Add Partial Content Delivery

This commits adds Partial Content Delivery, as asked in issue iron#93. This
enables the "Accept-Ranges" header on all files delivered via
static. It is possible to ask only a certain portion of bytes like
explicitely described in RFC 7233. Of the 3 ways to ask for a range of
bytes (byte x to byte y, everything from byte x to end of file, last y
bytes from end of file), every one of them is implemented, but if a
request is to ask multi ranges in a same request, this implementation
will only account the first range.

src/lib.rs

@@ -19,3 +19,4 @@ pub use static_handler::Cache;
 
 mod requested_path;
 mod static_handler;
+mod partial_file;

src/partial_file.rs

@@ -0,0 +1,132 @@
+use std::fs::File;
+use iron::headers::{ByteRangeSpec, ContentLength, ContentRange, ContentRangeSpec};
+use iron::response::{WriteBody, Response};
+use iron::modifier::Modifier;
+use iron::status::Status;
+use std::io::{self, SeekFrom, Seek, Read, Write};
+use std::path::Path;
+
+pub enum PartialFileRange {
+    AllFrom(u64),
+    FromTo(u64,u64),
+    Last(u64),
+}
+
+pub struct PartialFile {
+    file: File,
+    range: PartialFileRange,
+}
+
+struct PartialContentBody {
+    pub file: File,
+    pub offset: u64,
+    pub len: u64,
+}
+
+impl PartialFile {
+    pub fn new<Range>(file: File, range: Range) -> PartialFile
+        where Range: Into<PartialFileRange> {
+        let range = range.into();
+        PartialFile {
+            file: file,
+            range: range,
+        }
+    }
+
+    /// Panics if the file doesn't exist
+    pub fn from_path<P: AsRef<Path>, Range>(path: P, range: Range) -> PartialFile
+    where Range: Into<PartialFileRange> {
+        let file = File::open(path.as_ref())
+            .expect(&format!("No such file: {}", path.as_ref().display()));
+        Self::new(file, range)
+    }
+}
+
+impl From<ByteRangeSpec> for PartialFileRange {
+    fn from(b: ByteRangeSpec) -> PartialFileRange {
+        match b {
+            ByteRangeSpec::AllFrom(from) => PartialFileRange::AllFrom(from),
+            ByteRangeSpec::FromTo(from, to) => PartialFileRange::FromTo(from, to),
+            ByteRangeSpec::Last(last) => PartialFileRange::Last(last),
+        }
+    }
+}
+
+impl From<Vec<ByteRangeSpec>> for PartialFileRange {
+    fn from(v: Vec<ByteRangeSpec>) -> PartialFileRange {
+        match v.into_iter().next() {
+            // in the case no value is in "Range", return
+            // the whole file instead of panicking
+            // Note that an empty vec should never happen,
+            // but we can never be too sure
+            None => PartialFileRange::AllFrom(0),
+            Some(byte_range) => PartialFileRange::from(byte_range),
+        }
+    }
+}
+
+impl Modifier<Response> for PartialFile {
+    #[inline]
+    fn modify(self, res: &mut Response) {
+        use self::PartialFileRange::*;
+        let metadata : Option<_> = self.file.metadata().ok();
+        let file_length : Option<u64> = metadata.map(|m| m.len());
+        let range : Option<(u64, u64)> = match (self.range, file_length) {
+            (FromTo(from, to), Some(file_length)) => {
+                if from <= to && to < file_length {
+                    Some((from, to))
+                } else {
+                    None
+                }
+            },
+            (AllFrom(from), Some(file_length)) => {
+                if from < file_length {
+                    Some((from, file_length - 1))
+                } else {
+                    None
+                }
+            },
+            (Last(last), Some(file_length)) => {
+                if last < file_length {
+                    Some((file_length - last, file_length - 1))
+                } else {
+                    Some((0, file_length - 1))
+                }
+            },
+            (_, None) => None,
+
+        };
+        if let Some(range) = range {
+            let content_range = ContentRange(ContentRangeSpec::Bytes {
+                range: Some(range),
+                instance_length: file_length,
+            });
+            let content_len = range.1 - range.0 + 1;
+            res.headers.set(ContentLength(content_len));
+            res.headers.set(content_range);
+            let partial_content = PartialContentBody {
+                file: self.file,
+                offset: range.0,
+                len: content_len,
+            };
+            res.status = Some(Status::PartialContent);
+            res.body = Some(Box::new(partial_content));
+        } else {
+            if let Some(file_length) = file_length {
+                res.headers.set(ContentRange(ContentRangeSpec::Bytes {
+                    range: None,
+                    instance_length: Some(file_length),
+                }));
+            };
+            res.status = Some(Status::RangeNotSatisfiable);
+        }
+    }
+}
+
+impl WriteBody for PartialContentBody {
+    fn write_body(&mut self, res: &mut Write) -> io::Result<()> {
+        self.file.seek(SeekFrom::Start(self.offset))?;
+        let mut limiter = <File as Read>::by_ref(&mut self.file).take(self.len);
+        io::copy(&mut limiter, res).map(|_| ())
+    }
+}

src/static_handler.rs

@@ -10,13 +10,16 @@ use std::time::Duration;
 
 use iron::prelude::*;
 use iron::{Handler, Url, status};
+use iron::headers::{AcceptRanges, RangeUnit, Range};
 #[cfg(feature = "cache")]
 use iron::modifier::Modifier;
-use iron::modifiers::Redirect;
+use iron::modifiers::{Header, Redirect};
 use mount::OriginalUrl;
 use requested_path::RequestedPath;
 use url;
 
+use partial_file::PartialFile;
+
 /// The static file-serving `Handler`.
 ///
 /// This handler serves files from a single filesystem path, which may be absolute or relative.
@@ -76,7 +79,17 @@ impl Static {
     #[cfg(feature = "cache")]
     fn try_cache<P: AsRef<Path>>(&self, req: &mut Request, path: P) -> IronResult<Response> {
         match self.cache {
-            None => Ok(Response::with((status::Ok, path.as_ref()))),
+            None => {
+                let accept_range_header = Header(AcceptRanges(vec![RangeUnit::Bytes]));
+                match req.headers.get::<Range>() {
+                    None => Ok(Response::with((status::Ok, path.as_ref(), accept_range_header))),
+                    Some(&Range::Bytes(ref v)) => {
+                        let partial_file = PartialFile::from_path(path.as_ref(),v.clone());
+                        Ok(Response::with((partial_file, accept_range_header)))
+                    },
+                    Some(_) => Ok(Response::with((status::RangeNotSatisfiable, accept_range_header))),
+                }
+            },
             Some(ref cache) => cache.handle(req, path.as_ref()),
         }
     }
@@ -130,8 +143,27 @@ impl Handler for Static {
             Some(path) => self.try_cache(req, path),
             #[cfg(not(feature = "cache"))]
             Some(path) => {
-                let path: &Path = &path;
-                Ok(Response::with((status::Ok, path)))
+                let accept_range_header = Header(AcceptRanges(vec![RangeUnit::Bytes]));
+                let range_req_header = req.headers.get::<Range>().map(|h|{
+                    h.clone()
+                });
+                match range_req_header {
+                    None => {
+                        // deliver the whole file
+                        let path: &Path = &path;
+                        Ok(Response::with((status::Ok, path, accept_range_header)))
+                    },
+                    Some(range) => {
+                        // try to deliver partial content
+                        match range {
+                            Range::Bytes(vec_range) => {
+                                let partial_file = PartialFile::from_path(&path, vec_range);
+                                Ok(Response::with((status::Ok, partial_file, accept_range_header)))
+                            },
+                            _ => Ok(Response::with(status::RangeNotSatisfiable))
+                        }
+                    }
+                }
             },
         }
     }
@@ -190,7 +222,6 @@ impl Cache {
         use iron::headers::{ContentLength, ContentType, ETag, EntityTag};
         use iron::method::Method;
         use iron::mime::{Mime, TopLevel, SubLevel};
-        use iron::modifiers::Header;
 
         let seconds = self.duration.as_secs() as u32;
         let cache = vec![CacheDirective::Public, CacheDirective::MaxAge(seconds)];
@@ -206,9 +237,17 @@ impl Cache {
             };
             Response::with((status::Ok, Header(cont_type), Header(ContentLength(metadata.len()))))
         } else {
-            Response::with((status::Ok, path.as_ref()))
+            match req.headers.get::<Range>() {
+                None => Response::with((status::Ok, path.as_ref())),
+                Some(&Range::Bytes(ref v)) => {
+                    let partial_file = PartialFile::from_path(path.as_ref(),v.clone());
+                    Response::with(partial_file)
+                },
+                Some(_) => Response::with(status::RangeNotSatisfiable),
+            }
         };
 
+        response.headers.set(AcceptRanges(vec![RangeUnit::Bytes]));
         response.headers.set(CacheControl(cache));
         response.headers.set(LastModified(HttpDate(time::at(modified))));
         response.headers.set(ETag(EntityTag::weak(format!("{0:x}-{1:x}.{2:x}", size, modified.sec, modified.nsec))));