feat(builders): detect file MIME types from extension instead of hardcoding

lib/builders/document.ex

@@ -27,6 +27,7 @@ defmodule TelegramEx.Builder.Document do
   """
 
   alias TelegramEx.API
+  alias TelegramEx.MimeType
 
   @doc """
   Sets the document from a URL.
@@ -65,7 +66,7 @@ defmodule TelegramEx.Builder.Document do
     content = File.read!(path)
 
     Map.get(ctx, :payload, %{})
-    |> Map.put(:document, {content, filename: filename, content_type: "application/octet-stream"})
+    |> Map.put(:document, {content, filename: filename, content_type: MimeType.from_path(path)})
     |> then(&Map.put(ctx, :payload, &1))
   end
 

lib/builders/photo.ex

@@ -27,6 +27,7 @@ defmodule TelegramEx.Builder.Photo do
   """
 
   alias TelegramEx.API
+  alias TelegramEx.MimeType
 
   @doc """
   Sets the photo from a URL.
@@ -77,7 +78,7 @@ defmodule TelegramEx.Builder.Photo do
     content = File.read!(path)
 
     Map.get(ctx, :payload, %{})
-    |> Map.put(:photo, {content, filename: filename, content_type: "image/jpeg"})
+    |> Map.put(:photo, {content, filename: filename, content_type: MimeType.from_path(path)})
     |> then(&Map.put(ctx, :payload, &1))
   end
 

lib/builders/sticker.ex

@@ -24,6 +24,7 @@ defmodule TelegramEx.Builder.Sticker do
   """
 
   alias TelegramEx.API
+  alias TelegramEx.MimeType
 
   @doc """
   Sets the sticker by Telegram file ID.
@@ -81,7 +82,7 @@ defmodule TelegramEx.Builder.Sticker do
     content = File.read!(path)
 
     Map.get(ctx, :payload, %{})
-    |> Map.put(:sticker, {content, filename: filename, content_type: "image/webp"})
+    |> Map.put(:sticker, {content, filename: filename, content_type: MimeType.from_path(path)})
     |> then(&Map.put(ctx, :payload, &1))
   end
 

lib/builders/video.ex

@@ -26,6 +26,7 @@ defmodule TelegramEx.Builder.Video do
   """
 
   alias TelegramEx.API
+  alias TelegramEx.MimeType
 
   @doc """
   Sets the video by Telegram file ID.
@@ -83,7 +84,7 @@ defmodule TelegramEx.Builder.Video do
     content = File.read!(path)
 
     Map.get(ctx, :payload, %{})
-    |> Map.put(:video, {content, filename: filename, content_type: "video/mp4"})
+    |> Map.put(:video, {content, filename: filename, content_type: MimeType.from_path(path)})
     |> then(&Map.put(ctx, :payload, &1))
   end
 
@@ -124,7 +125,7 @@ defmodule TelegramEx.Builder.Video do
     content = File.read!(path)
 
     Map.get(ctx, :payload, %{})
-    |> Map.put(:cover, {content, filename: filename, content_type: "image/jpeg"})
+    |> Map.put(:cover, {content, filename: filename, content_type: MimeType.from_path(path)})
     |> then(&Map.put(ctx, :payload, &1))
   end
 

lib/mime_type.ex

@@ -0,0 +1,77 @@
+defmodule TelegramEx.MimeType do
+  @moduledoc """
+  Resolves MIME content types for local files based on their extension.
+
+  This is used by the file-based builders (`Photo`, `Video`, `Sticker`,
+  `Document`) so that uploaded media carries the correct `Content-Type`
+  header instead of a hardcoded value.
+  """
+
+  @types %{
+    ".jpg" => "image/jpeg",
+    ".jpeg" => "image/jpeg",
+    ".png" => "image/png",
+    ".gif" => "image/gif",
+    ".webp" => "image/webp",
+    ".bmp" => "image/bmp",
+    ".tif" => "image/tiff",
+    ".tiff" => "image/tiff",
+    ".svg" => "image/svg+xml",
+    ".mp4" => "video/mp4",
+    ".webm" => "video/webm",
+    ".mov" => "video/quicktime",
+    ".avi" => "video/x-msvideo",
+    ".mkv" => "video/x-matroska",
+    ".mpeg" => "video/mpeg",
+    ".mpg" => "video/mpeg",
+    ".mp3" => "audio/mpeg",
+    ".ogg" => "audio/ogg",
+    ".wav" => "audio/wav",
+    ".m4a" => "audio/mp4",
+    ".pdf" => "application/pdf",
+    ".zip" => "application/zip",
+    ".json" => "application/json",
+    ".txt" => "text/plain",
+    ".csv" => "text/csv",
+    ".html" => "text/html"
+  }
+
+  @default "application/octet-stream"
+
+  @doc """
+  Returns the MIME content type for the given file path.
+
+  The lookup is based on the lowercased file extension. Unknown extensions
+  fall back to `#{@default}`.
+
+  ## Parameters
+
+  - `path` - Path or filename of the file
+
+  ## Returns
+
+  A MIME content type string.
+
+  ## Examples
+
+      iex> TelegramEx.MimeType.from_path("photo.PNG")
+      "image/png"
+
+      iex> TelegramEx.MimeType.from_path("clip.webm")
+      "video/webm"
+
+      iex> TelegramEx.MimeType.from_path("archive.unknown")
+      "application/octet-stream"
+  """
+  @spec from_path(String.t()) :: String.t()
+  def from_path(path) do
+    extension = path |> Path.extname() |> String.downcase()
+    Map.get(@types, extension, @default)
+  end
+
+  @doc """
+  Returns the fallback MIME content type used for unknown extensions.
+  """
+  @spec default() :: String.t()
+  def default, do: @default
+end

test/mime_type_test.exs

@@ -0,0 +1,34 @@
+defmodule TelegramEx.MimeTypeTest do
+  use ExUnit.Case
+
+  doctest TelegramEx.MimeType
+
+  alias TelegramEx.MimeType
+
+  test "resolves image extensions to their MIME types" do
+    assert MimeType.from_path("avatar.png") == "image/png"
+    assert MimeType.from_path("animation.gif") == "image/gif"
+    assert MimeType.from_path("sticker.webp") == "image/webp"
+    assert MimeType.from_path("photo.jpg") == "image/jpeg"
+  end
+
+  test "resolves video extensions to their MIME types" do
+    assert MimeType.from_path("clip.webm") == "video/webm"
+    assert MimeType.from_path("movie.mp4") == "video/mp4"
+  end
+
+  test "lookup is case insensitive" do
+    assert MimeType.from_path("PHOTO.PNG") == "image/png"
+    assert MimeType.from_path("Clip.WebM") == "video/webm"
+  end
+
+  test "falls back to application/octet-stream for unknown extensions" do
+    assert MimeType.from_path("archive.unknown") == "application/octet-stream"
+    assert MimeType.from_path("noextension") == "application/octet-stream"
+    assert MimeType.from_path("report.pdf") == "application/pdf"
+  end
+
+  test "default/0 returns the safe fallback type" do
+    assert MimeType.default() == "application/octet-stream"
+  end
+end