go - Idiomatic way to handle template errors in golang -
say have html/template following:
<html> <body> <p>{{somefunc .somedata}}</p> </body> and somefunc returns error. there idiomatic way deal this?
if write directly responsewriter, status code 200 has been written before encounter error.
var tmpl *template.template func handler(w http.responsewriter, r *http.request) { err := tmpl.execute(w, data) // "<html><body><p>" has been written... // err? } preferably return status code 400 or such, can't see way if use template.execute directly on responsewriter. there i'm missing?
since template engine generates output on-the-fly, parts of template preceding somefunc call sent output. , if output not buffered, (along http 200 status) may sent.
you can't that.
what can perform check before call template.execute(). in trivial case should enough call somefunc() , check return value. if choose path , return value of somefunc() complex, not have call again template, can pass return value params pass template , refer value in template (so somefunc() won't have executed twice).
if not enough or can't control it, can create bytes.buffer, execute template directed buffer, , after execute() returns, check if there errors. if there errors, send proper error message / page. if went ok, can send content of buffer responsewriter.
this this:
buf := &bytes.buffer{} err := tmpl.execute(buf, data) if err != nil { // send error message, example: http.error(w, "hey, request bad!", http.statusbadrequest) // http 400 status } else { // no error, send content, http 200 response status implied buf.writeto(w) }
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