net: add HTTP Header struct and methods (#8991)

vlib/net/http/header_test.v

@@ -0,0 +1,48 @@
+import net.http
+
+fn test_header_new() {
+	h := http.new_header(
+		{key: .accept, value: 'nothing'},
+		{key: .expires, value: 'yesterday'}
+	)
+	assert h.contains_str('accept')
+	assert h.contains(.expires)
+	accept := h.get(.accept) or { '' }
+	expires := h.get(.expires) or { '' }
+	assert accept == 'nothing'
+	assert expires == 'yesterday'
+}
+
+fn test_header_invalid_key() {
+	mut h := http.new_header()
+	h.add_str('space is invalid', ':(') or { return }
+	panic('should have returned')
+}
+
+fn test_header_adds_multiple() {
+	mut h := http.new_header()
+	h.add(.accept, 'one')
+	h.add(.accept, 'two')
+
+	assert h.values(.accept) == ['one' 'two']
+}
+
+fn test_header_set() {
+	mut h := http.new_header(
+		{key: .dnt, value: 'one'},
+		{key: .dnt, value: 'two'}
+	)
+	assert h.values(.dnt) == ['one' 'two']
+	h.set_str('dnt', 'three')
+	assert h.values(.dnt) == ['three']
+}
+
+fn test_header_delete() {
+	mut h := http.new_header(
+		{key: .dnt, value: 'one'},
+		{key: .dnt, value: 'two'}
+	)
+	assert h.values(.dnt) == ['one' 'two']
+	h.delete_str('dnt')
+	assert h.values(.dnt) == []
+}