf[0]
+	}
+
+	// Decode the raw position
+	addr = decodeBufAddr([2]byte{raw[0], raw[1]})
+	row = addr % 80
+	col = (addr - row) / 80
+
+	debugf("Got position bytes %02x %02x, decoded to %d\n", raw[0], raw[1],
+		addr)
+
+	return row, col, addr, nil
+}
+
+func readFields(c net.Conn) error {
+	buf := make([]byte, 1)
+	var infield bool
+	var fieldpos int
+	var fieldval bytes.Buffer
+	var err error
+
+	// consume bytes until we get 0xffef
+	for {
+		// Read a byte
+		if _, err = c.Read(buf); err != nil {
+			return err
+		}
+
+		// Check for end of data stream (0xffef)
+		if buf[0] == 0xff {
+			// Finish the current field
+			if infield {
+				// TODO
+				debugf("Field %d: %s\n", fieldpos, e2a(fieldval.Bytes()))
+			}
+
+			// consume the next byte, which is probably 0xef
+			if _, err = c.Read(buf); err != nil {
+				return err
+			}
+			return nil
+		}
+
+		// No? Check for start-of-field
+		if buf[0] == 0x11 {
+			// Finish the previous field, if necessary
+			if infield {
+				// TODO
+				debugf("Field %d: %s\n", fieldpos, e2a(fieldval.Bytes()))
+			}
+			// Start a new field
+			infield = true
+			fieldval = bytes.Buffer{}
+			fieldpos = 0
+
+			if _, _, fieldpos, err = readPosition(c); err != nil {
+				return err
+			}
+			continue
+		}
+
+		// Consume all other bytes as field contents if we're in a field
+		if !infield {
+			debugf("Got unexpected byte while processing fields: %02x\n", buf[0])
+			continue
+		}
+		fieldval.WriteByte(buf[0])
+
+	}
+}
+
+// decodeBufAddr decodes a raw 2-byte encoded buffer address and returns the
+// integer value of the address (i.e. 0-1919)
+func decodeBufAddr(raw [2]byte) int {
+	hi := decodes[raw[0]] << 6
+	lo := decodes[raw[1]]
+	return hi | lo
+}