Fossil

Email Alerts
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Overview

Beginning with version 2.7, Fossil can send email messages to subscribers to alert them to changes in the repository:

Subscribers can elect to receive emails as soon as these events happen, or they can receive a daily digest of the events instead.

Email alerts are sent by a Fossil server, which must be set up by the Fossil administrator to send email.

Email alerts do not currently work if you are only using Fossil from the command line.

A bit of terminology: Fossil uses the terms "email alerts" and "notifications" interchangeably. We stick to the former term in this document except when referring to parts of the Fossil UI still using the latter term.

Setup Prerequisites

Much of this document describes how to set up Fossil's email alert system. To follow this guide, you will need a Fossil UI browser window open to the Admin → Notification Fossil UI screen on the the Fossil server that will be sending these email alerts, logged in as a user with Admin capability. It is not possible to work on a clone of the server's repository and push the configuration changes up to that repo as an Admin user, on purpose.

Important: Do not confuse that screen with Admin → Email-Server, which sets up a different subsystem within Fossil. That feature is related to this document's topic, but it is currently incomplete, so we do not cover it at this time.

You will also need a CLI window open with its working directory changed to a checkout directory of the Fossil repository you are setting up to send email. If you don't cd to such a checkout directory first, you'll need to add -R /path/to/repo.fossil to each fossil command below to tell Fossil which repository you mean it to apply the command to.

There are other prerequisites for email service, but since they vary depending on the configuration you choose, we'll cover these inline below.

Quick Email Service Setup

If you've already got a working Postfix, Exim, or Sendmail server on the machine running your Fossil instance(s), and you aren't using Fossil's chroot feature to wall Fossil off from the rest of the machine, it's fairly simple to set up email alerts.

(Otherwise, skip ahead to the sections on advanced email service setup.)

This is our "quick setup" option even though setting up an SMTP mail server is not trival, because there are many other reasons to have such a server set up already: internal project email service, cron notifications, server status monitoring notifications...

With that out of the way, the Fossil-specific steps are easy:

  1. Go to Admin → Notification and fill out all of the Required fields:

    • Canonical server URL — Use the suggested URL
    • "From" email address — forum-bounces@example.com is traditional, but suit yourself
    • Repository nickname — See the suggested examples on the web page.

  2. Set "Email Send Method" to "Pipe to a command"

  3. Set the "Administrator email address" to a suitable valid email address on that machine. It could be the same value you used for the "From" address above, or it could be a different value like admin@example.com.

Save your changes.

At the command line, say

  $ fossil set email-send-command

If that gives a blank value instead of sendmail -ti, say

  $ fossil set email-send-command "sendmail -ti"

to force the setting. That works around a known bug which may be squished by the time you read this.

If you're running Postfix or Exim, you might think that command is wrong, since you aren't running Sendmail. These mail servers provide a sendmail command for compatibility with software like Fossil that has no good reason to care exactly which SMTP server implementation is running at a given site. There may be other SMTP servers that also provide a compatible sendmail command, in which case they may work with Fossil using the same steps as above.

If you reload the Admin → Notification page, the Status section at the top should show:

  Outgoing Email: Piped to command "sendmail -ti"
  Pending Alerts: 0 normal, 0 digest
  Subscribers:    0 active, 0 total

Before you move on to the next section, you might like to read up on some subtleties with the "pipe to a command" method that we did not cover above.

Usage and Testing

Now that email service from Fossil is set up, you can test it and begin using it.

Subscribing to Alerts

In the Status output above, we saw that there are no subscribers, so the next step is to add the first one.

Go to the /subscribe page on your Fossil instance to sign up for email alerts. At the very least, you will need to sign up for "Forum Posts" and "Announcements" to complete the testing steps below.

If you're logged in with a Fossil repository user account and put the same user name and email address into this forum as you used for your user information under Admin → Users, Fossil will simply tie your alert preferences to your login record, and the email address in your user's Contact Info field will be considered already-verified. Otherwise, Fossil will create an alert-only record, and you will have to verify the email address before Fossil will send alerts to it.

This shows a key aspect of the way Fossil's email alerts system works, by the way: a user can be signed up for email alerts without having a full-fledged Fossil user account. Only when both user names are the same are the two records tied together under the hood. For more on this, see Users vs Subscribers below.

If you are seeing the following complaint from Fossil:

Use a different login with greater privilege than FOO to access /subscribe

...then the repository's administrator forgot to give the Alerts capability to that user or to a user category that the user is a member of.

After a subscriber signs up for alerts for the first time, a single verification email is sent to that subscriber's given email address. The new subscriber must click a link in that email in order to activate the subscription.

Subscription verification emails are only sent once. This is a defense against malicious robots that try to harass innocent Internet users by having subscription pages send multiple verification emails. If the initial subscription verification does not go through correctly, an administrator must intervene to reset the subscription.

Every subscriber-only email address has a long random hexadecimal security code that serves in place of a password. All email alerts contain a link in their footer back to the Fossil server, incorporating this security code, which allows the subscriber to adjust their subscription options. If a user doesn't have any of those emails, they can request a link via email by visiting the /alerts or /unsubscribe page on the repository.

Those with Fossil repository logins can adjust their email alert settings by visiting the /alerts page on the repository. With the default skin, you can get there by clicking the "Logout" link in the upper right corner of any Fossil UI page then clicking the "Email Alerts" link. That link is also available via the Sitemap (/sitemap) and via the default skin's hamburger menu (☰).

Unsubscribing

To unsubscribe from alerts, visit the /alerts page on the repository, click the "Unsubscribe" button, then check the "Unsbuscribe" checkbox to verify your action and press the "Unsubscribe" button a second time.

This interlock is intended to prevent accidental unsubscription.

Test Email Service

The easiest way to test email sending from Fossil is via the "Send Announcement" link at the top of the "Email Notification Setup" page. Put your email address in the "To:" line and a test message below, then press "Send Message" to verify that outgoing email is working.

Another method is from the command line:

  $ fossil alerts test-message you@example.com --body README.md --subject Test

That should send you an email with "Test" in the subject line and the contents of your project's README.md file in the body.

That command assumes that your project contains a "readme" file, but of course it does, because you have followed the Programming Style Guide Checklist, right? Right.

User Capabilities

Once email alerts are working, one must also adjust user permissions to allow users to subscribe to email alerts. In the capability list for each user on the Admin → Users page is a new capability called "Email Alerts". The corresponding capability letter is "7", which you must give to any user that needs to use the subscription setup pages, /subscribe and /alerts.

To allow any passer-by on the Internet to subscribe, give the "Email Alerts" capability to the "nobody" user category. To require that a person solve a simple CAPTCHA first, give that capability to the "anonymous" user category instead.

First Post

I suggest taking the time to compose a suitable introductory message especially for your project's forum, one which a new user would find helpful.

Wait a few seconds, and you should receive an email alert with the post's subject and body text in the email.

Troubleshooting

If email alerts aren't working, there are several useful commands you can give to figure out why.

(Be sure to cd into a repo checkout directory first!)

  $ fossil alerts status

This should give much the same information as you saw above. One difference is that, since you've created a forum post, the pending-alerts value should only be zero if you did in fact get the requested email alert. If it's zero, check your mailer's spam folder. If it's nonzero, continue with these troubleshooting steps.

  $ fossil backoffice

That forces Fossil to run its "back office" process. Its only purpose at the time of this writing is to push out alert emails, but it might do other things later. Sometimes it can get stuck and needs to be kicked. For that reason, you might want to set up a crontab entry to make sure it runs occasionally.

  $ fossil alerts send

This should also kick off the backoffice processing, if there are any pending alerts to send out.

  $ fossil alert pending

Show any pending alerts. The number of lines output here should equal the status output above.

  $ fossil test-add-alerts f5900
  $ fossil alert send

Manually create an email alert and push it out immediately.

The f in the first command's final parameter means you're scheduling a "forum" alert. The integer is the ID of a forum post, which you can find by visiting /timeline?showid on your Fossil instance.

The second command above is necessary because the test-add-alerts command doesn't kick off a backoffice run.

  $ fossil ale send

This only does the same thing as the final command above, rather than send you an ale, as you might be hoping. Sorry.

Advanced Email Setups

Fossil offers several methods of sending email:

  1. Pipe the email message text into a command.
  2. Store email messages as entries in a SQLite database.
  3. Store email messages as individual files in a directory.
  4. Send emails to an SMTP relay.
  5. Send emails directly to the recipients via SMTP.

This wide range of options allows Fossil to talk to pretty much any SMTP setup.

The first four options let Fossil delegate email handling to an existing MTA so that Fossil does not need to implement the roughly two dozen separate RFCs required in order to properly support SMTP email in this complex world we've built. As well, this design choice means you do not need to do duplicate configuration, such as to point Fossil at your server's TLS certificate in order to support users behind mail servers that require STARTTLS encryption.

Method 1: Pipe to a Command

This is our "quick setup" option above, but there are some details we ignored which we'll cover now.

Fossil pipes the email message in RFC 822 format to the standard input of the command you gave as the "Email Send Method", defaulting to sendmail -ti. This constitutes a protocol between Fossil and the SMTP message transfer agent (MTA). Any other MTA which speaks the same protocol can be used in place of the most common options: Sendmail, Exim, and Postfix.

The -t option tells the command to expect the list of email recipients in a To header in the RFC 822 message presented on its standard input. Without this option, the sendmail command expects to receive the recipient list on the command line, but that's not possible with the current design of this email sending method. Therefore, if you're attempting to use a less common MTA which cannot parse the recipient list from the To header in the email message, you might need to look for a different MTA.

The -i option is only needed for MTAs that take a dot/period at the beginning of a line of standard input text as "end of message." Fossil doesn't attempt to escape such dots, so if the line wrapping happens to occur such that a dot or period in an alert message is at the beginning of a line, you'll get a truncated email message without this option. Statistically, this will happen about once every 70 or so messages, so it is important to give this option if your MTA treats leading dots on a line this way.

We believe the msmtp SMTP client is compatible with this protocol if you give it the -t option. To our knowledge, this remains untested, but if it works, this would be a useful option on a server hosting a Fossil repository which doesn't otherwise require a separate SMTP server for other purposes.

It is probably also possible to configure procmail to work with this protocol. If you know how to do it, a patch to this document or a how-to on the Fossil forum would be appreciated.

Method 2: Store in a Database

The self-hosting Fossil repository at https://www.fossil-scm.org/ currently uses this method rather than the pipe method because it is running inside of a restrictive chroot jail which is unable to hand off messages to the local MTA directly.

When you configure a Fossil server this way, it adds outgoing email messages to a SQLite database file. A separate daemon process can then extract those messages for further disposition.

Fossil includes a copy of the daemon used on fossil-scm.org: it is just a short Tcl script that continuously monitors this database for new messages and hands any that it finds off to a local MTA using the same pipe to MTA protocol as above.

In this way, outbound email alerts escape the chroot jail without requiring that we insert a separate MTA configuration inside that jail. We only need to arrange that the same SQLite DB file be visible both inside and outside the chroot jail, which we do by naming the database file in the "Store Emails In This Database" setting under Admin → Notification. The Tcl script has this path hard-coded as /home/www/fossil/emailqueue.db, but you will probably need to adjust that for your local purposes.

This method may work with other similar technologies besides chroot: Docker containers, LXC containers, BSD jails, Solaris zones, etc.

With suitable file share mappings, this method may even work with virtual machine or distributed computing setups where the MTA and Fossil servers are not on the same machine, though beware the risk of DB corruption if used with a file sharing technology that doesn't use proper file locking.

You can start this Tcl script as a daemon automatically on most Unix and Unix-like systems by adding the following line to the /etc/rc.local file of the server that hosts the repository sending email alerts:

  /usr/bin/tclsh /home/www/fossil/email-sender.tcl &

Method 3: Store in a Directory

This method is functionally very similar to the DB method, differing only in that messages are written to a directory in the filesystem. You should therefore read that section and make the minor adjustments required by the storage method.

This method may work over a file sharing mechanism that doesn't do file locking properly, as long as the reading process is somehow restricted from reading a message file as it's being written.

It might be useful in testing and debugging to temporarily switch to this method, since you can easily read the generated email messages without needing to involve an MTA.

Method 4: SMTP Relay

In this configuration, the Fossil server contacts an open SMTP relay and sends the messages to it. This method is only appropriate when:

  1. You have a local MTA that doesn't accept the pipe protocol.

  2. The MTA is willing to accept anonymous submissions, since Fossil currently has no way to authenticate itself to the MTA. This is an unsafe configuration in most cases, but some SMTP servers make an exception for connections coming from a localhost or LAN address, choosing to accept such submissions as inherently safe.

If you have a local MTA meeting criterion #1 but not #2, we'd suggest using a more powerful SMTP client such as msmtp along with one of the other methods above.

Method 5: Direct SMTP Send

As of Fossil 2.7, the code to support this method is incomplete, so you cannot currently select it as an option in Admin → Notification.

Users vs Subscribers

Fossil makes a distinction between "users" and "subscribers". A user is someone with a username and password: that is, someone who can log into the Fossi repository. A subscriber is someone who receives email alerts. Users can also be subscribers and subscribers can be users, but that does not have to be the case. It is possible to be a user without being a subscriber and to be a subscriber without being a user.

In the repository database file, users are tracked with the user table and subscribers are tracked via the subscriber table.

Administrator Activities

The "List Subscribers" button at the top of the Admin → Notification screen gives a list of subscribers, which gives a Fossil server administrator a lot of power over those subscriptions.

Clicking an email address in this subscriber list opens the same /alerts page that the user can see for their own subscription, but with more information and functionality than normal users get:

This screen also allows a Fossil Admin user to perform other activities on behalf of a subscriber which they could do themselves, such as to unsubscribe them.

Cloning, Syncing, and Backups

The Admin → Notification settings are not replicated using clone or sync, and it is not possible to push such settings from one repository to another. In a network of peer repositories, you only want one repository sending email alerts. If you were to replicate the email alert settings to a separate repository, then subscribers would get multiple alerts for each event, which would be bad.

However, the subscriber list can be synced for backup purposes. Use the fossil config pull subscriber command to pull the latest subscriber list from a server into a backup repository.

The push, export, and import commands all work similarly.

Controlling the Email Alert System

This section collects the list of Fossil UI pages and CLI commands that control the email alert system, some of which have not been mentioned so far:

Commands:

Web pages available to users and subscribers:

Administrator-only web pages:

Design of Email Alerts

This section describes the low-level design of the email alert system in Fossil. This expands on the high-level administion focused material above with minimal repetition.

This section assumes expert-level systems knowledge. If the material above sufficed for your purposes, feel free to skip this section, which runs to the end of this document.

Data Design

There are three new tables in the repository database, starting with Fossil 2.7. These tables are not created in new repositories by default. The tables only come into existence as needed when email alerts are configured and used.

As pointed out above, "subscribers" are distinct from "users". The SUBSCRIBER.SUNAME field is the optional linkage between users and subscribers.

The "stdout" Method

The list of mail sending methods above left out an internal-only method called "stdout" which simply writes the text of the email message on standard output. The "stdout" method is used for testing and debugging. If you need something similar and can't modify your local Fossil instance to use this method, you might temporarily switch to the "dir" method instead.

Message Format

The email messages generated by Fossil have a well-formed header. The downstream processing is expected to extract the "To:", "From:", "Subject:" and whatever other attributes it needs from the email header text.

These emails use the text/plain MIME type with the UTF-8 character set. We currently use a transfer encoding of quoted-printable, but there is commented-out code in Fossil to switch to base64 encoding, which Fossil used in the early days leading up to the 2.7 release.

If you switch Fossil back to base64 mode, you may want to build a utility program that ships in the Fossil source tree named "tools/decode-email.c" which can decode these messages into a human-readable format.

Dealing with Inbound Email

Inbound email messages — for example, bounces from failed alert emails — should be relayed to the fossil email inbound command. That command is currently a no-op place-holder. At some point, we will need to design and write a bounce-message processing system for Fossil.

Passwords vs Subscriber Codes

When anonymous passers-by on the Internet sign up for email alerts, their email address must first be verified. An email message is sent to the address supplied inviting the user to click on a link. The link includes a pseudorandom 128-bit blob encoded as 32 hexadecimal digits, which serves in place of a password for that email address. (This is stored in the database as subscriber.subscriberCode.) If anyone visits the link, the email address is verified.

Knowledge of the subscriberCode is sufficient to control a subscription.

Because this code is included in plain text in email alert messages, it is not as secure as a separate password, but it has several virtues:

If the subscriberCodes for a Fossil repository are ever compromised, new ones can be generated as follows:

    UPDATE subscriber SET subscriberCode=randomblob(32);

Since this then affects all new email alerts going out from Fossil, your end users may never even realize that they're getting new codes, as long as they don't click on the URLs in the footer of old alert messages.

With that in mind, a Fossil server administrator could choose to randomize the subscriberCodes periodically, such as just before the daily digest emails are sent out each day.

Important: All of the above is distinct from the passwords for users with a Fossil repository login. Such users also have subscriber codes, but those codes can only be used to modify the user's email alert settings. That code cannot allow a user to log into the user's Fossil repository account.

Internal Processing Flow

Almost all of the email alert code is found in the src/alerts.c source file.

When email alerts are enabled, a trigger is created in the schema (email_trigger1) that adds a new entry to the PENDING_ALERT table every time a row is added to the EVENT table. During a fossil rebuild, the EVENT table is rebuilt from scratch; since we do not want users to get alerts for every historical check-in, the trigger is disabled during rebuild.

Email alerts are sent out by the alert_send_alerts() function, which is normally called automatically due to the email-autoexec setting, which defaults to enabled. If that setting is disabled or if the user simply wants to force email alerts to be sent immediately, they can give a fossil alert send command, such as via a cron script. Each time this function is called, the alert messages are moved further down the chain, so you cannot cause duplicate alerts by calling it too often.

Digests are handled by recording the time of the last digest in the email-last-digest setting, and only sending a new digest if the current time is one day or later after the last digest.

Individual emails are sent to each subscriber. I (drh) ran tests and found that I could send about 1200 emails/second, which is fast enough that I do not need to resort to trying to notify multiple subscribers with a single email. Because each subscriber gets a separate email, the system can include information in the email that is unique to the subscriber, such as a link to the page to edit their subscription. That link includes the subscriberCode.

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