Implement a file content predicate

Fixes #31

src/path/fc.rs

@@ -0,0 +1,85 @@
+// Copyright (c) 2018 The predicates-rs Project Developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::fmt;
+use std::fs;
+use std::io::{self, Read};
+use std::path;
+
+use Predicate;
+
+/// Predicate adaper that converts a `path` to file content predicate to byte predicate.
+///
+/// This is created by `pred.from_path()`.
+#[derive(Clone, Debug)]
+pub struct FileContentPredicate<P>
+where
+    P: Predicate<[u8]>,
+{
+    p: P,
+}
+
+impl<P> FileContentPredicate<P>
+where
+    P: Predicate<[u8]>,
+{
+    fn eval(&self, path: &path::Path) -> io::Result<bool> {
+        let mut buffer = Vec::new();
+
+        // read the whole file
+        fs::File::open(path)?.read_to_end(&mut buffer)?;
+        Ok(self.p.eval(&buffer))
+    }
+}
+
+impl<P> fmt::Display for FileContentPredicate<P>
+where
+    P: Predicate<[u8]>,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.p)
+    }
+}
+
+impl<P> Predicate<path::Path> for FileContentPredicate<P>
+where
+    P: Predicate<[u8]>,
+{
+    fn eval(&self, path: &path::Path) -> bool {
+        self.eval(path).unwrap_or(false)
+    }
+}
+
+/// `Predicate` extension adapting a `slice` Predicate.
+pub trait PredicateFileContentExt
+where
+    Self: Predicate<[u8]>,
+    Self: Sized,
+{
+    /// Returns a `FileContentPredicate` that adapts `Self` to a file content `Predicate`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use predicates::prelude::*;
+    /// use std::path::Path;
+    ///
+    /// let predicate_fn = predicate::str::is_empty().not().from_utf8().from_file_path();
+    /// assert_eq!(true, predicate_fn.eval(Path::new("./tests/hello_world")));
+    /// assert_eq!(false, predicate_fn.eval(Path::new("./tests/empty_file")));
+    /// ```
+    fn from_file_path(self) -> FileContentPredicate<Self> {
+        FileContentPredicate { p: self }
+    }
+}
+
+impl<P> PredicateFileContentExt for P
+where
+    P: Predicate<[u8]>,
+{
+}

src/path/mod.rs

@@ -14,3 +14,5 @@ mod existence;
 pub use self::existence::{exists, missing, ExistencePredicate};
 mod ft;
 pub use self::ft::{is_dir, is_file, is_symlink, FileTypePredicate};
+mod fc;
+pub use self::fc::{FileContentPredicate, PredicateFileContentExt};

src/prelude.rs

@@ -11,6 +11,7 @@
 pub use core::Predicate;
 pub use boolean::PredicateBooleanExt;
 pub use boxed::PredicateBoxExt;
+pub use path::PredicateFileContentExt;
 pub use str::PredicateStrExt;
 pub use name::PredicateNameExt;
 

tests/hello_world

@@ -0,0 +1 @@
+Hello World!