• Dexcom API
• Installation
• Basic Usage
  • Configuration
  • Determine if estimated glucose values exist for the previous 24 hours
  • Get estimated glucose values for the previous 24 hours
• API
  • setOptions
  • getSandboxAuthenticationToken
  • getEstimatedGlucoseValues
• Testing

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Dexcom API

An API that provides access to the developer.dexcom platform for acquiring Continuous Glucose Monitoring (CGM) data. The primary responsibility of this API is to provide a mechanism for a client to access Dexcom user data without having to use an HTTP interface. This API provides the following services:

• Access to all the developer.dexcom endpoints
• Automatic refreshing of Dexcom OAuth tokens

Since the Dexcom infrastructure does not support CORS, this package is suitable only for server-side systems. If you try to use this module from within a web application, the user's web browser will generate a CORS violation exception.

Installation

npm install @umlss/dexcom-js --save

Basic Usage

Users of this package are responsible for acquiring Dexcom OAuth tokens and packing those tokens within an object that is passed to most of this package's functions:

{
  timestamp: epochMilliseconds,
  dexcomOAuthToken: {
    access_token:  'your access token',
    expires_in:    timeToLiveInSeconds,
    token_type:    'Bearer',
    refresh_token: 'your refresh token'
  }
}

where

• timestamp is time, in epoch milliseconds (UTC), at which the Dexcom OAuth token was acquired
• dexcomOAuthToken is the Dexcom OAuth object issued by Dexcom

After the user has obtained the initial value of the Dexcom OAuth tokens, this package will be responsible for refreshing the OAuth tokens when the API functions are invoked.

If the object returned by a function in this package contains a property named oauthTokens, then the function automatically refreshed the OAuth tokens. In that case, the user is responsible for saving the value of oauthTokens and using the new value of that object as an argument to subsequent function calls.

Configuration

Prior to using any of this package's functions (other than function setOptions()), the user must specify the properties that provide access to the Dexcom platform:

const DexcomJS = require('@umlss/dexcom-js');

DexcomJS.setOptions({
  clientId:     'your application client identifier',
  clientSecret: 'your application client secret',
  redirectUri:  'your application redirect uniform resource identifier',
  apiUri:       'https://api.dexcom.com',
});

Determine if estimated glucose values exist for the previous 24 hours

The following example code illustrates how to use the getStatistics() function to determine if there are any estimated glucose values over the previous 24-hour period of time:

const secondsPerDay         = 86400;
const millisecondsPerSecond = 1000;

const oauthTokens = {
  timestamp: epochMilliseconds,
  dexcomOAuthToken: {
    access_token:  'your access token',
    expires_in:    timeToLiveInSeconds,
    token_type:    'Bearer',
    refresh_token: 'your refresh token'
  }
}

const endDate   = new Date().getTime();
const startDate = endDate - (secondsPerDay * millisecondsPerSecond); 

const results = await DexcomJS.getStatistics(oauthTokens, startDate, endDate);

if (('statistics' in results) && results.statistics.nValues) {
  // Do whatever is appropriate...
}

if ('oauthTokens' in results) {
  // Store the new OAuth tokens...
}

Get estimated glucose values for the previous 24 hours

The following example code illustrates how to use the getEstimatedGlucoseValues() function to obtain data samples that were collected over the previous 24-hour period of time:

const secondsPerDay = 86400;
const millisecondsPerSecond = 1000;

const oauthTokens = {
  timestamp: epochMilliseconds,
  dexcomOAuthToken: {
    access_token:  'your access token',
    expires_in:    timeToLiveInSeconds,
    token_type:    'Bearer',
    refresh_token: 'your refresh token'
  }
}

const endDate   = new Date().getTime();
const startDate = endDate - (secondsPerDay * millisecondsPerSecond); 

const results = await DexcomJS.getEstimatedGlucoseValues(oauthTokens, startDate, endDate);

if (estimatedGlucoseValues in results) {
  // Process the estimated glucose values
  results.estimatedGlucoseValues.egvs.forEach(item => {
    // See https://developer.dexcom.com/get-egvs
  });
}

if (oauthTokens in results) {
  // Store the new OAuth access and refresh tokens...
}

API

setOptions

setOptions(options)

Sets the options that will be used when refreshing an expired OAuth 2.0 access token.

Argument options is an object that contains the following properties:

Property Name	Property Type	Description
clientId	String	The client ID that was issued by Dexcom for your application.
clientSecret	String	The client secret that was issued by Dexcom for your application.
redirectUri	String	The redirect URI that Dexcom will use after the user completes the OAuth authentication process.
apiUri	String	The URI that will be used for accessing the Dexcom platform (typically https://api.dexcom.com)

Note that the redirectUri property will not be accessed by Dexcom's systems as part of using this package. It is used by the Dexcom API during the process of refreshing an expired access token.

getSandboxAuthenticationToken

getSandboxAuthenticationToken(user)

Obtains a Dexcom OAuth 2.0 access token for the Dexcom "sandbox" data.

Argument user is a String that may be any of the following values:

• SandboxUser1
• SandboxUser2
• SandboxUser3
• SandboxUser4
• SandboxUser5
• SandboxUser6

Note there was a breaking change on Dexcom's part on 4/27/2020. They used to support bypassing most of the authorization system, and one would pass uauthcode<n> in instead. This is still supported by this module but is deprecated and may go away at some point.

The return value is a Promise that wraps an Object with the following properties:

{
  "timestamp": epochMilliseconds,
  "dexcomOAuthToken": {
    "access_token": "your access token",
    "expires_in": timeToLiveInSeconds,
    "token_type": "Bearer",
    "refresh_token": "your refresh token"
  }
}

getEstimatedGlucoseValues

getEstimatedGlucoseValues(oauthTokens, startTime, endTime)

Obtains the estimated glucose values for the time range specified by arguments startDate and endDate.

Argument oauthTokens is an Object that contains the following properties:

{
  "timestamp": epochMilliseconds,
  "dexcomOAuthToken": {
    "access_token": "your access token",
    "expires_in": timeToLiveInSeconds,
    "token_type": "Bearer",
    "refresh_token": "your refresh token"
  }
}

Arguments startDate and endDate are integer Numbers in the epoch milliseconds (UTC) format.

The return value is a Promise that wraps an Object with the following properties:

{
  estimatedGlucoseValues: {<object returned by Dexcom API>},
  oauthTokens: {
    "timestamp": epochMilliseconds,
    "dexcomOAuthToken": {
      "access_token": "your access token",
      "expires_in": timeToLiveInSeconds,
      "token_type": "Bearer",
      "refresh_token": "your refresh token"
    }
  }
}

See also https://developer.dexcom.com/get-egvs

If argument oauthTokens.dexcomOAuthToken.access_token has expired, then property oauthTokens in the return value will exist. Otherwise, property oauthTokens will not exist in the return value.

Testing

All unit tests for this package are contained within the test directory. They are run within a Docker container, either interactively (via the Docker container's bash shell), or non-interactively. Furthermore, the unit tests interact with the Dexcom sandbox, thus requiring a network connection in order to function properly.

1. Create file test/secrets.yml.
   Do not commit that file to this, or any other repository, since it contains confidential information.
   The contents of the file should look similar to the following:

    clientId:     'your client ID'
    clientSecret: 'your client secret'
    redirectUri:  'your redirect URI'
    apiUri:       'https://sandbox-api.dexcom.com'
   

   The values in this file will be provided by your Dexcom My Apps page.

2. Run the test suite.
   Interactively:

   1. Invoke the Docker container's bash shell:

        docker-compose run datatest /bin/bash
      

   2. Run the unit tests:

        cd /home/test
        npm install
        npm test test/*.js
      

   Non-interactively:

        docker-compose run datatest