Add multipart/form-data response builders to axum-extra

axum-core/Cargo.toml

@@ -34,6 +34,7 @@ tower-service = "0.3"
 # optional dependencies
 tower-http = { version = "0.5.0", optional = true, features = ["limit"] }
 tracing = { version = "0.1.37", default-features = false, optional = true }
+true = { version = "0.1.0", optional = true }
 
 [dev-dependencies]
 axum = { path = "../axum", version = "0.7.2" }

axum-extra/src/lib.rs

@@ -83,6 +83,9 @@ pub mod routing;
 #[cfg(feature = "json-lines")]
 pub mod json_lines;
 
+#[cfg(feature = "multipart")]
+pub mod multipart_builder;
+
 #[cfg(feature = "typed-header")]
 pub mod typed_header;
 

axum-extra/src/multipart_builder.rs

@@ -0,0 +1,337 @@
+//! Generate forms to use in responses. You're probably looking for [MultipartForm].
+
+use axum::response::{IntoResponse, Response};
+use http::{header, HeaderMap};
+use std::time::{SystemTime, UNIX_EPOCH};
+
+/// The `Content-Transfer-Encoding` setting for a part.
+#[derive(Debug)]
+pub enum TransferEncoding {
+    /// If not specified, encoding defaults to UTF-8
+    Default,
+    /// If transferring raw binary data that is not guaranteed to be valid UTF-8.
+    Binary,
+}
+
+/// Create multipart forms to be used in API responses.
+/// This struct implements [IntoResponse], and so it can be returned from a handler like normal.
+#[derive(Debug)]
+pub struct MultipartForm {
+    parts: Vec<Part>,
+}
+
+impl MultipartForm {
+    /// Construct a new empty multipart form with no parts.
+    pub fn new() -> Self {
+        MultipartForm { parts: Vec::new() }
+    }
+
+    /// Initialize a new multipart form with the provided vector of parts.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use axum_extra::multipart_builder::{MultipartForm, Part};
+    ///
+    /// let parts: Vec<Part> = vec![Part::text("foo", "abc"), Part::text("bar", "def")];
+    /// let form = MultipartForm::with_parts(parts);
+    /// ```
+    pub fn with_parts(parts: Vec<Part>) -> Self {
+        MultipartForm { parts }
+    }
+
+    /// Add a new [Part] to the form
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use axum_extra::multipart_builder::{MultipartForm, Part};
+    ///
+    /// let mut form = MultipartForm::new();
+    /// form
+    ///     .part(Part::text("foo", "abc"))
+    ///     .part(Part::text("other_field_name", "def"))
+    ///     .part(Part::file("file", "file.txt", vec![0x68, 0x68, 0x20, 0x6d, 0x6f, 0x6d]));
+    /// ```
+    pub fn part(&mut self, part: Part) -> &mut Self {
+        self.parts.push(part);
+        self
+    }
+}
+
+impl IntoResponse for MultipartForm {
+    fn into_response(self) -> Response {
+        // see RFC2388 for details
+        let boundary = generate_boundary();
+        let mut headers = HeaderMap::new();
+        headers.insert(
+            header::CONTENT_TYPE,
+            format!("multipart/form-data; boundary={}", boundary)
+                .parse()
+                .unwrap(),
+        );
+        let mut serialized_form: Vec<u8> = Vec::new();
+        for part in self.parts {
+            // for each part, the boundary is preceded by two dashes
+            serialized_form.extend_from_slice(format!("--{}\r\n", boundary).as_bytes());
+            serialized_form.extend_from_slice(&part.serialize());
+        }
+        serialized_form.extend_from_slice(format!("--{}--", boundary).as_bytes());
+        (headers, serialized_form).into_response()
+    }
+}
+
+impl Default for MultipartForm {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+// Every part is expected to contain:
+// - a [Content-Disposition](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Disposition
+// header, where `Content-Disposition` is set to `form-data`, with a parameter of `name` that is set to
+// the name of the field in the form. In the below example, the name of the field is `user`:
+// ```
+// Content-Disposition: form-data; name="user"
+// ```
+// If the field contains a file, then the `filename` parameter may be set to the name of the file.
+// Handling for non-ascii field names is not done here, support for non-ascii characters may be encoded using
+// methodology described in RFC 2047.
+// - (optionally) a `Content-Type` header, which if not set, defaults to `text/plain`.
+// If the field contains a file, then the file should be identified with that file's MIME type (eg: `image/gif`).
+// If the `MIME` type is not known or specified, then the MIME type should be set to `application/octet-stream`.
+// - If the part does not conform to the default encoding, then the `Content-Transfer-Encoding` header may be supplied.
+// Valid settings for that header are: "base64", "quoted-printable", "8bit", "7bit", and "binary".
+/// A single part of a multipart form as defined by
+/// <https://www.w3.org/TR/html401/interact/forms.html#h-17.13.4>
+/// and RFC2388.
+#[derive(Debug)]
+pub struct Part {
+    /// The name of the part in question
+    name: String,
+    /// If the part should be treated as a file, the filename that should be attached that part
+    filename: Option<String>,
+    /// The `Content-Type` header. While not strictly required, it is always set here
+    mime_type: String,
+    /// The content/body of the part
+    contents: Vec<u8>,
+    /// The encoding that the contents should be encoded under
+    encoding: TransferEncoding,
+}
+
+impl Part {
+    /// Create a new part with `Content-Type` of `text/plain` with the supplied name and contents.
+    /// This form will not have a defined file name.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use axum_extra::multipart_builder::{MultipartForm, Part};
+    ///
+    /// // create a form with a single part that has a field with a name of "foo",
+    /// // and a value of "abc"
+    /// let parts: Vec<Part> = vec![Part::text("foo", "abc")];
+    /// let form = MultipartForm::with_parts(parts);
+    /// ```
+    pub fn text(name: &str, contents: &str) -> Self {
+        Self {
+            name: name.to_owned(),
+            filename: None,
+            mime_type: "text/plain".to_owned(),
+            contents: contents.as_bytes().to_vec(),
+            encoding: TransferEncoding::Default,
+        }
+    }
+
+    /// Create a new part containing a generic file, with a `Content-Type` of `application/octet-stream`
+    /// using the provided file name, field name, and contents. If the MIME type of the file is known, consider
+    /// using [Part::raw_part]. The contents of this part do not need to be valid UTF 8.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use axum_extra::multipart_builder::{MultipartForm, Part};
+    ///
+    /// // create a form with a single part that has a field with a name of "foo",
+    /// // with a file name of "foo.txt", and with the specified contents
+    /// let parts: Vec<Part> = vec![Part::file("foo", "foo.txt", vec![0x68, 0x68, 0x20, 0x6d, 0x6f, 0x6d])];
+    /// let form = MultipartForm::with_parts(parts);
+    /// ```
+    pub fn file(field_name: &str, file_name: &str, contents: Vec<u8>) -> Self {
+        Self {
+            name: field_name.to_owned(),
+            filename: Some(file_name.to_owned()),
+            // If the `MIME` type is not known or specified, then the MIME type should be set to `application/octet-stream`.
+            // See RFC2388 section 3 for specifics.
+            mime_type: "application/octet-stream".to_owned(),
+            contents,
+            encoding: TransferEncoding::Binary,
+        }
+    }
+
+    /// Create a new part with more fine-grained control over the semantics of that part. The caller
+    /// is assumed to have set a valid MIME type.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use axum_extra::multipart_builder::{MultipartForm, Part, TransferEncoding};
+    ///
+    /// // create a form with a single part that has a field with a name of "part_name",
+    /// // with a MIME type of "application/json", and the supplied contents. This part will not have an associated filename, but will be sent as binary, and does not
+    /// // need to be valid UTF-8.
+    /// let parts: Vec<Part> = vec![Part::raw_part("part_name", "application/json", vec![0x68, 0x68, 0x20, 0x6d, 0x6f, 0x6d], None, TransferEncoding::Binary)];
+    /// let form = MultipartForm::with_parts(parts);
+    /// ```
+    pub fn raw_part(
+        name: &str,
+        mime_type: &str,
+        contents: Vec<u8>,
+        filename: Option<&str>,
+        encoding: TransferEncoding,
+    ) -> Self {
+        Self {
+            name: name.to_owned(),
+            filename: filename.map(|f| f.to_owned()),
+            mime_type: mime_type.to_owned(),
+            contents,
+            encoding,
+        }
+    }
+
+    /// Serialize this part into a chunk that can be easily inserted into a larger form
+    pub(super) fn serialize(&self) -> Vec<u8> {
+        // A part is serialized in this general format:
+        // // the filename is optional
+        // Content-Disposition: form-data; name="FIELD_NAME"; filename="FILENAME"\r\n
+        // // the mime type (not strictly required by the spec, but always sent here)
+        // Content-Type: mime/type\r\n
+        // // if the part does not conform to the rest of the request's encoding,
+        // // this is specified
+        // Content-Transfer-Encoding: "ENCODING"\r\n
+        // // a blank line, then the contents of the file start
+        // \r\n
+        // CONTENTS\r\n
+
+        // Format what we can as a string, then handle the rest at a byte level
+        let mut serialized_part = format!("Content-Disposition: form-data; name=\"{}\"", self.name);
+        // specify a filename if one was set
+        if let Some(filename) = &self.filename {
+            serialized_part += &format!("; filename=\"{}\"", filename);
+        }
+        serialized_part += "\r\n";
+        // specify the MIME type
+        serialized_part += &format!("Content-Type: {}\r\n", self.mime_type);
+        // if an encoding was set, add that
+        // determine what encoding to label the body of the field with
+        let encoding: Option<&str> = match self.encoding {
+            TransferEncoding::Default => None,
+            TransferEncoding::Binary => Some("binary"),
+        };
+        if let Some(encoding) = encoding {
+            serialized_part += &format!("Content-Transfer-Encoding: {}\r\n", encoding);
+        }
+        serialized_part += "\r\n";
+        let mut part_bytes = serialized_part.as_bytes().to_vec();
+        part_bytes.extend_from_slice(&self.contents);
+        part_bytes.extend_from_slice(b"\r\n");
+
+        part_bytes
+    }
+}
+
+/// A boundary is defined as a user defined (arbitrary) value that does not occur in any of the data.
+/// Because the specification does not clearly define a methodology for generating boundaries, this implementation
+/// follow's Reqwest's, and generates a boundary in the format of `XXXXXXXX-XXXXXXXX-XXXXXXXX-XXXXXXXX` where `XXXXXXXX`
+/// is a hexadecimal representation of a pseudo randomly generated u64.
+fn generate_boundary() -> String {
+    let a = gen_boundary_portion();
+    let b = gen_boundary_portion();
+    let c = gen_boundary_portion();
+    let d = gen_boundary_portion();
+    format!("{a:016x}-{b:016x}-{c:016x}-{d:016x}")
+}
+
+/// Generate a single portion of the boundary by performing an xor
+/// shift on the current time
+fn gen_boundary_portion() -> u64 {
+    // *very* rudimentary xor-shift used
+    // the current time is used as a seed because it doesn't really matter what the data is, it should
+    // just be vaguely random
+    let mut x = SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .unwrap()
+        .as_millis() as u64;
+    x = x ^ (x << 13);
+    x = x ^ (x >> 17);
+    x = x ^ (x << 5);
+    x
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{MultipartForm, Part};
+    use axum::{body::Body, http};
+    use axum::{routing::get, Router};
+    use http::{Request, Response};
+    use http_body_util::BodyExt;
+    // for `collect`
+    use tower::ServiceExt; // for `call`, `oneshot`, and `ready`
+
+    #[tokio::test]
+    async fn process_form() -> Result<(), Box<dyn std::error::Error>> {
+        // create a boilerplate handle that returns a form
+        async fn handle() -> MultipartForm {
+            let mut form = MultipartForm::new();
+            form.part(Part::text("part1", "basictext"))
+                .part(Part::file(
+                    "part2",
+                    "file.txt",
+                    vec![0x68, 0x69, 0x20, 0x6d, 0x6f, 0x6d],
+                ))
+                .part(Part::raw_part(
+                    "part3",
+                    "text/plain",
+                    b"rawpart".to_vec(),
+                    None,
+                    super::TransferEncoding::Default,
+                ));
+            form
+        }
+
+        // make a request to that handle
+        let app = Router::new().route("/", get(handle));
+        let response: Response<_> = app
+            .oneshot(Request::builder().uri("/").body(Body::empty())?)
+            .await?;
+        // content_type header
+        let ct_header = response.headers().get("content-type").unwrap().to_str()?;
+        let boundary = ct_header.split("boundary=").nth(1).unwrap().to_owned();
+        let body: &[u8] = &response.into_body().collect().await?.to_bytes();
+        assert_eq!(
+            std::str::from_utf8(body)?,
+            &format!(
+                "--{boundary}\r\n\
+                Content-Disposition: form-data; name=\"part1\"\r\n\
+                Content-Type: text/plain\r\n\
+                \r\n\
+                basictext\r\n\
+                --{boundary}\r\n\
+                Content-Disposition: form-data; name=\"part2\"; filename=\"file.txt\"\r\n\
+                Content-Type: application/octet-stream\r\n\
+                Content-Transfer-Encoding: binary\r\n\
+                \r\n\
+                hi mom\r\n\
+                --{boundary}\r\n\
+                Content-Disposition: form-data; name=\"part3\"\r\n\
+                Content-Type: text/plain\r\n\
+                \r\n\
+                rawpart\r\n\
+                --{boundary}--",
+                boundary = boundary
+            )
+        );
+
+        Ok(())
+    }
+}