Adjust outgoing activity timestamp

[compulim]

Fixes #1954.

Changelog Entry

• Fix #1954. Estimate clock skew and adjust timestamp for outgoing activity, by @compulim in PR #2208

Description

If client clock is skewed significantly behind server clock (client clock < server clock for 5 seconds), the user-originated activity could be appears on top of the transcript momentarily until Direct Line Channel echo back the message with a corrected timestamp.

This is because the timestamp we temporarily assign to the user-originated activity is inaccurate. The insertion-sort put the outgoing activity before other activities received from the server. When server echo back the message, it will correct the timestamp.

This fix is to estimate the clock skew and applies to the outgoing activity.

Specific Changes

• Modify postActivity.js
  • Piggyback client timestamp to channelData.clientTimestamp, to estimate the clock skew by comparing it with timestamp field
  • When patching timestamp field on outgoing activity, adjust it with the estimated clock skew
• Add a new reducer, clockSkewAdjustment.js
  • Estimate adjustment on all incoming activity with channelData.clientTimestamp field

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• Testing Added

[coveralls]

Coverage increased (+0.3%) to 64.88% when pulling b3e04a2 on compulim:fix-1954 into cbee7cb on microsoft:master.

[corinagum]

@compulim can we get another PR in with the changes I suggested?