The best way to get a string from a Writer in Go
I have a piece of code that returns a web page using the built-in template system. It accepts a ResponseWriter to which the resulting markup is written. I now want to get to the markup as a string and put it in a database in some cases. I factored out a method that accepts a normal Writer instead of a ResponseWriter and am now trying to get to the written content. Aha - a Pipe may be what I need and then I can get the string with ReadString from the bufio library. But it turns out that the PipeReader coming out from the pipe is not compatible with Reader (that I would need for the ReadString method). W00t. Big surprise. So I could just read into byte[]s using the PipeReader but it feels a bit wrong when ReadString is there.
So what would be the best way to do it? Should I stick with the Pipe and read bytes or is there something better that I haven't found in the manual?
Answer
If your function accepts an io.Writer, you can pass a *bytes.Buffer to capture the output.
// import "bytes"
buf := new(bytes.Buffer)
f(buf)
buf.String() // returns a string of what was written to it
If it requires an http.ResponseWriter, you can use a *httptest.ResponseRecorder. A response recorder holds all information that can be sent to a ResponseWriter, but the body is just a *bytes.Buffer.
// import "net/http/httptest"
r := httptest.NewRecorder()
f(r)
r.Body.String() // r.Body is a *bytes.Buffer