[POA-1519] Allow HTTP response without reason phrase (#214)

Technically, the RFC requires a space even if the reason phrase is
empty, but at least one service has been observed to violate this. Add
unit tests for both correct and incorrect blank reason phrase, and a one
reproducing the original error to verify that Go's http parser is fine
with this.

akinet/http/parser_factory.go

@@ -149,13 +149,17 @@ func hasValidHTTPRequestLine(input memview.MemView) akinet.AcceptDecision {
 // RFC 2616 Section 6.1. The input should start right after the HTTP version.
 func hasValidHTTPResponseStatusLine(input memview.MemView) akinet.AcceptDecision {
 	if input.Len() < 5 {
-		// Need a 2 spaces plus 3 bytes for status code.
+		// Need a space, 3 bytes for status code, and a space or CR.
 		return akinet.NeedMoreData
 	}
 
 	// A space separates the HTTP version from status code.
 	// The format is SP Status-Code SP Reason-Phrase CR LF
-	if input.GetByte(0) != ' ' || input.GetByte(4) != ' ' {
+	// Some servers do not include the second 'SP" though and skip straight to 'CR'.
+	if input.GetByte(0) != ' ' {
+		return akinet.Reject
+	}
+	if input.GetByte(4) != ' ' && input.GetByte(4) != '\r' {
 		return akinet.Reject
 	}
 

akinet/http/parser_factory_test.go

@@ -226,6 +226,18 @@ func TestHTTPResponseParserFactoryAccepts(t *testing.T) {
 			expectedDecision: akinet.Accept,
 			expectedDF:       int64(len("OK")),
 		},
+		// This is technically illegal but we observed some Postman services sending it.
+		{
+			name:             "no reason message",
+			input:            "HTTP/1.1 200\r\n",
+			expectedDecision: akinet.Accept,
+		},
+		// This is technically legal, as the reason string can be zero bytes long.
+		{
+			name:             "no reason message",
+			input:            "HTTP/1.1 200 \r\n",
+			expectedDecision: akinet.Accept,
+		},
 		/*
 			// Currently failing -- does not look for response that spans the end of
 			// what is available.

akinet/http/parser_test.go

@@ -361,6 +361,28 @@ func TestHTTPResponseParser(t *testing.T) {
 				Body: memview.New([]byte("foobarbaz")),
 			},
 		},
+		{
+			name: "example response from Postman health check missing reason phrase",
+			input: "HTTP/1.1 200\r\nServer: nginx/1.25.3\r\nDate: Fri, 02 Aug 2024 03:04:14 GMT\r\n" +
+				"Content-Type: application/json; charset=utf-8\r\nContent-Length: 28\r\n" +
+				"Connection: close\r\nuWebSockets: 20\r\n\r\n{\"response\":\"Who is there?\"}",
+			expected: akinet.HTTPResponse{
+				StreamID:   uuid.UUID(testBidiID),
+				Seq:        522,
+				StatusCode: 200,
+				ProtoMajor: 1,
+				ProtoMinor: 1,
+				Header: map[string][]string{
+					"Server": {"nginx/1.25.3"},
+					// "Connection":     {"close"},    // ignored by parser
+					"Date":           {"Fri, 02 Aug 2024 03:04:14 GMT"},
+					"Uwebsockets":    {"20"}, // normalized
+					"Content-Length": {"28"},
+					"Content-Type":   {"application/json; charset=utf-8"},
+				},
+				Body: memview.New([]byte("{\"response\":\"Who is there?\"}")),
+			},
+		},
 		{
 			name: "ignore trailing bytes",
 			verbatimInput: []memview.MemView{