Question
Trying to use Go's http package, I can't work out the syntax of .Read
. The following marked by HERE is the only thing I have got to compile, although I tried several other things which were all rejected by the compiler.
package main
import "fmt";
import "http";
import "os";
func main () {
kinopiko_flair := "http://stackoverflow.com/users/flair/181548.json";
response, _, error := http.Get (kinopiko_flair);
if (error != nil) {
// I want to print out the error too.
fmt.Printf ("Error getting %s\n", kinopiko_flair);
os.Exit (1);
}
fmt.Printf ("Status is %s\n", response.Status);
var nr int;
var buf []byte;
nr, error = response.Body.Read (buf); // HERE
if (error != nil) {
// I want to print out the error too.
fmt.Printf ("Error reading response.\n");
os.Exit (1);
}
response.Body.Close ();
fmt.Printf ("Got %d bytes\n", nr);
fmt.Printf ("Got '%s'\n", buf);
}
The URL is OK, since wget
gets it fine, but when I run this buf
is just an empty string and nr
is always zero. What do I need to do to get the data out of response
? The compiler rejected .ReadAll
and other things I tried.
The output looks like this:
Status is 200 OK Got 0 bytes Got ''
Solution
Try giving the slice buf a size, e.g.
buf := make([]byte,128);
Reader reads up to len() of the buffer it is given.
From io.go
// Reader is the interface that wraps the basic Read method.
//
// Read reads up to len(p) bytes into p. It returns the number of bytes
// read (0 <= n <= len(p)) and any error encountered.
// Even if Read returns n < len(p),
// it may use all of p as scratch space during the call.
// If some data is available but not len(p) bytes, Read conventionally
// returns what is available rather than block waiting for more.
//
// At the end of the input stream, Read returns 0, os.EOF.
// Read may return a non-zero number of bytes with a non-nil err.
// In particular, a Read that exhausts the input may return n > 0, os.EOF.
OTHER TIPS
Trying to adapt the cat example from the tutorial:
fmt.Printf ("Status is %s\n", response.Status);
var nr int;
const NBUF = 512;
var buf [NBUF]byte;
for {
switch nr, _ := response.Body.Read(&buf); true {
case nr < 0:
os.Exit(1);
case nr == 0: // EOF
return;
case nr > 0:
if nw, _ := os.Stdout.Write(buf[0:nr]); nw != nr {
fmt.Printf("error\n");
}
}
}
Output:
$ ./8.out
Status is 200 OK
{"id":181548,"gravatarHtml":"\u003cimg src=\"http://www.gravatar.com/avatar/f4a286fa31d1359ee92113823a70a738?s=50&d=identicon&r=PG\" height=\"50\" width=\"50\" alt=\"\"\u003e","profileUrl":"http://stackoverflow.com/users/181548/kinopiko","displayName":"Kinopiko","reputation":"4,674","badgeHtml":"\u003cspan title=\"1 gold badge\"\u003e\u003cspan class=\"badge1\"\u003e●\u003c/span\u003e\u003cspan class=\"badgecount\"\u003e1\u003c/span\u003e\u003c/span\u003e\u003cspan title=\"5 silver badges\"\u003e\u003cspan class=\"badge2\"\u003e●\u003c/span\u003e\u003cspan class=\"badgecount\"\u003e5\u003c/span\u003e\u003c/span\u003e\u003cspan title=\"21 bronze badges\"\u003e\u003cspan class=\"badge3\"\u003e●\u003c/span\u003e\u003cspan class=\"badgecount\"\u003e21\u003c/span\u003e\u003c/span\u003e"}
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