Fixing build instructions (#59)

Author: rccarper

README.md

@@ -9,6 +9,42 @@ This library is licensed under the Apache 2.0 License.
 ## Usage
 
 ### Building
+
+#### Building s2n (Linux Only)
+
+If you are building on Linux, you will need to build s2n before being able to build aws-c-io.  For our CRT's, we build s2n at a specific commit, and recommend doing the same when using it with this library.  That commit hash can be found [here](https://github.com/awslabs/aws-crt-cpp/tree/main/crt).  The commands below will build s2n using OpenSSL 1.1.1.  For using other versions of OpenSSL, there is additional information in the [s2n Usage Guide](https://github.com/awslabs/s2n/blob/main/docs/USAGE-GUIDE.md).
+
+```
+git clone [email protected]:awslabs/s2n.git
+cd s2n
+git checkout <s2n-commit-hash-used-by-aws-crt-cpp>
+
+# We keep the build artifacts in the -build directory
+cd libcrypto-build
+
+# Download the latest version of OpenSSL
+curl -LO https://www.openssl.org/source/openssl-1.1.1-latest.tar.gz
+tar -xzvf openssl-1.1.1-latest.tar.gz
+
+# Build openssl libcrypto.  Note that the install path specified here must be absolute.
+cd `tar ztf openssl-1.1.1-latest.tar.gz | head -n1 | cut -f1 -d/`
+./config -fPIC no-shared              \
+         no-md2 no-rc5 no-rfc3779 no-sctp no-ssl-trace no-zlib     \
+         no-hw no-mdc2 no-seed no-idea enable-ec_nistp_64_gcc_128 no-camellia\
+         no-bf no-ripemd no-dsa no-ssl2 no-ssl3 no-capieng                  \
+         -DSSL_FORBID_ENULL -DOPENSSL_NO_DTLS1 -DOPENSSL_NO_HEARTBEATS      \
+         --prefix=<absolute-install-path>
+make
+make install
+
+# Build s2n
+cd ../../../
+cmake -DCMAKE_PREFIX_PATH=<install-path> -DCMAKE_INSTALL_PREFIX=<install-path> -S s2n -B s2n/build
+cmake --build s2n/build --target install
+```
+
+#### Building aws-c-event-stream and Remaining Dependencies
+
 Note that aws-c-event-stream has several dependencies:
 
 ```
@@ -20,6 +56,14 @@ git clone [email protected]:awslabs/aws-checksums.git
 cmake -DCMAKE_PREFIX_PATH=<install-path> -DCMAKE_INSTALL_PREFIX=<install-path> -S aws-checksums -B aws-checksums/build
 cmake --build aws-checksums/build --target install
 
+git clone [email protected]:awslabs/aws-c-cal.git
+cmake -DCMAKE_PREFIX_PATH=<install-path> -DCMAKE_INSTALL_PREFIX=<install-path> -S aws-c-cal -B aws-c-cal/build
+cmake --build aws-c-cal/build --target install
+
+git clone [email protected]:awslabs/aws-c-io.git
+cmake -DCMAKE_PREFIX_PATH=<install-path> -DCMAKE_INSTALL_PREFIX=<install-path> -S aws-c-io -B aws-c-io/build
+cmake --build aws-c-io/build --target install
+
 git clone [email protected]:awslabs/aws-c-event-stream.git
 cmake -DCMAKE_PREFIX_PATH=<install-path> -DCMAKE_INSTALL_PREFIX=<install-path> -S aws-c-event-stream -B aws-c-event-stream/build
 cmake --build aws-c-event-stream/build --target install