Add a SHA256 Ada example

Author: JacobBarthelmeh

Ada/README.md

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+This is a collection of examples using the wolfSSL Ada wrapper
+
+By default it is expecting the wolfssl directory to be located at wolfssl-examples/Ada/wolfssl
+but that can be adjusted by changing the directory path for `" with "../wolfssl/wrapper/Ada/wolfssl.gpr";"`
+at the top of sha256.gpr.
+
+An example of building for use with SHA256 would be:
+
+```
+cd wolfssl-examples/Ada
+git clone --depth=1 git@github.com:wolfssl/wolfssl
+cd sha256
+gprbuild sha256.gpr
+```
+
+And then running the example with:
+
+```
+bash-3.2$ ./obj/sha256_example
+Computing SHA256 hash of: Hello, World!
+SHA256 hash: DFFD6021BB2BD5B0AF676290809EC3A53191DD81C7F70A4B28688A362182986F
+SHA256 hashing completed successfully!
+```
+
+Which matches the hash used from shasum:
+
+```
+bash-3.2$ printf 'Hello, World!' | shasum -a 256
+dffd6021bb2bd5b0af676290809ec3a53191dd81c7f70a4b28688a362182986f  -
+```

Ada/sha256/sha256.gpr

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+with "../wolfssl/wrapper/Ada/wolfssl.gpr";
+
+project SHA256 is
+
+   type OS_Kind is ("Windows", "Linux_Or_Mac");
+
+   OS : OS_Kind := external ("OS", "Linux_Or_Mac");
+
+   for Languages use ("Ada");
+
+   for Source_Dirs use (".");
+
+   for Object_Dir use "obj";
+
+   for Main use ("sha256_example.adb");
+
+   package Naming is
+      for Spec_Suffix ("C") use ".h";
+   end Naming;
+
+   package Compiler is
+      for Switches ("C") use
+         ("-DWOLFSSL_USER_SETTINGS",  --  Use the user_settings.h file.
+          "-Wno-pragmas",
+          "-Wall",
+          "-Wextra",
+          "-Wunknown-pragmas",
+          "--param=ssp-buffer-size=1",
+          "-Waddress",
+          "-Warray-bounds",
+          "-Wbad-function-cast",
+          "-Wchar-subscripts",
+          "-Wcomment",
+          "-Wfloat-equal",
+          "-Wformat-security",
+          "-Wformat=2",
+          "-Wmaybe-uninitialized",
+          "-Wmissing-field-initializers",
+          "-Wmissing-noreturn",
+          "-Wmissing-prototypes",
+          "-Wnested-externs",
+          "-Wnormalized=id",
+          "-Woverride-init",
+          "-Wpointer-arith",
+          "-Wpointer-sign",
+          "-Wshadow",
+          "-Wsign-compare",
+          "-Wstrict-overflow=1",
+          "-Wstrict-prototypes",
+          "-Wswitch-enum",
+          "-Wundef",
+          "-Wunused",
+          "-Wunused-result",
+          "-Wunused-variable",
+          "-Wwrite-strings",
+          "-fwrapv");
+
+      for Switches ("Ada") use ("-g");
+   end Compiler;
+
+   package Linker is
+      case OS is
+         when "Windows" =>
+            for Switches ("Ada") use
+               ("-lm",         --  To include the math library (used by WolfSSL).
+                "-lcrypt32");  --  Needed on Windows.
+
+         when "Linux_Or_Mac" =>
+            for Switches ("Ada") use
+               ("-lm");  --  To include the math library (used by WolfSSL).
+      end case;
+   end Linker;
+
+   package Binder is
+      for Switches ("Ada") use ("-Es");  --  To include stack traces.
+   end Binder;
+
+end SHA256;

Ada/sha256/sha256_example.adb

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+with Ada.Text_IO;
+with WolfSSL;
+
+procedure SHA256_Example is
+   procedure Put (Text : String) renames Ada.Text_IO.Put;
+   procedure Put_Line (Text : String) renames Ada.Text_IO.Put_Line;
+   
+   use type WolfSSL.Subprogram_Result;
+   
+   Hash : WolfSSL.SHA256_Hash;
+   --  Example input data: "Hello, World!"
+   Input_Bytes : WolfSSL.Byte_Array := 
+     (1 => 'H', 2 => 'e', 3 => 'l', 4 => 'l', 5 => 'o',
+      6 => ',', 7 => ' ', 8 => 'W', 9 => 'o', 10 => 'r',
+      11 => 'l', 12 => 'd', 13 => '!');
+   SHA256 : WolfSSL.SHA256_Type;
+   R : Integer;
+   S : WolfSSL.SHA256_As_String;
+begin
+   Put_Line ("Computing SHA256 hash of: Hello, World!");
+   
+   --  Create SHA256 instance
+   WolfSSL.Create_SHA256 (Index => 1, SHA256 => SHA256, Result => R);
+   if R /= 0 then
+      Put_Line ("ERROR: SHA256 instance creation failed");
+      return;
+   end if;
+   
+   --  Update with input data
+   WolfSSL.Update_SHA256 (SHA256 => SHA256, Byte => Input_Bytes, Result => R);
+   if R /= 0 then
+      Put_Line ("ERROR: Update of SHA256 instance failed");
+      return;
+   end if;
+   
+   --  Finalize and get hash
+   WolfSSL.Finalize_SHA256 (SHA256 => SHA256,
+                            Hash   => Hash,
+                            Text   => S,
+                            Result => R);
+   if R = 0 then
+      Put ("SHA256 hash: ");
+      Put (S);
+      Put_Line ("");
+   else
+      Put_Line ("ERROR: Finalization of SHA256 instance failed");
+      return;
+   end if;
+   
+   Put_Line ("SHA256 hashing completed successfully!");
+end SHA256_Example;