export to api.txt file,such as
fmt.Println(params...)
net.LookupIP(params...)
...
line by line
I using this to IDE autocomplete
As others have said, gocode may well do what you want already. But anyway, to list the exported API of a package you can use go tool api <pkg>. e.g.
$ go tool api runtime | grep func
pkg runtime, func Breakpoint()
pkg runtime, func CPUProfile() []byte
pkg runtime, func Caller(int) (uintptr, string, int, bool)
pkg runtime, func Callers(int, []uintptr) int
pkg runtime, func FuncForPC(uintptr) *Func
pkg runtime, func GC()
...
Parse the package files, walk the TLDs, collect the exported and exposed identifiers, and you are almost where gocode is for years.
There is already a text file with the full Go1 API in the go repository: http://code.google.com/p/go/source/browse/api/go1.txt
But I recommend you to set up gocode (maybe by writing a small plugin for your IDE if there isn't any already). It provides context-sensitive auto-completion for variables and packages, even if they aren't part of the standard library or when they have been imported with a different name.