From d3f99e611f8a1862c925dc978b3f019348fc6682 Mon Sep 17 00:00:00 2001
From: Koala Yeung <koalay@gmail.com>
Date: Thu, 18 Feb 2021 12:02:29 +0800
Subject: [PATCH] idPool: fix initial request id compatibility to libfcgi

* libfcgi (the example implementation of fcgi) rejects request if
  requestId is 0. Thus should not allocate 0 as request id.
---
 client.go               | 15 ++++++++++-----
 client_internal_test.go |  4 ++--
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/client.go b/client.go
index a3466d1..6e9dc66 100644
--- a/client.go
+++ b/client.go
@@ -84,8 +84,11 @@ func (p *idPool) Release(id uint16) {
 func newIDs(limit uint32) (p idPool) {
 
 	// sanatize limit
-	if limit == 0 || limit > 65536 {
-		limit = 65536
+	if limit == 0 || limit > 65535 {
+		// Note: limit is the size of the pool
+		// Since 0 cannot be requestId, the effective
+		// pool is from 1 to 65535, hence size is 65535.
+		limit = 65535
 	}
 
 	// pool requestID for the client
@@ -98,11 +101,11 @@ func newIDs(limit uint32) (p idPool) {
 	// Ref: https://fast-cgi.github.io/spec#33-records
 	ids := make(chan uint16)
 	go func(maxID uint16) {
-		for i := uint16(0); i < maxID; i++ {
+		for i := uint16(1); i < maxID; i++ {
 			ids <- i
 		}
 		ids <- uint16(maxID)
-	}(uint16(limit - 1))
+	}(uint16(limit))
 
 	p.IDs = ids
 	return
@@ -387,7 +390,9 @@ type ClientFactory func() (Client, error)
 //
 // limit is the maximum number of request that the
 // applcation support. 0 means the maximum number
-// available for 16bit request id (65536).
+// available for 16bit request id (because 0 is not
+// a valid reqeust id, 65535).
+//
 // Default 0.
 //
 func SimpleClientFactory(connFactory ConnFactory, limit uint32) ClientFactory {
diff --git a/client_internal_test.go b/client_internal_test.go
index fb539de..8cc68a2 100644
--- a/client_internal_test.go
+++ b/client_internal_test.go
@@ -9,7 +9,7 @@ import (
 func TestIDPool_Alloc(t *testing.T) {
 	t.Logf("default limit: %d", 65535)
 	ids := newIDs(0)
-	for i := uint32(0); i <= 65535; i++ {
+	for i := uint32(1); i <= 65535; i++ {
 		if want, have := uint16(i), ids.Alloc(); want != have {
 			t.Errorf("expected %d, got %d", want, have)
 		}
@@ -51,7 +51,7 @@ func TestIDPool_Alloc_withLimit(t *testing.T) {
 	t.Logf("random limit: %d", limit)
 
 	ids := newIDs(limit)
-	for i := uint32(0); i < limit; i++ {
+	for i := uint32(1); i <= limit; i++ {
 		if want, have := uint16(i), ids.Alloc(); want != have {
 			t.Errorf("expected %d, got %d", want, have)
 		}