Preserve message bodies during verbose logging

src/discovery.jl

@@ -66,11 +66,7 @@ function perform_manifest_request(url::String, headers::Vector{HeaderPair}; http
     end
     response = http.request("GET", url; headers=request_headers, status_exception=false, transport_timeout_kwargs(DISCOVERY_TIMEOUT)...)
     if verbose
-        body_text = try
-            String(response.body)
-        catch err
-            string("(unavailable: ", sprint(showerror, err), ")")
-        end
+        body_text = client_response_body_text(response; streaming=false)
         header_pairs = headers_to_pairs(response.headers)
         printable_response = HTTP.Response(response.status, header_pairs, body_text)
         println("MCP discovery HTTP response:")

src/jsonrpc.jl

@@ -31,15 +31,15 @@ const JSONRPC_TIMEOUT = (connecttimeout=10, readtimeout=120)
 
 function client_request_body_text(body)
     body === nothing && return ""
-    return body isa AbstractString ? String(body) : String(body)
+    return body isa AbstractVector{UInt8} ? String(copy(body)) : String(body)
 end
 
 function client_response_body_text(response::HTTP.Response; streaming::Bool)
     if streaming
         return "(streaming body not logged)"
     end
     try
-        return String(response.body)
+        return client_request_body_text(response.body)
     catch err
         return string("(unavailable: ", sprint(showerror, err), ")")
     end

test/runtests.jl

@@ -480,6 +480,36 @@ stop_auth_stub_server(server) = close(server)
     @test ModelContextProtocol.find_session(shared_store, session_id) === nothing
 end
 
+@testset "verbose logging preserves message bodies" begin
+    text = "{\"jsonrpc\":\"2.0\",\"id\":\"1\",\"result\":{}}"
+    for wrap in (identity, x -> @view(x[:]), x -> codeunits(String(x)))
+        body = wrap(collect(codeunits(text)))
+        expected = collect(body)
+        @test ModelContextProtocol.client_request_body_text(body) == text
+        @test body == expected
+        response = HTTP.Response(200, [], body)
+        @test ModelContextProtocol.client_response_body_text(response; streaming=false) == text
+        @test response.body == expected
+    end
+    @test ModelContextProtocol.client_request_body_text(nothing) == ""
+    @test ModelContextProtocol.client_request_body_text(text) == text
+    _state, http_server = start_mcp_test_server()
+    try
+        redirect_stdout(devnull) do
+            discovery = discover_server(base_url(http_server); verbose=true)
+            client = prepare_manual_client(discovery; config=MCPClientConfig(verbose=true))
+            init = initialize_client!(client)
+            @test init["serverInfo"]["name"] == "Stub MCP Server"
+            @test client.initialized
+            @test isempty(ping(client))
+            @test !isempty(list_tools(client))
+            terminate_session!(client)
+        end
+    finally
+        stop_mcp_test_server(http_server)
+    end
+end
+
 @testset "MCP client over HTTP" begin
     state, http_server = start_mcp_test_server()
     base = base_url(http_server)