Cargo supports the ability to replace one source with another to express
strategies along the lines of mirrors or vendoring dependencies. Configuration
is currently done through the
.cargo/config configuration mechanism,
# The `source` table is where all keys related to source-replacement # are stored. [source] # Under the `source` table are a number of other tables whose keys are a # name for the relevant source. For example this section defines a new # source, called `my-awesome-source`, which comes from a directory # located at `vendor` relative to the directory containing this `.cargo/config` # file [source.my-awesome-source] directory = "vendor" # The crates.io default source for crates is available under the name # "crates-io", and here we use the `replace-with` key to indicate that it's # replaced with our source above. [source.crates-io] replace-with = "my-awesome-source"
With this configuration Cargo attempts to look up all crates in the directory "vendor" rather than querying the online registry at crates.io. Using source replacement Cargo can express:
Vendoring - custom sources can be defined which represent crates on the local filesystem. These sources are subsets of the source that they're replacing and can be checked into projects if necessary.
Mirroring - sources can be replaced with an equivalent version which acts as a cache for crates.io itself.
Cargo has a core assumption about source replacement that the source code is
exactly the same from both sources. In our above example Cargo assumes that all
of the crates coming from
my-awesome-source are the exact same as the copies
crates-io. Note that this also means that
my-awesome-source is not
allowed to have crates which are not present in the
As a consequence, source replacement is not appropriate for situations such as
patching a dependency or a private registry. Cargo supports patching
dependencies through the usage of the
[replace] key, and
private registry support is planned for a future version of Cargo.
Configuration of replacement sources is done through
and the full set of available keys are:
# Each source has its own table where the key is the name of the source [source.the-source-name] # Indicate that `the-source-name` will be replaced with `another-source`, # defined elsewhere replace-with = "another-source" # Available kinds of sources that can be specified (described below) registry = "https://example.com/path/to/index" local-registry = "path/to/registry" directory = "path/to/vendor"
crates-io represents the crates.io online registry (default source of
crates) and can be replaced with:
[source.crates-io] replace-with = 'another-source'
A "registry source" is one that is the same as crates.io itself. That is, it has an index served in a git repository which matches the format of the crates.io index. That repository then has configuration indicating where to download crates from.
Currently there is not an already-available project for setting up a mirror of crates.io. Stay tuned though!
Local Registry Sources
A "local registry source" is intended to be a subset of another registry
source, but available on the local filesystem (aka vendoring). Local registries
are downloaded ahead of time, typically sync'd with a
Cargo.lock, and are
made up of a set of
*.crate files and an index like the normal registry is.
The primary way to manage and crate local registry sources is through the
cargo-local-registry subcommand, available on
crates.io and can be installed with
cargo install cargo-local-registry.
Local registries are contained within one directory and contain a number of
*.crate files downloaded from crates.io as well as an
index directory with
the same format as the crates.io-index project (populated with just entries for
the crates that are present).
A "directory source" is similar to a local registry source where it contains a
number of crates available on the local filesystem, suitable for vendoring
dependencies. Also like local registries, directory sources can primarily be
managed by an external subcommand,
cargo-vendor, which can be
cargo install cargo-vendor.
Directory sources are distinct from local registries though in that they contain
the unpacked version of
*.crate files, making it more suitable in some
situations to check everything into source control. A directory source is just a
directory containing a number of other directories which contain the source code
for crates (the unpacked version of
*.crate files). Currently no restriction
is placed on the name of each directory.
Each crate in a directory source also has an associated metadata file indicating the checksum of each file in the crate to protect against accidental modifications.