114 lines
3.5 KiB
Markdown
114 lines
3.5 KiB
Markdown
# go-gemini
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[](https://godoc.org/git.sr.ht/~adnano/go-gemini)
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`go-gemini` implements the [Gemini protocol](https://gemini.circumlunar.space)
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in Go.
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It aims to provide an API similar to that of `net/http` to make it easy to
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develop Gemini clients and servers.
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## Examples
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There are a few examples provided in the `examples` directory.
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Some examples might require you to generate TLS certificates.
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To run the examples:
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go run -tags=example ./examples/server
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## Overview
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A quick overview of the Gemini protocol:
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1. Client opens connection
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2. Server accepts connection
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3. Client and server complete a TLS handshake
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4. Client validates server certificate
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5. Client sends request
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6. Server sends response header
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7. Server sends response body (only for successful responses)
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8. Server closes connection
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9. Client handles response
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The way this is implemented in this package is like so:
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1. Client makes a request with `NewRequest`. The client then sends the request
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with `(*Client).Send(*Request) (*Response, error)`. The client then determines whether
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to trust the certificate (see [Trust On First Use](#trust-on-first-use)).
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2. Server recieves the request and constructs a response.
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The server calls the `Serve(*ResponseWriter, *Request)` method on the
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`Handler` field. The handler writes the response. The server then closes
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the connection.
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3. Client recieves the response as a `*Response`. The client then handles the
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response.
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## Trust On First Use
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`go-gemini` makes it easy to implement Trust On First Use in your clients.
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The default client loads known hosts from `$XDG_DATA_HOME/gemini/known_hosts`.
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If that is all you need, you can simply use the top-level `Send` function:
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```go
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// Send uses the default client, which will load the default list of known hosts.
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req := gemini.NewRequest("gemini://example.com")
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gemini.Send(req)
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```
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Clients can also load their own list of known hosts:
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```go
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client := &Client{}
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if err := client.KnownHosts.LoadFrom("path/to/my/known_hosts"); err != nil {
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log.Fatal(err)
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}
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```
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Clients can then specify how to trust certificates in the `TrustCertificate`
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field:
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```go
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client.TrustCertificate = func(hostname string, cert *x509.Certificate, knownHosts *gemini.KnownHosts) error {
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// If the certificate is in the known hosts list, allow the connection
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return knownHosts.Lookup(hostname, cert)
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}
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```
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Advanced clients can prompt the user for what to do when encountering an unknown certificate:
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```go
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client.TrustCertificate = func(hostname string, cert *x509.Certificate, knownHosts *gemini.KnownHosts) error {
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err := knownHosts.Lookup(cert)
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if err != nil {
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switch err {
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case gemini.ErrCertificateNotTrusted:
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// Alert the user that the certificate is not trusted
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fmt.Printf("Warning: certificate for %s is not trusted!\n", hostname)
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fmt.Println("This could indicate a Man-in-the-Middle attack.")
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case gemini.ErrCertificateUnknown:
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// Prompt the user to trust the certificate
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if userTrustsCertificateTemporarily() {
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// Temporarily trust the certificate
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knownHosts.AddTemporary(hostname, cert)
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return nil
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} else if userTrustsCertificatePermanently() {
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// Add the certificate to the known hosts file
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knownHosts.Add(cert)
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return nil
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}
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}
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}
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return err
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}
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```
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See `examples/client` for an example client.
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## Client Authentication
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Gemini takes advantage of client certificates for authentication.
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See `examples/auth` for an example server which authenticates its users with a
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username and password, and uses their client certificate to remember sessions.
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