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Agate

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Simple Gemini server for static files

Agate is a server for the Gemini network protocol, built with the Rust programming language. Agate has very few features, and can only serve static files. It uses async I/O, and should be quite efficient even when running on low-end hardware and serving many concurrent requests.

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Installation and Setup

  1. Get a binary for agate. You can use any of the below ways:

Pre-compiled

Download and unpack the pre-compiled binary.

NixOS/Nix

Using the nix package manager run nix-env -i agate

Guix System

Deploy agate with GNU Guix System by adding the agate-service-type to your system services.

Arch Linux

Install the package agate-bin<sup>AUR</sup> for pre-compiled binary. Otherwise install the agate<sup>AUR</sup> package to get agate compiled from source.

Cargo

If you have the Rust toolchain installed, run cargo install agate to install agate from crates.io.

Source

Download the source code and run cargo build --release inside the source repository, then find the binary at target/release/agate.

You can use the install script in the tools directory for the remaining steps if there is one for your system.
If there is none, please consider contributing one to make it easier for less tech-savvy users!

  1. Run the server. You can use the following arguments to specify the locations of the content directory, IP address and port to listen on, host name to expect in request URLs, and default language code to include in the MIME type for text/gemini files: (Replace the hostname example.com with the address of your Gemini server.) If you have not done it yourself, Agate will generate a private key and certificate for you on the first run, using the specified hostname(s). See the section Certificates below for more.
agate --content path/to/content/ \
      --addr [::]:1965 \
      --addr 0.0.0.0:1965 \
      --hostname example.com \
      --lang en-US

All of the command-line arguments are optional. Run agate --help to see the default values used when arguments are omitted.

When a client requests the URL gemini://example.com/foo/bar, Agate will respond with the file at path/to/content/foo/bar. If any segment of the requested path starts with a dot, agate will respond with a status code 52, whether the file exists or not. This behaviour can be disabled with --serve-secret or by an entry for the specific file in the .meta configuration file (see Meta-Presets). If there is a directory at that path, Agate will look for a file named index.gmi inside that directory.

Configuration

Automatic Certificate generation

If the --hostname argument is used, Agate will generate keys and self signed certificates for each hostname specified. For Gemini it is recommended by the specification to use self signed certificates because Gemini uses the TOFU (Trust on first use) principle for certificates. Because of this, the generated certificates will also have a long expiration time of 4096-01-01.

For manual configuration of keys and certificates see the section on certificates below.

TLS versions

Agate by default supports TLSv1.2 and TLSv1.3. You can disable support for TLSv1.2 by using the flag --only-tls13 (or its short version -3). This is NOT RECOMMENDED as it may break compatibility with some clients. The Gemini specification requires compatibility with TLSv1.2 "for now" because not all platforms have good support for TLSv1.3 (cf. §4.1 of the specification).

Directory listing

You can enable a basic directory listing for a directory by putting a file called .directory-listing-ok in that directory. This does not have an effect on sub-directories. This file must be UTF-8 encoded text; it may be empty. Any text in the file will be prepended to the directory listing. The directory listing will hide files and directories whose name starts with a dot (e.g. the .directory-listing-ok file itself, the .meta configuration file, or the .. directory).

A file called index.gmi will always take precedence over a directory listing.

Meta-Presets

You can put a file called .meta in any content directory. This file stores some metadata about the adjacent files which Agate will use when serving these files. The .meta file must be UTF-8 encoded. You can also enable a central configuration file with the -C flag (or the long version --central-conf). In this case Agate will always look for the .meta configuration file in the content root directory and will ignore .meta files in other directories.

The .meta file has the following format (*1):

<path> is a case sensitive file path, which may or may not exist on disk. If <path> leads to a directory, it is ignored. If central configuration file mode is not used, using a path that is not a file in the current directory is undefined behaviour (for example ../index.gmi would be undefined behaviour). You can use Unix style patterns in existing paths. For example content/* will match any file within content, and content/** will additionally match any files in subdirectories of content. However, the * and ** globs on their own will by default not match files or directories that start with a dot because of their special meaning. This behaviour can be disabled with --serve-secret or by explicitly matching files starting with a dot with e.g. content/.* or content/**/.* respectively. For more information on the patterns you can use, please see the documentation of glob::Pattern. Rules can overwrite other rules, so if a file is matched by multiple rules, the last one applies.

<metadata> can take one of four possible forms:

  1. empty
    Agate will not send a default language parameter, even if it was specified on the command line.
  2. starting with a semicolon followed by MIME parameters
    Agate will append the specified string onto the MIME type, if the file is found.
  3. starting with a gemini status code (i.e. a digit 1-6 inclusive followed by another digit) and a space
    Agate will send the metadata whether the file exists or not. The file will not be sent or accessed.
  4. a MIME type, may include parameters
    Agate will use this MIME type instead of what it would guess, if the file is found. The default language parameter will not be used, even if it was specified on the command line.

If a line violates the format or looks like case 3, but is incorrect, it might be ignored. You should check your logs. Please know that this configuration file is first read when a file from the respective directory is accessed. So no log messages after startup does not mean the .meta file is okay.

Such a configuration file might look like this:

# This line will be ignored.
**/*.de.gmi: ;lang=de
nl/**/*.gmi: ;lang=nl
index.gmi: ;lang=en-GB
LICENSE: text/plain;charset=UTF-8
gone.gmi: 52 This file is no longer here, sorry.

If this is the .meta file in the content root directory and the -C flag is used, this will result in the following response headers:

(*1) In theory the syntax is that of a typical INI-like file and also allows for sections with [section] (the default section is set to mime in the parser), since all other sections are disregarded, this does not make a difference. This also means that you can in theory also use = instead of :. For even more information, you can visit the documentation of configparser.

Logging Verbosity

Agate uses the env_logger crate and allows you to set the logging verbosity by setting the RUST_LOG environment variable. To turn off all logging use RUST_LOG=off. For more information, please see the documentation of env_logger.

Virtual Hosts

Agate has basic support for virtual hosts. If you specify multiple --hostnames, Agate will look in a directory with the respective hostname within the content root directory. For example if one of the hostnames is example.com, and the content root directory is set to the default ./content, and gemini://example.com/file.gmi is requested, then Agate will look for ./content/example.com/file.gmi. This behaviour is only enabled if multiple --hostnames are specified. Agate also supports different certificates for different hostnames, see the section on certificates below.

If you want to serve the same content for multiple domains, you can instead disable the hostname check by not specifying --hostname. In this case Agate will disregard a request's hostname apart from checking that there is one.

When one or more --hostnames are specified, Agate will check that the hostnames and port in request URLs match the specified hostnames and the listening ports. If Agate is behind a proxy on another port and receives a request with an URL specifying the proxy port, this port may not match one of Agate's listening ports and the request will be rejected: it is possible to disable the port check with --skip-port-check.

Certificates

Agate has support for using multiple certificates with the --certs option. Agate will thus always require that a client uses SNI, which should not be a problem since the Gemini specification also requires SNI to be used.

Certificates are by default stored in the .certificates directory. This is a hidden directory for the purpose that uncautious people may set the content root directory to the current directory which may also contain the certificates directory. In this case, the certificates and private keys would still be hidden. The certificates are only loaded when Agate is started and are not reloaded while running. The certificates directory may directly contain a key and certificate pair, this is the default pair used if no other matching keys are present. The certificates directory may also contain subdirectories for specific domains, for example a folder for example.org and portal.example.org. Note that the subfolders for subdomains (like portal.example.org) should not be inside other subfolders but directly in the certificates directory. Agate will select the certificate/key pair whose name matches most closely. For example take the following directory structure:

.certificates
|-- cert.der     (1)
|-- key.der      (1)
|-- example.org
|   |-- cert.der (2)
|   `-- key.der  (2)
`-- portal.example.org
    |-- cert.der (3)
    `-- key.der  (3)

This would be understood like this:

Using a directory named just . causes undefined behaviour as this would have the same meaning as the top level certificate/key pair (pair (1) in the example above).

The files for a certificate/key pair have to be named cert.der and key.der respectively. The certificate has to be a X.509 certificate in a DER format file and has to include a subject alt name of the domain name. The private key has to be in DER format and must be either an RSA, ECDSA or Ed25519 key.

Logging

All requests via TCP sockets will be logged using this format:

<local ip>:<local port> <remote ip or dash> "<request>" <response status> "<response meta>"[ error:<error>]

All requests via Unix sockets will be logged using this format:

unix:[<unix socket name>] - "<request>" <response status> "<response meta>"[ error:<error>]

Square brackets indicate optional parts.

The "error:" part will only be logged if an error occurred. This should only be used for informative purposes as the status code should provide the information that an error occurred. If the error consisted in the connection not being established (e.g. because of TLS errors), special status codes listed below may be used.

By default, Agate will not log the remote IP addresses because that might be an issue because IPs are considered private data under the EU's GDPR. To enable logging of IP addresses, you can use the --log-ip option. Note that in this case some error conditions might still force Agate to log a dash instead of an IP address. IP addresses can also not be logged for connections via Unix sockets.

There are some lines apart from these that might occur in logs depending on the selected log level. For example the initial "Listening on..." line or information about listing a particular directory.

Agate uses some status codes that are not valid Gemini status codes when logging errors:

Security considerations

If you want to run agate on a multi-user system, you should be aware that all certificate and key data is loaded into memory and stored there until the server stops. Since the memory is also not explicitly overwritten or zeroed after use, the sensitive data might stay in memory after the server has terminated.