Robust Header Check

appsTransport.go

@@ -73,7 +73,7 @@ func (t *AppsTransport) RoundTrip(req *http.Request) (*http.Response, error) {
 	}
 
 	req.Header.Set("Authorization", "Bearer "+ss)
-	req.Header.Set("Accept", acceptHeader)
+	addAcceptHeader(req.Header)
 
 	resp, err := t.tr.RoundTrip(req)
 	return resp, err

transport.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"net/http"
+	"strings"
 	"sync"
 	"time"
 )
@@ -90,7 +91,7 @@ func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
 	}
 
 	req.Header.Set("Authorization", "token "+token)
-	req.Header.Add("Accept", acceptHeader) // We add to "Accept" header to avoid overwriting existing req headers.
+	addAcceptHeader(req.Header)
 	resp, err := t.tr.RoundTrip(req)
 	return resp, err
 }
@@ -134,3 +135,22 @@ func (t *Transport) refreshToken() error {
 
 	return nil
 }
+
+// addAcceptHeader adds acceptHeader value to "Accept" header, but only
+// if the current "Accept" header is not set, or if it already accepts JSON.
+func addAcceptHeader(headers http.Header) {
+	if headers.Get("Accept") == "" {
+		headers.Set("Accept", acceptHeader)
+		return
+	}
+
+	// Need to loop through all Accept headers in case there is more than one.
+	for _, header := range headers["Accept"] {
+		// Looks as though all media types (https://developer.github.com/v3/media/) that can accept json end with "json". 
+		// Only doing a suffix check to see if a json header already exists.
+		if strings.HasSuffix(header, "json") {
+			headers.Add("Accept", acceptHeader) // We add to "Accept" header to avoid overwriting existing req headers.
+			return
+		}
+	}
+}

transport_test.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"os"
+	"strings"
 	"testing"
 	"time"
 )
@@ -173,3 +174,78 @@ func TestNew_appendHeader(t *testing.T) {
 		t.Errorf("could not find %v in request's accept headers: %v", myheader, headers["Accept"])
 	}
 }
+
+func TestSingleAssetBinary_AddAcceptHeader(t *testing.T) {
+	req, err := http.NewRequest(http.MethodGet, "https://api.github.com/repos/bradleyfalzon/ghinstallation/releases/assets/1", http.NoBody)
+	if err != nil {
+		t.Fatalf("Failed to create test request: %s", err.Error())
+	}
+
+	req.Header.Set("Accept", "application/octet-stream")
+
+	addAcceptHeader(req.Header)
+
+	for headerName, headers := range req.Header {
+		if strings.ToLower(headerName) == "accept" {
+			for _, header := range headers {
+				if header == acceptHeader {
+					fmt.Printf("Header Name: %s, Header: %s", headerName, header)
+					t.Error("Set Accept header improperly for single asset call")
+				}
+			}
+		}
+	}
+}
+
+func TestNormal_AddAcceptHeader(t *testing.T) {
+	req, err := http.NewRequest(http.MethodGet, "https://api.github.com/repos", http.NoBody)
+	if err != nil {
+		t.Fatalf("Failed to create test request: %s", err.Error())
+	}
+
+	addAcceptHeader(req.Header)
+
+	if req.Header.Get("Accept") != acceptHeader {
+		t.Error("Did not correctly set 'Accept' header")
+	}
+}
+
+func TestAlreadyExists_AddAcceptHeader(t *testing.T) {
+	req, err := http.NewRequest(http.MethodGet, "https://api.github.com/repos", http.NoBody)
+	if err != nil {
+		t.Fatalf("Failed to create test request: %s", err.Error())
+	}
+
+	req.Header.Set("accept", "application/vnd.github.v3+json")
+
+	addAcceptHeader(req.Header)
+
+	found := false
+	for headerName, headers := range req.Header {
+		if strings.ToLower(headerName) == "accept" {
+			for _, header := range headers {
+				if header == acceptHeader {
+					found = true
+					break
+				}
+			}
+		}
+	}
+
+	if !found {
+		t.Errorf("Did not correctly append %s header", acceptHeader)
+	}
+}
+
+func TestSingleAssetJSON_AddAcceptHeader(t *testing.T) {
+	req, err := http.NewRequest(http.MethodGet, "https://api.github.com/repos/bradleyfalzon/ghinstallation/releases/assets/1", http.NoBody)
+	if err != nil {
+		t.Fatalf("Failed to create test request: %s", err.Error())
+	}
+
+	addAcceptHeader(req.Header)
+
+	if req.Header.Get("Accept") != acceptHeader {
+		t.Error("Did not correctly set 'Accept' header")
+	}
+}