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/**
* A Promise-like interface for running a sequence of commands.
*
* If a network error occurs while running a command, then a reconnect is automatically
* attempted and the sequence will resume by sending the same command again. Any other errors
* that occur while running a command will cause the entire sequence of commands to abort.
*
* @param {Mongo} conn - a connection to the server
*/
function CommandSequenceWithRetries(conn) {
"use strict";
if (!(this instanceof CommandSequenceWithRetries)) {
return new CommandSequenceWithRetries(conn);
}
const steps = [];
function attemptReconnect(conn) {
try {
conn.adminCommand({ping: 1});
} catch (e) {
return false;
}
return true;
}
this.then = function then(phase, action) {
steps.push({phase: phase, action: action});
return this;
};
this.execute = function execute() {
let i = 0;
let stepHadNetworkErrorAlready = false;
while (i < steps.length) {
try {
// Treat no explicit return statement inside the action function as returning
// {shouldStop: false} for syntactic convenience.
const result = steps[i].action(conn);
if (result !== undefined && result.shouldStop) {
return {ok: 0, msg: "giving up after " + steps[i].phase + ": " + result.reason};
}
} catch (e) {
if (!isNetworkError(e)) {
throw e;
}
// We retry running the action function a second time after a network error
// because it is possible that the node is in the process of stepping down. We
// won't be able to reconnect to the node until it has finished closing all of
// its open connections.
if (stepHadNetworkErrorAlready) {
return {
ok: 0,
msg: "giving up after " + steps[i].phase +
" because we encountered multiple network errors"
};
}
if (!attemptReconnect(conn)) {
return {
ok: 0,
msg: "giving up after " + steps[i].phase +
" because attempting to reconnect failed"
};
}
stepHadNetworkErrorAlready = true;
continue;
}
++i;
stepHadNetworkErrorAlready = false;
}
return {ok: 1};
};
}
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