Consistent off by one errors in go io.copy function for large content -

this 1 works consistently.

    _, err = io.copy(out, resp.body)     if err != nil {         errlog.fatal(err)     } 

this 1 gives pretty consistent off 1 errors (the last byte of downloaded content left off, in case closing ] in json response) large-ish responses (mbs).

    if _, err := io.copy(out, resp.body); err != nil {         errlog.fatal(err)     } 

from the examples on official golang blog, looks should valid syntax.

edit: more details , context

this error 2nd version of code (more compact error handling)

error: 2015/08/05 08:09:31 pull.go:257: unexpected end of json input 

from code in function

err = json.unmarshal(dat, &all_data) if err != nil {     return err } 

i found off 1 issue looking @ first 10 , last 10 characters of file in each case. here before , afters:

# before (with error) start:  [{"tags":[              end:    ersion":1} start:  [{"_create              end:    "tags":[]}  # after start:  [{"tags":[              end:    rsion":1}] start:  [{"_create              end:    tags":[]}] 

the files 15-20 mb json strings.

it turned out issue @ least partially result of race condition.

i not calling .close() on file out before exiting function. after adding have not been more issues.

why causing just last byte of file dropped mystery me.