This document is about replacing the crate index. You can read about overriding dependencies in the overriding dependencies section of this documentation.
A source is a provider that contains crates that may be included as dependencies for a package. Cargo supports the ability to replace one source with another to express strategies such as:
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 packages 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. Note that this also means that a replacement source is not allowed to have crates which are not present in the original source.
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
[patch] key, and private registry support is described in the Registries
When using source replacement, running commands like
cargo publish that need to
contact the registry require passing the
--registry option. This helps avoid
any ambiguity about which registry to contact, and will use the authentication
token for the specified registry.
Configuration of replacement sources is done through
and the full set of available keys are:
# 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-vendor-source`, which comes from a directory # located at `vendor` relative to the directory containing this `.cargo/config.toml` # file [source.my-vendor-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. # # The `replace-with` key can also reference an alternative registry name # defined in the `[registries]` table. [source.crates-io] replace-with = "my-vendor-source" # 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" # Several kinds of sources can be specified (described in more detail below): registry = "https://example.com/path/to/index" local-registry = "path/to/registry" directory = "path/to/vendor" # Git sources can optionally specify a branch/tag/rev as well git = "https://example.com/path/to/repo" # branch = "master" # tag = "v1.0.1" # rev = "313f44e8"
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!
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.
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. Directory sources are primarily managed by the
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.