Add option to link SSL libs statically

[berndv]

Currently it is not possible to link SSL libs on or for Linux systems statically.

Please add configuration option to enable static linking.

Proposal (based on tag 0.7.1):

diff --git a/paho-mqtt-sys/build.rs b/paho-mqtt-sys/build.rs
index 9c4a942..8af5dce 100644
--- a/paho-mqtt-sys/build.rs
+++ b/paho-mqtt-sys/build.rs
@@ -175,6 +175,7 @@
     use std::path::Path;
     use std::process::Command;
     use std::env;
+    use std::str::FromStr;
 
     pub fn main() {
         println!("debug:Running the bundled build for Paho C");
@@ -250,9 +251,19 @@
 
         // Link in the SSL libraries if configured for it.
         if cfg!(feature = "ssl") {
+            let ssl_link_static = match env::var("OPENSSL_LINK_STATIC") {
+                Ok(value) => bool::from_str(value.as_str()).unwrap(),
+                Err(_) => cfg!(windows),
+            };
+
+            let ssl_link_kind = match ssl_link_static {
+                true => "static",
+                false => "dylib",
+            };
+
             if cfg!(windows) {
-                println!("cargo:rustc-link-lib=libssl");
-                println!("cargo:rustc-link-lib=libcrypto");
+                println!("cargo:rustc-link-lib={}=libssl", ssl_link_kind);
+                println!("cargo:rustc-link-lib={}=libcrypto", ssl_link_kind);
                 if let Ok(ssl_sp) = env::var("OPENSSL_ROOT_DIR") {
                     println!("cargo:rustc-link-search={}\\lib", ssl_sp);
                 }
@@ -265,8 +276,8 @@
                 };
             }
             else {
-                println!("cargo:rustc-link-lib=ssl");
-                println!("cargo:rustc-link-lib=crypto");
+                println!("cargo:rustc-link-lib={}=ssl", ssl_link_kind);
+                println!("cargo:rustc-link-lib={}=crypto", ssl_link_kind);
                 if let Ok(ssl_sp) = env::var("OPENSSL_ROOT_DIR") {
                     println!("cargo:rustc-link-search={}/lib", ssl_sp);
                 }
@@ -340,4 +351,3 @@
         bindings::place_bindings(&Path::new(&inc_dir));
     }
 }
-

[fpagliughi]

Thanks! Could you submit this as a Pull Request?

[ryankurte]

would it perhaps be useful to farm out the openssl building/linking to openssl-sys? this already basically works with the usual OPENSSL_STATIC / OPENSSL_DIR args (though at this time you have to add openssl-sys to your crate to aid this resolution)

[fpagliughi]

OK. PR #92 added the openssl-sys to the build which should now allow static linking.