Add and document build customization options (#779)

* Add and document build customization to exclude Zlib and OpenSSL dependencies

Build/openssl.import.props

@@ -25,7 +25,7 @@
     <HCSettingsImported>true</HCSettingsImported>
   </PropertyGroup>
 
-  <ItemGroup Condition="'$(ConfigurationType)'!='StaticLibrary'">
+  <ItemGroup Condition="'$(ConfigurationType)'!='StaticLibrary' AND '$(HCNoOpenSSL)'!='true'">
     <ProjectReference Include="$(HCBuildRoot)\$(libsslName)\$(libsslName).vcxproj">
       <Project Condition="'$(HCLibPlatformType)' == 'Win32' and '$(opensslToolset)' == '141'">{A5EB6BDD-DD81-4B7B-83A0-A8AE0068FC3F}</Project>
       <Project Condition="'$(HCLibPlatformType)' == 'Win32' and '$(opensslToolset)' == '142'">{23104CDA-C598-4D41-B7FF-70405B2871EC}</Project>

README.md

@@ -49,6 +49,15 @@ libHttpClient provides a platform abstraction layer for HTTP and WebSocket, and
 * Optionally call HCSetHttpCallPerformFunction() to do your own HTTP handling using HCHttpCallRequestGet*(), HCHttpCallResponseSet*(), and HCSettingsGet*()
 * See sample CustomHttpImplWithCurl for an example of how to use this callback to make your own HTTP implementation.
 
+## Build customization
+
+If you are building libHttpClient from source, you can provide an hc_settings.props file with specific MSBuild properties to customize how the library gets built. When built, the libHttpClient projects look for an hc_settings.props file in any directory above the the repository root. Currently, the following build customizations are available:
+* Defining HCNoWebSockets will exclude WebSocket APIs (and all their dependencies) from the libHttpClient library
+* Defining HCNoZlib will exclude compression APIs and prevent libHttpClient from defining Zlib symbols within libHttpClient
+* Defining HCNoOpenSSL will prevent libHttpClient from referencing our private OpenSSL projects. If this is defined, you will need to manually include your own (compatible) version of OpenSSL when linking.
+
+An example customization file hc_settings.props.example can be found at the root of the repository.
+
 ## How to clone repo
 
 This repo contains submodules.  There are two ways to make sure you get submodules.

hc_settings.props.example

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <!-- Exclude Zlib symbols from the libHttpClient lib -->
+    <HCNoZlib>true</HCNoZlib> 
+    <!-- Exclude WebSocket APIs from libHttpClient lib, prevents pulling in 3rd party WebSocket dependencies -->
+    <HCNoWebSockets>true</HCNoWebSockets>
+    <!-- Prevents adding references to libHttpClient's private OpenSSL projects. Be sure to include your own OpenSSL binaries when linking -->
+    <HCNoOpenSSL>true</HCNoOpenSSL>
+  </PropertyGroup>
+</Project>

libHttpClient.props

@@ -32,7 +32,7 @@
 
   <PropertyGroup>
     <useWsppWebsockets>false</useWsppWebsockets>
-    <useWsppWebsockets Condition="'$(HCLibPlatformType)'=='Win32'">true</useWsppWebsockets>
+    <useWsppWebsockets Condition="'$(HCLibPlatformType)'=='Win32' and '$(HCNoWebSockets)'!='true'">true</useWsppWebsockets>
 
     <HCLibToolset>$(PlatformToolsetVersion)</HCLibToolset>
     <HCLibToolset Condition="'$(PlatformToolset)'=='v141'">141</HCLibToolset>
@@ -71,6 +71,16 @@
     </ProjectReference>
   </ItemGroup>
 
+  <ItemDefinitionGroup Condition="'$(HCNoWebSockets)'=='true'">
+    <ClCompile>
+      <PreprocessorDefinitions>
+        HC_NOWEBSOCKETS;
+        HC_WINHTTP_WEBSOCKETS=0;
+        %(PreprocessorDefinitions)
+      </PreprocessorDefinitions>
+    </ClCompile>
+  </ItemDefinitionGroup>
+
   <ItemDefinitionGroup>
     <ClCompile>
       <AdditionalIncludeDirectories>%(AdditionalIncludeDirectories);$(libHttpClientInclude)</AdditionalIncludeDirectories>