Trim leading or trailing space from trace ID

Without this change, a leading or trailing space in the trace ID, as received
from the user input, causes a bad error message to the user.  Here we trim the
input to ensure that no leading or trailing space is present before attempting
to decode the string.

pkg/util/http.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"strings"
 
 	"github.com/gorilla/mux"
 )
@@ -32,6 +33,10 @@ func ParseTraceID(r *http.Request) ([]byte, error) {
 }
 
 func hexStringToTraceID(id string) ([]byte, error) {
+	// the encoding/hex package does not handle non-hex characters.
+	// remove leading or trailing spaces if present.
+	id = strings.Trim(id, " ")
+
 	// the encoding/hex package does not like odd length strings.
 	// just append a bit here
 	if len(id)%2 == 1 {

pkg/util/http_test.go

@@ -36,6 +36,10 @@ func TestHexStringToTraceID(t *testing.T) {
 			id:       "234567890abcdef", // odd length
 			expected: []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0x34, 0x56, 0x78, 0x90, 0xab, 0xcd, 0xef},
 		},
+		{
+			id:       "1234567890abcdef ", // trailing space
+			expected: []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x12, 0x34, 0x56, 0x78, 0x90, 0xab, 0xcd, 0xef},
+		},
 	}
 
 	for _, tt := range tc {