Sccache is a [ccache](https://ccache.samba.org/)-like tool. It is used as a compiler wrapper and avoids compilation when possible, storing a cache in a remote storage using the S3 API, the GCS API, or Redis.
It works as a client-server. The client spawns a server if one is not running already, and sends the wrapped command line as a request to the server, which then does the work and returns stdout/stderr for the job. The client-server model allows the server to be more efficient in its handling of the remote storage.
We recommend you install Rust via [Rustup](https://rustup.rs/). The generated binaries can be built so that they are very portable, see [scripts/build-release.sh](scripts/build-release.sh). By default `sccache` supports a local disk cache. To build `sccache` with support for `S3` and/or `Redis` cache backends, add `--features=all` or select a specific feature by passing `s3`, `gcs`, and/or `redis`. Refer the [Cargo Documentation](http://doc.crates.io/manifest.html#the-features-section) for details.
sccache defaults to using local disk storage. You can set the `SCCACHE_DIR` environment variable to change the disk cache location. By default it will use a sensible location for the current platform: `~/.cache/sccache` on Linux, `%LOCALAPPDATA%\Mozilla\sccache` on Windows, `~/Library/Caches/sccache` on OS X.
If you want to use S3 storage for the sccache cache, you need to set the `SCCACHE_BUCKET` environment variable to the name of the S3 bucket to use. You can use `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` to set the S3 credentials and if you need to override the default endpoint you can set `SCCACHE_ENDPOINT`. To connect to a minio storage for example you can set `SCCACHE_ENDPOINT=<ip>:<port>`.
Set `SCCACHE_REDIS` to a [Redis](https://redis.io/) url in format `redis://[:<passwd>@]<hostname>[:port][/<db>]` to store the cache in a Redis instance.
You can set the `SCCACHE_LOG_LEVEL` environment variable to `debug` or `trace` (not recommended, it's *very verbose*) to cause sccache to output more fine grained logging about what it is doing. A log file named `sccache.log` will be output in the current working directory whenever sccache is invoked.
Alternately, you can run the server manually in foreground mode by running `SCCACHE_START_SERVER=1 SCCACHE_NO_DAEMON=1 sccache`, and send logging to stderr by setting the `RUST_LOG` environment variable, the format of which is described in more detail in the [env_logger](http://burntsushi.net/rustdoc/env_logger/index.html#enabling-logging) documentation.
You can set the `SCCACHE_ERROR_LOG` environment variable to a path to cause the server process to redirect its standard error output there, in order to capture the output of unhandled panics. (The server sets `RUST_BACKTRACE=1` internally.)
* Sccache doesn't try to be smart about the command line arguments it uses when computing a key for a given compilation result (like skipping preprocessor-specific arguments)
* It doesn't support all kinds of compiler flags, and is certainly broken with a few of them. Really only the flags used during Firefox builds have been tested.
