tower-http 0.7.0

Tower middleware and utilities for HTTP clients and servers
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216

use std::convert::TryFrom;
use std::fmt::{self, Debug, Formatter};
use std::sync::Arc;
use std::task::{Context, Poll};

use http::{Method, Request, Response, Uri};
use tower_service::Service;

use super::future::ResponseFuture;
use super::{
    BypassFn, DebugFn, DefaultResponseForProtectionError, Origins, ProtectionError,
    ProtectionErrorKind, ResponseForProtectionError,
};

/// Middleware that enforces cross-origin request forgery (CSRF) protection.
///
/// See the [module docs](crate::csrf) for an example.
#[derive(Clone)]
#[must_use]
pub struct Csrf<S, T = DefaultResponseForProtectionError> {
    inner: S,
    insecure_bypass: Option<Arc<BypassFn>>,
    rejection_response: T,
    trusted_origins: Origins,
}

impl<S, T> Csrf<S, T> {
    pub(super) fn new(
        inner: S,
        insecure_bypass: Option<Arc<BypassFn>>,
        rejection_response: T,
        trusted_origins: Origins,
    ) -> Self {
        Self {
            inner,
            insecure_bypass,
            rejection_response,
            trusted_origins,
        }
    }

    pub(super) fn verify<Body>(&self, req: &Request<Body>) -> Result<(), ProtectionError> {
        // Deliberately not Method::is_safe: it also treats TRACE as safe, but the
        // reference implementation only exempts GET/HEAD/OPTIONS, so we match it here.
        if matches!(
            req.method(),
            &Method::GET | &Method::HEAD | &Method::OPTIONS
        ) {
            #[cfg(feature = "tracing")]
            tracing::trace!(uri = %req.uri().path(), "request passed: safe method");
            return Ok(());
        }

        let origin = req.headers().get("origin").map(|h| h.as_bytes());

        let origin_uri = origin
            .filter(|b| !b.is_empty())
            .and_then(|b| Uri::try_from(b).ok())
            .filter(|u| matches!(u.scheme_str(), Some("http" | "https")));

        let sec_fetch_site = req.headers().get("sec-fetch-site").map(|h| h.as_bytes());

        let is_exempt = || -> bool {
            let bypass = self
                .insecure_bypass
                .as_ref()
                .map_or(false, |bypass| bypass(req.method(), req.uri()));

            if bypass {
                #[cfg(feature = "tracing")]
                tracing::trace!(uri = %req.uri().path(), "request passed: bypassed");
                return true;
            }

            // Strict byte match of the raw Origin header against the registered
            // set, mirroring the Go reference's `trustedOrigins[Origin]`.
            let trusted = origin.map_or(false, |b| self.trusted_origins.contains(b));

            if trusted {
                #[cfg(feature = "tracing")]
                tracing::trace!(uri = %req.uri().path(), "request passed: trusted origin");
                return true;
            }

            false
        };

        // Fetch spec mandates lowercase here; exact byte match is intentional.
        match sec_fetch_site {
            Some(b"same-origin" | b"none") => {
                #[cfg(feature = "tracing")]
                tracing::trace!(uri = %req.uri().path(), "request passed: sec-fetch-site is same-origin or none");
                return Ok(());
            }
            None | Some(b"") => {} // fall through to Origin check
            Some(_) if is_exempt() => return Ok(()),
            Some(_) => {
                return Err(ProtectionError::new(
                    ProtectionErrorKind::CrossOriginRequest,
                ))
            }
        }

        if matches!(origin, None | Some(b"")) {
            #[cfg(feature = "tracing")]
            tracing::trace!(uri = %req.uri().path(), "request passed: neither sec-fetch-site nor origin header (same-origin or not a browser request)");
            return Ok(());
        }

        let host = req.headers().get("host").map(|h| h.as_bytes());

        // Mirrors the reference's `url.Parse(origin).Host == req.Host`. Per RFC 7230
        // §5.3, req.Host is the request-target authority (absolute-form URI / HTTP/2
        // `:authority`) if present, else the Host header. Byte-exact and scheme-blind,
        // so an http→https mismatch can't be caught here — we fail open (HSTS helps).
        let effective_host = req
            .uri()
            .authority()
            .map(|a| a.as_str().as_bytes())
            .or(host);

        if let (Some(uri), Some(effective_host)) = (&origin_uri, effective_host) {
            if uri.authority().map(|a| a.as_str().as_bytes()) == Some(effective_host) {
                #[cfg(feature = "tracing")]
                tracing::trace!(uri = %req.uri().path(), "request passed: origin is same as host");
                return Ok(());
            }
        }

        if is_exempt() {
            return Ok(());
        }

        Err(ProtectionError::new(
            ProtectionErrorKind::CrossOriginRequestFromOldBrowser,
        ))
    }
}

impl<S, T> Default for Csrf<S, T>
where
    S: Default,
    T: Default,
{
    fn default() -> Self {
        Self {
            inner: S::default(),
            insecure_bypass: None,
            rejection_response: T::default(),
            trusted_origins: Origins::default(),
        }
    }
}

impl<S: Debug, T> Debug for Csrf<S, T> {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        f.debug_struct("Csrf")
            .field("inner", &self.inner)
            .field(
                "insecure_bypass",
                &self.insecure_bypass.as_ref().map(|_| DebugFn),
            )
            .field("trusted_origins", &self.trusted_origins)
            .field("rejection_response", &DebugFn)
            .finish()
    }
}

impl<S, T, ReqBody, ResBody> Service<Request<ReqBody>> for Csrf<S, T>
where
    S: Service<Request<ReqBody>, Response = Response<ResBody>>,
    T: ResponseForProtectionError<ResBody>,
{
    type Error = S::Error;
    type Future = ResponseFuture<S::Future>;
    type Response = Response<ResBody>;

    fn call(&mut self, req: Request<ReqBody>) -> Self::Future {
        match self.verify(&req) {
            Ok(_) => ResponseFuture::future(self.inner.call(req)),
            Err(err) => {
                #[cfg(feature = "tracing")]
                tracing::trace!(uri = %req.uri().path(), error = %err, "request rejected");

                let mut response = self
                    .rejection_response
                    .response_for_protection_error(err.clone());

                response.extensions_mut().insert(err);

                ResponseFuture::rejected(Ok(response))
            }
        }
    }

    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.inner.poll_ready(cx)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    // Guards the comment in `verify`: `Method::is_safe` exempts more than the
    // GET/HEAD/OPTIONS set the reference implementation uses, so we can't rely on it.
    #[test]
    fn method_is_safe_covers_more_than_get_head_options() {
        for method in [&Method::GET, &Method::HEAD, &Method::OPTIONS] {
            assert!(method.is_safe());
        }

        // TRACE is "safe" per RFC 7231 but is not in the reference implementation's set.
        assert!(Method::TRACE.is_safe());
    }
}