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CHT Gateway App

cht-gateway build

Download APKs from: https://github.com/medic/cht-gateway/releases

An SMS gateway for Android. Send and receive SMS from your webapp via an Android phone.

+--------+                 +-----------+
|  web   |                 |  cht-     | <-------- SMS
| server | <---- HTTP ---- |  gateway  |
|        |                 | (android) | --------> SMS
+--------+                 +-----------+

Use

Installation

Install the latest APK from https://github.com/medic/cht-gateway/releases

Configuration

CHT

If you're configuring cht-gateway for use with hosted CHT-Core, with a URL of e.g. https://myproject.dev.medicmobile.org and a username of gateway and a password of topSecret, fill in the settings as follows:

Medic-branded gateway

Please note that in the medic-branded build, the username is hard-coded as gateway, and cannot be changed.

Instance name: myproject [dev]
Password: topSecret

Generic-branded gateway

WebappUrl: https://gateway:[email protected]/api/sms

Other

If you're configuring cht-gateway for use with other services, you will need to use the generic build of cht-gateway, and find out the value for CHT URL from your tech support.

CDMA Compatibility Mode

Some CDMA networks have limited support for multipart SMS messages. This can occur within the same network, or only when sending SMS from a GSM network to a CDMA network. Check this box if cht-gateway is running on a GSM network and:

  • multipart messages sent to CDMA phones never arrive; or
  • multipart messages sent to CDMA phones are truncated

Passwords

When using HTTP Basic Auth with gateway, all characters in the password must be chosen from the ISO-8859-1 characterset, excluding #, /, ?, @.

API

This is the API specification for communications between cht-gateway and a web server. Messages in both directions are application/json.

Where a list of values is expected but there are no values provided, it is acceptable to:

  • provide a null value; or
  • provide an empty array ([]); or
  • omit the field completely

Bar array behaviour specified above, cht-gateway must include fields specified in this document, and the web server must include all expected fields in its responses. Either party may include extra fields as they see fit.

Idempotence

N.B. messages are considered duplicate by cht-gateway if they have identical values for id. The webapp is expected to do the same.

cht-gateway will not re-process duplicate webapp-originating messages.

cht-gateway may forward a webapp-terminating message to the webapp multiple times.

cht-gateway may forward a delivery status report to the webapp multiple times for the same message. This should indicate a change of state, but duplicate delivery reports may be delivered in some circumstances, including:

  • the phone receives multiple delivery status reports from the mobile network for the same message
  • cht-gateway failed to process the webapp's response when the delivery report was last forwarded from cht-gateway to webapp

Authorisation

cht-gateway supports HTTP Basic Auth. Just include the username and password for your web endpoint when configuring cht-gateway, e.g.:

https://username:[email protected]/cht-gateway-api-endpoint

Messages

The entire API should be implemented by a webapp at a single endpoint, e.g. https://exmaple.com/cht-gateway-api-endpoint

GET

Expected response:

{
	"medic-gateway": true
}

POST

cht-gateway will accept and process any relevant data received in a response. However, it may choose to only send certain types of information in a particular request (e.g. only provide a webapp-terminating SMS), and will also poll the web service periodically for webapp-originating messages, even if it has no new data to pass to the web service.

Request

Headers

The following headers will be set by requests:

header value
Accept application/json
Accept-Charset utf-8
Accept-Encoding gzip
Cache-Control no-cache
Content-Type application/json

Requests and responses may be sent with Content-Encoding set to gzip.

Content

{
	"messages": [
		{
			"id": <String: uuid, generated by `cht-gateway`>,
			"from": <String: international phone number>,
			"content": <String: message content>,
			"sms_sent": <long: ms since unix epoch that message was sent>,
			"sms_received": <long: ms since unix epoch that message was received>
		},
		...
	],
	"updates": [
		{
			"id": <String: uuid, generated by webapp>,
			"status": <String: PENDING|SENT|DELIVERED|FAILED>,
			"reason": <String: failure reason (optional - only present for status:FAILED)>
		},
		...
	],
}

The status field is defined as follows.

Status Description
PENDING The message has been sent to the gateway's network
SENT The message has been sent to the recipient's network
DELIVERED The message has been received by the recipient's phone
FAILED The delivery has failed and will not be retried

Response

Success

HTTP Status: 2xx

Clients may respond with any status code in the 200-299 range, as they feel is appropriate. cht-gateway will treat all of these statuses the same.

Content
{
	"messages": [
		{
			"id": <String: uuid, generated by webapp>,
			"to": <String: local or international phone number>,
			"content": <String: message content>
		},
		...
	],
}

HTTP Status 400+

Response codes of 400 and above will be treated as errors.

If the response's Content-Type header is set to application/json, cht-gateway will attempt to parse the body as JSON. The following structure is expected:

{
	"error": true,
	"message": <String: error message>
}

The message property may be logged and/or displayed to users in the cht-gateway UI.

Other response codes

Treatment of response codes below 200 and between 300 and 399 will probably be handled sensibly by Android.

SMS Retry Mechanism

Gateway will retry to send the SMS when any of these errors occurs: RESULT_ERROR_NO_SERVICE, RESULT_ERROR_NULL_PDU and RESULT_ERROR_RADIO_OFF.

  1. A possible temporary error occurs and Gateway retries sending the SMS: 1.1 SMS status will be updated to UNSENT, so Gateway will find it and add it into the send queue automatically. 1.2 SMS' retry counter increases by 1. 1.3 The retry attempt is scheduled based on this formula: SMS' last activity time + ( 1 minute * (retry counter ^ 1.5) ). This means the time between retries is incremental. 1.4 Gateway logs: the error, the retry counter and the retry scheduled time. Sample: Sending SMS to +1123123123 failed (cause: radio off) Retry #5 in 15 min

  2. Gateway has a maximum limit of attempts to retry sending SMS (currently 20), If this is reached then: 2.1 Gateway will hard fail the SMS by updating its status to FAILED and won't retry again. 2.2 Gateway logs error. Sample: Sending message to +1123123123 failed (cause: radio off) Not retrying

  3. At this point the user has the option of manually select the SMS and press Retry button. 3.1 If they do and SMS fails again, then the process will restart from step # 1.

Development

Requirements

Development guides are available in the "Android" section of the Community Health Toolkit Docs Site. You will find instructions of how to setup your development environment, build and test new features, how to work with "flavor" apps, release, publish... and so on.

demo-server

  • npm

Building locally

More details of how to setup and build the app here. The following are the most common tasks:

Build and install

To build locally and install to an attached android device:

make

Tests

To run unit tests and static analysis tools locally:

make test

To run end to end tests, first either connect a physical device, or start an emulated android device, and then:

make test-ui

End to end tests only run in devices with Android 4.4 - 9.0. Also it's possible that at the end of the tests when the SDK tries to uninstall the app from the device the following error is shown:

com.android.build.gradle.internal.testing.ConnectedDevice > runTests[4034G - 6.0] FAILED 
        com.android.builder.testing.api.DeviceException: com.android.ddmlib.InstallException: INSTALL_FAILED_VERSION_DOWNGRADE

Don't worry about that, it means the tests ran OK, but the SDK failed to remove the app for compatibility issues with your device, but this error only happens with the tests.

demo-server

There is a demonstration implementation of a server included for cht-gateway to communicate with. You can add messages to this server, and query it to see the interactions that it has with cht-gateway.

Local

To start the demo server locally:

make demo-server

To list the data stored on the server:

curl http://localhost:8000

To make the next good request to /app return an error:

curl --data '"Something failed!"' http://localhost:8000/error

To add a webapp-originating message (to be send by cht-gateway):

curl -vvv --data '{ "id": "3E105262-070C-4913-949B-E7ACA4F42B71", "to": "+447123555888", "content": "hi" }' http://localhost:8000

To simulate a request from cht-gateway:

curl http://localhost:8000/app -H "Accept: application/json" -H "Accept-Charset: utf-8" -H "Accept-Encoding: gzip" -H "Cache-Control: no-cache" -H "Content-Type: application/json" --data '{}'

To clear the data stored on the server:

curl -X DELETE http://localhost:8000

To set a username and password on the demo server:

curl --data '{"username":"alice", "password":"secret"}' http://localhost:8000/auth

Remote

It's simple to deploy the demo server to remote NodeJS hosts.

Heroku

TODO walkthrough

Modulus

TODO walkthrough

Releasing

  1. Create a git tag for the version, eg: v1.7.4.
  2. Push the tag to the repo and GitHub Actions will build and publish the apk to GitHub.
  3. Announce the release on the CHT forum, under the "Product - Releases" category.

Android Version Support

"Default SMS/Messaging app"

Some changes were made to the Android SMS APIs in 4.4 (Kitkat®). The significant change was this:

from android 4.4 onwards, apps cannot delete messages from the device inbox unless they are set, by the user, as the default messaging app for the device

Some reading on this can be found at:

Adding support for kitkat® means that there is some extra code in cht-gateway whose purpose is not obvious:

Non-existent activities in AndroidManifest.xml

Activities HeadlessSmsSendService and ComposeSmsActivity are declared in AndroidManifest.xml, but are not implemented in the code.

Unwanted permissions

The BROADCAST_WAP_PUSH permission is requested in AndroidManifest.xml, and an extra BroadcastReceiver, MmsIntentProcessor is declared. When cht-gateway is the default messaging app on a device, incoming MMS messages will be ignored. Actual WAP Push messages are probably ignored too.

Extra intents

To support being the default messaging app, cht-gateway listens for SMS_DELIVER as well as SMS_RECEIVED. If the default SMS app, we need to ignore SMS_RECEIVED.

Runtime Permissions

Since Android 6.0 (marshmallow), permissions for sending and receiving SMS must be requested both in AndroidManifest.xml and also at runtime. Read more at https://developer.android.com/intl/ru/about/versions/marshmallow/android-6.0-changes.html#behavior-runtime-permissions

Copyright

Copyright 2013-2021 Medic Mobile, Inc. [email protected]

License

The software is provided under AGPL-3.0. Contributions to this project are accepted under the same license.