tpl/data: Misc header improvements, tests, allow multiple headers of same key

Closes #5617

tpl/data/data.go

@@ -23,6 +23,10 @@ import (
 	"net/http"
 	"strings"
 
+	"github.com/gohugoio/hugo/common/maps"
+
+	"github.com/gohugoio/hugo/common/types"
+
 	"github.com/gohugoio/hugo/common/constants"
 	"github.com/gohugoio/hugo/common/loggers"
 
@@ -59,14 +63,10 @@ type Namespace struct {
 // If you provide multiple parts for the URL they will be joined together to the final URL.
 // GetCSV returns nil or a slice slice to use in a short code.
 func (ns *Namespace) GetCSV(sep string, args ...interface{}) (d [][]string, err error) {
-	url := joinURL(args)
+	url, headers := toURLAndHeaders(args)
 	cache := ns.cacheGetCSV
 
 	unmarshal := func(b []byte) (bool, error) {
-		if !bytes.Contains(b, []byte(sep)) {
-			return false, _errors.Errorf("cannot find separator %s in CSV for %s", sep, url)
-		}
-
 		if d, err = parseCSV(b, sep); err != nil {
 			err = _errors.Wrapf(err, "failed to parse CSV file %s", url)
 
@@ -82,17 +82,9 @@ func (ns *Namespace) GetCSV(sep string, args ...interface{}) (d [][]string, err
 		return nil, _errors.Wrapf(err, "failed to create request for getCSV for resource %s", url)
 	}
 
-	req.Header.Add("Accept", "text/csv")
-	req.Header.Add("Accept", "text/plain")
-
-	// Add custom user headers to the get request
-	finalArg := args[len(args)-1]
-
-	if userHeaders, ok := finalArg.(map[string]interface{}); ok {
-		for key, val := range userHeaders {
-			req.Header.Add(key, val.(string))
-		}
-	}
+	// Add custom user headers.
+	addUserProvidedHeaders(headers, req)
+	addDefaultHeaders(req, "text/csv", "text/plain")
 
 	err = ns.getResource(cache, unmarshal, req)
 	if err != nil {
@@ -108,7 +100,7 @@ func (ns *Namespace) GetCSV(sep string, args ...interface{}) (d [][]string, err
 // GetJSON returns nil or parsed JSON to use in a short code.
 func (ns *Namespace) GetJSON(args ...interface{}) (interface{}, error) {
 	var v interface{}
-	url := joinURL(args)
+	url, headers := toURLAndHeaders(args)
 	cache := ns.cacheGetJSON
 
 	req, err := http.NewRequest("GET", url, nil)
@@ -124,17 +116,8 @@ func (ns *Namespace) GetJSON(args ...interface{}) (interface{}, error) {
 		return false, nil
 	}
 
-	req.Header.Add("Accept", "application/json")
-	req.Header.Add("User-Agent", "Hugo Static Site Generator")
-
-	// Add custom user headers to the get request
-	finalArg := args[len(args)-1]
-
-	if userHeaders, ok := finalArg.(map[string]interface{}); ok {
-		for key, val := range userHeaders {
-			req.Header.Add(key, val.(string))
-		}
-	}
+	addUserProvidedHeaders(headers, req)
+	addDefaultHeaders(req, "application/json")
 
 	err = ns.getResource(cache, unmarshal, req)
 	if err != nil {
@@ -145,8 +128,64 @@ func (ns *Namespace) GetJSON(args ...interface{}) (interface{}, error) {
 	return v, nil
 }
 
-func joinURL(urlParts []interface{}) string {
-	return strings.Join(cast.ToStringSlice(urlParts), "")
+func addDefaultHeaders(req *http.Request, accepts ...string) {
+	for _, accept := range accepts {
+		if !hasHeaderValue(req.Header, "Accept", accept) {
+			req.Header.Add("Accept", accept)
+		}
+	}
+	if !hasHeaderKey(req.Header, "User-Agent") {
+		req.Header.Add("User-Agent", "Hugo Static Site Generator")
+	}
+}
+
+func addUserProvidedHeaders(headers map[string]interface{}, req *http.Request) {
+	if headers == nil {
+		return
+	}
+	for key, val := range headers {
+		vals := types.ToStringSlicePreserveString(val)
+		for _, s := range vals {
+			req.Header.Add(key, s)
+		}
+	}
+}
+
+func hasHeaderValue(m http.Header, key, value string) bool {
+	var s []string
+	var ok bool
+
+	if s, ok = m[key]; !ok {
+		return false
+	}
+
+	for _, v := range s {
+		if v == value {
+			return true
+		}
+	}
+	return false
+}
+
+func hasHeaderKey(m http.Header, key string) bool {
+	_, ok := m[key]
+	return ok
+}
+
+func toURLAndHeaders(urlParts []interface{}) (string, map[string]interface{}) {
+	if len(urlParts) == 0 {
+		return "", nil
+	}
+
+	// The last argument may be a map.
+	headers, err := maps.ToStringMapE(urlParts[len(urlParts)-1])
+	if err == nil {
+		urlParts = urlParts[:len(urlParts)-1]
+	} else {
+		headers = nil
+	}
+
+	return strings.Join(cast.ToStringSlice(urlParts), ""), headers
 }
 
 // parseCSV parses bytes of CSV data into a slice slice string or an error