file sniffer

file-sniffer/.exercism/config.json

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+{
+  "blurb": "Learn about binaries by verifying the mime type of files uploaded to your server.",
+  "authors": [
+    "neenjaw"
+  ],
+  "contributors": [
+    "angelikatyborska"
+  ],
+  "files": {
+    "solution": [
+      "lib/file_sniffer.ex"
+    ],
+    "test": [
+      "test/file_sniffer_test.exs"
+    ],
+    "exemplar": [
+      ".meta/exemplar.ex"
+    ]
+  },
+  "language_versions": ">=1.10"
+}

file-sniffer/.exercism/metadata.json

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+{"track":"elixir","exercise":"file-sniffer","id":"43cf1cb87b6b4e149de49c7d4c67710f","url":"https://exercism.org/tracks/elixir/exercises/file-sniffer","handle":"rjNemo","is_requester":true,"auto_approve":false}

file-sniffer/.formatter.exs

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+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

file-sniffer/.gitignore

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+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+match_binary-*.tar
+

file-sniffer/HELP.md

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+# Help
+
+## Running the tests
+
+From the terminal, change to the base directory of the exercise then execute the tests with:
+
+```bash
+$ mix test
+```
+
+This will execute the test file found in the `test` subfolder -- a file ending in `_test.exs`
+
+Documentation:
+
+* [`mix test` - Elixir's test execution tool](https://hexdocs.pm/mix/Mix.Tasks.Test.html)
+* [`ExUnit` - Elixir's unit test library](https://hexdocs.pm/ex_unit/ExUnit.html)
+
+## Pending tests
+
+In test suites of practice exercises, all but the first test have been tagged to be skipped.
+
+Once you get a test passing, you can unskip the next one by commenting out the relevant `@tag :pending` with a `#` symbol.
+
+For example:
+
+```elixir
+# @tag :pending
+test "shouting" do
+  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
+end
+```
+
+If you wish to run all tests at once, you can include all skipped test by using the `--include` flag on the `mix test` command:
+
+```bash
+$ mix test --include pending
+```
+
+Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the file `test/test_helper.exs`.
+
+```elixir
+# ExUnit.configure(exclude: :pending, trace: true)
+```
+
+## Useful `mix test` options
+
+* `test/<FILE>.exs:LINENUM` - runs only a single test, the test from `<FILE>.exs` whose definition is on line `LINENUM`
+* `--failed` - runs only tests that failed the last time they ran
+* `--max-failures` - the suite stops evaluating tests when this number of test failures
+is reached
+* `--seed 0` - disables randomization so the tests in a single file will always be ran
+in the same order they were defined in
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit lib/file_sniffer.ex` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Elixir track's documentation](https://exercism.org/docs/tracks/elixir)
+- [Exercism's support channel on gitter](https://gitter.im/exercism/support)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+If you're stuck on something, it may help to look at some of the [available resources](https://exercism.org/docs/tracks/elixir/resources) out there where answers might be found.
+If you can't find what you're looking for in the documentation, feel free to ask help in the Exercism's BEAM [gitter channel](https://gitter.im/exercism/xerlang).

file-sniffer/HINTS.md

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+# Hints
+
+## General
+
+- Remember to reference the table in the instructions.
+
+## 1. Given an extension, return the expected media type
+
+- Use [pattern matching][pattern-matching] to return the correct media type.
+- You can use [multiple function clauses][mfc].
+
+## 2. Given a binary file, return the expected media type
+
+- Use the [binary special form][special-forms] available to you for writing a binary literal.
+- Use [pattern matching][binary-matching] to match against the first few bytes of the file binary.
+
+## 3. Given an extension and a binary file, verify that the file matches the expected type
+
+- Reuse the functions you created for parts 1 and 2.
+- Compare the return value of each function, then return the appropriate value.
+  - You can use the [`if` macro conditional][if] for binary conditions.
+
+[binary-matching]: https://elixir-lang.org/getting-started/binaries-strings-and-char-lists.html#binaries
+[if]: https://elixir-lang.org/getting-started/case-cond-and-if.html#if-and-unless
+[mfc]: https://elixir-lang.org/getting-started/modules-and-functions.html#named-functions
+[mimetype]: https://en.wikipedia.org/wiki/Media_type
+[pattern-matching]: https://elixir-lang.org/getting-started/pattern-matching.html#pattern-matching
+[special-forms]: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#%3C%3C%3E%3E/1

file-sniffer/README.md

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+# File Sniffer
+
+Welcome to File Sniffer on Exercism's Elixir Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+If you get stuck on the exercise, check out `HINTS.md`, but try and solve it without using those first :)
+
+## Introduction
+
+## Binaries
+
+Elixir provides an elegant syntax for working with binary data as we have seen with the `<<>>` special form provided for working with _bitstrings_.
+
+The binary type is a specialization on the bitstring type. Where bitstrings could be of any length (any number of [bits][wiki-bit]), binaries are where the number of bits can be evenly divided by 8. That is, when working with binaries, we often think of things in terms of [bytes][wiki-byte] (8 bits). A byte can represent integer numbers from `0` to `255`. It is common to work with byte values in [hexadecimal][wiki-hexadecimal], `0x00 - 0xFF`.
+
+Binary literals are defined using the bitstring special form `<<>>`. When defining a binary literal, we can use integer and string literals. Integer values greater than 255 will overflow and only the last 8 bits of the integer will be used. By default, the `::binary` modifier is applied to the value. We can concatenate binaries with the `<>/2` operator.
+
+```elixir
+<<255>> == <<0xFF>>
+<<256>> == <<0>> # Overflowing bits are truncated
+<<2, 4, 6, 8, 10, 12, 14, 16>> == <<0x02, 0x04, 0x06, 0x08, 0x0A, 0x0C, 0x0E, 0x10>>
+```
+
+A _null-byte_ is another name for `<<0>>`.
+
+### Pattern matching on binary data
+
+Pattern matching is even extended to binaries, and we can pattern match on a portion of binary data much like we could for a list.
+
+```elixir
+# Ignore the first 8 bytes, match and bind the remaining to `body`
+<<_::binary-size(8), body::binary>>
+```
+
+Like with other types of pattern matching, we can use this in function signatures to match when selecting from multiple function clauses.
+
+[wiki-bit]: https://en.wikipedia.org/wiki/Bit
+[wiki-byte]: https://en.wikipedia.org/wiki/Byte
+[wiki-hexadecimal]: https://en.wikipedia.org/wiki/Hexadecimal
+
+## Instructions
+
+You have been working on a project which allows users to upload files to the server to be shared with other users. You have been tasked with writing a function to verify that an upload matches its [media type][mimetype]. You do some research and discover that the first few bytes of a file are generally unique to that file type, giving it a sort of signature.
+
+Use the following table for reference:
+
+| File type | Common extension | Media type                   | binary 'signature'                               |
+| --------- | ---------------- | ---------------------------- | ------------------------------------------------ |
+| ELF       | `"exe"`          | `"application/octet-stream"` | `0x7F, 0x45, 0x4C, 0x46`                         |
+| BMP       | `"bmp"`          | `"image/bmp"`                | `0x42, 0x4D`                                     |
+| PNG       | `"png"`          | `"image/png"`                | `0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A` |
+| JPG       | `"jpg"`          | `"image/jpg"`                | `0xFF, 0xD8, 0xFF`                               |
+| GIF       | `"gif"`          | `"image/gif"`                | `0x47, 0x49, 0x46`                               |
+
+## 1. Given an extension, return the expected media type
+
+Implement the `type_from_extension/1` function. It should take a file extension (string) and return the media type (string).
+
+```elixir
+FileSniffer.type_from_extension("exe")
+# => "application/octet-stream"
+```
+
+## 2. Given a binary file, return the expected media type
+
+Implement the `type_from_binary/1` function. It should take a file (binary) and return the media type (string).
+
+```elixir
+file = File.read!("application.exe")
+FileSniffer.type_from_binary(file)
+# => "application/octet-stream"
+```
+
+Don't worry about reading the file as a binary. Assume that has been done for you and is provided by the tests as an argument.
+
+## 3. Given an extension and a binary file, verify that the file matches the expected type
+
+Implement the `verify/2` function. It should take a file (binary) and extension (string) and return an `:ok` or `:error` tuple.
+
+```elixir
+file = File.read!("application.exe")
+
+FileSniffer.verify(file, "exe")
+# => {:ok, "application/octet-stream"}
+
+FileSniffer.verify(file, "png")
+# => {:error, "Warning, file format and file extension do not match."}
+```
+
+[mimetype]: https://en.wikipedia.org/wiki/Media_type
+
+## Source
+
+### Created by
+
+- @neenjaw
+
+### Contributed to by
+
+- @angelikatyborska

file-sniffer/lib/file_sniffer.ex

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+defmodule FileSniffer do
+  @mimi_types %{
+    "bmp" => "image/bmp",
+    "gif" => "image/gif",
+    "jpg" => "image/jpg",
+    "png" => "image/png",
+    "exe" => "application/octet-stream"
+  }
+  def type_from_extension(extension), do: Map.get(@mimi_types, extension)
+
+  def type_from_binary(<<0x42, 0x4D, _::binary>>), do: type_from_extension("bmp")
+  def type_from_binary(<<0x47, 0x49, 0x46, _::binary>>), do: type_from_extension("gif")
+  def type_from_binary(<<0xFF, 0xD8, 0xFF, _::binary>>), do: type_from_extension("jpg")
+
+  def type_from_binary(<<0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, _::binary>>),
+    do: type_from_extension("png")
+
+  def type_from_binary(<<0x7F, 0x45, 0x4C, 0x46, _::binary>>), do: type_from_extension("exe")
+
+  def verify(file_binary, extension) do
+    case {type_from_extension(extension), type_from_binary(file_binary)} do
+      {type, type} -> {:ok, type}
+      _ -> {:error, "Warning, file format and file extension do not match."}
+    end
+  end
+end

file-sniffer/mix.exs

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+defmodule FileSniffer.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :file_sniffer,
+      version: "0.1.0",
+      # elixir: "~> 1.10",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end

file-sniffer/test/file_sniffer_test.exs

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+defmodule FileSnifferTest do
+  use ExUnit.Case
+
+  @bmp_file File.read!(Path.join("assets", "bmp.bmp"))
+  @gif_file File.read!(Path.join("assets", "gif.gif"))
+  @jpg_file File.read!(Path.join("assets", "jpeg.jpg"))
+  @png_file File.read!(Path.join("assets", "png-transparent.png"))
+  @exe_file File.read!(Path.join("assets", "elf.o"))
+
+  describe "get type from extension:" do
+    @tag task_id: 1
+    test "bmp" do
+      assert FileSniffer.type_from_extension("bmp") == "image/bmp"
+    end
+
+    @tag task_id: 1
+    test "gif" do
+      assert FileSniffer.type_from_extension("gif") == "image/gif"
+    end
+
+    @tag task_id: 1
+    test "jpg" do
+      assert FileSniffer.type_from_extension("jpg") == "image/jpg"
+    end
+
+    @tag task_id: 1
+    test "png" do
+      assert FileSniffer.type_from_extension("png") == "image/png"
+    end
+
+    @tag task_id: 1
+    test "exe" do
+      assert FileSniffer.type_from_extension("exe") == "application/octet-stream"
+    end
+  end
+
+  describe "get type from binary:" do
+    @tag task_id: 2
+    test "bmp" do
+      assert FileSniffer.type_from_binary(@bmp_file) == "image/bmp"
+    end
+
+    @tag task_id: 2
+    test "gif" do
+      assert FileSniffer.type_from_binary(@gif_file) == "image/gif"
+    end
+
+    @tag task_id: 2
+    test "jpg" do
+      assert FileSniffer.type_from_binary(@jpg_file) == "image/jpg"
+    end
+
+    @tag task_id: 2
+    test "png" do
+      assert FileSniffer.type_from_binary(@png_file) == "image/png"
+    end
+
+    @tag task_id: 2
+    test "exe" do
+      assert FileSniffer.type_from_binary(@exe_file) == "application/octet-stream"
+    end
+  end
+
+  describe "verify valid files" do
+    @tag task_id: 3
+    test "bmp" do
+      assert FileSniffer.verify(@bmp_file, "bmp") == {:ok, "image/bmp"}
+    end
+
+    @tag task_id: 3
+    test "gif" do
+      assert FileSniffer.verify(@gif_file, "gif") == {:ok, "image/gif"}
+    end
+
+    @tag task_id: 3
+    test "jpg" do
+      assert FileSniffer.verify(@jpg_file, "jpg") == {:ok, "image/jpg"}
+    end
+
+    @tag task_id: 3
+    test "png" do
+      assert FileSniffer.verify(@png_file, "png") == {:ok, "image/png"}
+    end
+
+    @tag task_id: 3
+    test "exe" do
+      assert FileSniffer.verify(@exe_file, "exe") == {:ok, "application/octet-stream"}
+    end
+  end
+
+  describe "reject invalid files" do
+    @tag task_id: 3
+    test "bmp" do
+      assert FileSniffer.verify(@exe_file, "bmp") ==
+               {:error, "Warning, file format and file extension do not match."}
+    end
+
+    @tag task_id: 3
+    test "gif" do
+      assert FileSniffer.verify(@exe_file, "gif") ==
+               {:error, "Warning, file format and file extension do not match."}
+    end
+
+    @tag task_id: 3
+    test "jpg" do
+      assert FileSniffer.verify(@exe_file, "jpg") ==
+               {:error, "Warning, file format and file extension do not match."}
+    end
+
+    @tag task_id: 3
+    test "png" do
+      assert FileSniffer.verify(@exe_file, "png") ==
+               {:error, "Warning, file format and file extension do not match."}
+    end
+
+    @tag task_id: 3
+    test "exe" do
+      assert FileSniffer.verify(@png_file, "exe") ==
+               {:error, "Warning, file format and file extension do not match."}
+    end
+  end
+end

file-sniffer/test/test_helper.exs

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+ExUnit.start()
+ExUnit.configure(exclude: :pending, trace: true, seed: 0)