sms

A Go library for encoding and decoding SMSs.

sms is a Go library for encoding and decoding SMS TPDUs, as specified in 3GPP TS 23.040 and 3GPP TS 23.038.

The initial impetus was to provide functionality to send and receive SMSs via a GSM modem, but the library may be generally useful anywhere encoding and decoding SMS TPDUs or their fields is required.

Features

Supports the following functionality:

Creation of SMS TPDUs from UTF-8 strings, including emoji's 😁
Segmentation of long messages into several concatenated SMS TPDUs
Automatic selection of alphabet and language when encoding
Decoding of SMS TPDUs into UTF-8 strings
Reassembly of concatenated SMS TPDUs into a long message
Support for all GSM character sets
Encoding and decoding SMS TPDUs in PDU mode for exchange with GSM modems

Usage

import "github.com/warthog618/sms"

In the following usage examples the error handling is omitted for brevity.

Encode

Creating the TPDUs to contain a message is referred to as encoding.

A one-off message can be encoded using sms.Encode:

tpdus, _ := sms.Encode([]byte("hello world"))
for _, p := range tpdus {
    b, _ := p.MarshalBinary()
    // send binary TPDU...
}

Sending multiple messages requires maintaining multiple counter fields and encoding them in the TPDU. This is performed by an sms.Encoder:

e := sms.NewEncoder()
for {
    msg := <- msgChan
    tpdus, _ := e.Encode(msg)
    for _, p := range tpdus {
        b, _ := p.MarshalBinary()
        // send binary TPDU...
    }
}

Unmarshal

Reassembling received TPDUs into a complete message is a multi-step process. The first step is to unmarhsal the binary SMS TPDU into a TPDU object using sms.Unmarshal:

pdu, _ := sms.Unmarshal(bintpdu)

Decode

A single segment TPDU can be decoded using sms.Decode:

msg, _ := sms.Decode([]*tpdu.TPDUs{pdu})

For concatenated messages, the set of TPDUs containing a message is reassembled into a complete message using sms.Decode:

msg, _ := sms.Decode(tpdus)

Collect

The segments of concatenated messages must be collected before they can be decoded. The Collector collects received segments and returns the complete set once the final segment is received.

c := sms.NewCollector()
for {
    bintpdu := <- pduChan
    pdu, _ := sms.Unmarshal(bintpdu)
    tpdus, _ := c.Collect(pdu)
    if len(tpdus) > 0 {
        msg, _ := sms.Decode(tpdus)
        // handle msg...
    }
}

Options

The core API is aimed at the most common use cases, those performed to the mobile station. e.g. By default, sms.Encode creates an SMS-SUBMIT TPDU and only uses the default character set. By default, sms.Decode uses all character sets. By default, sms.Unmarshal assumes the TPDU is mobile terminating.

The behaviour of the core API functions can be altered for other use cases using optional parameters.

e.g. to specify the destination number for a SMS-SUBMIT message:

tpdus, _ := sms.Encode("hello",sms.To("12345"))

or to encode a message using a particular character set, if necessary:

tpdus, _ := sms.Encode("hello ٻ",sms.WithCharset(charset.Urdu))

or to specify the encoding of a SMS-DELIVER message:

tpdus, _ := sms.Encode("hello",sms.AsDeliver,sms.From("12345"))

or to unmarshal a TPDU from the mobile station:

pdu, _ := sms.Unmarshal(bintpdu,sms.AsMO)

The full set of supplied options:

Option	Category	Description
WithReassemblyTimeout(duration,handler)	Collect	Limit the time allowed to wait for the TPDUs of a complete reassembly
WithTemplate(tpdu)	Encode	Use the provided TPDU as the template for encoded TPDUs.
WithTemplateOption(tpdu.Option)	Encode	Apply the provided option to the template TPDU during encoding.
To(number)	Encode	Set the DA of the encoded TPDU to the number provided
From(number)	Encode	Set the OA of the encoded TPDU to the number provided
WithAllCharsets	Decode,Encode	Make all GSM7 character sets available
WithDefaultCharset	Decode,Encode	Make only the default character set available
WithCharset(nli...)	Decode,Encode	Make the specified character set(s) available
WithLockingCharset(nli...)	Decode,Encode	Make the specified character set(s) available as a locking character set
WithShiftCharset(nli...)	Decode,Encode	Make the specified character set(s) available as a shift character set
AsSubmit	Encode	Encode the TPDU as a SMS-SUBMIT (default)
AsDeliver	Encode	Encode the TPDU as a SMS-DELIVER
As8Bit	Encode	Force the encoding of user data as 8-bit
AsUCS2	Encode	Force the encoding of user data as UCS-2
AsMO	Unmarshal	Treat the TPDU as originating from the mobile station
AsMT	Unmarshal	Treat the TPDU as terminating at the mobile station (default)

Tools

The cmd directory contains basic commands tools to exercise, debug and demonstrate the core functionality of the library, including:

encoding messages into SMS-SUBMIT TPDUs (smssubmit)
decoding SMS-DELIVER TPDUs into messages (smsdeliver)
decoding arbitrary TPDUs (smsdecode)
displaying supported character sets (charsets).

The following examples demonstrate the example commands, and their code provides some examples of using the library.

Submit Encoding

Creating an SMS to send:

$ smssubmit -number 12345 -message "Hello world"
Submit TPDU:
010105912143f500000bc8329bfd06dddf723619

Long messages are split into a concatenated message spanning several TPDUs:

smssubmit -number 12345 -message "this is a very long message that does not fit in a single SMS message, at least it will if I keep adding more to it as 160 characters is more than you might think 😁"
Submit TPDU 1:
410105912143f500088c050003010301007400680069007300200069007300200061002000760065007200790020006c006f006e00670020006d0065007300730061006700650020007400680061007400200064006f006500730020006e006f0074002000660069007400200069006e00200061002000730069006e0067006c006500200053004d00530020006d0065007300730061
Submit TPDU 2:
410205912143f500088c05000301030200670065002c0020006100740020006c0065006100730074002000690074002000770069006c006c002000690066002000490020006b00650065007000200061006400640069006e00670020006d006f0072006500200074006f0020006900740020006100730020003100360030002000630068006100720061006300740065007200730020
Submit TPDU 3:
410305912143f5000844050003010303006900730020006d006f007200650020007400680061006e00200079006f00750020006d00690067006800740020007400680069006e006b0020d83dde01

Deliver Decoding

Decoding an SMS received from a GSM modem in PDU mode:

$ smsdeliver -p 07911614220991F1040B911605935713F200008140806113912304D7F79B0E
+61503975312: Woot

Concatenated Message Decoding

Concatenating and displaying a message split into multiple SMS-DELIVER TPDUs.

$ smsdeliver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
+61503975312: this is a very long message that does not fit in a single SMS message, at least it will if I keep adding more to it as 160 characters is more than you might think 😁

General TPDU Decoding

Decoding the Submit TPDU created above:

$ smsdecode -o 010105912143f500000bc8329bfd06dddf723619
TPDU: SMS-SUBMIT
TP-MTI: 0x01 Submit
TP-RD: false
TP-VPF: 0x00 Not Present
TP-RP: false
TP-UDHI: false
TP-SRR: false
TP-MR: 1
TP-DA: +12345
TP-PID: 0x00
TP-DCS: 0x00 7bit
TP-VP: Not Present
TP-UD: 00000000  48 65 6c 6c 6f 20 77 6f  72 6c 64                 |Hello world|

Decoding the Deliver TPDU above:

$ smsdecode -p 07911614220991F1040B911605935713F200008140806113912304D7F79B0E
SMSC: +61412290191
TPDU: SMS-DELIVER
TP-MTI: 0x00 Deliver
TP-MMS: true
TP-LP: false
TP-RP: false
TP-UDHI: false
TP-SRI: false
TP-OA: +61503975312
TP-PID: 0x00
TP-DCS: 0x00 7bit
TP-SCTS: 2018-04-08 16:31:19 +0800
TP-UD: 00000000  57 6f 6f 74                                       |Woot|

Decoding the first Deliver TPDU of the concatenated message above:

$ smsdecode 400B911605935713F20008814080611373238C050003C00301007400680069007300200069007300200061002000760065007200790020006C006F006E00670020006D0065007300730061006700650020007400680061007400200064006F006500730020006E006F0074002000660069007400200069006E00200061002000730069006E0067006C006500200053004D00530020006D0065007300730061
TPDU: SMS-DELIVER
TP-MTI: 0x00 Deliver
TP-MMS: false
TP-LP: false
TP-RP: false
TP-UDHI: true
TP-SRI: false
TP-OA: +61503975312
TP-PID: 0x00
TP-DCS: 0x08 UCS-2
TP-SCTS: 2018-04-08 16:31:37 +0800
TP-UDH: ID: 0  Data: [192 3 1]
TP-UD: 00000000  00 74 00 68 00 69 00 73  00 20 00 69 00 73 00 20  |.t.h.i.s. .i.s. |
       00000010  00 61 00 20 00 76 00 65  00 72 00 79 00 20 00 6c  |.a. .v.e.r.y. .l|
       00000020  00 6f 00 6e 00 67 00 20  00 6d 00 65 00 73 00 73  |.o.n.g. .m.e.s.s|
       00000030  00 61 00 67 00 65 00 20  00 74 00 68 00 61 00 74  |.a.g.e. .t.h.a.t|
       00000040  00 20 00 64 00 6f 00 65  00 73 00 20 00 6e 00 6f  |. .d.o.e.s. .n.o|
       00000050  00 74 00 20 00 66 00 69  00 74 00 20 00 69 00 6e  |.t. .f.i.t. .i.n|
       00000060  00 20 00 61 00 20 00 73  00 69 00 6e 00 67 00 6c  |. .a. .s.i.n.g.l|
       00000070  00 65 00 20 00 53 00 4d  00 53 00 20 00 6d 00 65  |.e. .S.M.S. .m.e|
       00000080  00 73 00 73 00 61                                 |.s.s.a|

Decoding the second Submit TPDU in the concatenated message above:

smsdecode -o 410205912143f500088c05000301030200670065002c0020006100740020006c0065006100730074002000690074002000770069006c006c002000690066002000490020006b00650065007000200061006400640069006e00670020006d006f0072006500200074006f0020006900740020006100730020003100360030002000630068006100720061006300740065007200730020
TPDU: SMS-SUBMIT
TP-MTI: 0x01 Submit
TP-RD: false
TP-VPF: 0x00 Not Present
TP-RP: false
TP-UDHI: true
TP-SRR: false
TP-MR: 2
TP-DA: +12345
TP-PID: 0x00
TP-DCS: 0x08 UCS-2
TP-VP: Not Present
TP-UDH: ID: 0  Data: [1 3 2]
TP-UD: 00000000  00 67 00 65 00 2c 00 20  00 61 00 74 00 20 00 6c  |.g.e.,. .a.t. .l|
       00000010  00 65 00 61 00 73 00 74  00 20 00 69 00 74 00 20  |.e.a.s.t. .i.t. |
       00000020  00 77 00 69 00 6c 00 6c  00 20 00 69 00 66 00 20  |.w.i.l.l. .i.f. |
       00000030  00 49 00 20 00 6b 00 65  00 65 00 70 00 20 00 61  |.I. .k.e.e.p. .a|
       00000040  00 64 00 64 00 69 00 6e  00 67 00 20 00 6d 00 6f  |.d.d.i.n.g. .m.o|
       00000050  00 72 00 65 00 20 00 74  00 6f 00 20 00 69 00 74  |.r.e. .t.o. .i.t|
       00000060  00 20 00 61 00 73 00 20  00 31 00 36 00 30 00 20  |. .a.s. .1.6.0. |
       00000070  00 63 00 68 00 61 00 72  00 61 00 63 00 74 00 65  |.c.h.a.r.a.c.t.e|
       00000080  00 72 00 73 00 20                                 |.r.s. |

Subpackages

The tpdu package provides the core TPDU types and conversions to and from their binary form.

The pdumode package provides encoding and decoding of PDUs exchanged with GSM modems in PDU mode.

A number of packages provide functionality to encode and decode TPDU fields:

The bcd package provides conversions to and from BCD format.

The gsm7 package provides conversions to and from 7bit packed user data.

The charset package provides the character sets used to encode user data in GSM 7bit format as specified in 3GPP TS 23.038.

The semioctet package provides conversions to and from semioctet format.

The ucs2 package provides conversions between UCS-2 and UTF-8.

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