check content type

src/apkallone.gleam

@@ -10,6 +10,8 @@ pub type Client {
 pub type Error {
   BadInstance
   FetchError(error: Dynamic)
-  ResponseError(status: Int)
+  UnexpectedStatus(status: Int)
+  UnexpectedContentType(content_type: String)
+  MissingContentType
   DecodeError(error: DecodeError)
 }

src/apkallone/internal.gleam

@@ -3,7 +3,9 @@ import gleam/http/request.{type Request}
 import gleam/http/response.{type Response}
 import gleam/httpc
 import gleam/json
+import gleam/pair
 import gleam/result
+import gleam/string
 
 import apkallone.{type Client, type Error}
 
@@ -22,14 +24,14 @@ pub fn prepare_request(
 }
 
 pub fn send_request(req: Request(String)) -> Result(Response(String), Error) {
-  use req <- result.try(
+  use res <- result.try(
     httpc.send(req)
     |> result.map_error(apkallone.FetchError),
   )
 
-  case req.status {
-    200 -> Ok(req)
-    other -> Error(apkallone.ResponseError(other))
+  case res.status {
+    200 -> Ok(res)
+    other -> Error(apkallone.UnexpectedStatus(other))
   }
 }
 
@@ -37,7 +39,30 @@ pub fn decode_response(
   res: Response(String),
   decoder: Decoder(a),
 ) -> Result(a, Error) {
+  use <- require_content_type(res, "application/json")
+
   res.body
   |> json.decode(decoder)
   |> result.map_error(apkallone.DecodeError)
 }
+
+fn require_content_type(
+  res: Response(String),
+  expected_type: String,
+  fun: fn() -> Result(a, Error),
+) -> Result(a, Error) {
+  use actual_type <- result.try(
+    response.get_header(res, "content-type")
+    |> result.replace_error(apkallone.MissingContentType),
+  )
+
+  let actual_type =
+    string.split_once(actual_type, on: ";")
+    |> result.map(pair.first)
+    |> result.unwrap(or: actual_type)
+
+  case actual_type == expected_type {
+    True -> fun()
+    False -> Error(apkallone.UnexpectedContentType(actual_type))
+  }
+}