Add Cookbook C01-C19 (draft)

docs-src/pages/en/cookbook/c08-post-file-body.md

@@ -0,0 +1,34 @@
+---
+title: "C08. POST a File as Raw Binary"
+order: 8
+status: "draft"
+---
+
+Sometimes you want to send a file's contents as the request body directly — no multipart wrapping. This is common for S3-compatible APIs or endpoints that take raw image data. For this, use `make_file_body()`.
+
+## Basic usage
+
+```cpp
+httplib::Client cli("https://storage.example.com");
+
+auto [size, provider] = httplib::make_file_body("backup.tar.gz");
+if (size == 0) {
+  std::cerr << "Failed to open file" << std::endl;
+  return 1;
+}
+
+auto res = cli.Put("/bucket/backup.tar.gz", size,
+                   provider, "application/gzip");
+```
+
+`make_file_body()` returns a pair of file size and a `ContentProvider`. Pass them to `Post()` or `Put()` and the file contents flow straight into the request body.
+
+The `ContentProvider` reads the file in chunks, so even huge files never sit fully in memory.
+
+## When the file can't be opened
+
+If the file can't be opened, `make_file_body()` returns `size` as `0` and `provider` as an empty function object. Sending that would produce garbage — always check `size` first.
+
+> **Warning:** `make_file_body()` needs to fix the Content-Length up front, so it reads the file size ahead of time. If the file size might change mid-upload, this API isn't the right fit.
+
+> To send the file as multipart form data instead, see C07. Upload a File as Multipart Form Data.