SiddiqSoft.sip2json 1.15.1

sip2json

<b>SIP Parser for Modern C++</b><br/> <small>Copyright ©2020 Abdelkareem Siddiq. All rights reserved.</small>

[[TOC]]

Design goals

A SIP parser for Modern C++. Here, we target C++20. Requires a C++20 compliant compiler.

A lot of parsers exist but they tend to be written (a long time ago) and are primarily in C or wrap around the C library.

JSON is one of the most widely used document storage formats and is the lingua-franca of the web and the various client applications written in JavaScript/TypeScript, C# as well as the myriad of No-SQL data stores.

Modern software architecture relies on many distributed systems and favors horizontal scaling rather than a very efficient, fast single node.

When solving for resilience and high-availability, using systems such as No-SQL stores from Microsoft, Google or Amazon tends to lean towards JSON as the document store.

JSON libraries feature patching, merging and diff'ing of JSON documents therefore we can offload the transforms to templates which can accomplish this task instead of manipulating bespoke C++ classes.

We skewed towards the following tradeoffs:

• API must be native C++17 without any wrappers or compromises.
• Simple, small code
• Dependencies should be widely-used and respected
• Transforms must be easy

Features

• Header only!
• Everything is stored in as json document in a simple json container
  • Start Line
  • Headers
  • Content
• Serialize to SIP message
• Deserialize from SIP message stream buffer to json document(s).
• Dependencies
  • The primary datastore is the json data structure
  • The fmtlib (for C++17 this is a nuget package whereas with C++20 this would be native)
  • C++17

Out of scope

This library is intendended to be used as a basis for you application and does not provide:

• IO facility
• Buffer management
• Encryption
• Managing CSeq
• Thread safety is your responsibility
• No statemachine is provided and the sipmessage class as well as the sip2json class are stateless.

Usage

The library is provided as a nuget package but can also be used as a header-only dependency.

#include "siddiqsoftware/sip2json.hpp"

// Assume a method invoked by the IO system on each "frame" read
// from the tcp stream.
void onReadCompleted(std::string& readBuffer)
{
  auto bufferStart= readBuffer.begin();
  
  // Invokes the callback per each decoded sipmessage from the buffer
  // Keep track of the bufferStart as it is advanced to reach the readBuffer.end()
  // as objects are parsed.
  sip2json::parseAsync(bufferStart,
          readBuffer.end(),
          [](sipmessage&& msg) {
              // Got a valid sipmessage object.. the object has been moved into this argument.
              // The parameter msg has been std::move()'d and therefore the lifetime ends when
              // the callback is completed. It is up to the client to ensure that they
              // make copies as necessary.
              if(!msg.empty()) {
                 // Do something..
              }
          },
          [](sip2jsonErrors& errCode, const std::string& msg){
              // Invoked for an error during the processing of the buffer.
      });

  // Client is responsible for managing the state of the readBuffer
  // the library uses an iterator to parse the stream and advances
  // as each SIP frame is processed.
  readBuffer.erase(readBuffer.begin(), bufferStart); // what remains can be processed as more data arrives
}

API

There are two primary objects: sipmessage and the factory sip2json objects.

#include "sip2json.hpp"
#include "sipmessage.hpp"

using namespace siddiqsoft;

void createINVITE()
{
  sipmessage sipm(METHOD_INVITE, "sip:user@mail.com");
  // Chain additional header values
  sipm.header("To", "sip:user@mail.com")
      .header("From", "sip:user@mail.com")
      .header("Contact", "sip:user@mail.com;tel=14155551212")
      .header("From", "sip:user@mail.com")
      .header("Content-Type", CONTENT_TYPE_APPLICATION_SDP)
      .header("Content-Length", 0);
  // Alternatively, you can use the headers() method to get access to the
  // object directly and perform an add to the array.
  sipm.headers()["Via"].push_back("SIP/2.0/TCP callcontrolserver.com");
  // Next, we set the body
  sipm.body("/sdp/0/v"_json_pointer, 0)
      .body("/sdp/0/t"_json_pointer, {999999, 0});
  .
  .
}

Roadmap

Tests

• There is a single C++ Native Unit Test using the Microsoft C++ Framework under vstest.
• Code Coverage is enabled (only if you're using Visual Studio Enterprise).
• Azure pipelines CI reports on the test results and the coverage results.
• There are to date 64 tests covering parsing and serialization.
• Use live SIP data found under the test\samples folder.
• Clang-Tidy is used as a linter to highlight issues with best-practices and static code analysis.
• Consistent formatting using Clang Format.

References

Json Schema

Container

The document contains single character entries: s, h, b and the diagnostic element meta which is used to track such items as version, time of arrival, time to decode, etc.

{
    "meta": {"version": "sip2json/1.10.2/1.0.1", "time": "2020-08-13T12:27:30.555Z", "ttx": 0},
    "s": {},
    "h": {},
    "b": null
}

This approach acknowledges the fact that SIP messages are generated at a very high rate and processing size of data matters. Keeping the data compact and mapping the raw SIP and SDP means less intermediate processing is involved and keeps our container usage to a single model (map).

SIP Start Line

SIP Headers

The object contains key-value elements found in the SIP header section.

• SIP headers with boolean value types are stored as JSON boolean.
• Default storage type is string
• The header field Content-Length is encoded as JSON number.
• When more than one item with the same header name is found, it is stored in an array.

    "h": { "Authorization": "",
           "Via": [ "via-1",
                    "via-2",
                    "via-3"
           ],
           "Content-Length": 0 }
  

• For header elements that are "empty", the JSON value "" is stored against that header key instead of null.

SIP Body

The object contains key-value elements found in the body section.

• Elements with boolean value types are stored as JSON boolean.
• Default storage type is string
• When more than one item with the same name is found, it is stored in an array. "a":{"rtpmap":""} or "a":{"rtpmap":["",""]}.

    "a": { "remote": "",
           "rtpmap": [ "",
                       ""],
           "new_change": true }
  

• Attribute keys that are a=new_change are stored as "a":{"new_change":true}

Request Document

{
    "meta": {"version": "sip2json/1.10.2/1.0.0", "time": "2020-08-13T12:27:30.555Z", "ttx": 0},
    "s": {
        "type": "request",
        "method": "INVITE",
        "uri": "sip:hello@world.com",
        "version": "SIP/.20"
    },
    "h": {},
    "b": {
        "sdp": [{
            "v": 0,
            "s": "",
            "c": {
                "type": "",
                "subtype": "",
                "dn": ""
            },
            "i": { "dn": "",
                   "name": "",
                   "type": ""
            },
            "o": {
                "user": "",
                "t1": "",
                "t2": "",
                "type": "",
                "subtype": "",
                "host": ""
            },
            "m": "",
            "t": [0, 0],
            "a": {}
        }]
    }
}

Response Document

{
    "meta": {"version": "sip2json/1.10.2/1.0.0", "time": "2020-08-13T12:27:30.555Z", "ttx": 0},
    "s": {
        "type": "response",
        "status": 100,
        "reason": "Trying",
        "version": "SIP/.20"
    },
    "h": {}
}

Request Sample

The source for the following is this sample SIP.

{
    "b": {
        "sdp": [
            {
                "a": {
                    "access_code": "0000000",
                    "acs_guid": "001010000004",
                    "audio_payload": "PCMU",
                    "cdr_start_time": "1594555399.0",
                    "cli-screening": "00",
                    "clir": "false",
                    "dial_once": "aaaa1-aaa13.aaaa2.com",
                    "dialout": "click_in",
                    "far_end": "10.254.254.33:12196",
                    "flags": "1049122",
                    "fmtp": "101 0-15",
                    "ivr": "dialout",
                    "legCallid": "1000000009@10.100.100.100",
                    "leg_no": "3",
                    "mediastatus": "nomedia",
                    "new_change": true,
                    "privs": "participant",
                    "remote": "10.254.254.38:12224",
                    "rtpmap": [
                        "0 pcmu/8000/1",
                        "101 telephone-event/8000"
                    ],
                    "server": "ukdc1-edm18.ring2.com",
                    "sipphone": "usecallid_80000000000000aa-aa-aaaaaa-00@10.254.254.33;port=5060",
                    "status": "(205) answered hold ",
                    "trunk": "8:chan:0",
                    "useforfrom": "hello@world.com",
                    "user-agent": "LoopUp eDial ACS 9.1.0b8050"
                },
                "c": {
                    "dn": "10.254.254.33",
                    "subtype": "IP4",
                    "type": "IN"
                },
                "i": {
                    "dn": "usecallid-leg-3",
                    "name": "usecallid-leg-3",
                    "type": "CallByPhone"
                },
                "m": "audio 8766 RTP/AVP 0 101",
                "o": {
                    "host": "localhost",
                    "subtype": "IP4",
                    "t1": "1011084562",
                    "t2": "804064065",
                    "type": "IN",
                    "user": "hello@world.com"
                },
                "s": "",
                "t": [
                    3803029099,
                    0
                ],
                "v": 0
            }
        ]
    },
    "h": {
        "CSeq": "9 NOTIFY",
        "Call-ID": "80000000000000aa-aa-aaaaaa-00",
        "Contact": "<sip:localhost:8443;transport=ssl>",
        "Content-Length": 880,
        "Content-Type": "application/sdp",
        "From": "sip:hello@world.com;pool=uk-ed-thames;box=ukdc1-edm18.ring2.com;tag=12345678",
        "To": "\"mmyers\" <sip:hello@world.com>",
        "Via": [
            "SIP/2.0/tcp localhost:8443",
            "SIP/2.0/tcp localhost:8443;branch=hello@world.com__eDial_sep__hello@world.com"
        ],
        "X-Billing-code-required": false,
        "X-Call-Instance-ID": "ODQ0NDMaNaU5MaaaOTa1aa1lZC10aGFtZXMtMDE6MTU5NDA0MDI3Naa2NjQ5Nja=",
        "X-Call-Start-Time": "1594040277.665005",
        "X-Call-URL": true,
        "X-Conf_no": "236398",
        "X-From": "hello@world.com",
        "X-Route-ID": "1",
        "X-Sticky": "1",
        "X-Video-SingleView": "0",
        "X-Video-UsingMCU": false,
        "X-client-address": "10.44.200.95",
        "X-control-master": "hello@world.com",
        "X-dialout": "allowed",
        "X-domain": "DEFAULT",
        "X-last-change": "1594040299",
        "X-leader-required": true,
        "X-legs-on-server": "244",
        "X-no-audio": false,
        "X-no-unmute": false,
        "X-no-video": false,
        "X-notify-im": false,
        "X-recording-enabled": true,
        "X-restrict-notify": false,
        "X-restrict-participants": false,
        "X-rollcall": "disabled",
        "X-rss-id": "",
        "X-slave-site": "localhost",
        "X-start-muted": false,
        "X-subject": "Robin Myers' Meeting Room",
        "X-suppress-system-im": false
    },
    "meta": {
        "version": "sip2json/1.10.2/1.0.0",
        "time": "2020-08-13T12:27:30.555Z",
        "ttx": 0
    },
    "s": {
        "method": "NOTIFY",
        "type": "request",
        "uri": "sip:hello@world.com",
        "version": "SIP/2.0"
    }
}

External resources

• JSON for Modern C++
• FMT Library
• GoogleTest primer
• SIP Messages Definition
• SDP specification
• SIP Response Codes