Ensure for SPARQL passthrough queries headers are passed through from…

… the original request and not the defaults supplied by httpx AsyncClient (e.g. compression).

Return more sensible error messages.

prez/repositories/remote_sparql.py

@@ -58,25 +58,45 @@ async def tabular_query_to_table(self, query: str, context: URIRef = None):
         return context, response.json()["results"]["bindings"]
 
     async def sparql(
-        self, query: str, raw_headers: list[tuple[bytes, bytes]], method: str = "GET"
+            self, query: str, raw_headers: list[tuple[bytes, bytes]], method: str = "GET"
     ):
-        """Sends a starlette Request object (containing a SPARQL query in the URL parameters) to a proxied SPARQL
-        endpoint."""
+        """Sends a request (containing a SPARQL query in the URL parameters) to a proxied SPARQL endpoint."""
+        # Convert raw_headers to a dict, excluding the 'host' header
+        headers = {k.decode('utf-8'): v.decode('utf-8') for k, v in raw_headers if k.lower() != b'host'}
 
-        headers = []
-        for header in raw_headers:
-            if header[0] != b"host":
-                headers.append(header)
-
-        # TODO: Global app settings should be passed in as a function argument.
         if method == 'GET':
-            query_escaped_as_bytes = f"query={quote_plus(query)}".encode("utf-8")
-            url = httpx.URL(url=settings.sparql_endpoint, query=query_escaped_as_bytes)
-            rp_req = self.async_client.build_request(method, url, headers=headers)
+            query_escaped = quote_plus(query)
+            url = f"{settings.sparql_endpoint}?query={query_escaped}"
+            request = httpx.Request(method, url, headers=headers)
         else:
-            url = httpx.URL(url=settings.sparql_endpoint)
-            rp_req = self.async_client.build_request(method, url, headers=headers, data={'query': query})
+            url = settings.sparql_endpoint
+            # Prepare form data
+            form_data = f"query={quote_plus(query)}"
+
+            # Set correct headers for form data
+            headers['content-type'] = 'application/x-www-form-urlencoded'
+            headers['content-length'] = str(len(form_data))
+
+            request = httpx.Request(
+                method,
+                url,
+                headers=headers,
+                content=form_data.encode('utf-8')
+            )
+
+        # Add the correct 'host' header
+        request.headers['host'] = httpx.URL(url).host
 
-        headers.append((b"host", str(url.host).encode("utf-8")))
+        response = await self.async_client.send(request, stream=True)
+        try:
+            response.raise_for_status()
+        except httpx.HTTPStatusError as e:
+            await response.aread()
+            print(f"Error content: {response.text}")
+            raise httpx.HTTPStatusError(
+                f"HTTP Error {response.status_code}: {response.text}",
+                request=request,
+                response=response
+            ) from e
 
-        return await self.async_client.send(rp_req, stream=True)
+        return response