Robot exclusion protocol in C++
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Latest commit a2f304e Feb 12, 2018

Robots Exclusion Protocol Parser for C++

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Supports the 1996 RFC, as well as some modern conventions, including:

  • wildcard matching (* and $)
  • sitemap listing
  • crawl-delay

This library deals in UTF-8-encoded strings.


A path may match multiple directives. For example, /some/path/page.html matches all of these rules:

Allow: /some/
Disallow: /some/path/
Allow: /*/page.html

Each directive is given a priority, and the highest-priority matching directive is used. We choose the length of the expression to be that priority. In the above example, the priorities are:

Allow: /some/            (priority = 6)
Disallow: /some/path/    (priority = 11)
Allow: /*/page.html      (priority = 12)


A Robots object is the result of parsing a single robots.txt file. It has a mapping of agent names to Agent objects, as well as a vector of the sitemaps listed in the file. An Agent object holds the crawl-delay and Directives associated with a particular user-agent.

Parsing and Querying

Here's an example of parsing a robots.txt file:

#include "robots.h"

std::string content = "...";
Rep::Robots robots = Rep::Robots(content);

// Is this path allowed to the provided agent?
robots.allowed("/some/path", "my-agent");

// Is this URL allowed to the provided agent?
robots.url_allowed("", "my-agent");

If a client is interested only in the exclusion rules of a single agent, then:

Rep::Agent agent = Rep::Robots(content).agent("my-agent");

// Is this path allowed to this agent?

// Is this URL allowed to this agent?


This library depends on url-cpp, which is included as a submodule. We provide two main targets, {debug,release}/librep.o:

git submodule update --init --recursive
make release/librep.o



To launch the vagrant image, we only need to vagrant up (though you may have to provide a --provider flag):

vagrant up

With a running vagrant instance, you can log in and run tests:

vagrant ssh
cd /vagrant

make test

Running Tests

Tests are run with the top-level Makefile:

make test


These are not all hard-and-fast rules, but in general PRs have the following expectations:

  • pass Travis -- or more generally, whatever CI is used for the particular project
  • be a complete unit -- whether a bug fix or feature, it should appear as a complete unit before consideration.
  • maintain code coverage -- some projects may include code coverage requirements as part of the build as well
  • maintain the established style -- this means the existing style of established projects, the established conventions of the team for a given language on new projects, and the guidelines of the community of the relevant languages and frameworks.
  • include failing tests -- in the case of bugs, failing tests demonstrating the bug should be included as one commit, followed by a commit making the test succeed. This allows us to jump to a world with a bug included, and prove that our test in fact exercises the bug.
  • be reviewed by one or more developers -- not all feedback has to be accepted, but it should all be considered.
  • avoid 'addressed PR feedback' commits -- in general, PR feedback should be rebased back into the appropriate commits that introduced the change. In cases, where this is burdensome, PR feedback commits may be used but should still describe the changed contained therein.

PR reviews consider the design, organization, and functionality of the submitted code.


Certain types of changes should be made in their own commits to improve readability. When too many different types of changes happen simultaneous to a single commit, the purpose of each change is muddled. By giving each commit a single logical purpose, it is implicitly clear why changes in that commit took place.

  • updating / upgrading dependencies -- this is especially true for invocations like bundle update or berks update.
  • introducing a new dependency -- often preceeded by a commit updating existing dependencies, this should only include the changes for the new dependency.
  • refactoring -- these commits should preserve all the existing functionality and merely update how it's done.
  • utility components to be used by a new feature -- if introducing an auxiliary class in support of a subsequent commit, add this new class (and its tests) in its own commit.
  • config changes -- when adjusting configuration in isolation
  • formatting / whitespace commits -- when adjusting code only for stylistic purposes.

New Features

Small new features (where small refers to the size and complexity of the change, not the impact) are often introduced in a single commit. Larger features or components might be built up piecewise, with each commit containing a single part of it (and its corresponding tests).

Bug Fixes

In general, bug fixes should come in two-commit pairs: a commit adding a failing test demonstrating the bug, and a commit making that failing test pass.

Tagging and Versioning

Whenever the version included in is changed (and it should be changed when appropriate using, a corresponding tag should be created with the same version number (formatted v<version>).

git tag -a v0.1.0 -m 'Version 0.1.0

This release contains an initial working version Rep::Robots.'

git push origin