read.go

// Copyright (c) 2012, Sean Treadway, SoundCloud Ltd.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Source code and contact info at http://github.com/streadway/amqp

package amqp

import (
	"bytes"
	"encoding/binary"
	"errors"
	"io"
	"time"
)

/*
Reads a frame from an input stream and returns an interface that can be cast into
one of the following:

   methodFrame
   PropertiesFrame
   bodyFrame
   heartbeatFrame

2.3.5  frame Details

All frames consist of a header (7 octets), a payload of arbitrary size, and a
'frame-end' octet that detects malformed frames:

  0      1         3             7                  size+7 size+8
  +------+---------+-------------+  +------------+  +-----------+
  | type | channel |     size    |  |  payload   |  | frame-end |
  +------+---------+-------------+  +------------+  +-----------+
   octet   short         long         size octets       octet

To read a frame, we:
  1. Read the header and check the frame type and channel.
	2. Depending on the frame type, we read the payload and process it.
  3. Read the frame end octet.

In realistic implementations where performance is a concern, we would use
“read-ahead buffering” or

“gathering reads” to avoid doing three separate system calls to read a frame.
*/
func (r *reader) ReadFrame() (frame frame, err error) {
	var scratch [7]byte

	if _, err = io.ReadFull(r.r, scratch[:7]); err != nil {
		return
	}

	typ := uint8(scratch[0])
	channel := binary.BigEndian.Uint16(scratch[1:3])
	size := binary.BigEndian.Uint32(scratch[3:7])

	switch typ {
	case frameMethod:
		if frame, err = r.parseMethodFrame(channel, size); err != nil {
			return
		}

	case frameHeader:
		if frame, err = r.parseHeaderFrame(channel, size); err != nil {
			return
		}

	case frameBody:
		if frame, err = r.parseBodyFrame(channel, size); err != nil {
			return nil, err
		}

	case frameHeartbeat:
		if frame, err = r.parseHeartbeatFrame(channel, size); err != nil {
			return
		}

	default:
		return nil, ErrFrame
	}

	if _, err = io.ReadFull(r.r, scratch[:1]); err != nil {
		return nil, err
	}

	if scratch[0] != frameEnd {
		return nil, ErrFrame
	}

	return
}

func readShortstr(r io.Reader) (v string, err error) {
	var length uint8
	if err = binary.Read(r, binary.BigEndian, &length); err != nil {
		return
	}

	bytes := make([]byte, length)
	if _, err = io.ReadFull(r, bytes); err != nil {
		return
	}
	return string(bytes), nil
}

func readLongstr(r io.Reader) (v string, err error) {
	var length uint32
	if err = binary.Read(r, binary.BigEndian, &length); err != nil {
		return
	}

	bytes := make([]byte, length)
	if _, err = io.ReadFull(r, bytes); err != nil {
		return
	}
	return string(bytes), nil
}

func readDecimal(r io.Reader) (v Decimal, err error) {
	if err = binary.Read(r, binary.BigEndian, &v.Scale); err != nil {
		return
	}
	if err = binary.Read(r, binary.BigEndian, &v.Value); err != nil {
		return
	}
	return
}

func readFloat32(r io.Reader) (v float32, err error) {
	if err = binary.Read(r, binary.BigEndian, &v); err != nil {
		return
	}
	return
}

func readFloat64(r io.Reader) (v float64, err error) {
	if err = binary.Read(r, binary.BigEndian, &v); err != nil {
		return
	}
	return
}

func readTimestamp(r io.Reader) (v time.Time, err error) {
	var sec int64
	if err = binary.Read(r, binary.BigEndian, &sec); err != nil {
		return
	}
	return time.Unix(sec, 0), nil
}

/*
'A': []interface{}
'D': Decimal
'F': Table
'I': int32
'S': string
'T': time.Time
'V': nil
'b': byte
'd': float64
'f': float32
'l': int64
's': int16
't': bool
'x': []byte
*/
func readField(r io.Reader) (v interface{}, err error) {
	var typ byte
	if err = binary.Read(r, binary.BigEndian, &typ); err != nil {
		return
	}

	switch typ {
	case 't':
		var value uint8
		if err = binary.Read(r, binary.BigEndian, &value); err != nil {
			return
		}
		return (value != 0), nil

	case 'b':
		var value [1]byte
		if _, err = io.ReadFull(r, value[0:1]); err != nil {
			return
		}
		return value[0], nil

	case 's':
		var value int16
		if err = binary.Read(r, binary.BigEndian, &value); err != nil {
			return
		}
		return value, nil

	case 'I':
		var value int32
		if err = binary.Read(r, binary.BigEndian, &value); err != nil {
			return
		}
		return value, nil

	case 'l':
		var value int64
		if err = binary.Read(r, binary.BigEndian, &value); err != nil {
			return
		}
		return value, nil

	case 'f':
		var value float32
		if err = binary.Read(r, binary.BigEndian, &value); err != nil {
			return
		}
		return value, nil

	case 'd':
		var value float64
		if err = binary.Read(r, binary.BigEndian, &value); err != nil {
			return
		}
		return value, nil

	case 'D':
		return readDecimal(r)

	case 'S':
		return readLongstr(r)

	case 'A':
		return readArray(r)

	case 'T':
		return readTimestamp(r)

	case 'F':
		return readTable(r)

	case 'x':
		var len int32
		if err = binary.Read(r, binary.BigEndian, &len); err != nil {
			return nil, err
		}

		value := make([]byte, len)
		if _, err = io.ReadFull(r, value); err != nil {
			return nil, err
		}
		return value, err

	case 'V':
		return nil, nil
	}

	return nil, ErrSyntax
}

/*
	Field tables are long strings that contain packed name-value pairs.  The
	name-value pairs are encoded as short string defining the name, and octet
	defining the values type and then the value itself.   The valid field types for
	tables are an extension of the native integer, bit, string, and timestamp
	types, and are shown in the grammar.  Multi-octet integer fields are always
	held in network byte order.
*/
func readTable(r io.Reader) (table Table, err error) {
	var nested bytes.Buffer
	var str string

	if str, err = readLongstr(r); err != nil {
		return
	}

	nested.Write([]byte(str))

	table = make(Table)

	for nested.Len() > 0 {
		var key string
		var value interface{}

		if key, err = readShortstr(&nested); err != nil {
			return
		}

		if value, err = readField(&nested); err != nil {
			return
		}

		table[key] = value
	}

	return
}

func readArray(r io.Reader) ([]interface{}, error) {
	var (
		size uint32
		err  error
	)

	if err = binary.Read(r, binary.BigEndian, &size); err != nil {
		return nil, err
	}

	var (
		lim   = &io.LimitedReader{R: r, N: int64(size)}
		arr   = []interface{}{}
		field interface{}
	)

	for {
		if field, err = readField(lim); err != nil {
			if err == io.EOF {
				break
			}
			return nil, err
		}
		arr = append(arr, field)
	}

	return arr, nil
}

// Checks if this bit mask matches the flags bitset
func hasProperty(mask uint16, prop int) bool {
	return int(mask)&prop > 0
}

func (r *reader) parseHeaderFrame(channel uint16, size uint32) (frame frame, err error) {
	hf := &headerFrame{
		ChannelId: channel,
	}

	if err = binary.Read(r.r, binary.BigEndian, &hf.ClassId); err != nil {
		return
	}

	if err = binary.Read(r.r, binary.BigEndian, &hf.weight); err != nil {
		return
	}

	if err = binary.Read(r.r, binary.BigEndian, &hf.Size); err != nil {
		return
	}

	var flags uint16

	if err = binary.Read(r.r, binary.BigEndian, &flags); err != nil {
		return
	}

	if hasProperty(flags, flagContentType) {
		if hf.Properties.ContentType, err = readShortstr(r.r); err != nil {
			return
		}
	}
	if hasProperty(flags, flagContentEncoding) {
		if hf.Properties.ContentEncoding, err = readShortstr(r.r); err != nil {
			return
		}
	}
	if hasProperty(flags, flagHeaders) {
		if hf.Properties.Headers, err = readTable(r.r); err != nil {
			return
		}
	}
	if hasProperty(flags, flagDeliveryMode) {
		if err = binary.Read(r.r, binary.BigEndian, &hf.Properties.DeliveryMode); err != nil {
			return
		}
	}
	if hasProperty(flags, flagPriority) {
		if err = binary.Read(r.r, binary.BigEndian, &hf.Properties.Priority); err != nil {
			return
		}
	}
	if hasProperty(flags, flagCorrelationId) {
		if hf.Properties.CorrelationId, err = readShortstr(r.r); err != nil {
			return
		}
	}
	if hasProperty(flags, flagReplyTo) {
		if hf.Properties.ReplyTo, err = readShortstr(r.r); err != nil {
			return
		}
	}
	if hasProperty(flags, flagExpiration) {
		if hf.Properties.Expiration, err = readShortstr(r.r); err != nil {
			return
		}
	}
	if hasProperty(flags, flagMessageId) {
		if hf.Properties.MessageId, err = readShortstr(r.r); err != nil {
			return
		}
	}
	if hasProperty(flags, flagTimestamp) {
		if hf.Properties.Timestamp, err = readTimestamp(r.r); err != nil {
			return
		}
	}
	if hasProperty(flags, flagType) {
		if hf.Properties.Type, err = readShortstr(r.r); err != nil {
			return
		}
	}
	if hasProperty(flags, flagUserId) {
		if hf.Properties.UserId, err = readShortstr(r.r); err != nil {
			return
		}
	}
	if hasProperty(flags, flagAppId) {
		if hf.Properties.AppId, err = readShortstr(r.r); err != nil {
			return
		}
	}
	if hasProperty(flags, flagReserved1) {
		if hf.Properties.reserved1, err = readShortstr(r.r); err != nil {
			return
		}
	}

	return hf, nil
}

func (r *reader) parseBodyFrame(channel uint16, size uint32) (frame frame, err error) {
	bf := &bodyFrame{
		ChannelId: channel,
		Body:      make([]byte, size),
	}

	if _, err = io.ReadFull(r.r, bf.Body); err != nil {
		return nil, err
	}

	return bf, nil
}

var errHeartbeatPayload = errors.New("Heartbeats should not have a payload")

func (r *reader) parseHeartbeatFrame(channel uint16, size uint32) (frame frame, err error) {
	hf := &heartbeatFrame{
		ChannelId: channel,
	}

	if size > 0 {
		return nil, errHeartbeatPayload
	}

	return hf, nil
}